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Package grpc_middleware

import "github.com/grpc-ecosystem/go-grpc-middleware"
Overview
Index
Subdirectories

Overview ▾

`grpc_middleware` is a collection of gRPC middleware packages: interceptors, helpers and tools.

Middleware

gRPC is a fantastic RPC middleware, which sees a lot of adoption in the Golang world. However, the upstream gRPC codebase is relatively bare bones.

This package, and most of its child packages provides commonly needed middleware for gRPC: client-side interceptors for retires, server-side interceptors for input validation and auth, functions for chaining said interceptors, metadata convenience methods and more.

Chaining

By default, gRPC doesn't allow one to have more than one interceptor either on the client nor on the server side. `grpc_middleware` provides convenient chaining methods

Simple way of turning a multiple interceptors into a single interceptor. Here's an example for server chaining: 

myServer := grpc.NewServer(
    grpc.StreamInterceptor(grpc_middleware.ChainStreamServer(loggingStream, monitoringStream, authStream)),
    grpc.UnaryInterceptor(grpc_middleware.ChainUnaryServer(loggingUnary, monitoringUnary, authUnary)),
)

These interceptors will be executed from left to right: logging, monitoring and auth.

Here's an example for client side chaining: 

clientConn, err = grpc.Dial(
    address,
        grpc.WithUnaryInterceptor(grpc_middleware.ChainUnaryClient(monitoringClientUnary, retryUnary)),
        grpc.WithStreamInterceptor(grpc_middleware.ChainStreamClient(monitoringClientStream, retryStream)),
)
client = pb_testproto.NewTestServiceClient(clientConn)
resp, err := client.PingEmpty(s.ctx, &myservice.Request{Msg: "hello"})

These interceptors will be executed from left to right: monitoring and then retry logic.

The retry interceptor will call every interceptor that follows it whenever when a retry happens.

Writing Your Own

Implementing your own interceptor is pretty trivial: there are interfaces for that. But the interesting bit exposing common data to handlers (and other middleware), similarly to HTTP Middleware design. For example, you may want to pass the identity of the caller from the auth interceptor all the way to the handling function.

For example, a client side interceptor example for auth looks like: 

func FakeAuthUnaryInterceptor(ctx context.Context, req interface{}, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (interface{}, error) {
   newCtx := context.WithValue(ctx, "user_id", "john@example.com")
   return handler(newCtx, req)
}

Unfortunately, it's not as easy for streaming RPCs. These have the `context.Context` embedded within the `grpc.ServerStream` object. To pass values through context, a wrapper (`WrappedServerStream`) is needed. For example: 

func FakeAuthStreamingInterceptor(srv interface{}, stream grpc.ServerStream, info *grpc.StreamServerInfo, handler grpc.StreamHandler) error {
   newStream := grpc_middleware.WrapServerStream(stream)
   newStream.WrappedContext = context.WithValue(ctx, "user_id", "john@example.com")
   return handler(srv, newStream)
}

func ChainStreamClient 

func ChainStreamClient(interceptors ...grpc.StreamClientInterceptor) grpc.StreamClientInterceptor

ChainStreamClient creates a single interceptor out of a chain of many interceptors.

Execution is done in left-to-right order, including passing of context. For example ChainStreamClient(one, two, three) will execute one before two before three.

func ChainStreamServer 

func ChainStreamServer(interceptors ...grpc.StreamServerInterceptor) grpc.StreamServerInterceptor

ChainStreamServer creates a single interceptor out of a chain of many interceptors.

Execution is done in left-to-right order, including passing of context. For example ChainUnaryServer(one, two, three) will execute one before two before three. If you want to pass context between interceptors, use WrapServerStream.

While this can be useful in some scenarios, it is generally advisable to use google.golang.org/grpc.ChainStreamInterceptor directly.

func ChainUnaryClient 

func ChainUnaryClient(interceptors ...grpc.UnaryClientInterceptor) grpc.UnaryClientInterceptor

ChainUnaryClient creates a single interceptor out of a chain of many interceptors.

Execution is done in left-to-right order, including passing of context. For example ChainUnaryClient(one, two, three) will execute one before two before three.

func ChainUnaryServer 

func ChainUnaryServer(interceptors ...grpc.UnaryServerInterceptor) grpc.UnaryServerInterceptor

ChainUnaryServer creates a single interceptor out of a chain of many interceptors.

Execution is done in left-to-right order, including passing of context. For example ChainUnaryServer(one, two, three) will execute one before two before three, and three will see context changes of one and two.

While this can be useful in some scenarios, it is generally advisable to use google.golang.org/grpc.ChainUnaryInterceptor directly.

func WithStreamServerChain 

func WithStreamServerChain(interceptors ...grpc.StreamServerInterceptor) grpc.ServerOption

WithStreamServerChain is a grpc.Server config option that accepts multiple stream interceptors. Basically syntactic sugar.

Deprecated: use google.golang.org/grpc.ChainStreamInterceptor instead.

func WithUnaryServerChain 

func WithUnaryServerChain(interceptors ...grpc.UnaryServerInterceptor) grpc.ServerOption

Chain creates a single interceptor out of a chain of many interceptors.

WithUnaryServerChain is a grpc.Server config option that accepts multiple unary interceptors. Basically syntactic sugar.

Deprecated: use google.golang.org/grpc.ChainUnaryInterceptor instead.

type WrappedServerStream

WrappedServerStream is a thin wrapper around grpc.ServerStream that allows modifying context. 

type WrappedServerStream struct {
    grpc.ServerStream
    // WrappedContext is the wrapper's own Context. You can assign it.
    WrappedContext context.Context
}

func WrapServerStream 

func WrapServerStream(stream grpc.ServerStream) *WrappedServerStream

WrapServerStream returns a ServerStream that has the ability to overwrite context.

func (*WrappedServerStream) Context 

func (w *WrappedServerStream) Context() context.Context

Context returns the wrapper's WrappedContext, overwriting the nested grpc.ServerStream.Context()

Subdirectories

Name Synopsis
..
auth `grpc_auth` a generic server-side auth middleware for gRPC.
logging grpc_logging is a "parent" package for gRPC logging middlewares.
kit `grpc_kit` is a gRPC logging middleware backed by go-kit loggers
ctxkit `ctxkit` is a ctxlogger that is backed by go-kit
logrus `grpc_logrus` is a gRPC logging middleware backed by Logrus loggers
ctxlogrus `ctxlogrus` is a ctxlogger that is backed by logrus
settable grpc_logsettable contains a thread-safe wrapper around grpc-logging infrastructure.
zap `grpc_zap` is a gRPC logging middleware backed by ZAP loggers
ctxzap `ctxzap` is a ctxlogger that is backed by Zap
ratelimit `ratelimit` a generic server-side ratelimit middleware for gRPC.
recovery `grpc_recovery` are interceptors that recover from gRPC handler panics.
retry `grpc_retry` provides client-side request retry logic for gRPC.
tags `grpc_ctxtags` adds a Tag object to the context that can be used by other middleware to add context about a request.
logrus
zap
testing
gogotestproto
testproto
tracing
opentracing `grpc_opentracing` adds OpenTracing
util
backoffutils Backoff Helper Utilities
metautils
validator `grpc_validator` is a generic request contents validator server-side middleware for gRPC.