grpc-gateway

gRPC to JSON proxy generator following the gRPC HTTP spec

View project on GitHub

How do I use this?

Installation

First you need to install ProtocolBuffers 3.0.0-beta-3 or later.

mkdir tmp
cd tmp
git clone https://github.com/google/protobuf
cd protobuf
./autogen.sh
./configure
make
make check
sudo make install

Then, go get -u as usual the following packages:

go get -u github.com/grpc-ecosystem/grpc-gateway/protoc-gen-grpc-gateway
go get -u github.com/grpc-ecosystem/grpc-gateway/protoc-gen-swagger
go get -u github.com/golang/protobuf/protoc-gen-go

Usage

Make sure that your $GOPATH/bin is in your $PATH.

  1. Define your service in gRPC

    your_service.proto:

    syntax = "proto3";
    package example;
    message StringMessage {
      string value = 1;
    }
       
    service YourService {
      rpc Echo(StringMessage) returns (StringMessage) {}
    }
    
  2. Add a custom option to the .proto file

    your_service.proto:

     syntax = "proto3";
     package example;
    +
    +import "google/api/annotations.proto";
    +
     message StringMessage {
       string value = 1;
     }
        
     service YourService {
    -  rpc Echo(StringMessage) returns (StringMessage) {}
    +  rpc Echo(StringMessage) returns (StringMessage) {
    +    option (google.api.http) = {
    +      post: "/v1/example/echo"
    +      body: "*"
    +    };
    +  }
     }
    

    If you do not want to modify the proto file for use with grpc-gateway you can alternatively use an external gRPC API Configuration file. Check our documentation for more information.

  3. Generate gRPC stub

    protoc -I/usr/local/include -I. \
      -I$GOPATH/src \
      -I$GOPATH/src/github.com/grpc-ecosystem/grpc-gateway/third_party/googleapis \
      --go_out=plugins=grpc:. \
      path/to/your_service.proto
    

    It will generate a stub file path/to/your_service.pb.go.

  4. Implement your service in gRPC as usual
    1. (Optional) Generate gRPC stub in the language you want.

    e.g.

      protoc -I/usr/local/include -I. \
        -I$GOPATH/src \
        -I$GOPATH/src/github.com/grpc-ecosystem/grpc-gateway/third_party/googleapis \
        --ruby_out=. \
        path/to/your/service_proto
         
      protoc -I/usr/local/include -I. \
        -I$GOPATH/src \
        -I$GOPATH/src/github.com/grpc-ecosystem/grpc-gateway/third_party/googleapis \
        --plugin=protoc-gen-grpc=grpc_ruby_plugin \
        --grpc-ruby_out=. \
        path/to/your/service.proto
    
    1. Add the googleapis-common-protos gem (or your language equivalent) as a dependency to your project.
    2. Implement your service
  5. Generate reverse-proxy

    protoc -I/usr/local/include -I. \
      -I$GOPATH/src \
      -I$GOPATH/src/github.com/grpc-ecosystem/grpc-gateway/third_party/googleapis \
      --grpc-gateway_out=logtostderr=true:. \
      path/to/your_service.proto
    

    It will generate a reverse proxy path/to/your_service.pb.gw.go.

    Note: After generating the code for each of the stubs, in order to build the code, you will want to run go get . from the directory containing the stubs.

  6. Write an entrypoint

    Now you need to write an entrypoint of the proxy server.

    package main
    
    import (
      "flag"
      "net/http"
       
      "github.com/golang/glog"
      "golang.org/x/net/context"
      "github.com/grpc-ecosystem/grpc-gateway/runtime"
      "google.golang.org/grpc"
       	
      gw "path/to/your_service_package"
    )
       
    var (
      echoEndpoint = flag.String("echo_endpoint", "localhost:9090", "endpoint of YourService")
    )
       
    func run() error {
      ctx := context.Background()
      ctx, cancel := context.WithCancel(ctx)
      defer cancel()
       
      mux := runtime.NewServeMux()
      opts := []grpc.DialOption{grpc.WithInsecure()}
      err := gw.RegisterYourServiceHandlerFromEndpoint(ctx, mux, *echoEndpoint, opts)
      if err != nil {
        return err
      }
       
      return http.ListenAndServe(":8080", mux)
    }
       
    func main() {
      flag.Parse()
      defer glog.Flush()
       
      if err := run(); err != nil {
        glog.Fatal(err)
      }
    }
    
  7. (Optional) Generate swagger definitions

    protoc -I/usr/local/include -I. \
      -I$GOPATH/src \
      -I$GOPATH/src/github.com/grpc-ecosystem/grpc-gateway/third_party/googleapis \
      --swagger_out=logtostderr=true:. \
      path/to/your_service.proto
    

Parameters and flags

protoc-gen-grpc-gateway supports custom mapping from Protobuf import to Golang import path. They are compatible to the parameters with same names in protoc-gen-go.

In addition we also support the request_context parameter in order to use the http.Request’s Context (only for Go 1.7 and above). This parameter can be useful to pass request scoped context between the gateway and the gRPC service.

protoc-gen-grpc-gateway also supports some more command line flags to control logging. You can give these flags together with parameters above. Run protoc-gen-grpc-gateway --help for more details about the flags.

Mapping gRPC to HTTP

  • How gRPC error codes map to HTTP status codes in the response
  • HTTP request source IP is added as X-Forwarded-For gRPC request header
  • HTTP request host is added as X-Forwarded-Host gRPC request header
  • HTTP Authorization header is added as authorization gRPC request header
  • Remaining Permanent HTTP header keys (as specified by the IANA here are prefixed with grpcgateway- and added with their values to gRPC request header
  • HTTP headers that start with ‘Grpc-Metadata-‘ are mapped to gRPC metadata (after removing prefix ‘Grpc-Metadata-‘)
  • While configurable, the default {un,}marshaling uses jsonpb with OrigName: true.