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70 lines
3.0 KiB
70 lines
3.0 KiB
// Copyright 2016 Michal Witkowski. All Rights Reserved.
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// See LICENSE for licensing terms.
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/*
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`grpc_middleware` is a collection of gRPC middleware packages: interceptors, helpers and tools.
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Middleware
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gRPC is a fantastic RPC middleware, which sees a lot of adoption in the Golang world. However, the
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upstream gRPC codebase is relatively bare bones.
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This package, and most of its child packages provides commonly needed middleware for gRPC:
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client-side interceptors for retires, server-side interceptors for input validation and auth,
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functions for chaining said interceptors, metadata convenience methods and more.
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Chaining
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By default, gRPC doesn't allow one to have more than one interceptor either on the client nor on
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the server side. `grpc_middleware` provides convenient chaining methods
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Simple way of turning a multiple interceptors into a single interceptor. Here's an example for
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server chaining:
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myServer := grpc.NewServer(
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grpc.StreamInterceptor(grpc_middleware.ChainStreamServer(loggingStream, monitoringStream, authStream)),
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grpc.UnaryInterceptor(grpc_middleware.ChainUnaryServer(loggingUnary, monitoringUnary, authUnary),
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)
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These interceptors will be executed from left to right: logging, monitoring and auth.
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Here's an example for client side chaining:
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clientConn, err = grpc.Dial(
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address,
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grpc.WithUnaryInterceptor(grpc_middleware.ChainUnaryClient(monitoringClientUnary, retryUnary)),
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grpc.WithStreamInterceptor(grpc_middleware.ChainStreamClient(monitoringClientStream, retryStream)),
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)
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client = pb_testproto.NewTestServiceClient(clientConn)
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resp, err := client.PingEmpty(s.ctx, &myservice.Request{Msg: "hello"})
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These interceptors will be executed from left to right: monitoring and then retry logic.
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The retry interceptor will call every interceptor that follows it whenever when a retry happens.
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Writing Your Own
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Implementing your own interceptor is pretty trivial: there are interfaces for that. But the interesting
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bit exposing common data to handlers (and other middleware), similarly to HTTP Middleware design.
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For example, you may want to pass the identity of the caller from the auth interceptor all the way
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to the handling function.
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For example, a client side interceptor example for auth looks like:
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func FakeAuthUnaryInterceptor(ctx context.Context, req interface{}, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (interface{}, error) {
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newCtx := context.WithValue(ctx, "user_id", "john@example.com")
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return handler(newCtx, req)
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}
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Unfortunately, it's not as easy for streaming RPCs. These have the `context.Context` embedded within
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the `grpc.ServerStream` object. To pass values through context, a wrapper (`WrappedServerStream`) is
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needed. For example:
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func FakeAuthStreamingInterceptor(srv interface{}, stream grpc.ServerStream, info *grpc.StreamServerInfo, handler grpc.StreamHandler) error {
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newStream := grpc_middleware.WrapServerStream(stream)
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newStream.WrappedContext = context.WithValue(ctx, "user_id", "john@example.com")
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return handler(srv, stream)
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}
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*/
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package grpc_middleware
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