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 classic RESTful APIs too for some reasons -- compatibility with 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.

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.

Define your service in gRPC

your_service.proto:

syntax = "proto3";
package example;
message StringMessage {
  string value = 1;
}

service YourService {
  rpc Echo(StringMessage) returns (StringMessage) {}
}

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: "*"
+    };
+  }
 }

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.

Implement your service in gRPC as usual

(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

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

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.

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)
  }
}

(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.

Contribution

See CONTRIBUTING.md.

License

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