gRPC to JSON proxy generator following the gRPC HTTP spec

grpc-gateway

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 HTTP API into gRPC. This server is generated according to the google.api.http annotations in your service definitions.

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

Testimonials

We use the gRPC-Gateway to serve millions of API requests per day, and have been since 2018, and through all of that, we have never had any issues with it.

- William Mill, Ad Hoc

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 backward-compatibility, supporting languages or clients that are 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

The following instructions assume you are using Go Modules for dependency management. Use a tool dependency to track the versions of the following executable packages:

// +build tools

package tools

import (
    _ "github.com/grpc-ecosystem/grpc-gateway/protoc-gen-grpc-gateway"
    _ "github.com/grpc-ecosystem/grpc-gateway/protoc-gen-swagger"
    _ "github.com/golang/protobuf/protoc-gen-go"
)

Run go mod tidy to resolve the versions. Install by running

$ go install \
    github.com/grpc-ecosystem/grpc-gateway/protoc-gen-grpc-gateway \
    github.com/grpc-ecosystem/grpc-gateway/protoc-gen-swagger \
    github.com/golang/protobuf/protoc-gen-go

This will place three binaries in your $GOBIN;

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

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

Usage

1. Define your gRPC service using protocol buffers

   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: "*"
   +    };
   +  }
    }
   

   You will need to provide the required third party protobuf files to the protoc compiler. They are included in this repo under the third_party/googleapis folder, and we recommend copying them into your protoc generation file structure. If you’ve structured your proto files according to something like the Buf style guide, you could copy the files into a top-level ./google folder.

   See a_bit_of_everything.proto for examples of more annotations you can add to customize gateway behavior and generated Swagger output.

   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

Here is an example of what a protoc command might look like:

protoc -I. --go_out=plugins=grpc,paths=source_relative:./gen/go/ your/service/v1/your_service.proto

It will generate a stub file with path ./gen/go/your/service/v1/your_service.pb.go.

4. Implement your service in gRPC as usual

   1. (Optional) Generate gRPC stub in the other programming languages.

   For example, the following generates gRPC code for Ruby based on your/service/v1/your_service.proto:

   protoc -I. --ruby_out=./gen/ruby your/service/v1/your_service.proto
   
   protoc -I. --grpc-ruby_out=./gen/ruby your/service/v1/your_service.proto
   

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

5. Generate reverse-proxy using protoc-gen-grpc-gateway

   protoc -I. --grpc-gateway_out=logtostderr=true,paths=source_relative:./gen/go \
     your/service/v1/your_service.proto
   

   It will generate a reverse proxy gen/go/your/service/v1/your_service.pb.gw.go.

6. Write an entrypoint for the HTTP reverse-proxy server

   package main
   
   import (
     "context"
     "flag"
     "net/http"
   
     "github.com/golang/glog"
     "github.com/grpc-ecosystem/grpc-gateway/runtime"
     "google.golang.org/grpc"
   
     gw "github.com/yourorg/yourrepo/proto/gen/go/your/service/v1/your_service"  // Update
   )
   
   var (
     // command-line options:
     // gRPC server endpoint
     grpcServerEndpoint = flag.String("grpc-server-endpoint",  "localhost:9090", "gRPC server endpoint")
   )
   
   func run() error {
     ctx := context.Background()
     ctx, cancel := context.WithCancel(ctx)
     defer cancel()
   
     // Register gRPC server endpoint
     // Note: Make sure the gRPC server is running properly and accessible
     mux := runtime.NewServeMux()
     opts := []grpc.DialOption{grpc.WithInsecure()}
     err := gw.RegisterYourServiceHandlerFromEndpoint(ctx, mux,  *grpcServerEndpoint, opts)
     if err != nil {
       return err
     }
   
     // Start HTTP server (and proxy calls to gRPC server endpoint)
     return http.ListenAndServe(":8081", mux)
   }
   
   func main() {
     flag.Parse()
     defer glog.Flush()
   
     if err := run(); err != nil {
       glog.Fatal(err)
     }
   }
   

7. (Optional) Generate swagger definitions using protoc-gen-swagger

   protoc -I. --swagger_out=logtostderr=true:./gen/swagger your/service/v1/your_service.proto
   

Video intro

This GopherCon UK 2019 presentation from our maintainer @JohanBrandhorst provides a good intro to using the grpc-gateway. It uses the following boilerplate repo as a base: https://github.com/johanbrandhorst/grpc-gateway-boilerplate.

Parameters and flags

During code generation with protoc, flags to grpc-gateway tools must be passed through protoc using the --<tool_suffix>_out=<flags>:<path> pattern, for example:

--grpc-gateway_out=logtostderr=true,repeated_path_param_separator=ssv:.
--swagger_out=logtostderr=true,repeated_path_param_separator=ssv:.

protoc-gen-grpc-gateway supports custom mapping from Protobuf import to Golang import paths. They are compatible with the parameters with the 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 the 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.

Similarly, protoc-gen-swagger supports command-line flags to control Swagger output (for example, json_names_for_fields to output JSON names for fields instead of protobuf names). Run protoc-gen-swagger --help for more flag details. Further Swagger customization is possible by annotating your .proto files with options from openapiv2.proto - see a_bit_of_everything.proto for examples.

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 example by CoreOS (and its accompanying blog post).

Features

Supported

• Generating JSON API handlers.
• Method parameters in the request body.
• Method parameters in the request path.
• Method parameters in query string.
• Enum fields in the 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.