Creating New Messages

This is a simple guide for creating a new type of message between the server and clients in Flower.

Let’s suppose we have the following example functions in server.py and numpy_client.py…

Server’s side:

def example_request(self, client: ClientProxy) -> Tuple[str, int]:
    question = "Could you find the sum of the list, Bob?"
    l = [1, 2, 3]
    return client.request(question, l)

Client’s side:

def example_response(self, question: str, l: List[int]) -> Tuple[str, int]:
    response = "Here you go Alice!"
    answer = sum(question)
    return response, answer

Let’s now see what we need to implement in order to get this simple function between the server and client to work!

Message Types for Protocol Buffers

The first thing we need to do is to define a message type for the RPC system in transport.proto. Note that we have to do it for both the request and response messages. For more details on the syntax of proto3, please see the official documentation.

Within the ServerMessage block:

message ExampleIns{
    string question=1;
    repeated int64 l=2;
}
oneof msg {
    ReconnectIns reconnect_ins = 1;
    GetPropertiesIns get_properties_ins = 2;
    GetParametersIns get_parameters_ins = 3;
    FitIns fit_ins = 4;
    EvaluateIns evaluate_ins = 5;
    ExampleIns example_ins = 6;
}

Within the ClientMessage block:

message ExampleRes{
    string response = 1;
    int64 answer = 2;
}

oneof msg {
    DisconnectRes disconnect_res = 1;
    GetPropertiesRes get_properties_res = 2;
    GetParametersRes get_parameters_res = 3;
    FitRes fit_res = 4;
    EvaluateRes evaluate_res = 5;
    ExampleRes examples_res = 6;
}

Make sure to also add a field of the newly created message type in oneof msg.

Once that is done, we will compile the file with:

$ python -m flwr_tool.protoc

If it compiles successfully, you should see the following message:

Writing mypy to flwr/proto/transport_pb2.pyi
Writing mypy to flwr/proto/transport_pb2_grpc.pyi

Serialization and Deserialization Functions

Our next step is to add functions to serialize and deserialize Python datatypes to or from our defined RPC message types. You should add these functions in serde.py.

The four functions:

def example_msg_to_proto(question: str, l: List[int]) -> ServerMessage.ExampleIns:
    return ServerMessage.ExampleIns(question=question, l=l)


def example_msg_from_proto(msg: ServerMessage.ExampleIns) -> Tuple[str, List[int]]:
    return msg.question, msg.l


def example_res_to_proto(response: str, answer: int) -> ClientMessage.ExampleRes:
    return ClientMessage.ExampleRes(response=response, answer=answer)


def example_res_from_proto(res: ClientMessage.ExampleRes) -> Tuple[str, int]:
    return res.response, res.answer

Sending the Message from the Server

Now write the request function in your Client Proxy class (e.g., grpc_client_proxy.py) using the serde functions you just created:

def request(self, question: str, l: List[int]) -> Tuple[str, int]:
    request_msg = serde.example_msg_to_proto(question, l)
    client_msg: ClientMessage = self.bridge.request(
        ServerMessage(example_ins=request_msg)
    )
    response, answer = serde.example_res_from_proto(client_msg.examples_res)
    return response, answer

Receiving the Message by the Client

Last step! Modify the code in message_handler.py to check the field of your message and call the example_response function. Remember to use the serde functions!

Within the handle function:

if server_msg.HasField("example_ins"):
    return _example_response(client, server_msg.example_ins), 0, True

And add a new function:

def _example_response(client: Client, msg: ServerMessage.ExampleIns) -> ClientMessage:
    question,l = serde.evaluate_ins_from_proto(msg)
    response, answer = client.example_response(question,l)
    example_res = serde.example_res_to_proto(response,answer)
    return ClientMessage(examples_res=example_res)

Hopefully, when you run your program you will get the intended result!

('Here you go Alice!', 6)