Try gRPC in Python

Install gRPC

First, install gRPC. It seems that Protocol Buffers, which is responsible for serializing RPC, will be installed along with gRPC.

$ curl -fsSL https://goo.gl/getgrpc | bash -s python

If you get the following error during installation, homebrew is out of date and you should try brew update. (For Mac)

Error: undefined method `desc' for Grpc:Class
Please report this bug:
    http://git.io/brew-troubleshooting
/usr/local/Library/Taps/grpc/homebrew-grpc/Formula/grpc.rb:2:in `<class:Grpc>'
・ ・ ・

Write .proto (IDL)

Write the IDL for Protocol Buffers. The following example defines an RPC that drives the servo.

gRPC itself is a plugin for Protocol Buffers. (There are many [RPC implementations] besides gRPC (https://github.com/google/protobuf/wiki/Third-Party-Add-ons#rpc-implementations))

gateway.proto

syntax = "proto3";

package gateway;

message MoveServoRequest {
  int32 servo_id = 1;
  int32 position = 2;
}

message MoveServoResponse {
  int32 current_position = 1;
}

service AVRGateway {
  rpc MoveServo (MoveServoRequest) returns (MoveServoResponse) {}
}

Compile IDL to generate gRPC python script

The following protoc command will generate gateway_pb2.py.

$ protoc --python_out=. --grpc_out=. --plugin=protoc-gen-grpc=`which grpc_python_plugin` gateway.proto

Write server / client code for gRPC

You can easily write a server / client by importing the Python script generated by the above command. Since the gRPC Python library itself is still Alpha version, various methods are prefixed with early_adopter_ *.

gateway_server.py

import time
import gateway_pb2

class AVRGateway(gateway_pb2.EarlyAdopterAVRGatewayServicer):
  def MoveServo(self, request, context):
    print 'servo_id: %d, position: %d' % (request.servo_id, request.position)
    return gateway_pb2.MoveServoResponse(current_position=150)

def serve():
  server = gateway_pb2.early_adopter_create_AVRGateway_server(AVRGateway(), 9494, None, None)
  server.start()
  try:
    while True:
      time.sleep(100000)
  except KeyboardInterrupt:
    server.stop()

if __name__ == '__main__':
  serve()

gateway_client.py

import gateway_pb2

def run():
  with gateway_pb2.early_adopter_create_AVRGateway_stub('localhost', 9494) as stub:
    response = stub.MoveServo(gateway_pb2.MoveServoRequest(servo_id=1, position=200), 10) 
    print "current position: " + str(response.current_position)

if __name__ == '__main__':
  run()

Run

First, start the server.

$ ls
gateway.proto      gateway_client.py  gateway_pb2.py      gateway_server.py
$ python gateway_server.py

And the client in another terminal.

$ python gateway_client.py
current position: 150
D0729 10:42:14.835677000 140735135564544 iomgr.c:119] Waiting for 1 iomgr objects to be destroyed and executing final callbacks

On the server side

$ python gateway_server.py 
servo_id: 1, position: 200

If it is output like that, it's OK.