grpc-gateway

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

Compile from source

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:

For Go 1.24 and later, prefer the tool directive in go.mod described in the "Tracking Tools in go.mod" section. The following blank-import pattern is mainly useful for projects that are not using Go 1.24 yet.

// +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.

If you want to emit OpenAPI 3.1 instead of (or in addition to) Swagger 2.0, install protoc-gen-openapiv3 as well:

go install github.com/grpc-ecosystem/grpc-gateway/v2/protoc-gen-openapiv3

⚠️ Alpha. protoc-gen-openapiv3 is new and its output is not yet stable — the emitted JSON shape for oneofs, wrappers, enums, and similar constructs may change in response to real-world feedback before the plugin graduates. Don't rely on the exact spec bytes being stable across minor releases; the proto-to-OpenAPI mapping rules are likely to tighten, and tooling-compatibility compromises (documented in the generator source) may be revisited as consumer OpenAPI 3.1 support matures. protoc-gen-openapiv2 is the production-stable option.

See OpenAPI 3.1 Output for what it supports and how it differs from protoc-gen-openapiv2.

Using the tool Directive in Go 1.24

Starting from Go 1.24, the tool directive in go.mod provides a structured way to track and manage executable dependencies. This replaces the previous workaround of using a separate tools.go file with blank imports.

Tracking Tools in go.mod

Instead of manually importing tool dependencies in a Go source file, you can now use the tool directive in go.mod to declare the tools your project depends on. For example:

module tools

go 1.24

tool (
	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
)

Managing Tool Dependencies

To add tools to your module, use the -tool flag with go get:

go get -tool github.com/grpc-ecosystem/grpc-gateway/v2/protoc-gen-grpc-gateway
go get -tool github.com/grpc-ecosystem/grpc-gateway/v2/protoc-gen-openapiv2
go get -tool google.golang.org/protobuf/cmd/protoc-gen-go
go get -tool google.golang.org/grpc/cmd/protoc-gen-go-grpc

This automatically updates go.mod, adding the tools under the tool directive along with require statements to ensure version tracking.

Install Tools

Once the tool dependencies are properly recorded in the go.mod file, simply execute the following command in the root directory of your project:

go install tool

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.

Download the binaries

You may alternatively download the binaries from the GitHub releases page. We generate SLSA3 signatures using the OpenSSF's slsa-framework/slsa-github-generator during the release process. To verify a release binary:

1. Install the verification tool from slsa-framework/slsa-verifier#installation.
2. Download the provenance file attestation.intoto.jsonl from the GitHub releases page.
3. Run the verifier:

slsa-verifier -artifact-path <the-binary> -provenance attestation.intoto.jsonl -source github.com/grpc-ecosystem/grpc-gateway -tag <the-tag>

Alternatively, see the section on remotely managed plugin versions below.

Usage

1.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) {}
 }

2. 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: v2
plugins:
  - local: protoc-gen-go
    out: gen/go
    opt:
      - paths=source_relative
  - local: protoc-gen-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

3. Implement your service in gRPC as usual.

4. 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

1. 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: v2
plugins:
  - local: protoc-gen-go
    out: gen/go
    opt:
      - paths=source_relative
  - local: protoc-gen-go-grpc
    out: gen/go
    opt:
      - paths=source_relative
  - local: protoc-gen-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 paths=source_relative \
    --grpc-gateway_opt generate_unbound_methods=true \
    your/service/v1/your_service.proto

2. 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: v2
name: buf.build/yourorg/myprotos
deps:
  - buf.build/googleapis/googleapis

Always run buf dep 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: v2
plugins:
  - local: protoc-gen-go
    out: gen/go
    opt:
      - paths=source_relative
  - local: protoc-gen-go-grpc
    out: gen/go
    opt:
      - paths=source_relative
  - local: protoc-gen-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_behavior.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 paths=source_relative \
    your/service/v1/your_service.proto

3. 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