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Package twirp

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Published: Sep 26, 2019 | License: Apache-2.0 | Module:


Package twirp provides core types used in generated Twirp servers and client.

Twirp services handle errors using the `twirp.Error` interface.

For example, a server method may return an InvalidArgumentError:

if req.Order != "DESC" && req.Order != "ASC" {
    return nil, twirp.InvalidArgumentError("Order", "must be DESC or ASC")

And the same twirp.Error is returned by the client, for example:

resp, err := twirpClient.RPCMethod(ctx, req)
if err != nil {
    if twerr, ok := err.(twirp.Error); ok {
        switch twerr.Code() {
        case twirp.InvalidArgument:
            log.Error("invalid argument "+twirp.Meta("argument"))

Clients may also return Internal errors if something failed on the system: the server, the network, or the client itself (i.e. failure parsing response).


func HTTPRequestHeaders

func HTTPRequestHeaders(ctx context.Context) (http.Header, bool)

func IsValidErrorCode

func IsValidErrorCode(code ErrorCode) bool

IsValidErrorCode returns true if is one of the valid predefined constants.

func MethodName

func MethodName(ctx context.Context) (string, bool)

MethodName extracts the name of the method being handled in the given context. If it is not known, it returns ("", false).

func PackageName

func PackageName(ctx context.Context) (string, bool)

PackageName extracts the fully-qualified protobuf package name of the service handling the given context. If it is not known, it returns ("", false). If the service comes from a proto file that does not declare a package name, it returns ("", true).

Note that the protobuf package name can be very different than the go package name; the two are unrelated.

func ServerHTTPStatusFromErrorCode

func ServerHTTPStatusFromErrorCode(code ErrorCode) int

ServerHTTPStatusFromErrorCode maps a Twirp error type into a similar HTTP response status. It is used by the Twirp server handler to set the HTTP response status code. Returns 0 if the ErrorCode is invalid.

func ServiceName

func ServiceName(ctx context.Context) (string, bool)

ServiceName extracts the name of the service handling the given context. If it is not known, it returns ("", false).

func SetHTTPResponseHeader

func SetHTTPResponseHeader(ctx context.Context, key, value string) error

SetHTTPResponseHeader sets an HTTP header key-value pair using a context provided by a twirp-generated server, or a child of that context. The server will include the header in its response for that request context.

This can be used to respond with custom HTTP headers like "Cache-Control". But note that HTTP headers are a Twirp implementation detail, only visible by middleware, not by the clients or their responses.

The header will be ignored (noop) if the context is invalid (i.e. using a new context.Background() instead of passing the context from the handler).

If called multiple times with the same key, it replaces any existing values associated with that key.

SetHTTPResponseHeader returns an error if the provided header key would overwrite a header that is needed by Twirp, like "Content-Type".

func StatusCode

func StatusCode(ctx context.Context) (string, bool)

StatusCode retrieves the status code of the response (as string like "200"). If it is known returns (status, true). If it is not known, it returns ("", false).

func WithHTTPRequestHeaders

func WithHTTPRequestHeaders(ctx context.Context, h http.Header) (context.Context, error)

WithHTTPRequestHeaders stores an http.Header in a context.Context. When using a Twirp-generated client, you can pass the returned context into any of the request methods, and the stored header will be included in outbound HTTP requests.

This can be used to set custom HTTP headers like authorization tokens or client IDs. But note that HTTP headers are a Twirp implementation detail, only visible by middleware, not by the server implementation.

WithHTTPRequestHeaders returns an error if the provided http.Header would overwrite a header that is needed by Twirp, like "Content-Type".

type Error

type Error interface {
	// Code is of the valid error codes.
	Code() ErrorCode

	// Msg returns a human-readable, unstructured messages describing the error.
	Msg() string

	// WithMeta returns a copy of the Error with the given key-value pair attached
	// as metadata. If the key is already set, it is overwritten.
	WithMeta(key string, val string) Error

	// Meta returns the stored value for the given key. If the key has no set
	// value, Meta returns an empty string. There is no way to distinguish between
	// an unset value and an explicit empty string.
	Meta(key string) string

	// MetaMap returns the complete key-value metadata map stored on the error.
	MetaMap() map[string]string

	// Error returns a string of the form "twirp error <Type>: <Msg>"
	Error() string

Error represents an error in a Twirp service call.

func InternalError

func InternalError(msg string) Error

InternalError constructor for the common Internal error. Should be used to specify that something bad or unexpected happened.

func InternalErrorWith

func InternalErrorWith(err error) Error

InternalErrorWith is an easy way to wrap another error. It adds the underlying error's type as metadata with a key of "cause", which can be useful for debugging. Should be used in the common case of an unexpected error returned from another API, but sometimes it is better to build a more specific error (like with NewError(Unknown, err.Error()), for example).

The returned error also has a Cause() method which will return the original error, if it is known. This can be used with the package to extract the root cause of an error. Information about the root cause of an error is lost when it is serialized, so this doesn't let a client know the exact root cause of a server's error.

func InvalidArgumentError

func InvalidArgumentError(argument string, validationMsg string) Error

InvalidArgumentError constructor for the common InvalidArgument error. Can be used when an argument has invalid format, is a number out of range, is a bad option, etc).

func NewError

func NewError(code ErrorCode, msg string) Error

NewError is the generic constructor for a twirp.Error. The ErrorCode must be one of the valid predefined constants, otherwise it will be converted to an error {type: Internal, msg: "invalid error type {{code}}"}. If you need to add metadata, use .WithMeta(key, value) method after building the error.

func NotFoundError

func NotFoundError(msg string) Error

NotFoundError constructor for the common NotFound error.

func RequiredArgumentError

func RequiredArgumentError(argument string) Error

RequiredArgumentError is a more specific constructor for InvalidArgument error. Should be used when the argument is required (expected to have a non-zero value).

type ErrorCode

type ErrorCode string

ErrorCode represents a Twirp error type.

const (
	// Canceled indicates the operation was cancelled (typically by the caller).
	Canceled ErrorCode = "canceled"

	// Unknown error. For example when handling errors raised by APIs that do not
	// return enough error information.
	Unknown ErrorCode = "unknown"

	// InvalidArgument indicates client specified an invalid argument. It
	// indicates arguments that are problematic regardless of the state of the
	// system (i.e. a malformed file name, required argument, number out of range,
	// etc.).
	InvalidArgument ErrorCode = "invalid_argument"

	// Malformed indicates an error occurred while decoding the client's request.
	// This may mean that the message was encoded improperly, or that there is a
	// disagreement in message format between the client and server.
	Malformed ErrorCode = "malformed"

	// DeadlineExceeded means operation expired before completion. For operations
	// that change the state of the system, this error may be returned even if the
	// operation has completed successfully (timeout).
	DeadlineExceeded ErrorCode = "deadline_exceeded"

	// NotFound means some requested entity was not found.
	NotFound ErrorCode = "not_found"

	// BadRoute means that the requested URL path wasn't routable to a Twirp
	// service and method. This is returned by the generated server, and usually
	// shouldn't be returned by applications. Instead, applications should use
	// NotFound or Unimplemented.
	BadRoute ErrorCode = "bad_route"

	// AlreadyExists means an attempt to create an entity failed because one
	// already exists.
	AlreadyExists ErrorCode = "already_exists"

	// PermissionDenied indicates the caller does not have permission to execute
	// the specified operation. It must not be used if the caller cannot be
	// identified (Unauthenticated).
	PermissionDenied ErrorCode = "permission_denied"

	// Unauthenticated indicates the request does not have valid authentication
	// credentials for the operation.
	Unauthenticated ErrorCode = "unauthenticated"

	// ResourceExhausted indicates some resource has been exhausted, perhaps a
	// per-user quota, or perhaps the entire file system is out of space.
	ResourceExhausted ErrorCode = "resource_exhausted"

	// FailedPrecondition indicates operation was rejected because the system is
	// not in a state required for the operation's execution. For example, doing
	// an rmdir operation on a directory that is non-empty, or on a non-directory
	// object, or when having conflicting read-modify-write on the same resource.
	FailedPrecondition ErrorCode = "failed_precondition"

	// Aborted indicates the operation was aborted, typically due to a concurrency
	// issue like sequencer check failures, transaction aborts, etc.
	Aborted ErrorCode = "aborted"

	// OutOfRange means operation was attempted past the valid range. For example,
	// seeking or reading past end of a paginated collection.
	// Unlike InvalidArgument, this error indicates a problem that may be fixed if
	// the system state changes (i.e. adding more items to the collection).
	// There is a fair bit of overlap between FailedPrecondition and OutOfRange.
	// We recommend using OutOfRange (the more specific error) when it applies so
	// that callers who are iterating through a space can easily look for an
	// OutOfRange error to detect when they are done.
	OutOfRange ErrorCode = "out_of_range"

	// Unimplemented indicates operation is not implemented or not
	// supported/enabled in this service.
	Unimplemented ErrorCode = "unimplemented"

	// Internal errors. When some invariants expected by the underlying system
	// have been broken. In other words, something bad happened in the library or
	// backend service. Do not confuse with HTTP Internal Server Error; an
	// Internal error could also happen on the client code, i.e. when parsing a
	// server response.
	Internal ErrorCode = "internal"

	// Unavailable indicates the service is currently unavailable. This is a most
	// likely a transient condition and may be corrected by retrying with a
	// backoff.
	Unavailable ErrorCode = "unavailable"

	// DataLoss indicates unrecoverable data loss or corruption.
	DataLoss ErrorCode = "data_loss"

	// NoError is the zero-value, is considered an empty error and should not be
	// used.
	NoError ErrorCode = ""

Valid Twirp error types. Most error types are equivalent to gRPC status codes and follow the same semantics.

type ServerHooks

type ServerHooks struct {
	// RequestReceived is called as soon as a request enters the Twirp
	// server at the earliest available moment.
	RequestReceived func(context.Context) (context.Context, error)

	// RequestRouted is called when a request has been routed to a
	// particular method of the Twirp server.
	RequestRouted func(context.Context) (context.Context, error)

	// ResponsePrepared is called when a request has been handled and a
	// response is ready to be sent to the client.
	ResponsePrepared func(context.Context) context.Context

	// ResponseSent is called when all bytes of a response (including an error
	// response) have been written. Because the ResponseSent hook is terminal, it
	// does not return a context.
	ResponseSent func(context.Context)

	// Error hook is called when an error occurs while handling a request. The
	// Error is passed as argument to the hook.
	Error func(context.Context, Error) context.Context

ServerHooks is a container for callbacks that can instrument a Twirp-generated server. These callbacks all accept a context and return a context. They can use this to add to the request context as it threads through the system, appending values or deadlines to it.

The RequestReceived and RequestRouted hooks are special: they can return errors. If they return a non-nil error, handling for that request will be stopped at that point. The Error hook will be triggered, and the error will be sent to the client. This can be used for stuff like auth checks before deserializing a request.

The RequestReceived hook is always called first, and it is called for every request that the Twirp server handles. The last hook to be called in a request's lifecycle is always ResponseSent, even in the case of an error.

Details on the timing of each hook are documented as comments on the fields of the ServerHooks type.

func ChainHooks

func ChainHooks(hooks ...*ServerHooks) *ServerHooks

ChainHooks creates a new *ServerHooks which chains the callbacks in each of the constituent hooks passed in. Each hook function will be called in the order of the ServerHooks values passed in.

For the erroring hooks, RequestReceived and RequestRouted, any returned errors prevent processing by later hooks.

Package Files

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

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