CODEWITHSUNDEEP
pythonpython-3.xpython-asynciopython-sockets
Hexdigit _
Hexdigit _

Reputation: 197

Asyncio: Problems with very simple write-and-disconnect UDP client

I wanted to try out the new asyncio module from Python 3.5.1. Here's my test code:

import asyncio

class EchoClientProtocol:
    def __init__(self, message, loop):
        self.message = message
        self.loop = loop
        self.transport = None

    def connection_made(self, transport):
        self.transport = transport
        print('Send:', self.message)
        self.transport.sendto(self.message.encode())
        self.transport.close()

    def datagram_received(self, data, addr):
        print("Received:", data.decode())

        print("Close the socket")
        #self.transport.close()

    def error_received(self, exc):
        print('Error received:', exc)

    def connection_lost(self, exc):
        print("Socket closed, stop the event loop")
        loop = asyncio.get_event_loop()
        loop.stop()

loop = asyncio.get_event_loop()
message = "Hello World!"
connect = loop.create_datagram_endpoint(
    lambda: EchoClientProtocol(message, loop),
    remote_addr=('127.0.0.1', 9999))
transport, protocol = loop.run_until_complete(connect)
loop.run_forever()
transport.close()
loop.close()

When I run this, the interpreter gives me:

Traceback (most recent call last):
  File "C:\Users\oxygen\Documents\GitProjects\tests\python\udp\client.py", line
35, in <module>
    loop.run_forever()
  File "C:\Python35-32\lib\asyncio\base_events.py", line 295, in run_forever
    self._run_once()
  File "C:\Python35-32\lib\asyncio\base_events.py", line 1218, in _run_once
    event_list = self._selector.select(timeout)
  File "C:\Python35-32\lib\selectors.py", line 314, in select
    r, w, _ = self._select(self._readers, self._writers, [], timeout)
  File "C:\Python35-32\lib\selectors.py", line 305, in _select
    r, w, x = select.select(r, w, w, timeout)
OSError: [WinError 10038] an operation was attempted on something that is not a socket

I think this is caused by the sequence of self.transport.sendto(self.message.encode()) and self.transport.close(). If I understand correctly, the sendto method is asynchronous and it actually gets invoked after I close the socket by calling the close method. Is there any way to solve this?

Upvotes: 0

Views: 3349

Answers (2)

frost-nzcr4
frost-nzcr4

Reputation: 1620

This one resolves on_con_lost future after send:

import asyncio


class EchoClientProtocol:
    def __init__(self, message, on_con_lost):
        self.message = message
        self.on_con_lost = on_con_lost

    def connection_made(self, transport):
        print("Send:", self.message)
        self.transport = transport
        self.transport.sendto(self.message.encode())
        self.on_con_lost.set_result(True)


async def main() -> None:
    loop = asyncio.get_running_loop()
    transport, protocol = await loop.create_datagram_endpoint(
        lambda: EchoClientProtocol(
            "Hello World!",
            on_con_lost=loop.create_future(),
        ),
        remote_addr=("127.0.0.1", 9999),
    )

    try:
        await asyncio.sleep(0.5)
        await protocol.on_con_lost
    finally:
        transport.close()


if __name__ == "__main__":
    asyncio.run(main())

Upvotes: 0

kwarunek
kwarunek

Reputation: 12577

The DatagramTransport (actually _SelectorDatagramTransport) schedules two actions on connection, the first one is connection_made from given protocol, the second is _read_ready (recvfrom) - in that order (https://github.com/python/asyncio/blob/master/asyncio/selector_events.py#L996).

Since you close transport on connection_made, the following action (_read_ready) fails. Remove self.transport.close() from there.

You might find interesting the asyncio udp examples.

Upvotes: 1

Related Questions