GRPC

This project is a pure-Crystal implementation of gRPC.

Installation

1. Add the dependency to your shard.yml:

   dependencies:
    grpc:
      github: jgaskins/grpc

2. Run shards install

3. Make sure you have Google's grpc tools installed

   • macOS: brew install grpc

Usage

1. Write a protos/hello_world.proto file that contains a service entry and any message types it depends on:

   syntax = "proto3";
   
   service HelloWorld {
    rpc MethodName (TheRequest) returns (TheResponse) {}
   }
   
   message TheRequest {
    string text = 1;
   }
   
   message TheResponse {
    string data = 1;
   }

2. Compile the .proto files. If your messages are defined in protos/hello_world.proto and you want your code written out to the app's src/protobufs directory, use the following command:

   $ protoc -I protos \
      --grpc_out=src/protobufs \
      --crystal_out=src/protobufs \
      --plugin=protoc-gen-grpc=bin/grpc_crystal \
      --plugin=protoc-gen-crystal=bin/protoc-gen-crystal \
      protos/hello_world.proto

   This compiles both the service and the messages.

Server

To handle gRPC requests for the above service definition, we need 3 things:

• One or more service handlers
• A gRPC server
• An HTTP/2 server to wrap the gRPC server (gRPC runs on top of HTTP/2)

Service Handlers

Services are compiled into abstract classes with the protoc command above. To implement a handler for a given service, we subclass the generated abstract class, defining the methods with snake_cased names:

require "./protobufs/hello_world_services.pb"
require "./protobufs/hello_world.pb"

class HelloWorldHandler < HelloWorld
  # You can define your own initialize method to inject dependencies

  def method_name(request : TheRequest) : TheResponse
    unless request.text.presence
      raise GRPC::BadStatus.new(:invalid_argument, "Text cannot be blank.")
    end

    TheResponse.new(data: "Hello #{request.text}")
  end
end

The methods defined in the service declaration are required to be implemented by this class. Your program will not compile without them.

gRPC Server

require "grpc"
grpc = GRPC::Server.new
grpc << HelloWorldHandler.new

You can add as many service handlers as you like.

HTTP/2 Server

The HTTP2::Server works similarly to HTTP::Server:

require "grpc/http2"
server = HTTP2::ClearTextServer.new([grpc]) # TLS isn't supported yet
server.listen "0.0.0.0", 50000

And now gRPC requests for your HelloWorld service will be handled by HelloWorldHandler.

Client

To write a client to consume the HelloWorld service, you simply use a Stub:

# Load the service and message definitions
require "./protobufs/hello_world_services.pb"
require "./protobufs/hello_world.pb"

HelloWorldService = HelloWorld::Stub.new("localhost", 50000)

# from anywhere in your app
pp HelloWorldService.method_name(TheRequest.new(text: "foo"))
# => TheResponse(@data="Hello foo")

Limitations

This implementation currently only supports "simple gRPC" — send a synchronous request, get a synchronous response. Streaming is not yet implemented.

Roadmap

Development

TODO: Write development instructions here

Contributing

1. Fork it (https://github.com/jgaskins/grpc/fork)
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

Contributors

• Jamie Gaskins - creator and maintainer