Happy eyeballs in Trio

happy_eyeballs.py

import trio

async def open_tcp_socket(host_name, port, patience_in_seconds=1):
    targets = await trio.socket.getaddrinfo(
        host_name, port, type=trio.socket.SOCK_STREAM
    )
    winning_socket = None

    async with trio.open_nursery() as nursery:
        for *socket_config, _, target in targets:
            attempt_failed = trio.Event()

            async def attempt_to_connect(socket_config):
                try:
                    socket = trio.socket.socket(*socket_config)
                    await socket.connect(target)
                except OSError:
                    attempt_failed.set()
                else:
                    nonlocal winning_socket
                    winning_socket = socket
                    nursery.cancel_scope.cancel()

            nursery.start_soon(attempt_to_connect, socket_config)

            with trio.move_on_after(patience_in_seconds):
                await attempt_failed.wait()

    if winning_socket is None:
        raise OSError("shoot")
    else:
        return winning_socket