---
category: documentation
---
# How do I use this?
## Installation
First you need to install ProtocolBuffers 3.0.0-beta-3 or later.
```sh
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:
```sh
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`.
1. Define your service in gRPC
your_service.proto:
```protobuf
syntax = "proto3";
package example;
message StringMessage {
string value = 1;
}
service YourService {
rpc Echo(StringMessage) returns (StringMessage) {}
}
```
2. Add a [custom option](https://cloud.google.com/service-management/reference/rpc/google.api#http) to the .proto file
your_service.proto:
```diff
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: "*"
+ };
+ }
}
```
See [a_bit_of_everything.proto](https://github.com/grpc-ecosystem/grpc-gateway/blob/master/examples/internal/proto/examplepb/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 API Configuration](https://cloud.google.com/endpoints/docs/grpc/grpc-service-config) file. [Check our documentation](grpcapiconfiguration.html) for more information.
3. Generate gRPC stub
```sh
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.
```sh
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
```
2. Add the googleapis-common-protos gem (or your language equivalent) as a dependency to your project.
3. Implement your service
5. Generate reverse-proxy
```sh
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.
6. Write an entrypoint
Now you need to write an entrypoint of the proxy server.
```go
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
```sh
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
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:
```sh
--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 path.
They are compatible to [the parameters with same names in `protoc-gen-go`](https://github.com/golang/protobuf#parameters).
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.
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](https://github.com/grpc-ecosystem/grpc-gateway/blob/master/protoc-gen-swagger/options/openapiv2.proto) - see
[a_bit_of_everything.proto](https://github.com/grpc-ecosystem/grpc-gateway/blob/master/examples/internal/proto/examplepb/a_bit_of_everything.proto)
for examples.
# Mapping gRPC to HTTP
* [How gRPC error codes map to HTTP status codes in the response](https://github.com/grpc-ecosystem/grpc-gateway/blob/master/runtime/errors.go#L15)
* 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](http://www.iana.org/assignments/message-headers/message-headers.xhtml) 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 (after removing prefix 'Grpc-Metadata-')
* While configurable, the default {un,}marshaling uses [jsonpb](https://godoc.org/github.com/golang/protobuf/jsonpb) with `OrigName: true`.