A gRPC server which handles requests by calling user-defined functions.

You should pass a GRPC.Service in when use the module:

defmodule Greeter.Service do
  use GRPC.Service, name: "ping"

  rpc :SayHello, Request, Reply
  rpc :SayGoodbye, stream(Request), stream(Reply)
end

defmodule Greeter.Server do
  use GRPC.Server, service: Greeter.Service

  def say_hello(request, _stream) do
    Reply.new(message: "Hello")
  end

  def say_goodbye(request_enum, stream) do
    requests = Enum.map request_enum, &(&1)
    GRPC.Server.send_reply(stream, reply1)
    GRPC.Server.send_reply(stream, reply2)
  end
end

Your functions should accept a client request and a GRPC.Server.Stream. The request will be a Enumerable.t(created by Elixir's Stream) of requests if it's streaming. If a reply is streaming, you need to call send_reply/2 to send replies one by one instead of returning reply in the end.

gRPC HTTP/JSON transcoding

Transcoding can be enabled by using the option http_transcode: true:

defmodule Greeter.Service do
  use GRPC.Service, name: "ping"

  rpc :SayHello, Request, Reply
  rpc :SayGoodbye, stream(Request), stream(Reply)
end

defmodule Greeter.Server do
  use GRPC.Server, service: Greeter.Service, http_transcode: true

  def say_hello(request, _stream) do
    Reply.new(message: "Hello" <> request.name)
  end

  def say_goodbye(request_enum, stream) do
    requests = Enum.map request_enum, &(&1)
    GRPC.Server.send_reply(stream, reply1)
    GRPC.Server.send_reply(stream, reply2)
  end
end

With transcoding enabled gRPC methods can be used over HTTP/1 with JSON i.e

POST localhost/helloworld.Greeter/SayHello`
Content-Type: application/json
{
  "message": "gRPC"
}

HTTP/1.1 200 OK
Content-Type: application/json
{
  "message": "Hello gRPC"
}

By using option (google.api.http) annotations in the .proto file the mapping between HTTP/JSON to gRPC methods and parameters can be customized:

syntax = "proto3";

import "google/api/annotations.proto";
import "google/protobuf/timestamp.proto";

package helloworld;

service Greeter {
  rpc SayHello (HelloRequest) returns (HelloReply) {
    option (google.api.http) = {
      get: "/v1/greeter/{name}"
    };
  }
}

message HelloRequest {
  string name = 1;
}

message HelloReply {
  string message = 1;
}

In addition to the POST localhost/helloworld.Greeter/SayHello route in the previous examples this creates an additional route: GET localhost/v1/greeter/:name

GET localhost/v1/greeter/gRPC
Accept: application/json

HTTP/1.1 200 OK
Content-Type: application/json
{
  "message": "Hello gRPC"
}

For more comprehensive documentation on annotation usage in .proto files see