[New-bugs-announce] [issue35302] create_connection with local_addr misses valid socket bindings

[Neil Booth]

New submission from Neil Booth <kyuupichan at gmail.com>:

I run a machine with IPv4 and IPv6 interfaces on MacOSX Mojave.

I try to loop.create_connection() to a remote machine whose domain resolves to an IPv6 address only, with a local_addr domain name argument that resolves to two local addresses: an IPv4 one first and an IPv6 one second.

The loop https://github.com/python/cpython/blob/master/Lib/asyncio/base_events.py#L927-L943 that loops through the local addresses, IPv4 then IPv6, successfully binds the IPv4 laddr_info to the IPv6 socket successfully (something I find surprising) and then the connection attempt fails with OSError(65, 'No route to host'), at which point the sockets is closed and the IPv6 laddr_info is never tried and the connection attempt fails.

If I reverse the order of the loop so that the IPv6 laddr_info is tried first then the connection succeeds.

I suggest either all laddr_info bindings should be tried for each outer loop of infos, rather than just 1, or that those of a different socket "type" (IPv4 vs IPv6) should be skipped in the inner loop before attempting a binding.

----------
components: asyncio
messages: 330354
nosy: asvetlov, kyuupichan, yselivanov
priority: normal
severity: normal
status: open
title: create_connection with local_addr misses valid socket bindings
type: behavior
versions: Python 3.5, Python 3.6, Python 3.7

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue35302>
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