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Published: Feb 7, 2024 License: BSD-3-Clause Imports: 39 Imported by: 274

Documentation

Overview

Package kgo provides a pure Go efficient Kafka client for Kafka 0.8+ with support for transactions, regex topic consuming, the latest partition strategies, and more. This client supports all client related KIPs.

This client aims to be simple to use while still interacting with Kafka in a near ideal way. For more overview of the entire client itself, please see the README on the project's Github page.

Index

Constants

This section is empty.

Variables

View Source
var (

	// ErrRecordTimeout is passed to produce promises when records are
	// unable to be produced within the RecordDeliveryTimeout.
	ErrRecordTimeout = errors.New("records have timed out before they were able to be produced")

	// ErrRecordRetries is passed to produce promises when records are
	// unable to be produced after RecordRetries attempts.
	ErrRecordRetries = errors.New("record failed after being retried too many times")

	// ErrMaxBuffered is returned when the maximum amount of records are
	// buffered and either manual flushing is enabled or you are using
	// TryProduce.
	ErrMaxBuffered = errors.New("the maximum amount of records are buffered, cannot buffer more")

	// ErrAborting is returned for all buffered records while
	// AbortBufferedRecords is being called.
	ErrAborting = errors.New("client is aborting buffered records")

	// ErrClientClosed is returned in various places when the client's
	// Close function has been called.
	//
	// For producing, records are failed with this error.
	//
	// For consuming, a fake partition is injected into a poll response
	// that has this error.
	//
	// For any request, the request is failed with this error.
	ErrClientClosed = errors.New("client closed")
)

Functions

func NodeName added in v1.14.0

func NodeName(nodeID int32) string

NodeName returns the name of a node, given the kgo internal node ID.

Internally, seed brokers are stored with very negative node IDs, and these node IDs are visible in the BrokerMetadata struct. You can use NodeName to convert the negative node ID into "seed_#". Brokers discovered through metadata responses have standard non-negative numbers and this function just returns the number as a string.

func ParseConsumerSyncAssignment added in v0.7.0

func ParseConsumerSyncAssignment(assignment []byte) (map[string][]int32, error)

ParseConsumerSyncAssignment returns an assignment as specified a kmsg.ConsumerMemberAssignment, that is, the type encoded in metadata for the consumer protocol.

func PreCommitFnContext added in v1.5.0

func PreCommitFnContext(ctx context.Context, fn func(*kmsg.OffsetCommitRequest) error) context.Context

PreCommitFnContext attaches fn to the context through WithValue. Using the context while committing allows fn to be called just before the commit is issued. This can be used to modify the actual commit, such as by associating metadata with partitions. If fn returns an error, the commit is not attempted.

func PreTxnCommitFnContext added in v1.15.0

func PreTxnCommitFnContext(ctx context.Context, fn func(*kmsg.TxnOffsetCommitRequest) error) context.Context

PreTxnCommitFnContext attaches fn to the context through WithValue. Using the context while committing a transaction allows fn to be called just before the commit is issued. This can be used to modify the actual commit, such as by associating metadata with partitions (for transactions, the default internal metadata is the client's current member ID). If fn returns an error, the commit is not attempted. This context can be used in either GroupTransactSession.End or in Client.EndTransaction.

func ValidateOpts added in v1.8.0

func ValidateOpts(opts ...Opt) error

ValidateOpts returns an error if the options are invalid.

Types

type Acks

type Acks struct {
	// contains filtered or unexported fields
}

Acks represents the number of acks a broker leader must have before a produce request is considered complete.

This controls the durability of written records and corresponds to "acks" in Kafka's Producer Configuration documentation.

The default is LeaderAck.

func AllISRAcks

func AllISRAcks() Acks

AllISRAcks ensures that all in-sync replicas have acknowledged they wrote a record before the leader replies success.

func LeaderAck

func LeaderAck() Acks

LeaderAck causes Kafka to reply that a record is written after only the leader has written a message. The leader does not wait for in-sync replica replies.

func NoAck

func NoAck() Acks

NoAck considers records sent as soon as they are written on the wire. The leader does not reply to records.

type BalancePlan added in v0.7.0

type BalancePlan struct {
	// contains filtered or unexported fields
}

BalancePlan is a helper type to build the result of balancing topics and partitions among group members.

func (*BalancePlan) AddPartition added in v0.7.0

func (p *BalancePlan) AddPartition(member *kmsg.JoinGroupResponseMember, topic string, partition int32)

AddPartition assigns a partition for the topic to a given member.

func (*BalancePlan) AddPartitions added in v0.7.0

func (p *BalancePlan) AddPartitions(member *kmsg.JoinGroupResponseMember, topic string, partitions []int32)

AddPartitions assigns many partitions for a topic to a given member.

func (*BalancePlan) AdjustCooperative added in v0.7.0

func (p *BalancePlan) AdjustCooperative(b *ConsumerBalancer)

AdjustCooperative performs the final adjustment to a plan for cooperative balancing.

Over the plan, we remove all partitions that migrated from one member (where it was assigned) to a new member (where it is now planned).

This allows members that had partitions removed to revoke and rejoin, which will then do another rebalance, and in that new rebalance, the planned partitions are now on the free list to be assigned.

func (*BalancePlan) AsMemberIDMap added in v1.5.0

func (p *BalancePlan) AsMemberIDMap() map[string]map[string][]int32

AsMemberIDMap returns the plan as a map of member IDs to their topic & partition assignments.

Internally, a BalancePlan is currently represented as this map. Any modification to the map modifies the plan. The internal representation of a plan may change in the future to include more metadata. If this happens, the map returned from this function may not represent all aspects of a plan. The client will attempt to mirror modifications to the map directly back into the underlying plan as best as possible.

func (*BalancePlan) IntoSyncAssignment added in v0.7.0

func (p *BalancePlan) IntoSyncAssignment() []kmsg.SyncGroupRequestGroupAssignment

IntoSyncAssignment satisfies the IntoSyncAssignment interface.

func (*BalancePlan) String added in v0.7.0

func (p *BalancePlan) String() string

type Broker

type Broker struct {
	// contains filtered or unexported fields
}

Broker pairs a broker ID with a client to directly issue requests to a specific broker.

func (*Broker) Request

func (b *Broker) Request(ctx context.Context, req kmsg.Request) (kmsg.Response, error)

Request issues a request to a broker. If the broker does not exist in the client, this returns an unknown broker error. Requests are not retried.

The passed context can be used to cancel a request and return early. Note that if the request is not canceled before it is written to Kafka, you may just end up canceling and not receiving the response to what Kafka inevitably does.

It is more beneficial to always use RetriableRequest.

func (*Broker) RetriableRequest added in v0.6.2

func (b *Broker) RetriableRequest(ctx context.Context, req kmsg.Request) (kmsg.Response, error)

RetriableRequest issues a request to a broker the same as Broker, but retries in the face of retryable broker connection errors. This does not retry on response internal errors.

type BrokerE2E added in v0.8.0

type BrokerE2E struct {
	// BytesWritten is the number of bytes written for this request.
	//
	// This may not be the whole request if there was an error while writing.
	BytesWritten int

	// BytesRead is the number of bytes read for this requests's response.
	//
	// This may not be the whole response if there was an error while
	// reading, and this will be zero if there was a write error.
	BytesRead int

	// WriteWait is the time spent waiting from when this request was
	// generated internally in the client to just before the request is
	// written to the connection. This number is not included in the
	// DurationE2E method.
	WriteWait time.Duration
	// TimeToWrite is how long a request took to be written on the wire.
	// This specifically tracks only how long conn.Write takes.
	TimeToWrite time.Duration
	// ReadWait tracks the span of time immediately following conn.Write
	// until conn.Read begins.
	ReadWait time.Duration
	// TimeToRead tracks how long conn.Read takes for this request to be
	// entirely read. This includes the time it takes to allocate a buffer
	// for the response after the initial four size bytes are read.
	TimeToRead time.Duration

	// WriteErr is any error encountered during writing. If a write error is
	// encountered, no read will be attempted.
	WriteErr error
	// ReadErr is any error encountered during reading.
	ReadErr error
}

BrokerE2E tracks complete information for a write of a request followed by a read of that requests's response.

Note that if this is for a produce request with no acks, there will be no read wait / time to read.

func (*BrokerE2E) DurationE2E added in v0.8.0

func (e *BrokerE2E) DurationE2E() time.Duration

DurationE2E returns the e2e time from the start of when a request is written to the end of when the response for that request was fully read. If a write or read error occurs, this hook is called with all information possible at the time (e.g., if a write error occurs, all write info is specified).

Kerberos SASL does not cause this hook, since it directly reads from the connection.

func (*BrokerE2E) Err added in v0.8.0

func (e *BrokerE2E) Err() error

Err returns the first of either the write err or the read err. If this return is non-nil, the request/response had an error.

type BrokerMetadata

type BrokerMetadata struct {
	// NodeID is the broker node ID.
	//
	// Seed brokers will have very negative IDs; kgo does not try to map
	// seed brokers to loaded brokers. You can use NodeName to convert
	// the seed node ID into a formatted string.
	NodeID int32

	// Port is the port of the broker.
	Port int32

	// Host is the hostname of the broker.
	Host string

	// Rack is an optional rack of the broker. It is invalid to modify this
	// field.
	//
	// Seed brokers will not have a rack.
	Rack *string
	// contains filtered or unexported fields
}

BrokerMetadata is metadata for a broker.

This struct mirrors kmsg.MetadataResponseBroker.

type Client

type Client struct {
	// contains filtered or unexported fields
}

Client issues requests and handles responses to a Kafka cluster.

func NewClient

func NewClient(opts ...Opt) (*Client, error)

NewClient returns a new Kafka client with the given options or an error if the options are invalid. Connections to brokers are lazily created only when requests are written to them.

By default, the client uses the latest stable request versions when talking to Kafka. If you use a broker older than 0.10.0, then you need to manually set a MaxVersions option. Otherwise, there is usually no harm in defaulting to the latest API versions, although occasionally Kafka introduces new required parameters that do not have zero value defaults.

NewClient also launches a goroutine which periodically updates the cached topic metadata.

func (*Client) AbortBufferedRecords

func (cl *Client) AbortBufferedRecords(ctx context.Context) error

AbortBufferedRecords fails all unflushed records with ErrAborted and waits for there to be no buffered records.

This accepts a context to quit the wait early, but quitting the wait may lead to an invalid state and should only be used if you are quitting your application. This function waits to abort records at safe points: if records are known to not be in flight. This function is safe to call multiple times concurrently, and safe to call concurrent with Flush.

NOTE: This aborting record waits until all inflight requests have known responses. The client must wait to ensure no duplicate sequence number issues. For more details, and for an immediate alternative, check the documentation on UnsafeAbortBufferedRecords.

func (*Client) AddConsumePartitions added in v1.14.0

func (cl *Client) AddConsumePartitions(partitions map[string]map[int32]Offset)

AddConsumePartitions adds new partitions to be consumed at the given offsets. This function works only for direct, non-regex consumers.

func (*Client) AddConsumeTopics added in v1.4.0

func (cl *Client) AddConsumeTopics(topics ...string)

AddConsumeTopics adds new topics to be consumed. This function is a no-op if the client is configured to consume via regex.

Note that if you are directly consuming and specified ConsumePartitions, this function will not add the rest of the partitions for a topic unless the topic has been previously purged. That is, if you directly consumed only one of five partitions originally, this will not add the other four until the entire topic is purged.

func (*Client) AllowRebalance added in v1.4.0

func (cl *Client) AllowRebalance()

AllowRebalance allows a consumer group to rebalance if it was blocked by you polling records in tandem with the BlockRebalanceOnPoll option.

You can poll many times before calling this function; this function internally resets the poll count and allows any blocked rebalances to continue. Rebalances take priority: if a rebalance is blocked, and you allow rebalances and then immediately poll, your poll will be blocked until the rebalance completes. Internally, this function simply waits for lost partitions to stop being fetched before allowing you to poll again.

func (*Client) BeginTransaction

func (cl *Client) BeginTransaction() error

BeginTransaction sets the client to a transactional state, erroring if there is no transactional ID, or if the producer is currently in a fatal (unrecoverable) state, or if the client is already in a transaction.

This must not be called concurrently with other client functions.

func (*Client) Broker

func (cl *Client) Broker(id int) *Broker

Broker returns a handle to a specific broker to directly issue requests to. Note that there is no guarantee that this broker exists; if it does not, requests will fail with with an unknown broker error.

func (*Client) BufferedFetchBytes added in v1.15.0

func (cl *Client) BufferedFetchBytes() int64

BufferedFetchBytes returns the number of bytes currently buffered from fetching within the client. This is the sum of all keys, values, and header keys/values. See the related [BufferedFetchRecords] for more information.

func (*Client) BufferedFetchRecords added in v0.8.7

func (cl *Client) BufferedFetchRecords() int64

BufferedFetchRecords returns the number of records currently buffered from fetching within the client.

This can be used as a gauge to determine how behind your application is for processing records the client has fetched. Note that it is perfectly normal to see a spike of buffered records, which would correspond to a fetch response being processed just before a call to this function. It is only problematic if for you if this function is consistently returning large values.

func (*Client) BufferedProduceBytes added in v1.15.0

func (cl *Client) BufferedProduceBytes() int64

BufferedProduceBytes returns the number of bytes currently buffered for producing within the client. This is the sum of all keys, values, and header keys/values. See the related [BufferedProduceRecords] for more information.

func (*Client) BufferedProduceRecords added in v0.8.7

func (cl *Client) BufferedProduceRecords() int64

BufferedProduceRecords returns the number of records currently buffered for producing within the client.

This can be used as a gauge to determine how far behind the client is for flushing records produced by your client (which can help determine network / cluster health).

func (*Client) Close

func (cl *Client) Close()

Close leaves any group and closes all connections and goroutines. This function waits for the group to be left. If you want to force leave a group immediately and ensure a speedy shutdown you can use LeaveGroupContext first (and then Close will be immediate).

If you are group consuming and have overridden the default OnPartitionsRevoked, you must manually commit offsets before closing the client.

If you are using the BlockRebalanceOnPoll option and have polled, this function does not automatically allow rebalancing. You must AllowRebalance before calling this function. Internally, this function leaves the group, and leaving a group causes a rebalance so that you can get one final notification of revoked partitions. If you want to automatically allow rebalancing, use CloseAllowingRebalance.

func (*Client) CloseAllowingRebalance added in v1.7.0

func (cl *Client) CloseAllowingRebalance()

CloseAllowingRebalance allows rebalances, leaves any group, and closes all connections and goroutines. This function is only useful if you are using the BlockRebalanceOnPoll option. Close itself does not allow rebalances and will hang if you polled, did not allow rebalances, and want to close. Close does not automatically allow rebalances because leaving a group causes a revoke, and the client does not assume that the final revoke is concurrency safe. The CloseAllowingRebalance function exists a a shortcut to opt into allowing rebalance while closing.

func (*Client) CommitMarkedOffsets added in v1.12.0

func (cl *Client) CommitMarkedOffsets(ctx context.Context) error

CommitMarkedOffsets issues a synchronous offset commit for any partition that has been consumed from that has marked offsets. Retryable errors are retried up to the configured retry limit, and any unretryable error is returned.

This function is only useful if you have marked offsets with MarkCommitRecords when using AutoCommitMarks, otherwise this is a no-op.

The recommended pattern for using this function is to have a poll / process / commit loop. First PollFetches, then process every record, call MarkCommitRecords for the records you wish the commit and then call CommitMarkedOffsets.

As an alternative if you want to commit specific records, see CommitRecords.

func (*Client) CommitOffsets

func (cl *Client) CommitOffsets(
	ctx context.Context,
	uncommitted map[string]map[int32]EpochOffset,
	onDone func(*Client, *kmsg.OffsetCommitRequest, *kmsg.OffsetCommitResponse, error),
)

CommitOffsets commits the given offsets for a group, calling onDone with the commit request and either the response or an error if the response was not issued. If uncommitted is empty or the client is not consuming as a group, onDone is called with (nil, nil, nil) and this function returns immediately. It is OK if onDone is nil, but you will not know if your commit succeeded.

This is an advanced function and is difficult to use correctly. For simpler, more easily understandable committing, see CommitRecords and CommitUncommittedOffsets.

This function itself does not wait for the commit to finish. By default, this function is an asynchronous commit. You can use onDone to make it sync. If autocommitting is enabled, this function blocks autocommitting until this function is complete and the onDone has returned.

It is invalid to use this function to commit offsets for a transaction.

Note that this function ensures absolute ordering of commit requests by canceling prior requests and ensuring they are done before executing a new one. This means, for absolute control, you can use this function to periodically commit async and then issue a final sync commit before quitting (this is the behavior of autocommiting and using the default revoke). This differs from the Java async commit, which does not retry requests to avoid trampling on future commits.

It is highly recommended to check the response's partition's error codes if the response is non-nil. While unlikely, individual partitions can error. This is most likely to happen if a commit occurs too late in a rebalance event.

Do not use this async CommitOffsets in OnPartitionsRevoked, instead use CommitOffsetsSync. If you commit async, the rebalance will proceed before this function executes, and you will commit offsets for partitions that have moved to a different consumer.

func (*Client) CommitOffsetsSync added in v0.8.1

func (cl *Client) CommitOffsetsSync(
	ctx context.Context,
	uncommitted map[string]map[int32]EpochOffset,
	onDone func(*Client, *kmsg.OffsetCommitRequest, *kmsg.OffsetCommitResponse, error),
)

CommitOffsetsSync cancels any active CommitOffsets, begins a commit that cannot be canceled, and waits for that commit to complete. This function will not return until the commit is done and the onDone callback is complete.

The purpose of this function is for use in OnPartitionsRevoked or committing before leaving a group, because you do not want to have a commit issued in OnPartitionsRevoked canceled.

This is an advanced function, and for simpler, more easily understandable committing, see CommitRecords and CommitUncommittedOffsets.

For more information about committing and committing asynchronously, see CommitOffsets.

func (*Client) CommitRecords added in v0.8.1

func (cl *Client) CommitRecords(ctx context.Context, rs ...*Record) error

CommitRecords issues a synchronous offset commit for the offsets contained within rs. Retryable errors are retried up to the configured retry limit, and any unretryable error is returned.

This function is useful as a simple way to commit offsets if you have disabled autocommitting. As an alternative if you always want to commit everything, see CommitUncommittedOffsets.

Simple usage of this function may lead to duplicate records if a consumer group rebalance occurs before or while this function is being executed. You can avoid this scenario by calling CommitRecords in a custom OnPartitionsRevoked, but for most workloads, a small bit of potential duplicate processing is fine. See the documentation on DisableAutoCommit for more details. You can also avoid this problem by using BlockRebalanceOnPoll, but that option comes with its own tradeoffs (refer to its documentation).

It is recommended to always commit records in order (per partition). If you call this function twice with record for partition 0 at offset 999 initially, and then with record for partition 0 at offset 4, you will rewind your commit.

A use case for this function may be to partially process a batch of records, commit, and then continue to process the rest of the records. It is not recommended to call this for every record processed in a high throughput scenario, because you do not want to unnecessarily increase load on Kafka.

If you do not want to wait for this function to complete before continuing processing records, you can call this function in a goroutine.

func (*Client) CommitUncommittedOffsets added in v0.8.1

func (cl *Client) CommitUncommittedOffsets(ctx context.Context) error

CommitUncommittedOffsets issues a synchronous offset commit for any partition that has been consumed from that has uncommitted offsets. Retryable errors are retried up to the configured retry limit, and any unretryable error is returned.

The recommended pattern for using this function is to have a poll / process / commit loop. First PollFetches, then process every record, then call CommitUncommittedOffsets.

As an alternative if you want to commit specific records, see CommitRecords.

func (*Client) CommittedOffsets

func (cl *Client) CommittedOffsets() map[string]map[int32]EpochOffset

CommittedOffsets returns the latest committed offsets. Committed offsets are updated from commits or from joining a group and fetching offsets.

If there are no committed offsets, this returns nil.

func (*Client) DiscoveredBrokers

func (cl *Client) DiscoveredBrokers() []*Broker

DiscoveredBrokers returns all brokers that were discovered from prior metadata responses. This does not actually issue a metadata request to load brokers; if you wish to ensure this returns all brokers, be sure to manually issue a metadata request before this. This also does not include seed brokers, which are internally saved under special internal broker IDs (but, it does include those brokers under their normal IDs as returned from a metadata response).

func (*Client) EndAndBeginTransaction added in v1.4.0

func (cl *Client) EndAndBeginTransaction(
	ctx context.Context,
	how EndBeginTxnHow,
	commit TransactionEndTry,
	onEnd func(context.Context, error) error,
) (rerr error)

EndAndBeginTransaction is a combination of EndTransaction and BeginTransaction, and relaxes the restriction that the client must have no buffered records. This function does not flush nor abort any buffered records. It is ok to concurrently produce while this function executes.

This function has different safety guarantees which are up to the user to decide. See the documentation on EndBeginTxnHow for which you would like to choose.

The onEnd function is called with your input context and the result of EndTransaction. Promises are paused while onEnd executes. If onEnd returns an error, BeginTransaction is not called and this function returns the result of onEnd. Otherwise, this function returns the result of BeginTransaction. See the documentation on EndTransaction and BeginTransaction for further details. It is invalid to call this function more than once at a time, and it is invalid to call concurrent with EndTransaction or BeginTransaction.

func (*Client) EndTransaction

func (cl *Client) EndTransaction(ctx context.Context, commit TransactionEndTry) error

EndTransaction ends a transaction and resets the client's internal state to not be in a transaction.

Flush and CommitOffsetsForTransaction must be called before this function; this function does not flush and does not itself ensure that all buffered records are flushed. If no record yet has caused a partition to be added to the transaction, this function does nothing and returns nil. Alternatively, AbortBufferedRecords should be called before aborting a transaction to ensure that any buffered records not yet flushed will not be a part of a new transaction.

If the producer ID has an error and you are trying to commit, this will return with kerr.OperationNotAttempted. If this happened, retry EndTransaction with TryAbort. Not other error is retryable, and you should not retry with TryAbort.

If records failed with UnknownProducerID and your Kafka version is at least 2.5, then aborting here will potentially allow the client to recover for more production.

Note that canceling the context will likely leave the client in an undesirable state, because canceling the context may cancel the in-flight EndTransaction request, making it impossible to know whether the commit or abort was successful. It is recommended to not cancel the context.

func (*Client) Flush

func (cl *Client) Flush(ctx context.Context) error

Flush hangs waiting for all buffered records to be flushed, stopping all lingers if necessary.

If the context finishes (Done), this returns the context's error.

This function is safe to call multiple times concurrently, and safe to call concurrent with Flush.

func (*Client) ForceMetadataRefresh added in v1.4.0

func (cl *Client) ForceMetadataRefresh()

ForceMetadataRefresh triggers the client to update the metadata that is currently used for producing & consuming.

Internally, the client already properly triggers metadata updates whenever a partition is discovered to be out of date (leader moved, epoch is old, etc). However, when partitions are added to a topic through a CreatePartitions request, it may take up to MetadataMaxAge for the new partitions to be discovered. In this case, you may want to forcefully refresh metadata manually to discover these new partitions sooner.

func (*Client) ForceRebalance added in v0.7.0

func (cl *Client) ForceRebalance()

ForceRebalance quits a group member's heartbeat loop so that the member rejoins with a JoinGroupRequest.

This function is only useful if you either (a) know that the group member is a leader, and want to force a rebalance for any particular reason, or (b) are using a custom group balancer, and have changed the metadata that will be returned from its JoinGroupMetadata method. This function has no other use; see KIP-568 for more details around this function's motivation.

If neither of the cases above are true (this member is not a leader, and the join group metadata has not changed), then Kafka will not actually trigger a rebalance and will instead reply to the member with its current assignment.

func (*Client) GroupMetadata added in v1.7.0

func (cl *Client) GroupMetadata() (string, int32)

GroupMetadata returns the current group member ID and generation, or an empty string and -1 if not in the group.

func (*Client) LeaveGroup added in v0.6.4

func (cl *Client) LeaveGroup()

LeaveGroup leaves a group. Close automatically leaves the group, so this is only necessary to call if you plan to leave the group but continue to use the client. If a rebalance is in progress, this function waits for the rebalance to complete before the group can be left. This is necessary to allow you to safely issue one final offset commit in OnPartitionsRevoked. If you have overridden the default revoke, you must manually commit offsets before leaving the group.

If you have configured the group with an InstanceID, this does not leave the group. With instance IDs, it is expected that clients will restart and re-use the same instance ID. To leave a group using an instance ID, you must manually issue a kmsg.LeaveGroupRequest or use an external tool (kafka scripts or kcl).

It is recommended to use LeaveGroupContext to see if the leave was successful.

func (*Client) LeaveGroupContext added in v1.15.0

func (cl *Client) LeaveGroupContext(ctx context.Context) error

LeaveGroup leaves a group. Close automatically leaves the group, so this is only necessary to call if you plan to leave the group but continue to use the client. If a rebalance is in progress, this function waits for the rebalance to complete before the group can be left. This is necessary to allow you to safely issue one final offset commit in OnPartitionsRevoked. If you have overridden the default revoke, you must manually commit offsets before leaving the group.

The context can be used to avoid waiting for the client to leave the group. Not waiting may result in your client being stuck in the group and the partitions this client was consuming being stuck until the session timeout. This function returns any leave group error or context cancel error. If the context is nil, this immediately leaves the group and does not wait and does not return an error.

If you have configured the group with an InstanceID, this does not leave the group. With instance IDs, it is expected that clients will restart and re-use the same instance ID. To leave a group using an instance ID, you must manually issue a kmsg.LeaveGroupRequest or use an external tool (kafka scripts or kcl).

func (*Client) MarkCommitRecords added in v0.10.3

func (cl *Client) MarkCommitRecords(rs ...*Record)

MarkCommitRecords marks records to be available for autocommitting. This function is only useful if you use the AutoCommitMarks config option, see the documentation on that option for more details. This function does not allow rewinds.

func (*Client) MarkedOffsets added in v1.11.0

func (cl *Client) MarkedOffsets() map[string]map[int32]EpochOffset

MarkedOffsets returns the latest marked offsets. When autocommitting, a marked offset is an offset that can be committed, in comparison to a dirty offset that cannot yet be committed. MarkedOffsets returns nil if you are not using AutoCommitMarks.

func (*Client) OptValue added in v1.13.0

func (cl *Client) OptValue(opt any) any

OptValue returns the value for the given configuration option. If the given option does not exist, this returns nil. This function takes either a raw Opt, or an Opt function name.

If a configuration option has multiple inputs, this function returns only the first input. If the function is a boolean function (such as BlockRebalanceOnPoll), this function returns the value of the internal bool. Variadic option inputs are returned as a single slice. Options that are internally stored as a pointer (ClientID, TransactionalID, and InstanceID) are returned as their string input; you can see if the option is internally nil by looking at the second value returned from OptValues.

var (
	cl, _ := NewClient(
		InstanceID("foo"),
		ConsumeTopics("foo", "bar"),
	)
	iid    = cl.OptValue(InstanceID)           // iid is "foo"
	gid    = cl.OptValue(ConsumerGroup)        // gid is "" since groups are not used
	topics = cl.OptValue("ConsumeTopics")      // topics is []string{"foo", "bar"}; string lookup for the option works
	bpoll  = cl.OptValue(BlockRebalanceOnPoll) // bpoll is false
	t      = cl.OptValue(SessionTimeout)       // t is 45s, the internal default
	td     = t.(time.Duration)                 // safe conversion since SessionTimeout's input is a time.Duration
	unk    = cl.OptValue("Unknown"),           // unk is nil
)

func (*Client) OptValues added in v1.13.0

func (cl *Client) OptValues(opt any) []any

OptValues returns all values for options. This method is useful for options that have multiple inputs (notably, SoftwareNameAndVersion). This is also useful for options that are internally stored as a pointer (ClientID, TransactionalID, and InstanceID) -- this function will return the string value of the option but also whether the option is non-nil. Boolean options are returned as a single-element slice with the bool value. Variadic inputs are returned as a signle slice. If the input option does not exist, this returns nil.

var (
	cl, _    = NewClient(
		InstanceID("foo"),
		ConsumeTopics("foo", "bar"),
	)
	idValues = cl.OptValues(InstanceID)           // idValues is []any{"foo", true}
	tValues  = cl.OptValues(SessionTimeout)       // tValues is []any{45 * time.Second}
	topics   = cl.OptValues(ConsumeTopics)        // topics is []any{[]string{"foo", "bar"}
	bpoll    = cl.OptValues(BlockRebalanceOnPoll) // bpoll is []any{false}
	unknown  = cl.OptValues("Unknown")            // unknown is nil
)

func (*Client) Opts added in v1.14.0

func (cl *Client) Opts() []Opt

Opts returns the options that were used to create this client. This can be as a base to generate a new client, where you can add override options to the end of the original input list. If you want to know a specific option value, you can use OptValue or OptValues.

func (*Client) PartitionLeader added in v1.7.0

func (cl *Client) PartitionLeader(topic string, partition int32) (leader, leaderEpoch int32, err error)

PartitionLeader returns the given topic partition's leader, leader epoch and load error. This returns -1, -1, nil if the partition has not been loaded.

func (*Client) PauseFetchPartitions added in v0.11.1

func (cl *Client) PauseFetchPartitions(topicPartitions map[string][]int32) map[string][]int32

PauseFetchPartitions sets the client to no longer fetch the given partitions and returns all currently paused partitions. Paused partitions persist until resumed. You can call this function with no partitions to simply receive the list of currently paused partitions.

Pausing individual partitions is independent from pausing topics with the PauseFetchTopics method. If you pause partitions for a topic with PauseFetchPartitions, and then pause that same topic with PauseFetchTopics, the individually paused partitions will not be unpaused if you only call ResumeFetchTopics.

func (*Client) PauseFetchTopics added in v0.11.1

func (cl *Client) PauseFetchTopics(topics ...string) []string

PauseFetchTopics sets the client to no longer fetch the given topics and returns all currently paused topics. Paused topics persist until resumed. You can call this function with no topics to simply receive the list of currently paused topics.

Pausing topics is independent from pausing individual partitions with the PauseFetchPartitions method. If you pause partitions for a topic with PauseFetchPartitions, and then pause that same topic with PauseFetchTopics, the individually paused partitions will not be unpaused if you only call ResumeFetchTopics.

func (*Client) Ping added in v1.3.0

func (cl *Client) Ping(ctx context.Context) error

Ping returns whether any broker is reachable, iterating over any discovered broker or seed broker until one returns a successful response to an ApiVersions request. No discovered broker nor seed broker is attempted more than once. If all requests fail, this returns final error.

func (*Client) PollFetches

func (cl *Client) PollFetches(ctx context.Context) Fetches

PollFetches waits for fetches to be available, returning as soon as any broker returns a fetch. If the context is nil, this function will return immediately with any currently buffered records.

If the client is closed, a fake fetch will be injected that has no topic, a partition of 0, and a partition error of ErrClientClosed. If the context is canceled, a fake fetch will be injected with ctx.Err. These injected errors can be used to break out of a poll loop.

It is important to check all partition errors in the returned fetches. If any partition has a fatal error and actually had no records, fake fetch will be injected with the error.

If you are group consuming, a rebalance can happen under the hood while you process the returned fetches. This can result in duplicate work, and you may accidentally commit to partitions that you no longer own. You can prevent this by using BlockRebalanceOnPoll, but this comes with different tradeoffs. See the documentation on BlockRebalanceOnPoll for more information.

func (*Client) PollRecords added in v0.6.10

func (cl *Client) PollRecords(ctx context.Context, maxPollRecords int) Fetches

PollRecords waits for records to be available, returning as soon as any broker returns records in a fetch. If the context is nil, this function will return immediately with any currently buffered records.

If the client is closed, a fake fetch will be injected that has no topic, a partition of -1, and a partition error of ErrClientClosed. If the context is canceled, a fake fetch will be injected with ctx.Err. These injected errors can be used to break out of a poll loop.

This returns a maximum of maxPollRecords total across all fetches, or returns all buffered records if maxPollRecords is <= 0.

It is important to check all partition errors in the returned fetches. If any partition has a fatal error and actually had no records, fake fetch will be injected with the error.

If you are group consuming, a rebalance can happen under the hood while you process the returned fetches. This can result in duplicate work, and you may accidentally commit to partitions that you no longer own. You can prevent this by using BlockRebalanceOnPoll, but this comes with different tradeoffs. See the documentation on BlockRebalanceOnPoll for more information.

func (*Client) Produce

func (cl *Client) Produce(
	ctx context.Context,
	r *Record,
	promise func(*Record, error),
)

Produce sends a Kafka record to the topic in the record's Topic field, calling an optional `promise` with the record and a potential error when Kafka replies. For a synchronous produce, see ProduceSync. Records are produced in order per partition if the record is produced successfully. Successfully produced records will have their attributes, offset, and partition set before the promise is called. All promises are called serially (and should be relatively fast). If a record's timestamp is unset, this sets the timestamp to time.Now.

If the topic field is empty, the client will use the DefaultProduceTopic; if that is also empty, the record is failed immediately. If the record is too large to fit in a batch on its own in a produce request, the record will be failed with immediately kerr.MessageTooLarge.

If the client is configured to automatically flush the client currently has the configured maximum amount of records buffered, Produce will block. The context can be used to cancel waiting while records flush to make space. In contrast, if flushing is configured, the record will be failed immediately with ErrMaxBuffered (this same behavior can be had with TryProduce).

Once a record is buffered into a batch, it can be canceled in three ways: canceling the context, the record timing out, or hitting the maximum retries. If any of these conditions are hit and it is currently safe to fail records, all buffered records for the relevant partition are failed. Only the first record's context in a batch is considered when determining whether the batch should be canceled.

If the client is transactional and a transaction has not been begun, the promise is immediately called with an error corresponding to not being in a transaction.

func (*Client) ProduceSync added in v0.7.0

func (cl *Client) ProduceSync(ctx context.Context, rs ...*Record) ProduceResults

ProduceSync is a synchronous produce. See the Produce documentation for an in depth description of how producing works.

This function produces all records in one range loop and waits for them all to be produced before returning.

func (*Client) ProducerID added in v1.7.0

func (cl *Client) ProducerID(ctx context.Context) (int64, int16, error)

ProducerID returns, loading if necessary, the current producer ID and epoch. This returns an error if the producer ID could not be loaded, if the producer ID has fatally errored, or if the context is canceled.

func (*Client) PurgeTopicsFromClient added in v1.4.0

func (cl *Client) PurgeTopicsFromClient(topics ...string)

PurgeTopicsFromClient internally removes all internal information about the input topics. If you you want to purge information for only consuming or only producing, see the related functions [PurgeTopicsFromConsuming] and [PurgeTopicsFromProducing].

For producing, this clears all knowledge that these topics have ever been produced to. Producing to the topic again may result in out of order sequence number errors, or, if idempotency is disabled and the sequence numbers align, may result in invisibly discarded records at the broker. Purging a topic that was previously produced to may be useful to free up resources if you are producing to many disparate and short lived topic in the lifetime of this client and you do not plan to produce to the topic anymore. You may want to flush buffered records before purging if records for a topic you are purging are currently in flight.

For consuming, this removes all concept of the topic from being consumed. This is different from PauseFetchTopics, which literally pauses the fetching of topics but keeps the topic information around for resuming fetching later. Purging a topic that was being consumed can be useful if you know the topic no longer exists, or if you are consuming via regex and know that some previously consumed topics no longer exist, or if you simply do not want to ever consume from a topic again. If you are group consuming, this function will likely cause a rebalance.

For admin requests, this deletes the topic from the cached metadata map for sharded requests. Metadata for sharded admin requests is only cached for MetadataMinAge anyway, but the map is not cleaned up one the metadata expires. This function ensures the map is purged.

func (*Client) PurgeTopicsFromConsuming added in v1.15.0

func (cl *Client) PurgeTopicsFromConsuming(topics ...string)

PurgeTopicsFromConsuming internally removes all internal information for consuming about the input topics. This runs the consumer bit of logic that is documented in [PurgeTopicsFromClient]; see that function for more details.

func (*Client) PurgeTopicsFromProducing added in v1.15.0

func (cl *Client) PurgeTopicsFromProducing(topics ...string)

PurgeTopicsFromProducing internally removes all internal information for producing about the input topics. This runs the producer bit of logic that is documented in [PurgeTopicsFromClient]; see that function for more details.

func (*Client) RemoveConsumePartitions added in v1.14.0

func (cl *Client) RemoveConsumePartitions(partitions map[string][]int32)

RemoveConsumePartitions removes partitions from being consumed. This function works only for direct, non-regex consumers.

This method does not purge the concept of any topics from the client -- if you remove all partitions from a topic that was being consumed, metadata fetches will still occur for the topic. If you want to remove the topic entirely, use PurgeTopicsFromClient.

If you specified ConsumeTopics and this function removes all partitions for a topic, the topic will no longer be consumed.

func (*Client) Request

func (cl *Client) Request(ctx context.Context, req kmsg.Request) (kmsg.Response, error)

Request issues a request to Kafka, waiting for and returning the response. If a retryable network error occurs, or if a retryable group / transaction coordinator error occurs, the request is retried. All other errors are returned.

If the request is an admin request, this will issue it to the Kafka controller. If the controller ID is unknown, this will attempt to fetch it. If the fetch errors, this will return an unknown controller error.

If the request is a group or transaction coordinator request, this will issue the request to the appropriate group or transaction coordinator.

For transaction requests, the request is issued to the transaction coordinator. However, if the request is an init producer ID request and the request has no transactional ID, the request goes to any broker.

Some requests need to be split and sent to many brokers. For these requests, it is *highly* recommended to use RequestSharded. Not all responses from many brokers can be cleanly merged. However, for the requests that are split, this does attempt to merge them in a sane way.

The following requests are split:

ListOffsets
OffsetFetch (if using v8+ for Kafka 3.0+)
FindCoordinator (if using v4+ for Kafka 3.0+)
DescribeGroups
ListGroups
DeleteRecords
OffsetForLeaderEpoch
DescribeConfigs
AlterConfigs
AlterReplicaLogDirs
DescribeLogDirs
DeleteGroups
IncrementalAlterConfigs
DescribeProducers
DescribeTransactions
ListTransactions

Kafka 3.0 introduced batch OffsetFetch and batch FindCoordinator requests. This function is forward and backward compatible: old requests will be batched as necessary, and batched requests will be split as necessary. It is recommended to always use batch requests for simplicity.

In short, this method tries to do the correct thing depending on what type of request is being issued.

The passed context can be used to cancel a request and return early. Note that if the request was written to Kafka but the context canceled before a response is received, Kafka may still operate on the received request.

If using this function to issue kmsg.ProduceRequest's, you must configure the client with the same RequiredAcks option that you use in the request. If you are issuing produce requests with 0 acks, you must configure the client with the same timeout you use in the request. The client will internally rewrite the incoming request's acks to match the client's configuration, and it will rewrite the timeout millis if the acks is 0. It is strongly recommended to not issue raw kmsg.ProduceRequest's.

func (*Client) RequestSharded added in v0.6.2

func (cl *Client) RequestSharded(ctx context.Context, req kmsg.Request) []ResponseShard

RequestSharded performs the same logic as Request, but returns all responses from any broker that the request was split to. This always returns at least one shard. If the request does not need to be issued (describing no groups), this issues the request to a random broker just to ensure that one shard exists.

There are only a few requests that are strongly recommended to explicitly use RequestSharded; the rest can by default use Request. These few requests are mentioned in the documentation for Request.

If, in the process of splitting a request, some topics or partitions are found to not exist, or Kafka replies that a request should go to a broker that does not exist, all those non-existent pieces are grouped into one request to the first seed broker. This will show up as a seed broker node ID (min int32) and the response will likely contain purely errors.

The response shards are ordered by broker metadata.

func (*Client) ResumeFetchPartitions added in v0.11.1

func (cl *Client) ResumeFetchPartitions(topicPartitions map[string][]int32)

ResumeFetchPartitions resumes fetching the input partitions if they were previously paused. Resuming partitions that are not currently paused is a per-topic no-op. See the documentation on PauseFetchPartitions for more details.

func (*Client) ResumeFetchTopics added in v0.11.1

func (cl *Client) ResumeFetchTopics(topics ...string)

ResumeFetchTopics resumes fetching the input topics if they were previously paused. Resuming topics that are not currently paused is a per-topic no-op. See the documentation on PauseTfetchTopics for more details.

func (*Client) SeedBrokers

func (cl *Client) SeedBrokers() []*Broker

SeedBrokers returns the all seed brokers.

func (*Client) SetOffsets

func (cl *Client) SetOffsets(setOffsets map[string]map[int32]EpochOffset)

SetOffsets sets any matching offsets in setOffsets to the given epoch/offset. Partitions that are not specified are not set. It is invalid to set topics that were not yet returned from a PollFetches: this function sets only partitions that were previously consumed, any extra partitions are skipped.

If directly consuming, this function operates as expected given the caveats of the prior paragraph.

If using transactions, it is advised to just use a GroupTransactSession and avoid this function entirely.

If using group consuming, It is strongly recommended to use this function outside of the context of a PollFetches loop and only when you know the group is not revoked (i.e., block any concurrent revoke while issuing this call) and to not use this concurrent with committing. Any other usage is prone to odd interactions.

func (*Client) TryProduce added in v1.4.0

func (cl *Client) TryProduce(
	ctx context.Context,
	r *Record,
	promise func(*Record, error),
)

TryProduce is similar to Produce, but rather than blocking if the client currently has MaxBufferedRecords or MaxBufferedBytes buffered, this fails immediately with ErrMaxBuffered. See the Produce documentation for more details.

func (*Client) UncommittedOffsets

func (cl *Client) UncommittedOffsets() map[string]map[int32]EpochOffset

UncommittedOffsets returns the latest uncommitted offsets. Uncommitted offsets are always updated on calls to PollFetches.

If there are no uncommitted offsets, this returns nil.

func (*Client) UnsafeAbortBufferedRecords added in v1.11.0

func (cl *Client) UnsafeAbortBufferedRecords()

UnsafeAbortBufferedRecords fails all unflushed records with ErrAborted and waits for there to be no buffered records. This function does NOT wait for any inflight produce requests to finish, meaning topics in the client may be in an invalid state and producing to an invalid-state topic may cause the client to enter a fatal failed state. If you want to produce to topics that were unsafely aborted, it is recommended to use PurgeTopicsFromClient to forcefully reset the topics before producing to them again.

When producing with idempotency enabled or with transactions, every record has a sequence number. The client must wait for inflight requests to have responses before failing a record, otherwise the client cannot know if a sequence number was seen by the broker and tracked or not seen by the broker and not tracked. By unsafely aborting, the client forcefully abandons all records, and producing to the topics again may re-use a sequence number and cause internal errors.

func (*Client) UpdateFetchMaxBytes added in v1.13.0

func (cl *Client) UpdateFetchMaxBytes(maxBytes, maxPartBytes int32)

UpdateFetchMaxBytes updates the max bytes that a fetch request will ask for and the max partition bytes that a fetch request will ask for each partition.

func (*Client) UpdateSeedBrokers added in v1.12.0

func (cl *Client) UpdateSeedBrokers(addrs ...string) error

UpdateSeedBrokers updates the client's list of seed brokers. Over the course of a long period of time, your might replace all brokers that you originally specified as seeds. This command allows you to replace the client's list of seeds.

This returns an error if any of the input addrs is not a host:port. If the input list is empty, the function returns without replacing the seeds.

type CompressionCodec

type CompressionCodec struct {
	// contains filtered or unexported fields
}

CompressionCodec configures how records are compressed before being sent.

Records are compressed within individual topics and partitions, inside of a RecordBatch. All records in a RecordBatch are compressed into one record for that batch.

func GzipCompression

func GzipCompression() CompressionCodec

GzipCompression enables gzip compression with the default compression level.

func Lz4Compression

func Lz4Compression() CompressionCodec

Lz4Compression enables lz4 compression with the fastest compression level.

func NoCompression

func NoCompression() CompressionCodec

NoCompression is a compression option that avoids compression. This can always be used as a fallback compression.

func SnappyCompression

func SnappyCompression() CompressionCodec

SnappyCompression enables snappy compression.

func ZstdCompression

func ZstdCompression() CompressionCodec

ZstdCompression enables zstd compression with the default compression level.

func (CompressionCodec) WithLevel

func (c CompressionCodec) WithLevel(level int) CompressionCodec

WithLevel changes the compression codec's "level", effectively allowing for higher or lower compression ratios at the expense of CPU speed.

For the zstd package, the level is a typed int; simply convert the type back to an int for this function.

If the level is invalid, compressors just use a default level.

type ConsumerBalancer added in v0.7.0

type ConsumerBalancer struct {
	// contains filtered or unexported fields
}

ConsumerBalancer is a helper type for writing balance plans that use the "consumer" protocol, such that each member uses a kmsg.ConsumerMemberMetadata in its join group request.

func NewConsumerBalancer added in v0.7.0

func NewConsumerBalancer(balance ConsumerBalancerBalance, members []kmsg.JoinGroupResponseMember) (*ConsumerBalancer, error)

NewConsumerBalancer parses the each member's metadata as a kmsg.ConsumerMemberMetadata and returns a ConsumerBalancer to use in balancing.

If any metadata parsing fails, this returns an error.

func (*ConsumerBalancer) Balance added in v0.7.0

Balance satisfies the GroupMemberBalancer interface, but is never called because GroupMemberBalancerOrError exists.

func (*ConsumerBalancer) BalanceOrError added in v1.5.0

func (b *ConsumerBalancer) BalanceOrError(topics map[string]int32) (IntoSyncAssignment, error)

BalanceOrError satisfies the GroupMemberBalancerOrError interface.

func (*ConsumerBalancer) EachMember added in v0.7.0

func (b *ConsumerBalancer) EachMember(fn func(member *kmsg.JoinGroupResponseMember, meta *kmsg.ConsumerMemberMetadata))

EachMember calls fn for each member and its corresponding metadata in the consumer group being balanced.

func (*ConsumerBalancer) MemberAt added in v0.7.0

MemberAt returns the nth member and its corresponding metadata.

func (*ConsumerBalancer) MemberTopics added in v0.7.0

func (b *ConsumerBalancer) MemberTopics() map[string]struct{}

MemberTopics returns the unique set of topics that all members are interested in.

This can safely be called if the balancer is nil; if so, this will return nil.

func (*ConsumerBalancer) Members added in v0.7.0

Members returns the list of input members for this group balancer.

func (*ConsumerBalancer) NewPlan added in v0.7.0

func (b *ConsumerBalancer) NewPlan() *BalancePlan

NewPlan returns a type that can be used to build a balance plan. The return satisfies the IntoSyncAssignment interface.

func (*ConsumerBalancer) SetError added in v1.5.0

func (b *ConsumerBalancer) SetError(err error)

SetError allows you to set any error that occurred while balancing. This allows you to fail balancing and return nil from Balance.

type ConsumerBalancerBalance added in v0.7.0

type ConsumerBalancerBalance interface {
	Balance(*ConsumerBalancer, map[string]int32) IntoSyncAssignment
}

ConsumerBalancerBalance is what the ConsumerBalancer invokes to balance a group.

This is a complicated interface, but in short, this interface has one function that implements the actual balancing logic: using the input balancer, balance the input topics and partitions. If your balancing can fail, you can use ConsumerBalancer.SetError(...) to return an error from balancing, and then you can simply return nil from Balance.

type ConsumerOpt

type ConsumerOpt interface {
	Opt
	// contains filtered or unexported methods
}

ConsumerOpt is a consumer specific option to configure a client. This is simply a namespaced Opt.

func ConsumePartitions

func ConsumePartitions(partitions map[string]map[int32]Offset) ConsumerOpt

ConsumePartitions sets partitions to consume from directly and the offsets to start consuming those partitions from.

This option is basically a way to explicitly consume from subsets of partitions in topics, or to consume at exact offsets. Offsets from this option have higher precedence than the ConsumeResetOffset.

This option is not compatible with group consuming and regex consuming. If you want to assign partitions directly, but still use Kafka to commit offsets, check out the kadm package's FetchOffsets and CommitOffsets methods. These will allow you to commit as a group outside the context of a Kafka group.

func ConsumePreferringLagFn added in v1.10.0

func ConsumePreferringLagFn(fn PreferLagFn) ConsumerOpt

ConsumePreferringLagFn allows you to re-order partitions before they are fetched, given each partition's current lag.

By default, the client rotates partitions fetched by one after every fetch request. Kafka answers fetch requests in the order that partitions are requested, filling the fetch response until FetchMaxBytes and FetchMaxPartitionBytes are hit. All partitions eventually rotate to the front, ensuring no partition is starved.

With this option, you can return topic order and per-topic partition ordering. These orders will sort to the front (first by topic, then by partition). Any topic or partitions that you do not return are added to the end, preserving their original ordering.

For a simple lag preference that sorts the laggiest topics and partitions first, use `kgo.ConsumePreferringLagFn(kgo.PreferLagAt(50))` (or some other similar lag number).

func ConsumeRegex added in v0.8.0

func ConsumeRegex() ConsumerOpt

ConsumeRegex sets the client to parse all topics passed to ConsumeTopics as regular expressions.

When consuming via regex, every metadata request loads *all* topics, so that all topics can be passed to any regular expressions. Every topic is evaluated only once ever across all regular expressions; either it permanently is known to match, or is permanently known to not match.

func ConsumeResetOffset

func ConsumeResetOffset(offset Offset) ConsumerOpt

ConsumeResetOffset sets the offset to start consuming from, or if OffsetOutOfRange is seen while fetching, to restart consuming from. The default is NewOffset().AtStart(), i.e., the earliest offset.

For direct consumers, this is the offset that partitions begin to consume from. For group consumers, this is the offset that partitions begin to consume from if a partition has no commits. If partitions have commits, the commit offset is used. While fetching, if OffsetOutOfRange is encountered, the partition resets to ConsumeResetOffset. Conversely, using NoResetOffset stops consuming a partition if the client encounters OffsetOutOfRange.

If you use an exact offset or relative offsets and the offset ends up out of range, the client chooses the nearest of either the log start offset or the high watermark: using At(3) when the partition starts at 8 results in the partition being consumed from offset 8.

In short form, the following determines the offset for when a partition is seen for the first time, or reset while fetching:

reset at start?                        => log start offset
reset at end?                          => high watermark
reset at exact?                        => this exact offset (3 means offset 3)
reset relative?                        => the above, + / - the relative amount
reset exact or relative out of bounds? => nearest boundary (start or end)
reset after millisec?                  => high watermark, or first offset after millisec if one exists

func ConsumeTopics

func ConsumeTopics(topics ...string) ConsumerOpt

ConsumeTopics adds topics to use for consuming.

By default, consuming will start at the beginning of partitions. To change this, use the ConsumeResetOffset option.

func DisableFetchSessions added in v1.2.4

func DisableFetchSessions() ConsumerOpt

DisableFetchSessions sets the client to not use fetch sessions (Kafka 1.0+).

A "fetch session" is is a way to reduce bandwidth for fetch requests & responses, and to potentially reduce the amount of work that brokers have to do to handle fetch requests. A fetch session opts into the broker tracking some state of what the client is interested in. For example, say that you are interested in thousands of topics, and most of these topics are receiving data only rarely. A fetch session allows the client to register that it is interested in those thousands of topics on the first request. On future requests, if the offsets for these topics have not changed, those topics will be elided from the request. The broker knows to reply with the extra topics if any new data is available, otherwise the topics are also elided from the response. This massively reduces the amount of information that needs to be included in requests or responses.

Using fetch sessions means more state is stored on brokers. Maintaining this state eats some memory. If you have thousands of consumers, you may not want fetch sessions to be used for everything. Brokers intelligently handle this by not creating sessions if they are at their configured limit, but you may consider disabling sessions if they are generally not useful to you. Brokers have metrics for the number of fetch sessions active, so you can monitor that to determine whether enabling or disabling sessions is beneficial or not.

For more details on fetch sessions, see KIP-227.

func FetchIsolationLevel

func FetchIsolationLevel(level IsolationLevel) ConsumerOpt

FetchIsolationLevel sets the "isolation level" used for fetching records, overriding the default ReadUncommitted.

func FetchMaxBytes

func FetchMaxBytes(b int32) ConsumerOpt

FetchMaxBytes sets the maximum amount of bytes a broker will try to send during a fetch, overriding the default 50MiB. Note that brokers may not obey this limit if it has records larger than this limit. Also note that this client sends a fetch to each broker concurrently, meaning the client will buffer up to <brokers * max bytes> worth of memory.

This corresponds to the Java fetch.max.bytes setting.

If bumping this, consider bumping BrokerMaxReadBytes.

If what you are consuming is compressed, and compressed well, it is strongly recommended to set this option so that decompression does not eat all of your RAM.

func FetchMaxPartitionBytes

func FetchMaxPartitionBytes(b int32) ConsumerOpt

FetchMaxPartitionBytes sets the maximum amount of bytes that will be consumed for a single partition in a fetch request, overriding the default 1MiB. Note that if a single batch is larger than this number, that batch will still be returned so the client can make progress.

This corresponds to the Java max.partition.fetch.bytes setting.

func FetchMaxWait

func FetchMaxWait(wait time.Duration) ConsumerOpt

FetchMaxWait sets the maximum amount of time a broker will wait for a fetch response to hit the minimum number of required bytes before returning, overriding the default 5s.

This corresponds to the Java fetch.max.wait.ms setting.

func FetchMinBytes added in v0.6.2

func FetchMinBytes(b int32) ConsumerOpt

FetchMinBytes sets the minimum amount of bytes a broker will try to send during a fetch, overriding the default 1 byte.

With the default of 1, data is sent as soon as it is available. By bumping this, the broker will try to wait for more data, which may improve server throughput at the expense of added latency.

This corresponds to the Java fetch.min.bytes setting.

func KeepControlRecords

func KeepControlRecords() ConsumerOpt

KeepControlRecords sets the client to keep control messages and return them with fetches, overriding the default that discards them.

Generally, control messages are not useful.

func KeepRetryableFetchErrors added in v1.14.0

func KeepRetryableFetchErrors() ConsumerOpt

KeepRetryableFetchErrors switches the client to always return any retryable broker error when fetching, rather than stripping them. By default, the client strips retryable errors from fetch responses; these are usually signals that a client needs to update its metadata to learn of where a partition has moved to (from one broker to another), or they are signals that one broker is temporarily unhealthy (broker not available). You can opt into keeping these errors if you want to specifically react to certain events. For example, if you want to react to you yourself deleting a topic, you can watch for either UNKNOWN_TOPIC_OR_PARTITION or UNKNOWN_TOPIC_ID errors being returned in fetches (and ignore the other errors).

func MaxConcurrentFetches added in v0.10.3

func MaxConcurrentFetches(n int) ConsumerOpt

MaxConcurrentFetches sets the maximum number of fetch requests to allow in flight or buffered at once, overriding the unbounded (i.e. number of brokers) default.

This setting, paired with FetchMaxBytes, can upper bound the maximum amount of memory that the client can use for consuming.

Requests are issued to brokers in a FIFO order: once the client is ready to issue a request to a broker, it registers that request and issues it in order with other registrations.

If Kafka replies with any data, the client does not track the fetch as completed until the user has polled the buffered fetch. Thus, a concurrent fetch is not considered complete until all data from it is done being processed and out of the client itself.

Note that brokers are allowed to hang for up to FetchMaxWait before replying to a request, so if this option is too constrained and you are consuming a low throughput topic, the client may take a long time before requesting a broker that has new data. For high throughput topics, or if the allowed concurrent fetches is large enough, this should not be a concern.

A value of 0 implies the allowed concurrency is unbounded and will be limited only by the number of brokers in the cluster.

func Rack

func Rack(rack string) ConsumerOpt

Rack specifies where the client is physically located and changes fetch requests to consume from the closest replica as opposed to the leader replica.

Consuming from a preferred replica can increase latency but can decrease cross datacenter costs. See KIP-392 for more information.

type EndBeginTxnHow added in v1.4.0

type EndBeginTxnHow uint8

EndBeginTxnHow controls the safety of how EndAndBeginTransaction executes.

const (
	// EndBeginTxnSafe ensures a "safe" execution of EndAndBeginTransaction
	// at the expense of speed. This option blocks all produce requests and
	// only resumes produce requests when onEnd finishes. Note that some
	// produce requests may have finished successfully and records that
	// were a part of a transaction may have their promises waiting to be
	// called: not all promises are guaranteed to be called.
	EndBeginTxnSafe EndBeginTxnHow = iota

	// EndBeginTxnUnsafe opts for less safe EndAndBeginTransaction flow to
	// achieve higher throughput. This option allows produce requests to
	// continue while EndTxn actually commits. This is unsafe because a
	// produce request itself only half begins a transaction. Internally,
	// AddPartitionsToTxn actually begins a transaction. If your
	// application dies before the client is able to successfully issue
	// AddPartitionsToTxn, then a transaction will have partially begun
	// within Kafka: the partial transaction will prevent the partition
	// from being consumable past where the transaction begun, and the
	// transaction will not timeout. You will have to restart your
	// application with the SAME transactional ID and produce to all the
	// same partitions to ensure to resume the transaction and unstick the
	// partitions.
	//
	// Also note: this option does not work on all broker implementations.
	// This relies on Kafka internals. Some brokers (notably Redpanda) are
	// more strict with enforcing transaction correctness and this option
	// cannot be used and will cause errors.
	//
	// Deprecated: Kafka 3.6 removed support for the hacky behavior that
	// this option was abusing. Thus, as of Kafka 3.6, this option does not
	// work against Kafka. This option also has never worked for Redpanda
	// becuse Redpanda always strictly validated that partitions were a
	// part of a transaction. Later versions of Kafka and Redpanda will
	// remove the need for AddPartitionsToTxn at all and thus this option
	// ultimately will be unnecessary anyway.
	EndBeginTxnUnsafe
)

type EpochOffset

type EpochOffset struct {
	// Epoch is the leader epoch of the record being committed. Truncation
	// detection relies on the epoch of the CURRENT record. For truncation
	// detection, the client asks "what is the the end of this epoch?",
	// which returns one after the end offset (see the next field, and
	// check the docs on kmsg.OffsetForLeaderEpochRequest).
	Epoch int32

	// Offset is the offset of a record. If committing, this should be one
	// AFTER a record's offset. Clients start consuming at the offset that
	// is committed.
	Offset int64
}

EpochOffset combines a record offset with the leader epoch the broker was at when the record was written.

func (EpochOffset) Less added in v1.7.0

func (e EpochOffset) Less(o EpochOffset) bool

Less returns whether the this EpochOffset is less than another. This is less than the other if this one's epoch is less, or the epoch's are equal and this one's offset is less.

type ErrDataLoss

type ErrDataLoss struct {
	// Topic is the topic data loss was detected on.
	Topic string
	// Partition is the partition data loss was detected on.
	Partition int32
	// ConsumedTo is what the client had consumed to for this partition before
	// data loss was detected.
	ConsumedTo int64
	// ResetTo is what the client reset the partition to; everything from
	// ResetTo to ConsumedTo was lost.
	ResetTo int64
}

ErrDataLoss is returned for Kafka >=2.1 when data loss is detected and the client is able to reset to the last valid offset.

func (*ErrDataLoss) Error

func (e *ErrDataLoss) Error() string

type ErrFirstReadEOF added in v1.9.0

type ErrFirstReadEOF struct {
	// contains filtered or unexported fields
}

ErrFirstReadEOF is returned for responses that immediately error with io.EOF. This is the client's guess as to why a read from a broker is failing with io.EOF. Two cases are currently handled,

  • When the client is using TLS but brokers are not, brokers close connections immediately because the incoming request looks wrong.
  • When SASL is required but missing, brokers close connections immediately.

There may be other reasons that an immediate io.EOF is encountered (perhaps the connection truly was severed before a response was received), but this error can help you quickly check common problems.

func (*ErrFirstReadEOF) Error added in v1.9.0

func (e *ErrFirstReadEOF) Error() string

func (*ErrFirstReadEOF) Unwrap added in v1.9.0

func (e *ErrFirstReadEOF) Unwrap() error

Unwrap returns io.EOF (or, if a custom dialer returned a wrapped io.EOF, this returns the custom dialer's wrapped error).

type ErrGroupSession added in v1.13.0

type ErrGroupSession struct {
	// contains filtered or unexported fields
}

ErrGroupSession is injected into a poll if an error occurred such that your consumer group member was kicked from the group or was never able to join the group.

func (*ErrGroupSession) Error added in v1.13.0

func (e *ErrGroupSession) Error() string

func (*ErrGroupSession) Unwrap added in v1.13.0

func (e *ErrGroupSession) Unwrap() error

type Fetch

type Fetch struct {
	// Topics are all topics being responded to from a fetch to a broker.
	Topics []FetchTopic
}

Fetch is an individual response from a broker.

type FetchBatchMetrics added in v0.8.1

type FetchBatchMetrics struct {
	// NumRecords is the number of records that were fetched in this batch.
	//
	// Note that this number includes transaction markers, which are not
	// actually returned to the user.
	//
	// If the batch has an encoding error, this will be 0.
	NumRecords int

	// UncompressedBytes is the number of bytes the records deserialized
	// into after decompresion.
	//
	// For record batches (Kafka v0.11.0+), this is the size of the records
	// in a batch, and does not include record batch overhead.
	//
	// For message sets, this size includes message set overhead.
	//
	// Note that this number may be higher than the corresponding number
	// when producing, because as an "optimization", Kafka can return
	// partial batches when fetching.
	UncompressedBytes int

	// CompressedBytes is the number of bytes actually read for this batch,
	// before decompression. If the batch was not compressed, this will be
	// equal to UncompressedBytes.
	//
	// For record batches, this is the size of the compressed records, and
	// does not include record batch overhead.
	//
	// For message sets, this is the size of the compressed message set.
	CompressedBytes int

	// CompressionType signifies which algorithm the batch was compressed
	// with.
	//
	// 0 is no compression, 1 is gzip, 2 is snappy, 3 is lz4, and 4 is
	// zstd.
	CompressionType uint8
}

FetchBatchMetrics tracks information about fetches of batches.

type FetchError

type FetchError struct {
	Topic     string
	Partition int32
	Err       error
}

FetchError is an error in a fetch along with the topic and partition that the error was on.

type FetchPartition

type FetchPartition struct {
	// Partition is the partition this is for.
	Partition int32
	// Err is an error for this partition in the fetch.
	//
	// Note that if this is a fatal error, such as data loss or non
	// retryable errors, this partition will never be fetched again.
	Err error
	// HighWatermark is the current high watermark for this partition, that
	// is, the current offset that is on all in sync replicas.
	HighWatermark int64
	// LastStableOffset is the offset at which all prior offsets have been
	// "decided". Non transactional records are always decided immediately,
	// but transactional records are only decided once they are committed
	// or aborted.
	//
	// The LastStableOffset will always be at or under the HighWatermark.
	LastStableOffset int64
	// LogStartOffset is the low watermark of this partition, otherwise
	// known as the earliest offset in the partition.
	LogStartOffset int64
	// Records contains feched records for this partition.
	Records []*Record
}

FetchPartition is a response for a partition in a fetched topic from a broker.

func (*FetchPartition) EachRecord added in v1.1.0

func (p *FetchPartition) EachRecord(fn func(*Record))

EachRecord calls fn for each record in the partition.

type FetchTopic

type FetchTopic struct {
	// Topic is the topic this is for.
	Topic string
	// Partitions contains individual partitions in the topic that were
	// fetched.
	Partitions []FetchPartition
}

FetchTopic is a response for a fetched topic from a broker.

func (*FetchTopic) EachPartition added in v1.1.0

func (t *FetchTopic) EachPartition(fn func(FetchPartition))

EachPartition calls fn for each partition in Fetches.

func (*FetchTopic) EachRecord added in v1.2.3

func (t *FetchTopic) EachRecord(fn func(*Record))

EachRecord calls fn for each record in the topic, in any partition order.

func (*FetchTopic) Records added in v1.2.3

func (t *FetchTopic) Records() []*Record

Records returns all records in all partitions in this topic.

This is a convenience function that does a single slice allocation. If you can process records individually, it is far more efficient to use the Each functions.

type FetchTopicPartition added in v0.6.10

type FetchTopicPartition struct {
	// Topic is the topic this is for.
	Topic string
	// FetchPartition is an individual partition within this topic.
	FetchPartition
}

FetchTopicPartition is similar to FetchTopic, but for an individual partition.

func (*FetchTopicPartition) EachRecord added in v0.6.10

func (r *FetchTopicPartition) EachRecord(fn func(*Record))

EachRecord calls fn for each record in the topic's partition.

type Fetches

type Fetches []Fetch

Fetches is a group of fetches from brokers.

func NewErrFetch added in v1.15.0

func NewErrFetch(err error) Fetches

NewErrFetch returns a fake fetch containing a single empty topic with a single zero partition with the given error.

func (Fetches) EachError added in v0.8.0

func (fs Fetches) EachError(fn func(string, int32, error))

EachError calls fn for every partition that had a fetch error with the topic, partition, and error.

This function has the same semantics as the Errors function; refer to the documentation on that function for what types of errors are possible.

func (Fetches) EachPartition added in v0.6.10

func (fs Fetches) EachPartition(fn func(FetchTopicPartition))

EachPartition calls fn for each partition in Fetches.

Partitions are not visited in any specific order, and a topic may be visited multiple times if it is spread across fetches.

func (Fetches) EachRecord added in v0.7.0

func (fs Fetches) EachRecord(fn func(*Record))

EachRecord calls fn for each record in Fetches.

This is very similar to using a record iter, and is solely a convenience function depending on which style you prefer.

func (Fetches) EachTopic added in v0.7.0

func (fs Fetches) EachTopic(fn func(FetchTopic))

EachTopic calls fn for each topic in Fetches.

This is a convenience function that groups all partitions for the same topic from many fetches into one FetchTopic. A map is internally allocated to group partitions per topic before calling fn.

func (Fetches) Empty added in v1.7.0

func (fs Fetches) Empty() bool

Empty checks whether the fetch result empty. This method is faster than NumRecords() == 0.

func (Fetches) Err added in v1.5.1

func (fs Fetches) Err() error

Err returns the first error in all fetches, if any. This can be used to quickly check if the client is closed or your poll context was canceled, or to check if there's some other error that requires deeper investigation with EachError. This function performs a linear scan over all fetched partitions. It is recommended to always check all errors. If you would like to more quickly check ahead of time if a poll was canceled because of closing the client or canceling the context, you can use Err0.

func (Fetches) Err0 added in v1.7.0

func (fs Fetches) Err0() error

Err0 returns the error at the 0th index fetch, topic, and partition. This can be used to quickly check if polling returned early because the client was closed or the context was canceled and is faster than performing a linear scan over all partitions with Err. When the client is closed or the context is canceled, fetches will contain only one partition whose Err field indicates the close / cancel. Note that this returns whatever the first error is, nil or non-nil, and does not check for a specific error value.

func (Fetches) Errors

func (fs Fetches) Errors() []FetchError

Errors returns all errors in a fetch with the topic and partition that errored.

There are a few classes of errors possible:

  1. a normal kerr.Error; these are usually the non-retryable kerr.Errors, but theoretically a non-retryable error can be fixed at runtime (auth error? fix auth). It is worth restarting the client for these errors if you do not intend to fix this problem at runtime.

  2. an injected *ErrDataLoss; these are informational, the client automatically resets consuming to where it should and resumes. This error is worth logging and investigating, but not worth restarting the client for.

  3. an untyped batch parse failure; these are usually unrecoverable by restarts, and it may be best to just let the client continue. However, restarting is an option, but you may need to manually repair your partition.

  4. an injected ErrClientClosed; this is a fatal informational error that is returned from every Poll call if the client has been closed. A corresponding helper function IsClientClosed can be used to detect this error.

  5. an injected context error; this can be present if the context you were using for polling timed out or was canceled.

  6. an injected ErrGroupSession; this is an informational error that is injected once a group session is lost in a way that is not the standard rebalance. This error can signify that your consumer member is not able to connect to the group (ACL problems, unreachable broker), or you blocked rebalancing for too long, or your callbacks took too long.

This list may grow over time.

func (Fetches) IsClientClosed added in v0.8.1

func (fs Fetches) IsClientClosed() bool

IsClientClosed returns whether the fetches include an error indicating that the client is closed.

This function is useful to break out of a poll loop; you likely want to call this function before calling Errors. If you may cancel the context to poll, you may want to use Err0 and manually check errors.Is(ErrClientClosed) or errors.Is(context.Canceled).

func (Fetches) NumRecords added in v1.7.0

func (fs Fetches) NumRecords() (n int)

NumRecords returns the total number of records across all fetched partitions.

func (Fetches) RecordIter

func (fs Fetches) RecordIter() *FetchesRecordIter

RecordIter returns an iterator over all records in a fetch.

Note that errors should be inspected as well.

func (Fetches) Records added in v0.11.1

func (fs Fetches) Records() []*Record

Records returns all records in all fetches.

This is a convenience function that does a single slice allocation. If you can process records individually, it is far more efficient to use the Each functions or the RecordIter.

type FetchesRecordIter

type FetchesRecordIter struct {
	// contains filtered or unexported fields
}

FetchesRecordIter iterates over records in a fetch.

func (*FetchesRecordIter) Done

func (i *FetchesRecordIter) Done() bool

Done returns whether there are any more records to iterate over.

func (*FetchesRecordIter) Next

func (i *FetchesRecordIter) Next() *Record

Next returns the next record from a fetch.

type FirstErrPromise added in v0.7.0

type FirstErrPromise struct {
	// contains filtered or unexported fields
}

FirstErrPromise is a helper type to capture only the first failing error when producing a batch of records with this type's Promise function.

This is useful for when you only care about any record failing, and can use that as a signal (i.e., to abort a batch). The AbortingFirstErrPromise function can be used to abort all records as soon as the first error is encountered. If you do not need to abort, you can use this type with no constructor.

This is similar to using ProduceResult's FirstErr function.

func AbortingFirstErrPromise added in v0.7.4

func AbortingFirstErrPromise(cl *Client) *FirstErrPromise

AbortingFirstErrPromise returns a FirstErrPromise that will call the client's AbortBufferedRecords function if an error is encountered.

This can be used to quickly exit when any error is encountered, rather than waiting while flushing only to discover things errored.

func (*FirstErrPromise) Err added in v0.7.0

func (f *FirstErrPromise) Err() error

Err waits for all promises to complete and then returns any stored error.

func (*FirstErrPromise) Promise added in v0.7.0

func (f *FirstErrPromise) Promise() func(*Record, error)

Promise returns a promise for producing that will store the first error encountered.

The returned promise must eventually be called, because a FirstErrPromise does not return from 'Err' until all promises are completed.

type GroupBalancer

type GroupBalancer interface {
	// ProtocolName returns the name of the protocol, e.g. roundrobin,
	// range, sticky.
	ProtocolName() string

	// JoinGroupMetadata returns the metadata to use in JoinGroup, given
	// the topic interests and the current assignment and group generation.
	//
	// It is safe to modify the input topics and currentAssignment. The
	// input topics are guaranteed to be sorted, as are the partitions for
	// each topic in currentAssignment. It is recommended for your output
	// to be ordered by topic and partitions. Since Kafka uses the output
	// from this function to determine whether a rebalance is needed, a
	// deterministic output will avoid accidental rebalances.
	JoinGroupMetadata(
		topicInterests []string,
		currentAssignment map[string][]int32,
		generation int32,
	) []byte

	// ParseSyncAssignment returns assigned topics and partitions from an
	// encoded SyncGroupResponse's MemberAssignment.
	ParseSyncAssignment(assignment []byte) (map[string][]int32, error)

	// MemberBalancer returns a GroupMemberBalancer for the given group
	// members, as well as the topics that all the members are interested
	// in. If the client does not have some topics in the returned topics,
	// the client issues a metadata request to load the number of
	// partitions in those topics before calling the GroupMemberBalancer's
	// Balance function.
	//
	// The input group members are guaranteed to be sorted first by
	// instance ID, if non-nil, and then by member ID.
	//
	// It is up to the user to decide how to decode each member's
	// ProtocolMetadata field. The default client group protocol of
	// "consumer" by default uses join group metadata's of type
	// kmsg.ConsumerMemberMetadata. If this is the case for you, it may be
	// useful to use the ConsumerBalancer type to help parse the metadata
	// and balance.
	//
	// If the member metadata cannot be deserialized correctly, this should
	// return a relevant error.
	MemberBalancer(members []kmsg.JoinGroupResponseMember) (b GroupMemberBalancer, topics map[string]struct{}, err error)

	// IsCooperative returns if this is a cooperative balance strategy.
	IsCooperative() bool
}

GroupBalancer balances topics and partitions among group members.

A GroupBalancer is roughly equivalent to Kafka's PartitionAssignor.

func CooperativeStickyBalancer

func CooperativeStickyBalancer() GroupBalancer

CooperativeStickyBalancer performs the sticky balancing strategy, but additionally opts the consumer group into "cooperative" rebalancing.

Cooperative rebalancing differs from "eager" (the original) rebalancing in that group members do not stop processing partitions during the rebalance. Instead, once they receive their new assignment, each member determines which partitions it needs to revoke. If any, they send a new join request (before syncing), and the process starts over. This should ultimately end up in only two join rounds, with the major benefit being that processing never needs to stop.

NOTE once a group is collectively using cooperative balancing, it is unsafe to have a member join the group that does not support cooperative balancing. If the only-eager member is elected leader, it will not know of the new multiple join strategy and things will go awry. Thus, once a group is entirely on cooperative rebalancing, it cannot go back.

Migrating an eager group to cooperative balancing requires two rolling bounce deploys. The first deploy should add the cooperative-sticky strategy as an option (that is, each member goes from using one balance strategy to two). During this deploy, Kafka will tell leaders to continue using the old eager strategy, since the old eager strategy is the only one in common among all members. The second rolling deploy removes the old eager strategy. At this point, Kafka will tell the leader to use cooperative-sticky balancing. During this roll, all members in the group that still have both strategies continue to be eager and give up all of their partitions every rebalance. However, once a member only has cooperative-sticky, it can begin using this new strategy and things will work correctly. See KIP-429 for more details.

func RangeBalancer

func RangeBalancer() GroupBalancer

RangeBalancer returns a group balancer that, per topic, maps partitions to group members. Since this works on a topic level, uneven partitions per topic to the number of members can lead to slight partition consumption disparities.

Suppose there are two members M0 and M1, two topics t0 and t1, and each topic has three partitions p0, p1, and p2. The partition balancing will be

M0: [t0p0, t0p1, t1p0, t1p1]
M1: [t0p2, t1p2]

This is equivalent to the Java range balancer.

func RoundRobinBalancer

func RoundRobinBalancer() GroupBalancer

RoundRobinBalancer returns a group balancer that evenly maps topics and partitions to group members.

Suppose there are two members M0 and M1, two topics t0 and t1, and each topic has three partitions p0, p1, and p2. The partition balancing will be

M0: [t0p0, t0p2, t1p1]
M1: [t0p1, t1p0, t1p2]

If all members subscribe to all topics equally, the roundrobin balancer will give a perfect balance. However, if topic subscriptions are quite unequal, the roundrobin balancer may lead to a bad balance. See KIP-49 for one example (note that the fair strategy mentioned in KIP-49 does not exist).

This is equivalent to the Java roundrobin balancer.

func StickyBalancer

func StickyBalancer() GroupBalancer

StickyBalancer returns a group balancer that ensures minimal partition movement on group changes while also ensuring optimal balancing.

Suppose there are three members M0, M1, and M2, and two topics t0 and t1 each with three partitions p0, p1, and p2. If the initial balance plan looks like

M0: [t0p0, t0p1, t0p2]
M1: [t1p0, t1p1, t1p2]
M2: [t2p0, t2p2, t2p2]

If M2 disappears, both roundrobin and range would have mostly destructive reassignments.

Range would result in

M0: [t0p0, t0p1, t1p0, t1p1, t2p0, t2p1]
M1: [t0p2, t1p2, t2p2]

which is imbalanced and has 3 partitions move from members that did not need to move (t0p2, t1p0, t1p1).

RoundRobin would result in

M0: [t0p0, t0p2, t1p1, t2p0, t2p2]
M1: [t0p1, t1p0, t1p2, t2p1]

which is balanced, but has 2 partitions move when they do not need to (t0p1, t1p1).

Sticky balancing results in

M0: [t0p0, t0p1, t0p2, t2p0, t2p2]
M1: [t1p0, t1p1, t1p2, t2p1]

which is balanced and does not cause any unnecessary partition movement. The actual t2 partitions may not be in that exact combination, but they will be balanced.

An advantage of the sticky consumer is that it allows API users to potentially avoid some cleanup until after the consumer knows which partitions it is losing when it gets its new assignment. Users can then only cleanup state for partitions that changed, which will be minimal (see KIP-54; this client also includes the KIP-351 bugfix).

Note that this API implements the sticky partitioning quite differently from the Java implementation. The Java implementation is difficult to reason about and has many edge cases that result in non-optimal balancing (albeit, you likely have to be trying to hit those edge cases). This API uses a different algorithm to ensure optimal balancing while being an order of magnitude faster.

Since the new strategy is a strict improvement over the Java strategy, it is entirely compatible. Any Go client sharing a group with a Java client will not have its decisions undone on leadership change from a Go consumer to a Java one. Java balancers do not apply the strategy it comes up with if it deems the balance score equal to or worse than the original score (the score being effectively equal to the standard deviation of the mean number of assigned partitions). This Go sticky balancer is optimal and extra sticky. Thus, the Java balancer will never back out of a strategy from this balancer.

type GroupMemberBalancer added in v0.7.0

type GroupMemberBalancer interface {
	// Balance balances topics and partitions among group members, where
	// the int32 in the topics map corresponds to the number of partitions
	// known to be in each topic.
	Balance(topics map[string]int32) IntoSyncAssignment
}

GroupMemberBalancer balances topics amongst group members. If your balancing can fail, you can implement GroupMemberBalancerOrError.

type GroupMemberBalancerOrError added in v1.5.0

type GroupMemberBalancerOrError interface {
	GroupMemberBalancer
	BalanceOrError(topics map[string]int32) (IntoSyncAssignment, error)
}

GroupMemberBalancerOrError is an optional extension interface for GroupMemberBalancer. This can be implemented if your balance function can fail.

For interface purposes, it is required to implement GroupMemberBalancer, but Balance will never be called.

type GroupOpt

type GroupOpt interface {
	Opt
	// contains filtered or unexported methods
}

GroupOpt is a consumer group specific option to configure a client. This is simply a namespaced Opt.

func AdjustFetchOffsetsFn added in v1.3.0

func AdjustFetchOffsetsFn(adjustOffsetsBeforeAssign func(context.Context, map[string]map[int32]Offset) (map[string]map[int32]Offset, error)) GroupOpt

AdjustFetchOffsetsFn sets the function to be called when a group is joined after offsets are fetched so that a user can adjust offsets before consumption begins.

This function should not exceed the rebalance interval. It is possible for the group, immediately after finishing a balance, to re-enter a new balancing session. This function is passed a context that is canceled if the current group session finishes (i.e., after revoking).

If you are resetting the position of the offset, you may want to clear any existing "epoch" with WithEpoch(-1). If the epoch is non-negative, the client performs data loss detection, which may result in errors and unexpected behavior.

This function is called after OnPartitionsAssigned and may be called before or after OnPartitionsRevoked.

func AutoCommitCallback added in v0.11.0

func AutoCommitCallback(fn func(*Client, *kmsg.OffsetCommitRequest, *kmsg.OffsetCommitResponse, error)) GroupOpt

AutoCommitCallback sets the callback to use if autocommitting is enabled. This overrides the default callback that logs errors and continues.

func AutoCommitInterval

func AutoCommitInterval(interval time.Duration) GroupOpt

AutoCommitInterval sets how long to go between autocommits, overriding the default 5s.

func AutoCommitMarks added in v0.10.3

func AutoCommitMarks() GroupOpt

AutoCommitMarks switches the autocommitting behavior to only commit "marked" records, which can be done with the MarkCommitRecords method.

This option is basically a halfway point between autocommitting and manually committing. If you have slow batch processing of polls, then you can manually mark records to be autocommitted before you poll again. This way, if you usually take a long time between polls, your partial work can still be automatically checkpointed through autocommitting.

func Balancers

func Balancers(balancers ...GroupBalancer) GroupOpt

Balancers sets the group balancers to use for dividing topic partitions among group members, overriding the current default [cooperative-sticky]. This option is equivalent to Kafka's partition.assignment.strategies option.

For balancing, Kafka chooses the first protocol that all group members agree to support.

Note that if you opt into cooperative-sticky rebalancing, cooperative group balancing is incompatible with eager (classical) rebalancing and requires a careful rollout strategy (see KIP-429).

func BlockRebalanceOnPoll added in v1.4.0

func BlockRebalanceOnPoll() GroupOpt

BlockRebalanceOnPoll switches the client to block rebalances whenever you poll until you explicitly call AllowRebalance. This option also ensures that any OnPartitions{Assigned,Revoked,Lost} callbacks are only called when you allow rebalances; they cannot be called if you have polled and are processing records.

By default, a consumer group is managed completely independently of consuming. A rebalance may occur at any moment. If you poll records, and then a rebalance happens, and then you commit, you may be committing to partitions you no longer own. This will result in duplicates. In the worst case, you could rewind commits that a different member has already made (risking duplicates if another rebalance were to happen before that other member commits again).

By blocking rebalancing after you poll until you call AllowRebalances, you can be sure that you commit records that your member currently owns. However, the big tradeoff is that by blocking rebalances, you put your group member at risk of waiting so long that the group member is kicked from the group because it exceeded the rebalance timeout. To compare clients, Sarama takes the default choice of blocking rebalancing; this option makes kgo more similar to Sarama.

If you use this option, you should ensure that you always process records quickly, and that your OnPartitions{Assigned,Revoked,Lost} callbacks are fast. It is recommended you also use PollRecords rather than PollFetches so that you can bound how many records you process at once. You must always AllowRebalances when you are done processing the records you received. Only rebalances that lose partitions are blocked; rebalances that are strictly net additions or non-modifications do not block (the On callbacks are always blocked so that you can ensure their serialization).

This function can largely replace any commit logic you may want to do in OnPartitionsRevoked.

Lastly, note that this actually blocks any rebalance from calling OnPartitions{Assigned,Revoked,Lost}. If you are using a cooperative rebalancer such as CooperativeSticky, a rebalance can begin right before you poll, and you will still receive records because no partitions are lost yet. The in-progress rebalance only blocks if you are assigned new partitions or if any of your partitions are revoked.

func ConsumerGroup added in v0.8.0

func ConsumerGroup(group string) GroupOpt

ConsumerGroup sets the consumer group for the client to join and consume in. This option is required if using any other group options.

Note that when group consuming, the default is to autocommit every 5s. To be safe, autocommitting only commits what is *previously* polled. If you poll once, nothing will be committed. If you poll again, the first poll is available to be committed. This ensures at-least-once processing, but does mean there is likely some duplicate processing during rebalances. When your client shuts down, you should issue one final synchronous commit before leaving the group (because you will not be polling again, and you are not waiting for an autocommit).

func DisableAutoCommit

func DisableAutoCommit() GroupOpt

DisableAutoCommit disable auto committing.

If you disable autocommitting, you may want to use a custom OnPartitionsRevoked, otherwise you may end up doubly processing records (which is fine, just leads to duplicate processing). Consider the scenario: you, member A, are processing partition 0, and previously committed offset 4 and have now locally processed through offset 30. A rebalance happens, and partition 0 moves to member B. If you use OnPartitionsRevoked, you can detect that you are losing this partition and commit your work through offset 30, so that member B can start processing at offset 30. If you do not commit (i.e. you do not use a custom OnPartitionsRevoked), the other member will start processing at offset 4. It may process through offset 50, leading to double processing of offsets 4 through 29. Worse, you, member A, can rewind member B's commit, because member B may commit offset 50 and you may finally eventually commit offset 30. If a rebalance happens, then even more duplicate processing will occur of offsets 30 through 49.

Again, OnPartitionsRevoked is not necessary, and not using it just means double processing, which for most workloads is fine since a simple group consumer is not EOS / transactional, only at-least-once. But, this is something to be aware of.

func GreedyAutoCommit added in v0.10.2

func GreedyAutoCommit() GroupOpt

GreedyAutoCommit opts into committing everything that has been polled when autocommitting (the dirty offsets), rather than committing what has previously been polled. This option may result in message loss if your application crashes.

func GroupProtocol added in v0.6.10

func GroupProtocol(protocol string) GroupOpt

GroupProtocol sets the group's join protocol, overriding the default value "consumer". The only reason to override this is if you are implementing custom join and sync group logic.

func HeartbeatInterval

func HeartbeatInterval(interval time.Duration) GroupOpt

HeartbeatInterval sets how long a group member goes between heartbeats to Kafka, overriding the default 3,000ms.

Kafka uses heartbeats to ensure that a group member's session stays active. This value can be any value lower than the session timeout, but should be no higher than 1/3rd the session timeout.

This corresponds to Kafka's heartbeat.interval.ms.

func InstanceID

func InstanceID(id string) GroupOpt

InstanceID sets the group consumer's instance ID, switching the group member from "dynamic" to "static".

Prior to Kafka 2.3, joining a group gave a group member a new member ID. The group leader could not tell if this was a rejoining member. Thus, any join caused the group to rebalance.

Kafka 2.3 introduced the concept of an instance ID, which can persist across restarts. This allows for avoiding many costly rebalances and allows for stickier rebalancing for rejoining members (since the ID for balancing stays the same). The main downsides are that you, the user of a client, have to manage instance IDs properly, and that it may take longer to rebalance in the event that a client legitimately dies.

When using an instance ID, the client does NOT send a leave group request when closing. This allows for the client to restart with the same instance ID and rejoin the group to avoid a rebalance. It is strongly recommended to increase the session timeout enough to allow time for the restart (remember that the default session timeout is 10s).

To actually leave the group, you must use an external admin command that issues a leave group request on behalf of this instance ID (see kcl), or you can manually use the kmsg package with a proper LeaveGroupRequest.

NOTE: Leaving a group with an instance ID is only supported in Kafka 2.4+.

NOTE: If you restart a consumer group leader that is using an instance ID, it will not cause a rebalance even if you change which topics the leader is consuming. If your cluster is 3.2+, this client internally works around this limitation and you do not need to trigger a rebalance manually.

func OnOffsetsFetched added in v1.5.0

func OnOffsetsFetched(onFetched func(context.Context, *Client, *kmsg.OffsetFetchResponse) error) GroupOpt

OnOffsetsFetched sets a function to be called after offsets have been fetched after a group has been balanced. This function is meant to allow users to inspect offset commit metadata. An error can be returned to exit this group session and exit back to join group.

This function should not exceed the rebalance interval. It is possible for the group, immediately after finishing a balance, to re-enter a new balancing session. This function is passed a context that is canceled if the current group session finishes (i.e., after revoking).

This function is called after OnPartitionsAssigned and may be called before or after OnPartitionsRevoked.

func OnPartitionsAssigned added in v0.11.0

func OnPartitionsAssigned(onAssigned func(context.Context, *Client, map[string][]int32)) GroupOpt

OnPartitionsAssigned sets the function to be called when a group is joined after partitions are assigned before fetches for those partitions begin.

This function, combined with OnPartitionsRevoked, should not exceed the rebalance interval. It is possible for the group to re-enter a new balancing session immediately after finishing a balance.

This function is passed the client's context, which is only canceled if the client is closed.

This function is not called concurrent with any other OnPartitions callback, and this function is given a new map that the user is free to modify.

This function can be called at any time you are polling or processing records. If you want to ensure this function is called serially with processing, consider the BlockRebalanceOnPoll option.

func OnPartitionsLost added in v0.11.0

func OnPartitionsLost(onLost func(context.Context, *Client, map[string][]int32)) GroupOpt

OnPartitionsLost sets the function to be called on "fatal" group errors, such as IllegalGeneration, UnknownMemberID, and authentication failures. This function differs from OnPartitionsRevoked in that it is unlikely that commits will succeed when partitions are outright lost, whereas commits likely will succeed when revoking partitions.

Because this function is called on any fatal group error, it is possible for this function to be called without the group ever being joined.

This function is not called concurrent with any other OnPartitions callback, and this function is given a new map that the user is free to modify.

This function can be called at any time you are polling or processing records. If you want to ensure this function is called serially with processing, consider the BlockRebalanceOnPoll option.

func OnPartitionsRevoked added in v0.11.0

func OnPartitionsRevoked(onRevoked func(context.Context, *Client, map[string][]int32)) GroupOpt

OnPartitionsRevoked sets the function to be called once this group member has partitions revoked.

This function, combined with OnPartitionsAssigned, should not exceed the rebalance interval. It is possible for the group to re-enter a new balancing session immediately after finishing a balance.

If autocommit is enabled, the default OnPartitionsRevoked is a blocking commit of all non-dirty offsets (where "dirty" is the most recent poll).

The OnPartitionsRevoked function is passed the client's context, which is only canceled if the client is closed. OnPartitionsRevoked function is called at the end of a group session even if there are no partitions being revoked. If you are committing offsets manually (have disabled autocommitting), it is highly recommended to do a proper blocking commit in OnPartitionsRevoked.

This function is not called concurrent with any other OnPartitions callback, and this function is given a new map that the user is free to modify.

This function can be called at any time you are polling or processing records. If you want to ensure this function is called serially with processing, consider the BlockRebalanceOnPoll option.

This function is called if a "fatal" group error is encountered and you have not set OnPartitionsLost. See OnPartitionsLost for more details.

func RebalanceTimeout

func RebalanceTimeout(timeout time.Duration) GroupOpt

RebalanceTimeout sets how long group members are allowed to take when a a rebalance has begun, overriding the default 60,000ms. This timeout is how long all members are allowed to complete work and commit offsets, minus the time it took to detect the rebalance (from a heartbeat).

Kafka uses the largest rebalance timeout of all members in the group. If a member does not rejoin within this timeout, Kafka will kick that member from the group.

This corresponds to Kafka's rebalance.timeout.ms.

func RequireStableFetchOffsets

func RequireStableFetchOffsets() GroupOpt

RequireStableFetchOffsets sets the group consumer to require "stable" fetch offsets before consuming from the group. Proposed in KIP-447 and introduced in Kafka 2.5, stable offsets are important when consuming from partitions that a transactional producer could be committing to.

With this option, Kafka will block group consumers from fetching offsets for partitions that are in an active transaction. This option is **strongly** recommended to help prevent duplication problems. See this repo's KIP-447 doc to learn more.

Because this can block consumption, it is strongly recommended to set transactional timeouts to a small value (10s) rather than the default 60s. Lowering the transactional timeout will reduce the chance that consumers are entirely blocked.

func SessionTimeout

func SessionTimeout(timeout time.Duration) GroupOpt

SessionTimeout sets how long a member in the group can go between heartbeats, overriding the default 45,000ms. If a member does not heartbeat in this timeout, the broker will remove the member from the group and initiate a rebalance.

If you are using a GroupTransactSession for EOS, wish to lower this, and are talking to a Kafka cluster pre 2.5, consider lowering the TransactionTimeout. If you do not, you risk a transaction finishing after a group has rebalanced, which could lead to duplicate processing. If you are talking to a Kafka 2.5+ cluster, you can safely use the RequireStableFetchOffsets group option and prevent any problems.

This option corresponds to Kafka's session.timeout.ms setting and must be within the broker's group.min.session.timeout.ms and group.max.session.timeout.ms.

type GroupTransactSession

type GroupTransactSession struct {
	// contains filtered or unexported fields
}

GroupTransactSession abstracts away the proper way to begin and end a transaction when consuming in a group, modifying records, and producing (EOS).

If you are running Kafka 2.5+, it is strongly recommended that you also use RequireStableFetchOffsets. See that config option's documentation for more details.

func NewGroupTransactSession added in v0.8.0

func NewGroupTransactSession(opts ...Opt) (*GroupTransactSession, error)

NewGroupTransactSession is exactly the same as NewClient, but wraps the client's OnPartitionsRevoked / OnPartitionsLost to ensure that transactions are correctly aborted whenever necessary so as to properly provide EOS.

When ETLing in a group in a transaction, if a rebalance happens before the transaction is ended, you either (a) must block the rebalance from finishing until you are done producing, and then commit before unblocking, or (b) allow the rebalance to happen, but abort any work you did.

The problem with (a) is that if your ETL work loop is slow, you run the risk of exceeding the rebalance timeout and being kicked from the group. You will try to commit, and depending on the Kafka version, the commit may even be erroneously successful (pre Kafka 2.5). This will lead to duplicates.

Instead, for safety, a GroupTransactSession favors (b). If a rebalance occurs at any time before ending a transaction with a commit, this will abort the transaction.

This leaves the risk that ending the transaction itself exceeds the rebalance timeout, but this is just one request with no cpu logic. With a proper rebalance timeout, this single request will not fail and the commit will succeed properly.

If this client detects you are talking to a pre-2.5 cluster, OR if you have not enabled RequireStableFetchOffsets, the client will sleep for 200ms after a successful commit to allow Kafka's txn markers to propagate. This is not foolproof in the event of some extremely unlikely communication patterns and **potentially** could allow duplicates. See this repo's transaction's doc for more details.

func (*GroupTransactSession) Begin

func (s *GroupTransactSession) Begin() error

Begin begins a transaction, returning an error if the client has no transactional id or is already in a transaction. Begin must be called before producing records in a transaction.

func (*GroupTransactSession) Client added in v0.8.0

func (s *GroupTransactSession) Client() *Client

Client returns the underlying client that this transact session wraps. This can be useful for functions that require a client, such as raw requests. The returned client should not be used to manage transactions (leave that to the GroupTransactSession).

func (*GroupTransactSession) Close added in v0.8.0

func (s *GroupTransactSession) Close()

Close is a wrapper around Client.Close, with the exact same semantics. Refer to that function's documentation.

This function must be called to leave the group before shutting down.

func (*GroupTransactSession) End

func (s *GroupTransactSession) End(ctx context.Context, commit TransactionEndTry) (committed bool, err error)

End ends a transaction, committing if commit is true, if the group did not rebalance since the transaction began, and if committing offsets is successful. If any of these conditions are false, this aborts. This flushes or aborts depending on `commit`.

This returns whether the transaction committed or any error that occurred. No returned error is retryable. Either the transactional ID has entered a failed state, or the client retried so much that the retry limit was hit, and odds are you should not continue. While a context is allowed, canceling it will likely leave the client in an invalid state. Canceling should only be done if you want to shut down.

func (*GroupTransactSession) PollFetches added in v0.6.10

func (s *GroupTransactSession) PollFetches(ctx context.Context) Fetches

PollFetches is a wrapper around Client.PollFetches, with the exact same semantics. Refer to that function's documentation.

It is invalid to call PollFetches concurrently with Begin or End.

func (*GroupTransactSession) PollRecords added in v0.6.10

func (s *GroupTransactSession) PollRecords(ctx context.Context, maxPollRecords int) Fetches

PollRecords is a wrapper around Client.PollRecords, with the exact same semantics. Refer to that function's documentation.

It is invalid to call PollRecords concurrently with Begin or End.

func (*GroupTransactSession) Produce added in v0.6.10

func (s *GroupTransactSession) Produce(ctx context.Context, r *Record, promise func(*Record, error))

Produce is a wrapper around Client.Produce, with the exact same semantics. Refer to that function's documentation.

It is invalid to call Produce concurrently with Begin or End.

func (*GroupTransactSession) ProduceSync added in v0.7.0

func (s *GroupTransactSession) ProduceSync(ctx context.Context, rs ...*Record) ProduceResults

ProduceSync is a wrapper around Client.ProduceSync, with the exact same semantics. Refer to that function's documentation.

It is invalid to call ProduceSync concurrently with Begin or End.

func (*GroupTransactSession) TryProduce added in v1.4.0

func (s *GroupTransactSession) TryProduce(ctx context.Context, r *Record, promise func(*Record, error))

TryProduce is a wrapper around Client.TryProduce, with the exact same semantics. Refer to that function's documentation.

It is invalid to call TryProduce concurrently with Begin or End.

type Hook

type Hook any

Hook is a hook to be called when something happens in kgo.

The base Hook interface is useless, but wherever a hook can occur in kgo, the client checks if your hook implements an appropriate interface. If so, your hook is called.

This allows you to only hook in to behavior you care about, and it allows the client to add more hooks in the future.

All hook interfaces in this package have Hook in the name. Hooks must be safe for concurrent use. It is expected that hooks are fast; if a hook needs to take time, then copy what you need and ensure the hook is async.

type HookBrokerConnect added in v0.7.0

type HookBrokerConnect interface {
	// OnBrokerConnect is passed the broker metadata, how long it took to
	// dial, and either the dial's resulting net.Conn or error.
	OnBrokerConnect(meta BrokerMetadata, dialDur time.Duration, conn net.Conn, err error)
}

HookBrokerConnect is called after a connection to a broker is opened.

type HookBrokerDisconnect added in v0.7.0

type HookBrokerDisconnect interface {
	// OnBrokerDisconnect is passed the broker metadata and the connection
	// that is closing.
	OnBrokerDisconnect(meta BrokerMetadata, conn net.Conn)
}

HookBrokerDisconnect is called when a connection to a broker is closed.

type HookBrokerE2E added in v0.7.7

type HookBrokerE2E interface {
	// OnBrokerE2E is passed the broker metadata, the key for the
	// request/response that was written/read, and the e2e info for the
	// request and response.
	OnBrokerE2E(meta BrokerMetadata, key int16, e2e BrokerE2E)
}

HookBrokerE2E is called after a write to a broker that errors, or after a read to a broker.

This differs from HookBrokerRead and HookBrokerWrite by tracking all E2E info for a write and a read, which allows for easier e2e metrics. This hook can replace both the read and write hook.

type HookBrokerRead added in v0.7.0

type HookBrokerRead interface {
	// OnBrokerRead is passed the broker metadata, the key for the response
	// that was read, the number of bytes read (may not be the whole read
	// if there was an error), how long the client waited before reading
	// the response, how long it took to read the response, and any error.
	//
	// The bytes read does not count any tls overhead.
	OnBrokerRead(meta BrokerMetadata, key int16, bytesRead int, readWait, timeToRead time.Duration, err error)
}

HookBrokerRead is called after a read from a broker.

Kerberos SASL does not cause read hooks, since it directly reads from the connection.

type HookBrokerThrottle added in v0.7.0

type HookBrokerThrottle interface {
	// OnBrokerThrottle is passed the broker metadata, the imposed
	// throttling interval, and whether the throttle was applied before
	// Kafka responded to them request or after.
	//
	// For Kafka < 2.0, the throttle is applied before issuing a response.
	// For Kafka >= 2.0, the throttle is applied after issuing a response.
	//
	// If throttledAfterResponse is false, then Kafka already applied the
	// throttle. If it is true, the client internally will not send another
	// request until the throttle deadline has passed.
	OnBrokerThrottle(meta BrokerMetadata, throttleInterval time.Duration, throttledAfterResponse bool)
}

HookBrokerThrottle is called after a response to a request is read from a broker, and the response identifies throttling in effect.

type HookBrokerWrite added in v0.7.0

type HookBrokerWrite interface {
	// OnBrokerWrite is passed the broker metadata, the key for the request
	// that was written, the number of bytes that were written (may not be
	// the whole request if there was an error), how long the request
	// waited before being written (including throttling waiting), how long
	// it took to write the request, and any error.
	//
	// The bytes written does not count any tls overhead.
	OnBrokerWrite(meta BrokerMetadata, key int16, bytesWritten int, writeWait, timeToWrite time.Duration, err error)
}

HookBrokerWrite is called after a write to a broker.

Kerberos SASL does not cause write hooks, since it directly writes to the connection.

type HookClientClosed added in v1.13.0

type HookClientClosed interface {
	// OnClientClosed is passed the client that has been closed, after
	// all client-internal close cleanup has happened.
	OnClientClosed(*Client)
}

HookClientClosed is called in Close or CloseAfterRebalance after a client has been closed. This hook can be used to perform final cleanup work.

type HookFetchBatchRead added in v0.8.1

type HookFetchBatchRead interface {
	// OnFetchBatchRead is called per batch read from a topic partition.
	OnFetchBatchRead(meta BrokerMetadata, topic string, partition int32, metrics FetchBatchMetrics)
}

HookFetchBatchRead is called whenever a batch if read within the client.

Note that this hook is called when processing, but a batch may be internally discarded after processing in some uncommon specific circumstances.

If the client reads v0 or v1 message sets, and they are not compressed, then this hook will be called per record.

type HookFetchRecordBuffered added in v0.8.7

type HookFetchRecordBuffered interface {
	// OnFetchRecordBuffered is passed a record that is now buffered, ready
	// to be polled.
	OnFetchRecordBuffered(*Record)
}

HookFetchRecordBuffered is called when a record is internally buffered after fetching, ready to be polled.

This hook can be used to write gauge metrics regarding the number of records or bytes buffered, or to write interceptors that modify a record before being returned from polling. If you just want a metric for the number of records buffered, use the client's BufferedFetchRecords method, as it is faster.

Note that this hook will slow down high-volume consuming a bit.

type HookFetchRecordUnbuffered added in v0.8.7

type HookFetchRecordUnbuffered interface {
	// OnFetchRecordUnbuffered is passwed a record that is being
	// "unbuffered" within the client, and whether the record is being
	// returned from polling.
	OnFetchRecordUnbuffered(r *Record, polled bool)
}

HookFetchRecordUnbuffered is called when a fetched record is unbuffered.

A record can be internally discarded after being in some scenarios without being polled, such as when the internal assignment changes.

As an example, if using HookFetchRecordBuffered for a gauge of how many record bytes are buffered ready to be polled, this hook can be used to decrement the gauge.

Note that this hook may slow down high-volume consuming a bit.

type HookGroupManageError added in v0.7.0

type HookGroupManageError interface {
	// OnGroupManageError is passed the error that killed a group session.
	// This can be used to detect potentially fatal errors and act on them
	// at runtime to recover (such as group auth errors, or group max size
	// reached).
	OnGroupManageError(error)
}

HookGroupManageError is called after every error that causes the client, operating as a group member, to break out of the group managing loop and backoff temporarily.

Specifically, any error that would result in OnPartitionsLost being called will result in this hook being called.

type HookNewClient added in v0.8.7

type HookNewClient interface {
	// OnNewClient is passed the newly initialized client, before any
	// client goroutines are started.
	OnNewClient(*Client)
}

HookNewClient is called in NewClient after a client is initialized. This hook can be used to perform final setup work in your hooks.

type HookProduceBatchWritten added in v0.8.1

type HookProduceBatchWritten interface {
	// OnProduceBatchWritten is called per successful batch written to a
	// topic partition
	OnProduceBatchWritten(meta BrokerMetadata, topic string, partition int32, metrics ProduceBatchMetrics)
}

HookProduceBatchWritten is called whenever a batch is known to be successfully produced.

type HookProduceRecordBuffered added in v0.8.7

type HookProduceRecordBuffered interface {
	// OnProduceRecordBuffered is passed a record that is buffered.
	//
	// This hook is called immediately after Produce is called, after the
	// function potentially sets the default topic.
	OnProduceRecordBuffered(*Record)
}

HookProduceRecordBuffered is called when a record is buffered internally in the client from a call to Produce.

This hook can be used to write metrics that gather the number of records or bytes buffered, or the hook can be used to write interceptors that modify a record's key / value / headers before being produced. If you just want a metric for the number of records buffered, use the client's BufferedProduceRecords method, as it is faster.

Note that this hook may slow down high-volume producing a bit.

type HookProduceRecordPartitioned added in v1.13.0

type HookProduceRecordPartitioned interface {
	// OnProduceRecordPartitioned is passed a record that has been
	// partitioned and the current broker leader for the partition
	// (note that the leader may change if the partition is moved).
	//
	// This hook is called once a record is queued to be flushed. The
	// record's Partition and Timestamp fields are safe to read.
	OnProduceRecordPartitioned(*Record, int32)
}

HookProduceRecordPartitioned is called when a record is partitioned and internally ready to be flushed.

This hook can be used to create metrics of buffered records per partition, and then you can correlate that to partition leaders and determine which brokers are having problems.

Note that this hook will slow down high-volume producing and it is recommended to only use this temporarily or if you are ok with the performance hit.

type HookProduceRecordUnbuffered added in v0.8.7

type HookProduceRecordUnbuffered interface {
	// OnProduceRecordUnbuffered is passed a record that is just about to
	// have its produce promise called, as well as the error that the
	// promise will be called with.
	OnProduceRecordUnbuffered(*Record, error)
}

HookProduceRecordUnbuffered is called just before a record's promise is finished; this is effectively a mirror of a record promise.

As an example, if using HookProduceRecordBuffered for a gauge of how many record bytes are buffered, this hook can be used to decrement the gauge.

Note that this hook will slow down high-volume producing a bit.

type IntoSyncAssignment added in v0.7.0

type IntoSyncAssignment interface {
	IntoSyncAssignment() []kmsg.SyncGroupRequestGroupAssignment
}

IntoSyncAssignment takes a balance plan and returns a list of assignments to use in a kmsg.SyncGroupRequest.

It is recommended to ensure the output is deterministic and ordered by member / topic / partitions.

type IsolationLevel

type IsolationLevel struct {
	// contains filtered or unexported fields
}

IsolationLevel controls whether uncommitted or only committed records are returned from fetch requests.

func ReadCommitted

func ReadCommitted() IsolationLevel

ReadCommitted is an isolation level to only fetch committed records.

func ReadUncommitted

func ReadUncommitted() IsolationLevel

ReadUncommitted (the default) is an isolation level that returns the latest produced records, be they committed or not.

type LogLevel

type LogLevel int8

LogLevel designates which level the logger should log at.

const (
	// LogLevelNone disables logging.
	LogLevelNone LogLevel = iota
	// LogLevelError logs all errors. Generally, these should not happen.
	LogLevelError
	// LogLevelWarn logs all warnings, such as request failures.
	LogLevelWarn
	// LogLevelInfo logs informational messages, such as requests. This is
	// usually the default log level.
	LogLevelInfo
	// LogLevelDebug logs verbose information, and is usually not used in
	// production.
	LogLevelDebug
)

func (LogLevel) String

func (l LogLevel) String() string

type Logger

type Logger interface {
	// Level returns the log level to log at.
	//
	// Implementations can change their log level on the fly, but this
	// function must be safe to call concurrently.
	Level() LogLevel

	// Log logs a message with key, value pair arguments for the given log
	// level. Keys are always strings, while values can be any type.
	//
	// This must be safe to call concurrently.
	Log(level LogLevel, msg string, keyvals ...any)
}

Logger is used to log informational messages.

func BasicLogger

func BasicLogger(dst io.Writer, level LogLevel, prefixFn func() string) Logger

BasicLogger returns a logger that will print to dst in the following format:

prefix [LEVEL] message; key: val, key: val

prefixFn is optional; if non-nil, it is called for a per-message prefix.

Writes to dst are not checked for errors.

type Offset

type Offset struct {
	// contains filtered or unexported fields
}

Offset is a message offset in a partition.

func NewOffset

func NewOffset() Offset

NewOffset creates and returns an offset to use in ConsumePartitions or ConsumeResetOffset.

The default offset begins at the end.

func NoResetOffset added in v1.4.0

func NoResetOffset() Offset

NoResetOffset returns an offset that can be used as a "none" option for the ConsumeResetOffset option. By default, NoResetOffset starts consuming from the beginning of partitions (similar to NewOffset().AtStart()). This can be changed with AtEnd, Relative, etc.

Using this offset will make it such that if OffsetOutOfRange is ever encountered while consuming, rather than trying to recover, the client will return the error to the user and enter a fatal state (for the partition).

func (Offset) AfterMilli added in v1.5.0

func (o Offset) AfterMilli(millisec int64) Offset

AfterMilli returns an offset that consumes from the first offset after a given timestamp. This option is not compatible with At/Relative/WithEpoch; using any of those will clear the special millisecond state.

This option can be used to consume at the end of existing partitions, but at the start of any new partitions that are created later:

AfterMilli(time.Now().UnixMilli())

By default when using this offset, if consuming encounters an OffsetOutOfRange error, consuming will reset to the first offset after this timestamp. You can use NoResetOffset().AfterMilli(...) to instead switch the client to a fatal state.

func (Offset) At

func (o Offset) At(at int64) Offset

At returns a copy of the calling offset, changing the returned offset to begin at exactly the requested offset.

There are two potential special offsets to use: -2 allows for consuming at the start, and -1 allows for consuming at the end. These two offsets are equivalent to calling AtStart or AtEnd.

If the offset is less than -2, the client bounds it to -2 to consume at the start.

func (Offset) AtEnd

func (o Offset) AtEnd() Offset

AtEnd returns a copy of the calling offset, changing the returned offset to begin at the end of a partition. If you want to consume at the end of the topic as it exists right now, but at the beginning of new partitions as they are added to the topic later, check out AfterMilli.

func (Offset) AtStart

func (o Offset) AtStart() Offset

AtStart returns a copy of the calling offset, changing the returned offset to begin at the beginning of a partition.

func (Offset) EpochOffset added in v1.14.0

func (o Offset) EpochOffset() EpochOffset

EpochOffset returns this offset as an EpochOffset, allowing visibility into what this offset actually currently is.

func (Offset) MarshalJSON added in v0.10.3

func (o Offset) MarshalJSON() ([]byte, error)

MarshalJSON implements json.Marshaler.

func (Offset) Relative

func (o Offset) Relative(n int64) Offset

Relative returns a copy of the calling offset, changing the returned offset to be n relative to what it currently is. If the offset is beginning at the end, Relative(-100) will begin 100 before the end.

func (Offset) String added in v1.2.3

func (o Offset) String() string

String returns the offset as a string; the purpose of this is for logs.

func (Offset) WithEpoch

func (o Offset) WithEpoch(e int32) Offset

WithEpoch returns a copy of the calling offset, changing the returned offset to use the given epoch. This epoch is used for truncation detection; the default of -1 implies no truncation detection.

type Opt

type Opt interface {
	// contains filtered or unexported methods
}

Opt is an option to configure a client.

func AllowAutoTopicCreation added in v0.8.0

func AllowAutoTopicCreation() Opt

AllowAutoTopicCreation enables topics to be auto created if they do not exist when fetching their metadata.

func BrokerMaxReadBytes added in v0.6.2

func BrokerMaxReadBytes(v int32) Opt

BrokerMaxReadBytes sets the maximum response size that can be read from Kafka, overriding the default 100MiB.

This is a safety measure to avoid OOMing on invalid responses. This is slightly double FetchMaxBytes; if bumping that, consider bump this. No other response should run the risk of hitting this limit.

func BrokerMaxWriteBytes

func BrokerMaxWriteBytes(v int32) Opt

BrokerMaxWriteBytes upper bounds the number of bytes written to a broker connection in a single write, overriding the default 100MiB.

This number corresponds to the a broker's socket.request.max.bytes, which defaults to 100MiB.

The only Kafka request that could come reasonable close to hitting this limit should be produce requests, and thus this limit is only enforced for produce requests.

func ClientID

func ClientID(id string) Opt

ClientID uses id for all requests sent to Kafka brokers, overriding the default "kgo".

func ConcurrentTransactionsBackoff added in v1.4.0

func ConcurrentTransactionsBackoff(backoff time.Duration) Opt

ConcurrentTransactionsBackoff sets the backoff interval to use during transactional requests in case we encounter CONCURRENT_TRANSACTIONS error, overriding the default 20ms.

Sometimes, when a client begins a transaction quickly enough after finishing a previous one, Kafka will return a CONCURRENT_TRANSACTIONS error. Clients are expected to backoff slightly and retry the operation. Lower backoffs may increase load on the brokers, while higher backoffs may increase transaction latency in clients.

Note that if brokers are hanging in this concurrent transactions state for too long, the client progressively increases the backoff.

func ConnIdleTimeout added in v0.6.11

func ConnIdleTimeout(timeout time.Duration) Opt

ConnIdleTimeout is a rough amount of time to allow connections to idle before they are closed, overriding the default 20.

In the worst case, a connection can be allowed to idle for up to 2x this time, while the average is expected to be 1.5x (essentially, a uniform distribution from this interval to 2x the interval).

It is possible that a connection can be reaped just as it is about to be written to, but the client internally retries in these cases.

Connections are not reaped if they are actively being written to or read from; thus, a request can take a really long time itself and not be reaped (however, this may lead to the RequestTimeoutOverhead).

func ConsiderMissingTopicDeletedAfter added in v1.15.0

func ConsiderMissingTopicDeletedAfter(t time.Duration) Opt

ConsiderMissingTopicDeletedAfter sets the amount of time a topic can be missing from metadata responses _after_ loading it at least once before it is considered deleted, overriding the default of 15s. Note that for newer versions of Kafka, it may take a bit of time (~15s) for the cluster to fully recognize a newly created topic. If this option is set too low, there is some risk that the client will internally purge and re-see a topic a few times until the cluster fully broadcasts the topic creation.

func DialTLS added in v1.14.0

func DialTLS() Opt

DialTLS opts into dialing brokers with TLS. This is a shortcut for DialTLSConfig with an empty config. See DialTLSConfig for more details.

func DialTLSConfig added in v0.10.0

func DialTLSConfig(c *tls.Config) Opt

DialTLSConfig opts into dialing brokers with the given TLS config with a 10s dial timeout. This is a shortcut for manually specifying a tls dialer using the Dialer option. You can also change the default 10s timeout with DialTimeout.

Every dial, the input config is cloned. If the config's ServerName is not specified, this function uses net.SplitHostPort to extract the host from the broker being dialed and sets the ServerName. In short, it is not necessary to set the ServerName.

func DialTimeout added in v1.9.0

func DialTimeout(timeout time.Duration) Opt

DialTimeout sets the dial timeout, overriding the default of 10s. This option is useful if you do not want to set a custom dialer, and is useful in tandem with DialTLSConfig.

func Dialer

func Dialer(fn func(ctx context.Context, network, host string) (net.Conn, error)) Opt

Dialer uses fn to dial addresses, overriding the default dialer that uses a 10s dial timeout and no TLS.

The context passed to the dial function is the context used in the request that caused the dial. If the request is a client-internal request, the context is the context on the client itself (which is canceled when the client is closed).

This function has the same signature as net.Dialer's DialContext and tls.Dialer's DialContext, meaning you can use this function like so:

kgo.Dialer((&net.Dialer{Timeout: 10*time.Second}).DialContext)

or

kgo.Dialer((&tls.Dialer{...}).DialContext)

func MaxVersions

func MaxVersions(versions *kversion.Versions) Opt

MaxVersions sets the maximum Kafka version to try, overriding the internal unbounded (latest stable) versions.

Note that specific max version pinning is required if trying to interact with versions pre 0.10.0. Otherwise, unless using more complicated requests that this client itself does not natively use, it is generally safe to opt for the latest version. If using the kmsg package directly to issue requests, it is recommended to pin versions so that new fields on requests do not get invalid default zero values before you update your usage.

func MetadataMaxAge

func MetadataMaxAge(age time.Duration) Opt

MetadataMaxAge sets the maximum age for the client's cached metadata, overriding the default 5m, to allow detection of new topics, partitions, etc.

This corresponds to Kafka's metadata.max.age.ms.

func MetadataMinAge

func MetadataMinAge(age time.Duration) Opt

MetadataMinAge sets the minimum time between metadata queries, overriding the default 5s. You may want to raise or lower this to reduce the number of metadata queries the client will make. Notably, if metadata detects an error in any topic or partition, it triggers itself to update as soon as allowed.

func MinVersions added in v0.6.2

func MinVersions(versions *kversion.Versions) Opt

MinVersions sets the minimum Kafka version a request can be downgraded to, overriding the default of the lowest version.

This option is useful if you are issuing requests that you absolutely do not want to be downgraded; that is, if you are relying on features in newer requests, and you are not sure if your brokers can handle those features. By setting a min version, if the client detects it needs to downgrade past the version, it will instead avoid issuing the request.

Unlike MaxVersions, if a request is issued that is unknown to the min versions, the request is allowed. It is assumed that there is no lower bound for that request.

func RequestRetries

func RequestRetries(n int) Opt

RequestRetries sets the number of tries that retryable requests are allowed, overriding the default of 20.

This option does not apply to produce requests; to limit produce request retries / record retries, see RecordRetries.

func RequestTimeoutOverhead added in v0.11.0

func RequestTimeoutOverhead(overhead time.Duration) Opt

RequestTimeoutOverhead uses the given time as overhead while deadlining requests, overriding the default overhead of 10s.

For most requests, the overhead will simply be this timeout. However, for any request with a TimeoutMillis field, the overhead is added on top of the request's TimeoutMillis. This ensures that we give Kafka enough time to actually process the request given the timeout, while still having a deadline on the connection as a whole to ensure it does not hang.

For writes, the timeout is always the overhead. We buffer writes in our client before one quick flush, so we always expect the write to be fast.

Note that hitting the timeout kills a connection, which will fail any other active writes or reads on the connection.

This option is roughly equivalent to request.timeout.ms, but grants additional time to requests that have timeout fields.

func RetryBackoffFn added in v0.10.0

func RetryBackoffFn(backoff func(int) time.Duration) Opt

RetryBackoffFn sets the backoff strategy for how long to backoff for a given amount of retries, overriding the default jittery exponential backoff that ranges from 250ms min to 2.5s max.

This (roughly) corresponds to Kafka's retry.backoff.ms setting and retry.backoff.max.ms (which is being introduced with KIP-500).

func RetryTimeout

func RetryTimeout(t time.Duration) Opt

RetryTimeout sets the upper limit on how long we allow requests to retry, overriding the default of:

JoinGroup: cfg.SessionTimeout (default 45s)
SyncGroup: cfg.SessionTimeout (default 45s)
Heartbeat: cfg.SessionTimeout (default 45s)
   others: 30s

This timeout applies to any request issued through a client's Request function. It does not apply to fetches nor produces.

A value of zero indicates no request timeout.

The timeout is evaluated after a request is issued. If a retry backoff places the next request past the retry timeout deadline, the request will still be tried once more once the backoff expires.

func RetryTimeoutFn added in v0.10.0

func RetryTimeoutFn(t func(int16) time.Duration) Opt

RetryTimeoutFn sets the per-request upper limit on how long we allow requests to retry, overriding the default of:

JoinGroup: cfg.SessionTimeout (default 45s)
SyncGroup: cfg.SessionTimeout (default 45s)
Heartbeat: cfg.SessionTimeout (default 45s)
   others: 30s

This timeout applies to any request issued through a client's Request function. It does not apply to fetches nor produces.

The function is called with the request key that is being retried. While it is not expected that the request key will be used, including it gives users the opportinuty to have different retry timeouts for different keys.

If the function returns zero, there is no retry timeout.

The timeout is evaluated after a request is issued. If a retry backoff places the next request past the retry timeout deadline, the request will still be tried once more once the backoff expires.

func SASL

func SASL(sasls ...sasl.Mechanism) Opt

SASL appends sasl authentication options to use for all connections.

SASL is tried in order; if the broker supports the first mechanism, all connections will use that mechanism. If the first mechanism fails, the client will pick the first supported mechanism. If the broker does not support any client mechanisms, connections will fail.

func SeedBrokers

func SeedBrokers(seeds ...string) Opt

SeedBrokers sets the seed brokers for the client to use, overriding the default 127.0.0.1:9092.

Any seeds that are missing a port use the default Kafka port 9092.

func SoftwareNameAndVersion

func SoftwareNameAndVersion(name, version string) Opt

SoftwareNameAndVersion sets the client software name and version that will be sent to Kafka as part of the ApiVersions request as of Kafka 2.4, overriding the default "kgo" and internal version number.

Kafka exposes this through metrics to help operators understand the impact of clients.

It is generally not recommended to set this. As well, if you do, the name and version must match the following regular expression:

[a-zA-Z0-9](?:[a-zA-Z0-9\.-]*[a-zA-Z0-9])?

Note this means neither the name nor version can be empty.

func WithHooks

func WithHooks(hooks ...Hook) Opt

WithHooks sets hooks to call whenever relevant.

Hooks can be used to layer in metrics (such as Prometheus hooks) or anything else. The client will call all hooks in order. See the Hooks interface for more information, as well as any interface that contains "Hook" in the name to know the available hooks. A single hook can implement zero or all hook interfaces, and only the hooks that it implements will be called.

func WithLogger

func WithLogger(l Logger) Opt

WithLogger sets the client to use the given logger, overriding the default to not use a logger.

It is invalid to use a nil logger; doing so will cause panics.

type Partitioner

type Partitioner interface {
	// forTopic returns a partitioner for an individual topic. It is
	// guaranteed that only one record will use the an individual topic's
	// topicPartitioner at a time, meaning partitioning within a topic does
	// not require locks.
	ForTopic(string) TopicPartitioner
}

Partitioner creates topic partitioners to determine which partition messages should be sent to.

Note that a record struct is unmodified (minus a potential default topic) from producing through partitioning, so you can set fields in the record struct before producing to aid in partitioning with a custom partitioner.

func BasicConsistentPartitioner added in v0.8.1

func BasicConsistentPartitioner(partition func(string) func(r *Record, n int) int) Partitioner

BasicConsistentPartitioner wraps a single function to provide a Partitioner and TopicPartitioner (that function is essentially a combination of Partitioner.ForTopic and TopicPartitioner.Partition).

As a minimal example, if you do not care about the topic and you set the partition before producing:

kgo.BasicConsistentPartitioner(func(topic) func(*Record, int) int {
        return func(r *Record, n int) int {
                return int(r.Partition)
        }
})

func LeastBackupPartitioner added in v0.10.1

func LeastBackupPartitioner() Partitioner

LeastBackupPartitioner prioritizes partitioning by three factors, in order:

  1. pin to the current pick until there is a new batch
  2. on new batch, choose the least backed up partition (the partition with the fewest amount of buffered records)
  3. if multiple partitions are equally least-backed-up, choose one at random

This algorithm prioritizes least-backed-up throughput, which may result in unequal partitioning. It is likely that this algorithm will talk most to the broker that it has the best connection to.

This algorithm is resilient to brokers going down: if a few brokers die, it is possible your throughput will be so high that the maximum buffered records will be reached in the now-offline partitions before metadata responds that the broker is offline. With the standard partitioning algorithms, the only recovery is if the partition is remapped or if the broker comes back online. With the least backup partitioner, downed partitions will see slight backup, but then the other partitions that are still accepting writes will get all of the writes and your client will not be blocked.

Under ideal scenarios (no broker / connection issues), StickyPartitioner is equivalent to LeastBackupPartitioner. This partitioner is only recommended if you are a producer consistently dealing with flaky connections or problematic brokers and do not mind uneven load on your brokers.

func ManualPartitioner added in v0.8.1

func ManualPartitioner() Partitioner

ManualPartitioner is a partitioner that simply returns the Partition field that is already set on any record.

Any record with an invalid partition will be immediately failed. This partitioner is simply the partitioner that is demonstrated in the BasicConsistentPartitioner documentation.

func RoundRobinPartitioner added in v0.10.2

func RoundRobinPartitioner() Partitioner

RoundRobinPartitioner is a partitioner that round-robin's through all available partitions. This algorithm has lower throughput and causes higher CPU load on brokers, but can be useful if you want to ensure an even distribution of records to partitions.

func StickyKeyPartitioner

func StickyKeyPartitioner(hasher PartitionerHasher) Partitioner

StickyKeyPartitioner mirrors the default Java partitioner from Kafka's 2.4 release (see KIP-480 and KAFKA-8601) until their 3.3 release. This was replaced in 3.3 with the uniform sticky partitioner (KIP-794), which is reimplemented in this client as the UniformBytesPartitioner.

This is the same "hash the key consistently, if no key, choose random partition" strategy that the Java partitioner has always used, but rather than always choosing a random partition, the partitioner pins a partition to produce to until that partition rolls over to a new batch. Only when rolling to new batches does this partitioner switch partitions.

The benefit with this pinning is less CPU utilization on Kafka brokers. Over time, the random distribution is the same, but the brokers are handling on average larger batches.

hasher is optional; if nil, this will return a partitioner that partitions exactly how Kafka does. Specifically, the partitioner will use murmur2 to hash keys, will mask out the 32nd bit, and then will mod by the number of potential partitions.

func StickyPartitioner

func StickyPartitioner() Partitioner

StickyPartitioner is the same as StickyKeyPartitioner, but with no logic to consistently hash keys. That is, this only partitions according to the sticky partition strategy.

func UniformBytesPartitioner added in v1.6.0

func UniformBytesPartitioner(bytes int, adaptive, keys bool, hasher PartitionerHasher) Partitioner

UniformBytesPartitioner is a redux of the StickyPartitioner, proposed in KIP-794 and release with the Java client in Kafka 3.3. This partitioner returns the same partition until 'bytes' is hit. At that point, a re-partitioning happens. If adaptive is false, this chooses a new random partition, otherwise this chooses a broker based on the inverse of the backlog currently buffered for that broker. If keys is true, this uses standard hashing based on record key for records with non-nil keys. hasher is optional; if nil, the default hasher murmur2 (Kafka's default).

The point of this hasher is to create larger batches while producing the same amount to all partitions over the long run. Adaptive opts in to a slight imbalance so that this can produce more to brokers that are less loaded.

This implementation differs slightly from Kafka's because this does not account for the compressed size of a batch, nor batch overhead. For overhead, in practice, the overhead is relatively constant so it would affect all batches equally. For compression, this client does not compress until after a batch is created and frozen, so it is not possible to track compression. This client also uses the number of records for backup calculation rather than number of bytes, but the heuristic should be similar. Lastly, this client does not have a timeout for partition availability. Realistically, these will be the most backed up partitions so they should be chosen the least.

NOTE: This implementation may create sub-optimal batches if lingering is enabled. This client's default is to disable lingering. The patch used to address this in Kafka is KAFKA-14156 (which itself is not perfect in the context of disabling lingering). For more details, read KAFKA-14156.

type PartitionerHasher

type PartitionerHasher func([]byte, int) int

PartitionerHasher returns a partition to use given the input data and number of partitions.

func KafkaHasher

func KafkaHasher(hashFn func([]byte) uint32) PartitionerHasher

KafkaHasher returns a PartitionerHasher using hashFn that mirrors how Kafka partitions after hashing data. In Kafka, after hashing into a uint32, the hash is converted to an int32 and the high bit is stripped. Kafka by default uses murmur2 hashing, and the StickyKeyPartiitoner uses this by default. Using this KafkaHasher function is only necessary if you want to change the underlying hashing algorithm.

func SaramaCompatHasher added in v1.16.0

func SaramaCompatHasher(hashFn func([]byte) uint32) PartitionerHasher

SaramaCompatHasher returns a PartitionerHasher using hashFn that mirrors how Sarama partitions after hashing data.

Sarama has two differences from Kafka when partitioning:

1) In Kafka, when converting the uint32 hash to an int32, Kafka masks the high bit. In Sarama, if the high bit is 1 (i.e., the number as an int32 is negative), Sarama negates the number.

2) Kafka by default uses the murmur2 hashing algorithm. Sarama by default uses fnv-1a.

Sarama added a NewReferenceHashPartitioner function that attempted to align with Kafka, but the reference partitioner only fixed the first difference, not the second. Further customization options were added later that made it possible to exactly match Kafka when hashing.

In short, to *exactly* match the Sarama defaults, use the following:

kgo.StickyKeyPartitioner(kgo.SaramaCompatHasher(fnv.New32a()))

func SaramaHasher

func SaramaHasher(hashFn func([]byte) uint32) PartitionerHasher

SaramaHasher is a historical misnamed partitioner. This library's original implementation of the SaramaHasher was incorrect, if you want an exact match for the Sarama partitioner, use the SaramaCompatHasher.

This partitioner remains because as it turns out, other ecosystems provide a similar partitioner and this partitioner is useful for compatibility.

In particular, using this function with a crc32.ChecksumIEEE hasher makes this partitioner match librdkafka's consistent partitioner, or the zendesk/ruby-kafka partitioner.

type PreferLagFn added in v1.10.0

type PreferLagFn func(lag map[string]map[int32]int64, torderPrior []string, porderPrior map[string][]int32) ([]string, map[string][]int32)

PreferLagFn accepts topic and partition lag, the previously determined topic order, and the previously determined per-topic partition order, and returns a new topic and per-topic partition order.

Most use cases will not need to look at the prior orders, but they exist if you want to get fancy.

You can return partial results: if you only return topics, partitions within each topic keep their prior ordering. If you only return some topics but not all, the topics you do not return / the partitions you do not return will retain their original ordering *after* your given ordering.

NOTE: torderPrior and porderPrior must not be modified. To avoid a bit of unnecessary allocations, these arguments are views into data that is used to build a fetch request.

func PreferLagAt added in v1.10.0

func PreferLagAt(preferLagAt int64) PreferLagFn

PreferLagAt is a simple PreferLagFn that orders the largest lag first, for any topic that is collectively lagging more than preferLagAt, and for any partition that is lagging more than preferLagAt.

The function does not prescribe any ordering for topics that have the same lag. It is recommended to use a number more than 0 or 1: if you use 0, you may just always undo client ordering when there is no actual lag.

type ProduceBatchMetrics added in v0.8.1

type ProduceBatchMetrics struct {
	// NumRecords is the number of records that were produced in this
	// batch.
	NumRecords int

	// UncompressedBytes is the number of bytes the records serialized as
	// before compression.
	//
	// For record batches (Kafka v0.11.0+), this is the size of the records
	// in a batch, and does not include record batch overhead.
	//
	// For message sets, this size includes message set overhead.
	UncompressedBytes int

	// CompressedBytes is the number of bytes actually written for this
	// batch, after compression. If compression is not used, this will be
	// equal to UncompresedBytes.
	//
	// For record batches, this is the size of the compressed records, and
	// does not include record batch overhead.
	//
	// For message sets, this is the size of the compressed message set.
	CompressedBytes int

	// CompressionType signifies which algorithm the batch was compressed
	// with.
	//
	// 0 is no compression, 1 is gzip, 2 is snappy, 3 is lz4, and 4 is
	// zstd.
	CompressionType uint8
}

ProduceBatchMetrics tracks information about successful produces to partitions.

type ProduceResult added in v0.7.0

type ProduceResult struct {
	// Record is the produced record. It is always non-nil.
	//
	// If this record was produced successfully, its attrs / offset / id /
	// epoch / etc. fields are filled in on return if possible (i.e. when
	// producing with acks required).
	Record *Record

	// Err is a potential produce error. If this is non-nil, the record was
	// not produced successfully.
	Err error
}

ProduceResult is the result of producing a record in a synchronous manner.

type ProduceResults added in v0.7.0

type ProduceResults []ProduceResult

ProduceResults is a collection of produce results.

func (ProduceResults) First added in v0.7.0

func (rs ProduceResults) First() (*Record, error)

First the first record and error in the produce results.

This function is useful if you only passed one record to ProduceSync.

func (ProduceResults) FirstErr added in v0.7.0

func (rs ProduceResults) FirstErr() error

FirstErr returns the first erroring result, if any.

type ProducerOpt

type ProducerOpt interface {
	Opt
	// contains filtered or unexported methods
}

ProducerOpt is a producer specific option to configure a client. This is simply a namespaced Opt.

func DefaultProduceTopic added in v0.8.0

func DefaultProduceTopic(t string) ProducerOpt

DefaultProduceTopic sets the default topic to produce to if the topic field is empty in a Record.

If this option is not used, if a record has an empty topic, the record cannot be produced and will be failed immediately.

func DisableIdempotentWrite added in v0.6.10

func DisableIdempotentWrite() ProducerOpt

DisableIdempotentWrite disables idempotent produce requests, opting out of Kafka server-side deduplication in the face of reissued requests due to transient network problems. Disabling idempotent write by default upper-bounds the number of in-flight produce requests per broker to 1, vs. the default of 5 when using idempotency.

Idempotent production is strictly a win, but does require the IDEMPOTENT_WRITE permission on CLUSTER (pre Kafka 3.0), and not all clients can have that permission.

This option is incompatible with specifying a transactional id.

func ManualFlushing

func ManualFlushing() ProducerOpt

ManualFlushing disables auto-flushing when producing. While you can still set lingering, it would be useless to do so.

With manual flushing, producing while MaxBufferedRecords or MaxBufferedBytes have already been produced and not flushed will return ErrMaxBuffered.

func MaxBufferedBytes added in v1.15.0

func MaxBufferedBytes(n int) ProducerOpt

MaxBufferedBytes sets the max amount of bytes that the client will buffer while producing, blocking produces until records are finished if this limit is reached. This overrides the unlimited default.

Note that this option does _not_ apply for consuming: the client cannot limit bytes buffered for consuming because of decompression. You can roughly control consuming memory by using MaxConcurrentFetches, FetchMaxBytes, and FetchMaxPartitionBytes.

If you produce a record that is larger than n, the record is immediately failed with kerr.MessageTooLarge.

Note that this limit applies after MaxBufferedRecords.

func MaxBufferedRecords

func MaxBufferedRecords(n int) ProducerOpt

MaxBufferedRecords sets the max amount of records the client will buffer, blocking produces until records are finished if this limit is reached. This overrides the default of 10,000.

func MaxProduceRequestsInflightPerBroker added in v1.4.0

func MaxProduceRequestsInflightPerBroker(n int) ProducerOpt

MaxProduceRequestsInflightPerBroker changes the number of allowed produce requests in flight per broker if you disable idempotency, overriding the default of 1. If using idempotency, this option has no effect: the maximum in flight for Kafka v0.11 is 1, and from v1 onward is 5.

Using more than 1 may result in out of order records and may result in duplicates if there are connection issues.

func ProduceRequestTimeout

func ProduceRequestTimeout(limit time.Duration) ProducerOpt

ProduceRequestTimeout sets how long Kafka broker's are allowed to respond to produce requests, overriding the default 10s. If a broker exceeds this duration, it will reply with a request timeout error.

This somewhat corresponds to Kafka's request.timeout.ms setting, but only applies to produce requests. This settings sets the TimeoutMillis field in the produce request itself. The RequestTimeoutOverhead is applied as a write limit and read limit in addition to this.

func ProducerBatchCompression added in v0.11.0

func ProducerBatchCompression(preference ...CompressionCodec) ProducerOpt

ProducerBatchCompression sets the compression codec to use for producing records.

Compression is chosen in the order preferred based on broker support. For example, zstd compression was introduced in Kafka 2.1, so the preference can be first zstd, fallback snappy, fallback none.

The default preference is [snappy, none], which should be fine for all old consumers since snappy compression has existed since Kafka 0.8.0. To use zstd, your brokers must be at least 2.1 and all consumers must be upgraded to support decoding zstd records.

func ProducerBatchMaxBytes added in v0.11.0

func ProducerBatchMaxBytes(v int32) ProducerOpt

ProducerBatchMaxBytes upper bounds the size of a record batch, overriding the default 1,000,012 bytes. This mirrors Kafka's max.message.bytes.

Record batches are independent of a ProduceRequest: a record batch is specific to a topic and partition, whereas the produce request can contain many record batches for many topics.

If a single record encodes larger than this number (before compression), it will will not be written and a callback will have the appropriate error.

Note that this is the maximum size of a record batch before compression. If a batch compresses poorly and actually grows the batch, the uncompressed form will be used.

func ProducerLinger added in v0.11.0

func ProducerLinger(linger time.Duration) ProducerOpt

ProducerLinger sets how long individual topic partitions will linger waiting for more records before triggering a request to be built.

Note that this option should only be used in low volume producers. The only benefit of lingering is to potentially build a larger batch to reduce cpu usage on the brokers if you have many producers all producing small amounts.

If a produce request is triggered by any topic partition, all partitions with a possible batch to be sent are used and all lingers are reset.

As mentioned, the linger is specific to topic partition. A high volume producer will likely be producing to many partitions; it is both unnecessary to linger in this case and inefficient because the client will have many timers running (and stopping and restarting) unnecessarily.

func ProducerOnDataLossDetected added in v0.11.0

func ProducerOnDataLossDetected(fn func(string, int32)) ProducerOpt

ProducerOnDataLossDetected sets a function to call if data loss is detected when producing records if the client is configured to continue on data loss. Thus, this option is mutually exclusive with StopProducerOnDataLossDetected.

The passed function will be called with the topic and partition that data loss was detected on.

func RecordDeliveryTimeout added in v0.11.0

func RecordDeliveryTimeout(timeout time.Duration) ProducerOpt

RecordDeliveryTimeout sets a rough time of how long a record can sit around in a batch before timing out, overriding the unlimited default.

If idempotency is enabled (as it is by default), this option is only enforced if it is safe to do so without creating invalid sequence numbers. It is safe to enforce if a record was never issued in a request to Kafka, or if it was requested and received a response.

The timeout for all records in a batch inherit the timeout of the first record in that batch. That is, once the first record's timeout expires, all records in the batch are expired. This generally is a non-issue unless using this option with lingering. In that case, simply add the linger to the record timeout to avoid problems.

If a record times out, all records buffered in the same partition are failed as well. This ensures gapless ordering: the client will not fail one record only to produce a later one successfully. This also allows for easier sequence number ordering internally.

The timeout is only evaluated evaluated before writing a request or after a produce response. Thus, a sink backoff may delay record timeout slightly.

This option is roughly equivalent to delivery.timeout.ms.

func RecordPartitioner

func RecordPartitioner(partitioner Partitioner) ProducerOpt

RecordPartitioner uses the given partitioner to partition records, overriding the default UniformBytesPartitioner(64KiB, true, true, nil).

func RecordRetries added in v0.10.0

func RecordRetries(n int) ProducerOpt

RecordRetries sets the number of tries for producing records, overriding the unlimited default.

If idempotency is enabled (as it is by default), this option is only enforced if it is safe to do so without creating invalid sequence numbers. It is safe to enforce if a record was never issued in a request to Kafka, or if it was requested and received a response.

If a record fails due to retries, all records buffered in the same partition are failed as well. This ensures gapless ordering: the client will not fail one record only to produce a later one successfully. This also allows for easier sequence number ordering internally.

If a topic repeatedly fails to load with UNKNOWN_TOPIC_OR_PARTITION, it has a different limit (the UnknownTopicRetries option). All records for a topic that repeatedly cannot be loaded are failed when that limit is hit.

This option is different from RequestRetries to allow finer grained control of when to fail when producing records.

func RequiredAcks

func RequiredAcks(acks Acks) ProducerOpt

RequiredAcks sets the required acks for produced records, overriding the default RequireAllISRAcks.

func StopProducerOnDataLossDetected added in v0.11.0

func StopProducerOnDataLossDetected() ProducerOpt

StopProducerOnDataLossDetected sets the client to stop producing if data loss is detected, overriding the default false.

Note that if using this option, it is strongly recommended to not have a retry limit. Doing so may lead to errors where the client fails a batch on a recoverable error, which internally bumps the idempotent sequence number used for producing, which may then later cause an inadvertent out of order sequence number and false "data loss" detection.

func TransactionTimeout

func TransactionTimeout(timeout time.Duration) ProducerOpt

TransactionTimeout sets the allowed for a transaction, overriding the default 40s. It is a good idea to keep this less than a group's session timeout, so that a group member will always be alive for the duration of a transaction even if connectivity dies. This helps prevent a transaction finishing after a rebalance, which is problematic pre-Kafka 2.5. If you are on Kafka 2.5+, then you can use the RequireStableFetchOffsets option when assigning the group, and you can set this to whatever you would like.

Transaction timeouts begin when the first record is produced within a transaction, not when a transaction begins.

func TransactionalID

func TransactionalID(id string) ProducerOpt

TransactionalID sets a transactional ID for the client, ensuring that records are produced transactionally under this ID (exactly once semantics).

For Kafka-to-Kafka transactions, the transactional ID is only one half of the equation. You must also assign a group to consume from.

To produce transactionally, you first BeginTransaction, then produce records consumed from a group, then you EndTransaction. All records produced outside of a transaction will fail immediately with an error.

After producing a batch, you must commit what you consumed. Auto committing offsets is disabled during transactional consuming / producing.

Note that unless using Kafka 2.5, a consumer group rebalance may be problematic. Production should finish and be committed before the client rejoins the group. It may be safer to use an eager group balancer and just abort the transaction. Alternatively, any time a partition is revoked, you could abort the transaction and reset offsets being consumed.

If the client detects an unrecoverable error, all records produced thereafter will fail.

Lastly, the default read level is READ_UNCOMMITTED. Be sure to use the ReadIsolationLevel option if you want to only read committed.

func UnknownTopicRetries added in v1.4.0

func UnknownTopicRetries(n int) ProducerOpt

UnknownTopicRetries sets the number of times a record can fail with UNKNOWN_TOPIC_OR_PARTITION, overriding the default 4.

This is a separate limit from RecordRetries because unknown topic or partition errors should only happen if the topic does not exist. It is pointless for the client to continue producing to a topic that does not exist, and if we repeatedly see that the topic does not exist across multiple metadata queries (which are going to different brokers), then we may as well stop trying and fail the records.

If this is -1, the client never fails records with this error.

type Record

type Record struct {
	// Key is an optional field that can be used for partition assignment.
	//
	// This is generally used with a hash partitioner to cause all records
	// with the same key to go to the same partition.
	Key []byte
	// Value is blob of data to write to Kafka.
	Value []byte

	// Headers are optional key/value pairs that are passed along with
	// records.
	//
	// These are purely for producers and consumers; Kafka does not look at
	// this field and only writes it to disk.
	Headers []RecordHeader

	// Timestamp is the timestamp that will be used for this record.
	//
	// Record batches are always written with "CreateTime", meaning that
	// timestamps are generated by clients rather than brokers.
	//
	// When producing, if this field is not yet set, it is set to time.Now.
	Timestamp time.Time

	// Topic is the topic that a record is written to.
	//
	// This must be set for producing.
	Topic string

	// Partition is the partition that a record is written to.
	//
	// For producing, this is left unset. This will be set by the client
	// before the record is unbuffered. If you use the ManualPartitioner,
	// the value of this field is always the partition chosen when
	// producing (i.e., you partition manually ahead of time).
	Partition int32

	// Attrs specifies what attributes were on this record.
	//
	// For producing, this is left unset. This will be set by the client
	// before the record is unbuffered.
	Attrs RecordAttrs

	// ProducerEpoch is the producer epoch of this message if it was
	// produced with a producer ID. An epoch and ID of 0 means it was not.
	//
	// For producing, this is left unset. This will be set by the client
	// before the record is unbuffered.
	ProducerEpoch int16

	// ProducerEpoch is the producer ID of this message if it was produced
	// with a producer ID. An epoch and ID of 0 means it was not.
	//
	// For producing, this is left unset. This will be set by the client
	// before the record is unbuffered.
	ProducerID int64

	// LeaderEpoch is the leader epoch of the broker at the time this
	// record was written, or -1 if on message sets.
	//
	// For committing records, it is not recommended to modify the
	// LeaderEpoch. Clients use the LeaderEpoch for data loss detection.
	LeaderEpoch int32

	// Offset is the offset that a record is written as.
	//
	// For producing, this is left unset. This will be set by the client
	// before the record is unbuffered. If you are producing with no acks,
	// this will just be the offset used in the produce request and does
	// not mirror the offset actually stored within Kafka.
	Offset int64

	// Context is an optional field that is used for enriching records.
	//
	// If this field is nil when producing, it is set to the Produce ctx
	// arg. This field can be used to propagate record enrichment across
	// producer hooks. It can also be set in a consumer hook to propagate
	// enrichment to consumer clients.
	Context context.Context
}

Record is a record to write to Kafka.

func KeySliceRecord added in v0.7.0

func KeySliceRecord(key, value []byte) *Record

KeySliceRecord returns a Record with the Key and Value fields set to the input key and value slices. For producing, this function is useful in tandem with the client-level DefaultProduceTopic option.

func KeyStringRecord added in v0.7.0

func KeyStringRecord(key, value string) *Record

KeyStringRecord returns a Record with the Key and Value fields set to the input key and value strings. For producing, this function is useful in tandem with the client-level DefaultProduceTopic option.

This function uses the 'unsafe' package to avoid copying value into a slice.

NOTE: It is NOT SAFE to modify the record's value. This function should only be used if you only ever read record fields. This function can safely be used for producing; the client never modifies a record's key nor value fields.

func SliceRecord added in v0.7.0

func SliceRecord(value []byte) *Record

SliceRecord returns a Record with the Value field set to the input value slice. For producing, this function is useful in tandem with the client-level DefaultProduceTopic option.

func StringRecord added in v0.7.0

func StringRecord(value string) *Record

StringRecord returns a Record with the Value field set to the input value string. For producing, this function is useful in tandem with the client-level DefaultProduceTopic option.

This function uses the 'unsafe' package to avoid copying value into a slice.

NOTE: It is NOT SAFE to modify the record's value. This function should only be used if you only ever read record fields. This function can safely be used for producing; the client never modifies a record's key nor value fields.

func (*Record) AppendFormat added in v1.2.0

func (r *Record) AppendFormat(b []byte, layout string) ([]byte, error)

AppendFormat appends a record to b given the layout or returns an error if the layout is invalid. This is a one-off shortcut for using NewRecordFormatter. See that function's documentation for the layout specification.

type RecordAttrs

type RecordAttrs struct {
	// contains filtered or unexported fields
}

RecordAttrs contains additional meta information about a record, such as its compression or timestamp type.

func (RecordAttrs) CompressionType

func (a RecordAttrs) CompressionType() uint8

CompressionType signifies with which algorithm this record was compressed.

0 is no compression, 1 is gzip, 2 is snappy, 3 is lz4, and 4 is zstd.

func (RecordAttrs) IsControl

func (a RecordAttrs) IsControl() bool

IsControl returns whether a record is a "control" record (ABORT or COMMIT). These are generally not visible unless explicitly opted into.

func (RecordAttrs) IsTransactional

func (a RecordAttrs) IsTransactional() bool

IsTransactional returns whether a record is a part of a transaction.

func (RecordAttrs) TimestampType

func (a RecordAttrs) TimestampType() int8

TimestampType specifies how Timestamp was determined.

The default, 0, means that the timestamp was determined in a client when the record was produced.

An alternative is 1, which is when the Timestamp is set in Kafka.

Records pre 0.10.0 did not have timestamps and have value -1.

type RecordFormatter added in v1.2.0

type RecordFormatter struct {
	// contains filtered or unexported fields
}

RecordFormatter formats records.

func NewRecordFormatter added in v1.2.0

func NewRecordFormatter(layout string) (*RecordFormatter, error)

NewRecordFormatter returns a formatter for the given layout, or an error if the layout is invalid.

The formatter is very powerful, as such there is a lot to describe. This documentation attempts to be as succinct as possible.

Similar to the fmt package, record formatting is based off of slash escapes and percent "verbs" (copying fmt package lingo). Slashes are used for common escapes,

\t \n \r \\ \xNN

printing tabs, newlines, carriage returns, slashes, and hex encoded characters.

Percent encoding opts in to printing aspects of either a record or a fetch partition:

%t    topic
%T    topic length
%k    key
%K    key length
%v    value
%V    value length
%h    begin the header specification
%H    number of headers
%p    partition
%o    offset
%e    leader epoch
%d    timestamp (date, formatting described below)
%a    record attributes (formatting required, described below)
%x    producer id
%y    producer epoch

For AppendPartitionRecord, the formatter also undersands the following three formatting options:

%[    partition log start offset
%|    partition last stable offset
%]    partition high watermark

The formatter internally tracks the number of times AppendRecord or AppendPartitionRecord have been called. The special option %i prints the iteration / call count:

%i    format iteration number (starts at 1)

Lastly, there are three escapes to print raw characters that are usually used for formatting options:

%%    percent sign
%{    left brace (required if a brace is after another format option)
%}    right brace

Header specification

Specifying headers is essentially a primitive nested format option, accepting the key and value escapes above:

%K    header key length
%k    header key
%V    header value length
%v    header value

For example, "%H %h{%k %v }" will print the number of headers, and then each header key and value with a space after each.

Verb modifiers

Most of the previous verb specifications can be modified by adding braces with a given modifier, e.g., "%V{ascii}". All modifiers are described below.

Numbers

All number verbs accept braces that control how the number is printed:

%v{ascii}       the default, print the number as ascii
%v{number}      alias for ascii

%v{hex64}       print 16 hex characters for the number
%v{hex32}       print 8 hex characters for the number
%v{hex16}       print 4 hex characters for the number
%v{hex8}        print 2 hex characters for the number
%v{hex4}        print 1 hex characters for the number
%v{hex}         print as many hex characters as necessary for the number

%v{big64}       print the number in big endian uint64 format
%v{big32}       print the number in big endian uint32 format
%v{big16}       print the number in big endian uint16 format
%v{big8}        alias for byte

%v{little64}    print the number in little endian uint64 format
%v{little32}    print the number in little endian uint32 format
%v{little16}    print the number in little endian uint16 format
%v{little8}     alias for byte

%v{byte}        print the number as a single byte
%v{bool}        print "true" if the number is non-zero, otherwise "false"

All numbers are truncated as necessary per each given format.

Timestamps

Timestamps can be specified in three formats: plain number formatting, native Go timestamp formatting, or strftime formatting. Number formatting is follows the rules above using the millisecond timestamp value. Go and strftime have further internal format options:

%d{go##2006-01-02T15:04:05Z07:00##}
%d{strftime[%F]}

An arbitrary amount of pounds, braces, and brackets are understood before beginning the actual timestamp formatting. For Go formatting, the format is simply passed to the time package's AppendFormat function. For strftime, all "man strftime" options are supported. Time is always in UTC.

Attributes

Records attributes require formatting, where each formatting option selects which attribute to print and how to print it.

%a{compression}
%a{compression;number}
%a{compression;big64}
%a{compression;hex8}

By default, prints the compression as text ("none", "gzip", ...). Compression can be printed as a number with ";number", where number is any number formatting option described above.

%a{timestamp-type}
%a{timestamp-type;big64}

Prints -1 for pre-0.10 records, 0 for client generated timestamps, and 1 for broker generated. Number formatting can be controlled with ";number".

%a{transactional-bit}
%a{transactional-bit;bool}

Prints 1 if the record is a part of a transaction or 0 if it is not. Number formatting can be controlled with ";number".

%a{control-bit}
%a{control-bit;bool}

Prints 1 if the record is a commit marker or 0 if it is not. Number formatting can be controlled with ";number".

Text

Topics, keys, and values have "base64", "base64raw", "hex", and "unpack" formatting options:

%t{hex}
%k{unpack{<bBhH>iIqQc.$}}
%v{base64}
%v{base64raw}

Unpack formatting is inside of enclosing pounds, braces, or brackets, the same way that timestamp formatting is understood. The syntax roughly follows Python's struct packing/unpacking rules:

x    pad character (does not parse input)
<    parse what follows as little endian
>    parse what follows as big endian

b    signed byte
B    unsigned byte
h    int16  ("half word")
H    uint16 ("half word")
i    int32
I    uint32
q    int64  ("quad word")
Q    uint64 ("quad word")

c    any character
.    alias for c
s    consume the rest of the input as a string
$    match the end of the line (append error string if anything remains)

Unlike python, a '<' or '>' can appear anywhere in the format string and affects everything that follows. It is possible to switch endianness multiple times. If the parser needs more data than available, or if the more input remains after '$', an error message will be appended.

func (*RecordFormatter) AppendPartitionRecord added in v1.2.0

func (f *RecordFormatter) AppendPartitionRecord(b []byte, p *FetchPartition, r *Record) []byte

AppendPartitionRecord appends a record and partition to b given the parsed format and returns the updated slice.

func (*RecordFormatter) AppendRecord added in v1.2.0

func (f *RecordFormatter) AppendRecord(b []byte, r *Record) []byte

AppendRecord appends a record to b given the parsed format and returns the updated slice.

type RecordHeader

type RecordHeader struct {
	Key   string
	Value []byte
}

RecordHeader contains extra information that can be sent with Records.

type RecordReader added in v1.2.0

type RecordReader struct {
	// contains filtered or unexported fields
}

RecordReader reads records from an io.Reader.

func NewRecordReader added in v1.2.0

func NewRecordReader(reader io.Reader, layout string) (*RecordReader, error)

NewRecordReader returns a record reader for the given layout, or an error if the layout is invalid.

Similar to the RecordFormatter, the RecordReader parsing is quite powerful. There is a bit less to describe in comparison to RecordFormatter, but still, this documentation attempts to be as succinct as possible.

Similar to the fmt package, record parsing is based off of slash escapes and percent "verbs" (copying fmt package lingo). Slashes are used for common escapes,

\t \n \r \\ \xNN

reading tabs, newlines, carriage returns, slashes, and hex encoded characters.

Percent encoding reads into specific values of a Record:

%t    topic
%T    topic length
%k    key
%K    key length
%v    value
%V    value length
%h    begin the header specification
%H    number of headers
%p    partition
%o    offset
%e    leader epoch
%d    timestamp
%x    producer id
%y    producer epoch

If using length / number verbs (i.e., "sized" verbs), they must occur before what they are sizing.

There are three escapes to parse raw characters, rather than opting into some formatting option:

%%    percent sign
%{    left brace
%}    right brace

Unlike record formatting, timestamps can only be read as numbers because Go or strftime formatting can both be variable length and do not play too well with delimiters. Timestamps numbers are read as milliseconds.

Numbers

All size numbers can be parsed in the following ways:

%v{ascii}       parse numeric digits until a non-numeric
%v{number}      alias for ascii

%v{hex64}       read 16 hex characters for the number
%v{hex32}       read 8 hex characters for the number
%v{hex16}       read 4 hex characters for the number
%v{hex8}        read 2 hex characters for the number
%v{hex4}        read 1 hex characters for the number

%v{big64}       read the number as big endian uint64 format
%v{big32}       read the number as big endian uint32 format
%v{big16}       read the number as big endian uint16 format
%v{big8}        alias for byte

%v{little64}    read the number as little endian uint64 format
%v{little32}    read the number as little endian uint32 format
%v{little16}    read the number as little endian uint16 format
%v{little8}     read the number as a byte

%v{byte}        read the number as a byte
%v{bool}        read "true" as 1, "false" as 0
%v{3}           read 3 characters (any number)

Header specification

Similar to number formatting, headers are parsed using a nested primitive format option, accepting the key and value escapes previously mentioned.

Text

Topics, keys, and values can be decoded using "base64", "hex", and "json" formatting options. Any size specification is the size of the encoded value actually being read (i.e., size as seen, not size when decoded). JSON values are compacted after being read.

%T%t{hex}     -  4abcd reads four hex characters "abcd"
%V%v{base64}  -  2z9 reads two base64 characters "z9"
%v{json} %k   -  {"foo" : "bar"} foo reads a JSON object and then "foo"

As well, these text options can be parsed with regular expressions:

%k{re[\d*]}%v{re[\s+]}

func (*RecordReader) ReadRecord added in v1.2.0

func (r *RecordReader) ReadRecord() (*Record, error)

ReadRecord reads the next record in the reader and returns it, or returns a parsing error.

This will return io.EOF only if the underlying reader returns io.EOF at the start of a new record. If an io.EOF is returned mid record, this returns io.ErrUnexpectedEOF. It is expected for this function to be called until it returns io.EOF.

func (*RecordReader) ReadRecordInto added in v1.2.0

func (r *RecordReader) ReadRecordInto(rec *Record) error

ReadRecordInto reads the next record into the given record and returns any parsing error

This will return io.EOF only if the underlying reader returns io.EOF at the start of a new record. If an io.EOF is returned mid record, this returns io.ErrUnexpectedEOF. It is expected for this function to be called until it returns io.EOF.

func (*RecordReader) SetReader added in v1.2.0

func (r *RecordReader) SetReader(reader io.Reader)

SetReader replaces the underlying reader with the given reader.

type ResponseShard added in v0.6.2

type ResponseShard struct {
	// Meta contains the broker that this request was issued to, or an
	// unknown (node ID -1) metadata if the request could not be issued.
	//
	// Requests can fail to even be issued if an appropriate broker cannot
	// be loaded of if the client cannot understand the request.
	Meta BrokerMetadata

	// Req is the request that was issued to this broker.
	Req kmsg.Request

	// Resp is the response received from the broker, if any.
	Resp kmsg.Response

	// Err, if non-nil, is the error that prevented a response from being
	// received or the request from being issued.
	Err error
}

ResponseShard ties together a request with either the response it received or an error that prevented a response from being received.

type TopicBackupIter added in v0.10.2

type TopicBackupIter interface {
	// Next returns the next partition index and the total buffered records
	// for the partition. If Rem returns 0, calling this function again
	// will panic.
	Next() (int, int64)
	// Rem returns the number of elements left to iterate through.
	Rem() int
}

TopicBackupIter is an iterates through partition indices.

type TopicBackupPartitioner added in v0.10.1

type TopicBackupPartitioner interface {
	TopicPartitioner

	// PartitionByBackup is similar to Partition, but has an additional
	// backupIter. This iterator will return the number of buffered records
	// per partition index. The iterator's Next function can only be called
	// up to n times, calling it any more will panic.
	PartitionByBackup(r *Record, n int, backupIter TopicBackupIter) int
}

TopicBackupPartitioner is an optional extension interface to TopicPartitioner that can partition by the number of records buffered.

If a partitioner implements this interface, the Partition function will never be called.

type TopicPartitioner

type TopicPartitioner interface {
	// RequiresConsistency returns true if a record must hash to the same
	// partition even if a partition is down.
	// If true, a record may hash to a partition that cannot be written to
	// and will error until the partition comes back.
	RequiresConsistency(*Record) bool
	// Partition determines, among a set of n partitions, which index should
	// be chosen to use for the partition for r.
	Partition(r *Record, n int) int
}

TopicPartitioner partitions records in an individual topic.

type TopicPartitionerOnNewBatch added in v0.10.2

type TopicPartitionerOnNewBatch interface {
	// OnNewBatch is called when producing a record if that record would
	// trigger a new batch on its current partition.
	OnNewBatch()
}

TopicPartitionerOnNewBatch is an optional extension interface to TopicPartitioner that calls OnNewBatch before any new batch is created. If buffering a record would cause a new batch, OnNewBatch is called.

This interface allows for partitioner implementations that effectively pin to a partition until a new batch is created, after which the partitioner can choose which next partition to use.

type TransactionEndTry

type TransactionEndTry bool

TransactionEndTry is simply a named bool.

const (
	// TryAbort attempts to end a transaction with an abort.
	TryAbort TransactionEndTry = false

	// TryCommit attempts to end a transaction with a commit.
	TryCommit TransactionEndTry = true
)

Directories

Path Synopsis
internal
sticky
Package sticky provides sticky partitioning strategy for Kafka, with a complete overhaul to be faster, more understandable, and optimal.
Package sticky provides sticky partitioning strategy for Kafka, with a complete overhaul to be faster, more understandable, and optimal.

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