gRPC-Gateway

gRPC to JSON proxy generator following the gRPC HTTP spec

About

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.

Docs

You can read our docs at:

https://grpc-ecosystem.github.io/grpc-gateway/

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

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 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/v2/protoc-gen-grpc-gateway"
    _ "github.com/grpc-ecosystem/grpc-gateway/v2/protoc-gen-openapiv2"
    _ "google.golang.org/grpc/cmd/protoc-gen-go-grpc"
    _ "google.golang.org/protobuf/cmd/protoc-gen-go"
)

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

$ go install \
    github.com/grpc-ecosystem/grpc-gateway/v2/protoc-gen-grpc-gateway \
    github.com/grpc-ecosystem/grpc-gateway/v2/protoc-gen-openapiv2 \
    google.golang.org/protobuf/cmd/protoc-gen-go \
    google.golang.org/grpc/cmd/protoc-gen-go-grpc

This will place four binaries in your $GOBIN;

protoc-gen-grpc-gateway
protoc-gen-openapiv2
protoc-gen-go
protoc-gen-go-grpc

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

Usage

Define your gRPC service using protocol buffers

your_service.proto:

 syntax = "proto3";
 package your.service.v1;
 option go_package = "github.com/yourorg/yourprotos/gen/go/your/service/v1";

 message StringMessage {
   string value = 1;
 }

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

Generate gRPC stubs

This step generates the gRPC stubs that you can use to implement the service and consume from clients:

Here's an example buf.gen.yaml you can use to generate the stubs with buf:
```
version: v1beta1
plugins:
  - name: go
    out: gen/go
    opt:
      - paths=source_relative
  - name: go-grpc
    out: gen/go
    opt:
      - paths=source_relative
```
With this file in place, you can generate your files using buf generate.

For a complete example of using buf generate to generate protobuf stubs, see the boilerplate repo. For more information on generating the stubs with buf, see the official documentation.

If you are using protoc to generate stubs, here's an example of what a command might look like:
```
protoc -I . \
    --go_out ./gen/go/ --go_opt paths=source_relative \
    --go-grpc_out ./gen/go/ --go-grpc_opt paths=source_relative \
    your/service/v1/your_service.proto
```
Implement your service in gRPC as usual.

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

At this point, you have 3 options:

no further modifications, use the default mapping to HTTP semantics (method, path, etc.)
- this will work on any .proto file, but will not allow setting HTTP paths, request parameters or similar
additional .proto modifications to use a custom mapping
- relies on parameters in the .proto file to set custom HTTP mappings
no .proto modifications, but use an external configuration file
- relies on an external configuration file to set custom HTTP mappings
- mostly useful when the source proto file isn't under your control

Using the default mapping

This requires no additional modification to the .proto file but does require enabling a specific option when executing the plugin. The generate_unbound_methods should be enabled.

Here's what a buf.gen.yaml file might look like with this option enabled:

version: v1beta1
plugins:
  - name: go
    out: gen/go
    opt:
      - paths=source_relative
  - name: go-grpc
    out: gen/go
    opt:
      - paths=source_relative
  - name: grpc-gateway
    out: gen/go
    opt:
      - paths=source_relative
      - generate_unbound_methods=true

With protoc (just the grpc-gateway stubs):

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

With custom annotations

Add a google.api.http annotation to your .proto file

your_service.proto:

 syntax = "proto3";
 package your.service.v1;
 option go_package = "github.com/yourorg/yourprotos/gen/go/your/service/v1";
+
+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 protobuf compiler. If you are using buf, this dependency can be added to the deps array in your buf.yaml under the name buf.build/googleapis/googleapis:
version: v1beta1
name: buf.build/yourorg/myprotos
deps:
  - buf.build/googleapis/googleapis
Always run buf mod update after adding a dependency to your buf.yaml.

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

Here's what a buf.gen.yaml file might look like:

version: v1beta1
plugins:
  - name: go
    out: gen/go
    opt:
      - paths=source_relative
  - name: go-grpc
    out: gen/go
    opt:
      - paths=source_relative
  - name: grpc-gateway
    out: gen/go
    opt:
      - paths=source_relative

If you are using protoc to generate stubs, you need to ensure the required dependencies are available to the compiler at compile time. These can be found by manually cloning and copying the relevant files from the googleapis repository, and providing them to protoc when running. The files you will need are:

google/api/annotations.proto
google/api/field_behaviour.proto
google/api/http.proto
google/api/httpbody.proto

Here's what a protoc execution might look like:

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

External configuration If you do not want to (or cannot) 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. This is best combined with the standalone=true option to generate a file that can live in its own package, separate from the files generated by the source protobuf file.

Here's what a buf.gen.yaml file might look like with this option enabled:

version: v1beta1
plugins:
  - name: go
    out: gen/go
    opt:
      - paths=source_relative
  - name: go-grpc
    out: gen/go
    opt:
      - paths=source_relative
  - name: grpc-gateway
    out: gen/go
    opt:
      - paths=source_relative
      - grpc_api_configuration=path/to/config.yaml
      - standalone=true

With protoc (just the grpc-gateway stubs):

protoc -I . --grpc-gateway_out ./gen/go \
    --grpc-gateway_opt logtostderr=true \
    --grpc-gateway_opt paths=source_relative \
    --grpc-gateway_opt grpc_api_configuration=path/to/config.yaml \
    --grpc-gateway_opt standalone=true \
    your/service/v1/your_service.proto

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/v2/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)
  }
}

(Optional) Generate OpenAPI definitions using protoc-gen-openapiv2

Here's what a buf.gen.yaml file might look like:
```
version: v1beta1
plugins:
  - name: go
    out: gen/go
    opt:
      - paths=source_relative
  - name: go-grpc
    out: gen/go
    opt:
      - paths=source_relative
  - name: grpc-gateway
    out: gen/go
    opt:
      - paths=source_relative
  - name: openapiv2
    out: gen/openapiv2
```
To use the custom protobuf annotations supported by protoc-gen-openapiv2, we need another dependency added to our protobuf generation step. If you are using buf, you can add the buf.build/grpc-ecosystem/grpc-gateway dependency to your deps array:
```
version: v1beta1
name: buf.build/yourorg/myprotos
deps:
  - buf.build/googleapis/googleapis
  - buf.build/grpc-ecosystem/grpc-gateway
```
With protoc (just the swagger file):
```
protoc -I . --openapiv2_out ./gen/openapiv2 \
    --openapiv2_opt logtostderr=true \
    your/service/v1/your_service.proto
```
If you are using protoc to generate stubs, you will need to copy the protobuf files from the protoc-gen-openapiv2/options directory of this repository, and providing them to protoc when running.

Note that this plugin also supports generating OpenAPI definitions for unannotated methods; use the generate_unbound_methods option to enable this.

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

When using buf to generate stubs, flags and parameters are passed through the opt field in your buf.gen.yaml file, for example:

version: v1beta1
plugins:
  - name: grpc-gateway
    out: gen/go
    opt:
      - paths=source_relative
      - grpc_api_configuration=path/to/config.yaml
      - standalone=true

During code generation with protoc, flags to gRPC-Gateway tools must be passed through protoc using one of 2 patterns:

as part of the --<tool_suffix>_out protoc parameter: --<tool_suffix>_out=<flags>:<path>

--grpc-gateway_out=logtostderr=true,repeated_path_param_separator=ssv:.
--openapiv2_out=logtostderr=true,repeated_path_param_separator=ssv:.

using additional --<tool_suffix>_opt parameters: --<tool_suffix>_opt=<flag>[,<flag>]*

--grpc-gateway_opt logtostderr=true,repeated_path_param_separator=ssv
# or separately
--grpc-gateway_opt logtostderr=true --grpc-gateway_opt repeated_path_param_separator=ssv
--openapiv2_opt logtostderr=true,repeated_path_param_separator=ssv
# or separately
--openapiv2_opt logtostderr=true --openapiv2_opt repeated_path_param_separator=ssv

More examples

More examples are available under the 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 the 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 patches are 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 protojson.

Contribution

See CONTRIBUTING.md.

License

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

erikshafer/grpc-gateway