CODEWITHSUNDEEP
pythonclient-serverpython-3.4python-asyncio
sargas
sargas

Reputation: 6180

Why is this Python 3 asyncio client sending the bytes only after the Python process is interrupted?

Why is my client timing out at code line:

response = yield from asyncio.wait_for(reader.read(), timeout=3.0)

instead of getting a message back?

The server piece only registers it got a message from this client after the client times out and I actually issue a ctrl + d to kill the Python interpreter

client.py

@asyncio.coroutine
def test_connection(host, port):
    # Get the streams for the socket
    print('Starting client connection')
    reader, writer = yield from asyncio.open_connection(host, port)

    message = 'Test Message'.encode('ascii')

    # Start communication
    print('Sending message to {}:{} - {}'.format(host, port, message))
    writer.write(message)

    print('Waiting 3 sec for response...')
    response = yield from asyncio.wait_for(reader.read(), timeout=3.0)
    print('Got response: {}'.format(response.decode('ascii')))

    writer.close()


def run():
    loop = asyncio.get_event_loop()
    task = asyncio.async(test_connection())
    loop.run_until_complete(task)
    loop.close()

Upvotes: 3

Views: 1724

Answers (1)

dano
dano

Reputation: 94891

The problem is likely that you're calling reader.read() on the server-side (and also on the client-side), which will block until an EOF is sent from the server. But presumably you're not doing that - you're just sending some bytes over and keeping the connection open.

Instead, you need either to call readline() and make sure to append b'\n' to your mess payloads, call read with some size to limit the number of bytes you wait for, or call writer.write_eof() after writing your message payload, assuming you don't plan to use the writer anymore. Using readline() or write_eof are probably your safest options. Here's a complete example demonstrating using readline():

client.py

import asyncio

@asyncio.coroutine
def test_connection(host, port):
    # Get the streams for the socket
    print('Starting client connection')
    reader, writer = yield from asyncio.open_connection(host, port)

    message = 'Test Message\n'.encode('ascii')

    # Start communication
    print('Sending message to {}:{} - {}'.format(host, port, message))
    writer.write(message)

    print('Waiting 3 sec for response...')
    response = yield from asyncio.wait_for(reader.readline(), timeout=5.0)
    print('Got response: {}'.format(response.decode('ascii')))

    writer.close()


def run():
    loop = asyncio.get_event_loop()
    task = asyncio.async(test_connection('localhost', 5000))
    loop.run_until_complete(task)
    loop.close()

run()

server.py

import asyncio

@asyncio.coroutine
def got_connection(reader, writer):
    msg = yield from reader.readline()
    message = 'another Test Message\n'.encode('ascii')
    print('Sending message to {}:{} - {}'.format('localhost', 5000, message))
    writer.write(message)


def run():
    loop = asyncio.get_event_loop()
    server = loop.run_until_complete(asyncio.start_server(
                                        got_connection, 'localhost', 5000))
    loop.run_until_complete(server.wait_closed())
    loop.close()

run()

And here are the changes to use write_eof():

client.py

@asyncio.coroutine
def test_connection(host, port):
    # Get the streams for the socket
    print('Starting client connection')
    reader, writer = yield from asyncio.open_connection(host, port)

    message = 'Test Message'.encode('ascii')

    # Start communication
    print('Sending message to {}:{} - {}'.format(host, port, message))
    writer.write(message)
    writer.write_eof()

    print('Waiting 3 sec for response...')
    response = yield from asyncio.wait_for(reader.read(), timeout=5.0)
    print('Got response: {}'.format(response.decode('ascii')))

    writer.close()

server.py

@asyncio.coroutine
def got_connection(reader, writer):
    msg = yield from reader.read()
    message = 'another Test Message'.encode('ascii')
    print('Sending message to {}:{} - {}'.format('localhost', 5000, message))
    writer.write(message)
    writer.write_eof()

Upvotes: 3

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