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github.com/jackc/pgconn

Package pgconn

v1.6.4
Latest Go to latest

The latest major version is .

Published: Jul 30, 2020 | License: MIT | Module: github.com/jackc/pgconn

Overview

Package pgconn is a low-level PostgreSQL database driver.

pgconn provides lower level access to a PostgreSQL connection than a database/sql or pgx connection. It operates at nearly the same level is the C library libpq.

Establishing a Connection

Use Connect to establish a connection. It accepts a connection string in URL or DSN and will read the environment for libpq style environment variables.

Executing a Query

ExecParams and ExecPrepared execute a single query. They return readers that iterate over each row. The Read method reads all rows into memory.

Executing Multiple Queries in a Single Round Trip

Exec and ExecBatch can execute multiple queries in a single round trip. They return readers that iterate over each query result. The ReadAll method reads all query results into memory.

Context Support

All potentially blocking operations take a context.Context. If a context is canceled while the method is in progress the method immediately returns. In most circumstances, this will close the underlying connection.

The CancelRequest method may be used to request the PostgreSQL server cancel an in-progress query without forcing the client to abort.

Example

Code:

package main

import (
	"context"
	"fmt"
	"github.com/jackc/pgconn"
	"log"
	"os"
)

func main() {
	pgConn, err := pgconn.Connect(context.Background(), os.Getenv("PGX_TEST_CONN_STRING"))
	if err != nil {
		log.Fatalln(err)
	}
	defer pgConn.Close(context.Background())

	result := pgConn.ExecParams(context.Background(), "select generate_series(1,3)", nil, nil, nil, nil).Read()
	if result.Err != nil {
		log.Fatalln(result.Err)
	}

	for _, row := range result.Rows {
		fmt.Println(string(row[0]))
	}

	fmt.Println(result.CommandTag)
}
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Index

Examples

func NetworkAddress

func NetworkAddress(host string, port uint16) (network, address string)

NetworkAddress converts a PostgreSQL host and port into network and address suitable for use with net.Dial.

func SafeToRetry

func SafeToRetry(err error) bool

SafeToRetry checks if the err is guaranteed to have occurred before sending any data to the server.

func Timeout

func Timeout(err error) bool

Timeout checks if err was was caused by a timeout. To be specific, it is true if err is or was caused by a context.Canceled, context.Canceled or an implementer of net.Error where Timeout() is true.

func ValidateConnectTargetSessionAttrsReadWrite

func ValidateConnectTargetSessionAttrsReadWrite(ctx context.Context, pgConn *PgConn) error

ValidateConnectTargetSessionAttrsReadWrite is an ValidateConnectFunc that implements libpq compatible target_session_attrs=read-write.

type AfterConnectFunc

type AfterConnectFunc func(ctx context.Context, pgconn *PgConn) error

type Batch

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

Batch is a collection of queries that can be sent to the PostgreSQL server in a single round-trip.

func (*Batch) ExecParams

func (batch *Batch) ExecParams(sql string, paramValues [][]byte, paramOIDs []uint32, paramFormats []int16, resultFormats []int16)

ExecParams appends an ExecParams command to the batch. See PgConn.ExecParams for parameter descriptions.

func (*Batch) ExecPrepared

func (batch *Batch) ExecPrepared(stmtName string, paramValues [][]byte, paramFormats []int16, resultFormats []int16)

ExecPrepared appends an ExecPrepared e command to the batch. See PgConn.ExecPrepared for parameter descriptions.

type BuildFrontendFunc

type BuildFrontendFunc func(r io.Reader, w io.Writer) Frontend

BuildFrontendFunc is a function that can be used to create Frontend implementation for connection.

type CommandTag

type CommandTag []byte

CommandTag is the result of an Exec function

func (CommandTag) Delete

func (ct CommandTag) Delete() bool

Delete is true if the command tag starts with "DELETE".

func (CommandTag) Insert

func (ct CommandTag) Insert() bool

Insert is true if the command tag starts with "INSERT".

func (CommandTag) RowsAffected

func (ct CommandTag) RowsAffected() int64

RowsAffected returns the number of rows affected. If the CommandTag was not for a row affecting command (e.g. "CREATE TABLE") then it returns 0.

func (CommandTag) Select

func (ct CommandTag) Select() bool

Select is true if the command tag starts with "SELECT".

func (CommandTag) String

func (ct CommandTag) String() string

func (CommandTag) Update

func (ct CommandTag) Update() bool

Update is true if the command tag starts with "UPDATE".

type Config

type Config struct {
	Host           string // host (e.g. localhost) or absolute path to unix domain socket directory (e.g. /private/tmp)
	Port           uint16
	Database       string
	User           string
	Password       string
	TLSConfig      *tls.Config // nil disables TLS
	ConnectTimeout time.Duration
	DialFunc       DialFunc   // e.g. net.Dialer.DialContext
	LookupFunc     LookupFunc // e.g. net.Resolver.LookupHost
	BuildFrontend  BuildFrontendFunc
	RuntimeParams  map[string]string // Run-time parameters to set on connection as session default values (e.g. search_path or application_name)

	Fallbacks []*FallbackConfig

	// ValidateConnect is called during a connection attempt after a successful authentication with the PostgreSQL server.
	// It can be used to validate that the server is acceptable. If this returns an error the connection is closed and the next
	// fallback config is tried. This allows implementing high availability behavior such as libpq does with target_session_attrs.
	ValidateConnect ValidateConnectFunc

	// AfterConnect is called after ValidateConnect. It can be used to set up the connection (e.g. Set session variables
	// or prepare statements). If this returns an error the connection attempt fails.
	AfterConnect AfterConnectFunc

	// OnNotice is a callback function called when a notice response is received.
	OnNotice NoticeHandler

	// OnNotification is a callback function called when a notification from the LISTEN/NOTIFY system is received.
	OnNotification NotificationHandler
	// contains filtered or unexported fields
}

Config is the settings used to establish a connection to a PostgreSQL server. It must be created by ParseConfig. A manually initialized Config will cause ConnectConfig to panic.

func ParseConfig

func ParseConfig(connString string) (*Config, error)

ParseConfig builds a *Config with similar behavior to the PostgreSQL standard C library libpq. It uses the same defaults as libpq (e.g. port=5432) and understands most PG* environment variables. connString may be a URL or a DSN. It also may be empty to only read from the environment. If a password is not supplied it will attempt to read the .pgpass file.

# Example DSN
user=jack password=secret host=pg.example.com port=5432 dbname=mydb sslmode=verify-ca

# Example URL
postgres://jack:secret@pg.example.com:5432/mydb?sslmode=verify-ca

The returned *Config may be modified. However, it is strongly recommended that any configuration that can be done through the connection string be done there. In particular the fields Host, Port, TLSConfig, and Fallbacks can be interdependent (e.g. TLSConfig needs knowledge of the host to validate the server certificate). These fields should not be modified individually. They should all be modified or all left unchanged.

ParseConfig supports specifying multiple hosts in similar manner to libpq. Host and port may include comma separated values that will be tried in order. This can be used as part of a high availability system. See https://www.postgresql.org/docs/11/libpq-connect.html#LIBPQ-MULTIPLE-HOSTS for more information.

# Example URL
postgres://jack:secret@foo.example.com:5432,bar.example.com:5432/mydb

ParseConfig currently recognizes the following environment variable and their parameter key word equivalents passed via database URL or DSN:

PGHOST
PGPORT
PGDATABASE
PGUSER
PGPASSWORD
PGPASSFILE
PGSERVICE
PGSERVICEFILE
PGSSLMODE
PGSSLCERT
PGSSLKEY
PGSSLROOTCERT
PGAPPNAME
PGCONNECT_TIMEOUT
PGTARGETSESSIONATTRS

See http://www.postgresql.org/docs/11/static/libpq-envars.html for details on the meaning of environment variables.

See https://www.postgresql.org/docs/11/libpq-connect.html#LIBPQ-PARAMKEYWORDS for parameter key word names. They are usually but not always the environment variable name downcased and without the "PG" prefix.

Important Security Notes:

ParseConfig tries to match libpq behavior with regard to PGSSLMODE. This includes defaulting to "prefer" behavior if not set.

See http://www.postgresql.org/docs/11/static/libpq-ssl.html#LIBPQ-SSL-PROTECTION for details on what level of security each sslmode provides.

The sslmode "prefer" (the default), sslmode "allow", and multiple hosts are implemented via the Fallbacks field of the Config struct. If TLSConfig is manually changed it will not affect the fallbacks. For example, in the case of sslmode "prefer" this means it will first try the main Config settings which use TLS, then it will try the fallback which does not use TLS. This can lead to an unexpected unencrypted connection if the main TLS config is manually changed later but the unencrypted fallback is present. Ensure there are no stale fallbacks when manually setting TLCConfig.

Other known differences with libpq:

If a host name resolves into multiple addresses, libpq will try all addresses. pgconn will only try the first.

When multiple hosts are specified, libpq allows them to have different passwords set via the .pgpass file. pgconn does not.

In addition, ParseConfig accepts the following options:

min_read_buffer_size
	The minimum size of the internal read buffer. Default 8192.
servicefile
	libpq only reads servicefile from the PGSERVICEFILE environment variable. ParseConfig accepts servicefile as a
	part of the connection string.

func (*Config) Copy

func (c *Config) Copy() *Config

Copy returns a deep copy of the config that is safe to use and modify. The only exception is the TLSConfig field: according to the tls.Config docs it must not be modified after creation.

type DialFunc

type DialFunc func(ctx context.Context, network, addr string) (net.Conn, error)

DialFunc is a function that can be used to connect to a PostgreSQL server.

type FallbackConfig

type FallbackConfig struct {
	Host      string // host (e.g. localhost) or path to unix domain socket directory (e.g. /private/tmp)
	Port      uint16
	TLSConfig *tls.Config // nil disables TLS
}

FallbackConfig is additional settings to attempt a connection with when the primary Config fails to establish a network connection. It is used for TLS fallback such as sslmode=prefer and high availability (HA) connections.

type Frontend

type Frontend interface {
	Receive() (pgproto3.BackendMessage, error)
}

Frontend used to receive messages from backend.

type HijackedConn

type HijackedConn struct {
	Conn              net.Conn          // the underlying TCP or unix domain socket connection
	PID               uint32            // backend pid
	SecretKey         uint32            // key to use to send a cancel query message to the server
	ParameterStatuses map[string]string // parameters that have been reported by the server
	TxStatus          byte
	Frontend          Frontend
	Config            *Config
}

HijackedConn is the result of hijacking a connection.

Due to the necessary exposure of internal implementation details, it is not covered by the semantic versioning compatibility.

type LookupFunc

type LookupFunc func(ctx context.Context, host string) (addrs []string, err error)

LookupFunc is a function that can be used to lookup IPs addrs from host.

type MultiResultReader

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

MultiResultReader is a reader for a command that could return multiple results such as Exec or ExecBatch.

func (*MultiResultReader) Close

func (mrr *MultiResultReader) Close() error

Close closes the MultiResultReader and returns the first error that occurred during the MultiResultReader's use.

func (*MultiResultReader) NextResult

func (mrr *MultiResultReader) NextResult() bool

NextResult returns advances the MultiResultReader to the next result and returns true if a result is available.

func (*MultiResultReader) ReadAll

func (mrr *MultiResultReader) ReadAll() ([]*Result, error)

ReadAll reads all available results. Calling ReadAll is mutually exclusive with all other MultiResultReader methods.

func (*MultiResultReader) ResultReader

func (mrr *MultiResultReader) ResultReader() *ResultReader

ResultReader returns the current ResultReader.

type Notice

type Notice PgError

Notice represents a notice response message reported by the PostgreSQL server. Be aware that this is distinct from LISTEN/NOTIFY notification.

type NoticeHandler

type NoticeHandler func(*PgConn, *Notice)

NoticeHandler is a function that can handle notices received from the PostgreSQL server. Notices can be received at any time, usually during handling of a query response. The *PgConn is provided so the handler is aware of the origin of the notice, but it must not invoke any query method. Be aware that this is distinct from LISTEN/NOTIFY notification.

type Notification

type Notification struct {
	PID     uint32 // backend pid that sent the notification
	Channel string // channel from which notification was received
	Payload string
}

Notification is a message received from the PostgreSQL LISTEN/NOTIFY system

type NotificationHandler

type NotificationHandler func(*PgConn, *Notification)

NotificationHandler is a function that can handle notifications received from the PostgreSQL server. Notifications can be received at any time, usually during handling of a query response. The *PgConn is provided so the handler is aware of the origin of the notice, but it must not invoke any query method. Be aware that this is distinct from a notice event.

type PgConn

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

PgConn is a low-level PostgreSQL connection handle. It is not safe for concurrent usage.

func Connect

func Connect(ctx context.Context, connString string) (*PgConn, error)

Connect establishes a connection to a PostgreSQL server using the environment and connString (in URL or DSN format) to provide configuration. See documention for ParseConfig for details. ctx can be used to cancel a connect attempt.

func ConnectConfig

func ConnectConfig(ctx context.Context, config *Config) (pgConn *PgConn, err error)

Connect establishes a connection to a PostgreSQL server using config. config must have been constructed with ParseConfig. ctx can be used to cancel a connect attempt.

If config.Fallbacks are present they will sequentially be tried in case of error establishing network connection. An authentication error will terminate the chain of attempts (like libpq: https://www.postgresql.org/docs/11/libpq-connect.html#LIBPQ-MULTIPLE-HOSTS) and be returned as the error. Otherwise, if all attempts fail the last error is returned.

func Construct

func Construct(hc *HijackedConn) (*PgConn, error)

Construct created a PgConn from an already established connection to a PostgreSQL server. This is the inverse of PgConn.Hijack. The connection must be in an idle state.

Due to the necessary exposure of internal implementation details, it is not covered by the semantic versioning compatibility.

func (*PgConn) CancelRequest

func (pgConn *PgConn) CancelRequest(ctx context.Context) error

CancelRequest sends a cancel request to the PostgreSQL server. It returns an error if unable to deliver the cancel request, but lack of an error does not ensure that the query was canceled. As specified in the documentation, there is no way to be sure a query was canceled. See https://www.postgresql.org/docs/11/protocol-flow.html#id-1.10.5.7.9

func (*PgConn) Close

func (pgConn *PgConn) Close(ctx context.Context) error

Close closes a connection. It is safe to call Close on a already closed connection. Close attempts a clean close by sending the exit message to PostgreSQL. However, this could block so ctx is available to limit the time to wait. The underlying net.Conn.Close() will always be called regardless of any other errors.

func (*PgConn) Conn

func (pgConn *PgConn) Conn() net.Conn

Conn returns the underlying net.Conn.

func (*PgConn) CopyFrom

func (pgConn *PgConn) CopyFrom(ctx context.Context, r io.Reader, sql string) (CommandTag, error)

CopyFrom executes the copy command sql and copies all of r to the PostgreSQL server.

Note: context cancellation will only interrupt operations on the underlying PostgreSQL network connection. Reads on r could still block.

func (*PgConn) CopyTo

func (pgConn *PgConn) CopyTo(ctx context.Context, w io.Writer, sql string) (CommandTag, error)

CopyTo executes the copy command sql and copies the results to w.

func (*PgConn) EscapeString

func (pgConn *PgConn) EscapeString(s string) (string, error)

EscapeString escapes a string such that it can safely be interpolated into a SQL command string. It does not include the surrounding single quotes.

The current implementation requires that standard_conforming_strings=on and client_encoding="UTF8". If these conditions are not met an error will be returned. It is possible these restrictions will be lifted in the future.

func (*PgConn) Exec

func (pgConn *PgConn) Exec(ctx context.Context, sql string) *MultiResultReader

Exec executes SQL via the PostgreSQL simple query protocol. SQL may contain multiple queries. Execution is implicitly wrapped in a transaction unless a transaction is already in progress or SQL contains transaction control statements.

Prefer ExecParams unless executing arbitrary SQL that may contain multiple queries.

func (*PgConn) ExecBatch

func (pgConn *PgConn) ExecBatch(ctx context.Context, batch *Batch) *MultiResultReader

ExecBatch executes all the queries in batch in a single round-trip. Execution is implicitly transactional unless a transaction is already in progress or SQL contains transaction control statements.

func (*PgConn) ExecParams

func (pgConn *PgConn) ExecParams(ctx context.Context, sql string, paramValues [][]byte, paramOIDs []uint32, paramFormats []int16, resultFormats []int16) *ResultReader

ExecParams executes a command via the PostgreSQL extended query protocol.

sql is a SQL command string. It may only contain one query. Parameter substitution is positional using $1, $2, $3, etc.

paramValues are the parameter values. It must be encoded in the format given by paramFormats.

paramOIDs is a slice of data type OIDs for paramValues. If paramOIDs is nil, the server will infer the data type for all parameters. Any paramOID element that is 0 that will cause the server to infer the data type for that parameter. ExecParams will panic if len(paramOIDs) is not 0, 1, or len(paramValues).

paramFormats is a slice of format codes determining for each paramValue column whether it is encoded in text or binary format. If paramFormats is nil all params are text format. ExecParams will panic if len(paramFormats) is not 0, 1, or len(paramValues).

resultFormats is a slice of format codes determining for each result column whether it is encoded in text or binary format. If resultFormats is nil all results will be in text format.

ResultReader must be closed before PgConn can be used again.

func (*PgConn) ExecPrepared

func (pgConn *PgConn) ExecPrepared(ctx context.Context, stmtName string, paramValues [][]byte, paramFormats []int16, resultFormats []int16) *ResultReader

ExecPrepared enqueues the execution of a prepared statement via the PostgreSQL extended query protocol.

paramValues are the parameter values. It must be encoded in the format given by paramFormats.

paramFormats is a slice of format codes determining for each paramValue column whether it is encoded in text or binary format. If paramFormats is nil all params are text format. ExecPrepared will panic if len(paramFormats) is not 0, 1, or len(paramValues).

resultFormats is a slice of format codes determining for each result column whether it is encoded in text or binary format. If resultFormats is nil all results will be in text format.

ResultReader must be closed before PgConn can be used again.

func (*PgConn) Hijack

func (pgConn *PgConn) Hijack() (*HijackedConn, error)

Hijack extracts the internal connection data. pgConn must be in an idle state. pgConn is unusable after hijacking. Hijacking is typically only useful when using pgconn to establish a connection, but taking complete control of the raw connection after that (e.g. a load balancer or proxy).

Due to the necessary exposure of internal implementation details, it is not covered by the semantic versioning compatibility.

func (*PgConn) IsBusy

func (pgConn *PgConn) IsBusy() bool

IsBusy reports if the connection is busy.

func (*PgConn) IsClosed

func (pgConn *PgConn) IsClosed() bool

IsClosed reports if the connection has been closed.

func (*PgConn) PID

func (pgConn *PgConn) PID() uint32

PID returns the backend PID.

func (*PgConn) ParameterStatus

func (pgConn *PgConn) ParameterStatus(key string) string

ParameterStatus returns the value of a parameter reported by the server (e.g. server_version). Returns an empty string for unknown parameters.

func (*PgConn) Prepare

func (pgConn *PgConn) Prepare(ctx context.Context, name, sql string, paramOIDs []uint32) (*StatementDescription, error)

Prepare creates a prepared statement. If the name is empty, the anonymous prepared statement will be used. This allows Prepare to also to describe statements without creating a server-side prepared statement.

func (*PgConn) ReceiveMessage

func (pgConn *PgConn) ReceiveMessage(ctx context.Context) (pgproto3.BackendMessage, error)

ReceiveMessage receives one wire protocol message from the PostgreSQL server. It must only be used when the connection is not busy. e.g. It is an error to call ReceiveMessage while reading the result of a query. The messages are still handled by the core pgconn message handling system so receiving a NotificationResponse will still trigger the OnNotification callback.

This is a very low level method that requires deep understanding of the PostgreSQL wire protocol to use correctly. See https://www.postgresql.org/docs/current/protocol.html.

func (*PgConn) SecretKey

func (pgConn *PgConn) SecretKey() uint32

SecretKey returns the backend secret key used to send a cancel query message to the server.

func (*PgConn) SendBytes

func (pgConn *PgConn) SendBytes(ctx context.Context, buf []byte) error

SendBytes sends buf to the PostgreSQL server. It must only be used when the connection is not busy. e.g. It is as error to call SendBytes while reading the result of a query.

This is a very low level method that requires deep understanding of the PostgreSQL wire protocol to use correctly. See https://www.postgresql.org/docs/current/protocol.html.

func (*PgConn) TxStatus

func (pgConn *PgConn) TxStatus() byte

TxStatus returns the current TxStatus as reported by the server.

func (*PgConn) WaitForNotification

func (pgConn *PgConn) WaitForNotification(ctx context.Context) error

WaitForNotification waits for a LISTON/NOTIFY message to be received. It returns an error if a notification was not received.

type PgError

type PgError struct {
	Severity         string
	Code             string
	Message          string
	Detail           string
	Hint             string
	Position         int32
	InternalPosition int32
	InternalQuery    string
	Where            string
	SchemaName       string
	TableName        string
	ColumnName       string
	DataTypeName     string
	ConstraintName   string
	File             string
	Line             int32
	Routine          string
}

PgError represents an error reported by the PostgreSQL server. See http://www.postgresql.org/docs/11/static/protocol-error-fields.html for detailed field description.

func ErrorResponseToPgError

func ErrorResponseToPgError(msg *pgproto3.ErrorResponse) *PgError

ErrorResponseToPgError converts a wire protocol error message to a *PgError.

func (*PgError) Error

func (pe *PgError) Error() string

func (*PgError) SQLState

func (pe *PgError) SQLState() string

SQLState returns the SQLState of the error.

type Result

type Result struct {
	FieldDescriptions []pgproto3.FieldDescription
	Rows              [][][]byte
	CommandTag        CommandTag
	Err               error
}

Result is the saved query response that is returned by calling Read on a ResultReader.

type ResultReader

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

ResultReader is a reader for the result of a single query.

func (*ResultReader) Close

func (rr *ResultReader) Close() (CommandTag, error)

Close consumes any remaining result data and returns the command tag or error.

func (*ResultReader) FieldDescriptions

func (rr *ResultReader) FieldDescriptions() []pgproto3.FieldDescription

FieldDescriptions returns the field descriptions for the current result set. The returned slice is only valid until the ResultReader is closed.

func (*ResultReader) NextRow

func (rr *ResultReader) NextRow() bool

NextRow advances the ResultReader to the next row and returns true if a row is available.

func (*ResultReader) Read

func (rr *ResultReader) Read() *Result

Read saves the query response to a Result.

func (*ResultReader) Values

func (rr *ResultReader) Values() [][]byte

Values returns the current row data. NextRow must have been previously been called. The returned [][]byte is only valid until the next NextRow call or the ResultReader is closed. However, the underlying byte data is safe to retain a reference to and mutate.

type StatementDescription

type StatementDescription struct {
	Name      string
	SQL       string
	ParamOIDs []uint32
	Fields    []pgproto3.FieldDescription
}

type ValidateConnectFunc

type ValidateConnectFunc func(ctx context.Context, pgconn *PgConn) error

Package Files

Documentation was rendered with GOOS=linux and GOARCH=amd64.

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