gRPC-Gateway

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. This server is generated according to custom options in your gRPC definition.

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

Background

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 a traditional RESTful API as well. Reasons can range from maintaining backwards-compatibility, supporting languages or clients not well supported by gRPC to simply maintaining the aesthetics and tooling involved with a RESTful architecture.

This project aims to provide that HTTP+JSON interface to your gRPC service. A small amount of configuration in your service to attach HTTP semantics is all that's needed to generate a reverse-proxy with this library.

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: "*"
   +    };
   +  }
    }

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

   2. Add the googleapis-common-protos gem (or your language equivalent) as a dependency to your project.
   3. 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.

More Examples

More examples are available under examples directory.

• examplepb/echo_service.proto, examplepb/a_bit_of_everything.proto: service definition
  • examplepb/echo_service.pb.go, examplepb/a_bit_of_everything.pb.go: [generated] stub of the service
  • examplepb/echo_service.pb.gw.go, examplepb/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

To use the same port for custom HTTP handlers (e.g. serving swagger.json), gRPC-gateway, and a gRPC server, see this code example by CoreOS (and its accompanying blog post)

Features

Supported

• Generating JSON API handlers
• Method parameters in request body
• Method parameters in request path
• Method parameters in query string
• Enum fields in path parameter (including repeated enum fields).
• Mapping streaming APIs to newline-delimited JSON streams
• Mapping HTTP headers with Grpc-Metadata- prefix to gRPC metadata (prefixed with grpcgateway-)
• Optionally emitting API definition for Swagger.
• Setting gRPC timeouts through inbound HTTP Grpc-Timeout header.

Want to support

But not yet.

• bytes fields in path parameter. #5
• Optionally generating the entrypoint. #8
• import_path parameter

No plan to support

But patch is welcome.

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

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 (prefixed with grpcgateway-)
• While configurable, the default {un,}marshaling uses jsonpb with OrigName: true.