Check whether an exception is a connection error

is_connection_err.py

"""
Blog post:
https://gmpy.dev/blog/2023/recognize-connection-errors
"""

import errno, socket, ssl

# Network errors, usually related to DHCP or wpa_supplicant (Wi-Fi).
NETWORK_ERRNOS = frozenset((
    errno.ENETUNREACH,  # "Network is unreachable"
    errno.ENETDOWN,  # "Network is down"
    errno.ENETRESET,  # "Network dropped connection on reset"
    errno.ENONET,  # "Machine is not on the network"
))

def is_connection_err(exc):
    """Return True if an exception is connection-related."""
    if isinstance(exc, ConnectionError):
        # https://docs.python.org/3/library/exceptions.html#ConnectionError
        # ConnectionError includes:
        # * BrokenPipeError (EPIPE, ESHUTDOWN)
        # * ConnectionAbortedError (ECONNABORTED)
        # * ConnectionRefusedError (ECONNREFUSED)
        # * ConnectionResetError (ECONNRESET)
        return True
    if isinstance(exc, socket.gaierror):
        # failed DNS resolution on connect()
        return True
    if isinstance(exc, (socket.timeout, TimeoutError)):
        # timeout on connect(), recv(), send()
        return True
    if isinstance(exc, OSError):
        # ENOTCONN == "Transport endpoint is not connected"
        return (exc.errno in NETWORK_ERRNOS) or (exc.errno == errno.ENOTCONN)
    if isinstance(exc, ssl.SSLError):
        # Let's consider any SSL error a connection error. Usually this is:
        # * ssl.SSLZeroReturnError: "TLS/SSL connection has been closed"
        # * ssl.SSLError: [SSL: BAD_LENGTH] bad length
        return True
    return False