Function close_graceful

gunicorn/util.py:282–313

Close a TCP socket following RFC 9112 section 9.6. Half-closes the write side to send FIN, then lingers on the read side to drain the kernel recv buffer until the peer closes or a cap is hit, then fully closes. This avoids the kernel sending RST (truncating the last response segment

(sock, timeout=2.0, max_drain=65536)

def close_graceful(sock, timeout=2.0, max_drain=65536):
    """Close a TCP socket following RFC 9112 section 9.6.

    Half-closes the write side to send FIN, then lingers on the read side
    to drain the kernel recv buffer until the peer closes or a cap is hit,
    then fully closes. This avoids the kernel sending RST (truncating the
    last response segment) when unread request data remains in the buffer.
    """
    try:
        try:
            sock.shutdown(socket.SHUT_WR)
        except OSError:
            return
        deadline = time.monotonic() + timeout
        drained = 0
        while drained < max_drain:
            remaining = deadline - time.monotonic()
            if remaining <= 0:
                break
            try:
                sock.settimeout(remaining)
                data = sock.recv(4096)
            except (socket.timeout, OSError):
                break
            if not data:
                break
            drained += len(data)
    finally:
        try:
            sock.close()
        except OSError:
            pass


try: