grpc-gateway is a plugin of protoc. It reads gRPC service definition, and generates a reverse-proxy server which translates a RESTful JSON API into gRPC.

It helps you to provide your APIs in both gRPC and RESTful style at the same time.

gRPC is great -- it generates API clients and server stubs in many programming languages, it is fast, easy-to-use, bandwidth-efficient and its design is combat-proven by Google. However, you might still want to provide classic RESTful APIs too for some reasons -- compatiblity to languages not supported by gRPC, API backward-compatibility or aesthetics of RESTful architecture.

That's what grpc-gateway helps you to do. You just need to implement your gRPC service with a small amount of custom options. Then the reverse-proxy generated by grpc-gateway serves RESTful API on top of the gRPC service.

First you need to install ProtocolBuffers 3.0 or later.

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

Then, go get as usual.

go get github.com/gengo/grpc-gateway/protoc-gen-grpc-gateway
go get github.com/golang/protobuf/protoc-gen-go

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 "github.com/gengo/grpc-gateway/options/options.proto";
    
    message StringMessage {
      string value = 1;
    }
    
    service YourService {
   -  rpc Echo(StringMessage) returns (StringMessage) {}
   +  rpc Echo(StringMessage) returns (StringMessage) {
   +    option (gengo.grpc.gateway.ApiMethodOptions.api_options) = {
   +      path: "/v1/example/echo"
   +      method: "POST"
   +    };
   +  }
    }

3. Generate gRPC stub

   protoc -I/usr/local/include -I. -I$GOPATH/src \
     --go_out=plugins=grpc:. \
     path/to/your_service.proto

   It will generate a stub file path/to/your_service.pb.go. Now you can implement your service on top of the stub.

4. Generate reverse-proxy

   protoc -I/usr/local/include -I. -I$GOPATH/src \
     --grpc-gateway_out=logtostderr=true:. \
     path/to/your_service.proto

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

5. Write an entrypoint

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

   package main
   import (
     "flag"
     "net/http"
   
     "github.com/golang/glog"
     "github.com/zenazn/goji/web"
     "golang.org/x/net/context"
   	
     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 := web.New()
     err := gw.RegisterYourServiceHandlerFromEndpoint(ctx, mux, *echoEndpoint)
     if err != nil {
       return err
     }
   
     http.ListenAndServe(":8080", mux)
     return nil
   }
   
   func main() {
     flag.Parse()
     defer glog.Flush()
   
     if err := run(); err != nil {
       glog.Fatal(err)
     }
   }

More examples are available under examples directory.

• echo_service.proto, a_bit_of_everything.proto: service definition
  • echo_service.pb.go, a_bit_of_everything.pb.go: [generated] stub of the service
  • echo_service.pb.gw.go, a_bit_of_everything.pb.gw.go: [generated] reverse proxy for the service
• server/main.go: service implementation
• main.go: entrypoint of the generated reverse proxy

• Generating JSON API handlers
• Method parameters in request body
• Method parameters in request path
• Mapping streaming APIs to JSON streams

But not yet.

• Integrated authentication
• bytes and enum fields in path parameter
• Method parameters in query string
• Encoding request/response body in application/x-www-form-urlencoded
• Optionally generating the entrypoint
• Optionally emitting API definition for Swagger

But patch is welcome.

• Method parameters in HTTP headers
• Handling header/trailer metadata
• Encoding request/response body in XML
• True bi-directional streaming. (Probably impossible?)

grpc-gateway is licensed under the BSD 3-Clause License. See LICENSE.txt for more details.