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grpc-gateway

CircleCI

The grpc-gateway is a plugin of the Google protocol buffers compiler protoc. It reads protobuf service definitions and generates a reverse-proxy server which translates a RESTful JSON API into gRPC. This server is generated according to the google.api.http annotations in your service definitions.

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

architecture introduction diagram

Check out our documentation!

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 JSON 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 JSON 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

The grpc-gateway requires a local installation of the Google protocol buffers compiler protoc v3.0.0 or above. Please install this via your local package manager or by downloading one of the releases from the official repository:

https://github.com/protocolbuffers/protobuf/releases

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

This will place three binaries in your $GOBIN;

  • protoc-gen-grpc-gateway
  • protoc-gen-grpc-swagger
  • protoc-gen-go

Make sure that your $GOBIN is in your $PATH.

Usage

  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 google.api.http annotation to your .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 Service 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.

  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 paths. They are compatible to the parameters with same names in protoc-gen-go (except source_relative).

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.

  • proto/examplepb/echo_service.proto, proto/examplepb/a_bit_of_everything.proto, proto/examplepb/unannotated_echo_service.proto: service definition
    • proto/examplepb/echo_service.pb.go, proto/examplepb/a_bit_of_everything.pb.go, proto/examplepb/unannotated_echo_service.pb.go: [generated] stub of the service
    • proto/examplepb/echo_service.pb.gw.go, proto/examplepb/a_bit_of_everything.pb.gw.go, proto/examplepb/uannotated_echo_service.pb.gw.go: [generated] reverse proxy for the service
    • proto/examplepb/unannotated_echo_service.yaml: gRPC API Configuration for unannotated_echo_service.proto
  • 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 definitions for OpenAPI (Swagger) v2.
  • Setting gRPC timeouts through inbound HTTP Grpc-Timeout header.
  • Partial support for gRPC API Configuration files as an alternative to annotation.
  • Automatically translating PATCH requests into Field Mask gRPC requests. See the docs for more information.

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.

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.