Pure-Crystal implementation of gRPC grpc protobuf
0.1.6 Latest release released


This project is a pure-Crystal implementation of gRPC.


  1. Add the dependency to your shard.yml:

        github: jgaskins/grpc
  2. Run shards install

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

    • macOS: brew install grpc


  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 \

    This compiles both the service and the messages.


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 "Hello #{request.text}")

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 <<

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 =[grpc]) # TLS isn't supported yet
server.listen "", 50000

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


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 ="localhost", 50000)

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


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



TODO: Write development instructions here


  1. Fork it (
  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


  github: jgaskins/grpc
  version: ~> 0.1.6
License MIT
Crystal 0.36.0


Dependencies 1

  • protobuf master
    {'branch' => 'master', 'github' => 'jeromegn/'}

Development Dependencies 0

Dependents 0

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