Hacktoberfest 2026: as issues que os mantenedores marcaram para outubro, abertas e boas para iniciantes. Ver issues do Hacktoberfest

UDPTransport.abort() with a queued datagram reports a fatal write error and a resume_writing() AttributeError

Aberta
  • Algo errado?
#771 0 comentários 0 reações 0 responsáveis Ver no GitHub

@graingert já está trabalhando nisso.

Desde 5/10/2026.

  • #772 de @graingert — aberto

Avaliação

Dificuldade
3/5
Tempo estimado
1-2 dias
Facilidade para iniciantes
68/100
Tipo de issue
Bug
Clareza
Claramente especificada
Status de atividade
Ativa
Stack de tecnologia
python
Domínio
networking

Direção de pesquisa

Start by reproducing the issue with the provided script, then trace UDPTransport.abort() and UVBaseTransport._maybe_resume_protocol to see how queued-send cancellation and protocol detachment interact. Compare the exception-handler output with vanilla asyncio; done means abort discards the queued datagram without reporting either error, while connection_lost(None) still occurs.

Escrita pelo modelo de indexação a partir do texto da issue.

Descrição

  • uvloop version: 0.23.0 (also 0.22.1)
  • Python version: 3.12.3
  • Platform: Linux (x86_64, glibc 2.39)
  • Can you reproduce the bug with PYTHONASYNCIODEBUG in env?: Yes
  • Does uvloop behave differently from vanilla asyncio? How?: Yes. With vanilla asyncio, abort() silently discards the queued datagram and calls connection_lost(None). With uvloop, connection_lost(None) is called too, but two errors are also passed to the loop's exception handler.

Calling abort() on a UDPTransport while a datagram is still queued (because the OS refused it with EAGAIN) reports two errors to the loop's exception handler:

  1. Fatal error on transport UDPTransport (Fatal write error on datagram transport), with exception=CancelledError(). The queued send is cancelled because we aborted, so this is not an error.
  2. protocol.resume_writing() failed, with AttributeError("'NoneType' object has no attribute 'resume_writing'"), raised from UVBaseTransport._maybe_resume_protocol after the protocol has already been detached.

A UNIX datagram socket is used to make the OS refuse datagrams, because UDP on loopback never exerts back-pressure. The peer never reads, so the send buffer fills up.

import asyncio
import socket
import sys
import tempfile

import uvloop


class Protocol(asyncio.DatagramProtocol):
    def connection_made(self, transport):
        transport.set_write_buffer_limits(0)

    def connection_lost(self, exc):
        print("connection_lost", exc)


async def main():
    loop = asyncio.get_running_loop()
    errors = []
    loop.set_exception_handler(lambda loop, context: errors.append(context))

    path = f"{tempfile.mkdtemp()}/peer.sock"
    peer = socket.socket(socket.AF_UNIX, socket.SOCK_DGRAM)
    peer.bind(path)  # never read from

    sock = socket.socket(socket.AF_UNIX, socket.SOCK_DGRAM)
    sock.connect(path)
    sock.setblocking(False)
    transport, _ = await loop.create_datagram_endpoint(Protocol, sock=sock)

    # Send until the OS refuses a datagram and the transport has to queue it
    while not transport.get_write_buffer_size():
        transport.sendto(b"x" * 64)

    transport.abort()
    await asyncio.sleep(0.1)
    for context in errors:
        print("exception handler:", context["message"], repr(context.get("exception")))


if sys.argv[1:] == ["uvloop"]:
    uvloop.run(main())
else:
    asyncio.run(main())

Output with python repro.py:

connection_lost None

Output with python repro.py uvloop:

connection_lost None

exception handler: Fatal error on transport UDPTransport (Fatal write error on datagram transport) CancelledError()
exception handler: protocol.resume_writing() failed AttributeError("'NoneType' object has no attribute 'resume_writing'")

Expected: the same as vanilla asyncio, i.e. the queued datagram is silently discarded and nothing is reported to the exception handler.

Found via anyio, whose UDP socket aclose() aborts the transport.

Linguagem predominante
Cython
Estrelas
11.9k
Forks
616
Merge médio
4h 43min
PRs com merge (30d)
3

Preparar o ambiente

Este projeto não oferece contêiner de desenvolvimento, Dockerfile nem guia de contribuição, então a configuração fica por sua conta: comece pelo README e veja nosso guia da primeira contribuição para os passos gerais.

Primeiros passos

  1. Leia a issue inteira e depois o guia de contribuição do projeto.
  2. Comente na issue dizendo que vai assumir — evita que duas pessoas façam o mesmo trabalho.
  3. Faça um fork do repositório e trabalhe em uma branch.
  4. Abra um pull request que referencie o número da issue.

Mais de MagicStack/uvloop

Todas as issues de MagicStack/uvloop

Issues semelhantes

Mais issues de Networking

Receba novas issues na sua caixa de entrada

Um resumo curto de issues do GitHub para quem está começando.