URL decode and deserialization fails

Using Protocol Buffer I serialize data and transfer it by adding it as a parameter to HTTP GET requests being sent to Flask. The deserialization of the data sometimes fails depending on the content of the parameters (e.g. if the url parameter contains "%F0").

I tried using different charsets for encoding/decoding and also tried to add a proper header to the request setting content-type to application/x-protobuf.

This is the code of flask handling the incoming GET request.

def _ai_request_stub(min_params: List[str], on_parameter_available: Callable[[], Response]) -> Response:
    """
    This stub is designed for GET requests.
    """
    from flask import request
    missing_params = list(filter(lambda p: p not in request.args, min_params))
    if missing_params:
        return Response(response="The request misses one of the parameters [\"" + "\", ".join(missing_params) + "\"]",
                        status=400, mimetype="text/plain")
    else:
        return on_parameter_available()


@app.route("/ai/control", methods=["GET"])
def control():
    def do() -> Response:
        from aiExchangeMessages_pb2 import Control
        from flask import request
        control_msg = Control()
        control_msg.ParseFromString(request.args["control"].encode())
        return Response(response="Fine", status=200, mimetype="application/x-protobuf")

    return _ai_request_stub(["control"], do)

This is the code creating and sending the GET request.

class AIExchangeService:
    from aiExchangeMessages_pb2 import SimStateResponse, DataRequest, DataResponse, Control, Void, AiID
    from typing import Dict, AnyStr, Any

    def __init__(self, host: str, port: int):
        self.host = host
        self.port = port

    [...]

    def _do_get_request(self, address: str, params: Dict[str, AnyStr]) -> HTTPResponse:
        """
        :return: The response object of the request
        """
        from urllib.parse import urlencode
        from http.client import HTTPConnection
        connection = HTTPConnection(host=self.host, port=self.port)
        print(params)
        connection.request("GET", address + "?" + urlencode(params),
                           headers={"content-type": "application/x-protobuf; charset=utf-8"})
        return connection.getresponse()

    def control(self, commands: Control) -> Void:
        response = self._do_get_request("/ai/control", {"control": commands.SerializeToString()})
        if response.status == 200:
            print("Controlled")
        else:
            print(response.status)
            print(response.reason)

    [...]

This is the protobuffer code showing the structure of the Control object.

message AiID {
    [...]
}

message Control {
    message AvCommand {
        double accelerate = 1;
        double steer = 2;
        double brake = 3;
    }

    enum SimCommand {
        RESUME = 0;
        FAIL = 1;
        CANCEL = 2;
    }
    AiID aid = 1;
    oneof command {
        AvCommand avCommand = 2;
        SimCommand simCommand = 3;
    }
}

The call commands.SerializeToString() in the second snippet in method control(...) yields b'\n\x13\n\n\n\x08fancySid\x12\x05\n\x03ego\x12\t\t\x00\x00\x00\x00\x00\x00\xf0?'. The evaluation of address + "?" + urlencode(params) in the second snippet in method _do_get_request(...) produces the output /ai/control?control=%0A%13%0A%0A%0A%08fancySid%12%05%0A%03ego%12%09%09%00%00%00%00%00%00%F0%3F which seems to be the same but urlencoded.

When sending this GET request to flask request.args["control"] in the first snippet in method control() yields '\n\x13\n\n\n\x08fancySid\x12\x05\n\x03ego\x12\t\t\x00\x00\x00\x00\x00\x00�?' which is not the same serialized string anymore. Trying to deserialize this string fails with the error google.protobuf.message.DecodeError: Error parsing message.

What can I do to make flask read the parameter correctly?

The GET request is not made for shipping huge raw binary data. Instead a POST request has to be used. And indeed a post request works just fine.