[issue30945] loop.create_server does not detect if the interface is IPv6 enabled

[Nic Watson]

Change by Nic Watson :


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[issue30945] loop.create_server does not detect if the interface is IPv6 enabled

[Yury Selivanov]

Change by Yury Selivanov :


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stage:  -> patch review

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[issue30945] loop.create_server does not detect if the interface is IPv6 enabled

[Yury Selivanov]

Yury Selivanov  added the comment:

> asyncio is picking ipv6 because of this code:

> https://github.com/python/cpython/blob/a445feb72902e4a3c5ae712f0c289309e1580d52/Lib/asyncio/base_events.py#L1334-L1340

> despite my host not actually having an ipv6 network hooked up.

Which should be fine; create_server enumerates all addresses and tries to 
connect to each one. IPV6_V6ONLY is only applied to one socket for one IPv6 
address.  I think Antoine's patch is OK.

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[issue30945] loop.create_server does not detect if the interface is IPv6 enabled

[Yury Selivanov]

Yury Selivanov  added the comment:

Does anybody wants to make a PR to fix this?

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[issue30945] loop.create_server does not detect if the interface is IPv6 enabled

[Cecile Tonglet]

Cecile Tonglet  added the comment:

I see that the patch hasn't been applied to master on GitHub. Is there anything 
else expected from me on this ticket?

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[issue30945] loop.create_server does not detect if the interface is IPv6 enabled

[Anthony Sottile]

Anthony Sottile  added the comment:

Applying this patch makes the tests pass for me, but I don't think the patch is 
appropriate (just hides the bug):

```
$ git diff
diff --git a/Lib/test/test_asyncio/test_unix_events.py 
b/Lib/test/test_asyncio/test_unix_events.py
index 5bd76d3..ff6c4e1 100644
--- a/Lib/test/test_asyncio/test_unix_events.py
+++ b/Lib/test/test_asyncio/test_unix_events.py
@@ -480,7 +480,7 @@ class 
SelectorEventLoopUnixSockSendfileTests(test_utils.TestCase):
 proto = self.MyProto(self.loop)
 port = support.find_unused_port()
 server = self.run_loop(self.loop.create_server(
-lambda: proto, support.HOST, port))
+lambda: proto, support.HOSTv4, port))
 self.run_loop(self.loop.sock_connect(sock, (support.HOST, port)))
 
 def cleanup():
```

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[issue30945] loop.create_server does not detect if the interface is IPv6 enabled

[Anthony Sottile]

Anthony Sottile  added the comment:

Actually, my issue seems to be something more strange.

The host being passed in is `localhost` which resolves to:

```
>>> pprint.pprint(socket.getaddrinfo('localhost', 80))
[(,
  ,
  6,
  '',
  ('127.0.0.1', 80)),
 (,
  ,
  17,
  '',
  ('127.0.0.1', 80)),
 (,
  ,
  0,
  '',
  ('127.0.0.1', 80)),
 (,
  ,
  6,
  '',
  ('::1', 80, 0, 0)),
 (,
  ,
  17,
  '',
  ('::1', 80, 0, 0)),
 (,
  ,
  0,
  '',
  ('::1', 80, 0, 0))]
```

asyncio is picking ipv6 because of this code:

https://github.com/python/cpython/blob/a445feb72902e4a3c5ae712f0c289309e1580d52/Lib/asyncio/base_events.py#L1334-L1340

despite my host not actually having an ipv6 network hooked up.

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[issue30945] loop.create_server does not detect if the interface is IPv6 enabled

[Anthony Sottile]

Anthony Sottile  added the comment:

Seeing this as well when running the cpython test suite in docker:

```
$ ./python -m test.test_asyncio

...

[18 similar traces omitted]
==
ERROR: test_sock_sendfile_zero_size 
(test.test_asyncio.test_unix_events.SelectorEventLoopUnixSockSendfileTests)
--
Traceback (most recent call last):
  File "/code/Lib/test/test_asyncio/test_unix_events.py", line 559, in 
test_sock_sendfile_zero_size
sock, proto = self.prepare()
  File "/code/Lib/test/test_asyncio/test_unix_events.py", line 483, in prepare
lambda: proto, support.HOST, port))
  File "/code/Lib/test/test_asyncio/test_unix_events.py", line 476, in run_loop
return self.loop.run_until_complete(coro)
  File "/code/Lib/asyncio/base_events.py", line 566, in run_until_complete
return future.result()
  File "/code/Lib/asyncio/base_events.py", line 1346, in create_server
% (sa, err.strerror.lower())) from None
OSError: [Errno 99] error while attempting to bind on address ('::1', 39527, 0, 
0): cannot assign requested address

--

```


I'm going to try and write a patch to skip these tests (there's already a 
helper)

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[issue30945] loop.create_server does not detect if the interface is IPv6 enabled

[Antoine Pitrou]

Antoine Pitrou added the comment:

Cécile, thank you.  The reason the message is still displayed is that I turned 
the error into a warning (in other words, it is expected).

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[issue30945] loop.create_server does not detect if the interface is IPv6 enabled

[Cecile Tonglet]

Cecile Tonglet added the comment:

Sure! It seems to work, the process returns an exit code of 0 and I see no 
traceback but the message is still displayed in the terminal.

(Also I did something weird because your patch applies on branch master and I 
ran it with Python 3.6... I suppose it shouldn't be a problem)


[0] [11:54:13] /tmp > d run -it --rm -v /tmp:/tmp:ro -v 
~/repos/cpython/Lib/asyncio:/usr/local/lib/python3.6/asyncio:ro python:3.6 
python /tmp/test_ipv6.py
error while attempting to bind on address ('::1', 27015, 0, 0): cannot assign 
requested address
[0] [11:54:19] /tmp > d run -it --rm -v /tmp:/tmp:ro python:3.6 python 
/tmp/test_ipv6.py
Traceback (most recent call last):
  File "/usr/local/lib/python3.6/asyncio/base_events.py", line 1043, in 
create_server
sock.bind(sa)
OSError: [Errno 99] Cannot assign requested address

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/tmp/test_ipv6.py", line 11, in 
server = loop.run_until_complete(server_creation)
  File "/usr/local/lib/python3.6/asyncio/base_events.py", line 466, in 
run_until_complete
return future.result()
  File "/usr/local/lib/python3.6/asyncio/base_events.py", line 1047, in 
create_server
% (sa, err.strerror.lower()))
OSError: [Errno 99] error while attempting to bind on address ('::1', 27015, 0, 
0): cannot assign requested address
[1] [11:54:52] /tmp >

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[issue30945] loop.create_server does not detect if the interface is IPv6 enabled

[Antoine Pitrou]

Antoine Pitrou added the comment:

Cécile, could you try the following patch?  I have no easy way to test here.

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Added file: http://bugs.python.org/file47026/eaddrnotavail_asyncio.patch

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[issue30945] loop.create_server does not detect if the interface is IPv6 enabled

[Yury Selivanov]

Yury Selivanov added the comment:

> Better than trying to detect IPv6 compatibility beforehand would probably to 
> recognize the error and simply ignore it.


+1

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[issue30945] loop.create_server does not detect if the interface is IPv6 enabled

[Antoine Pitrou]

Antoine Pitrou added the comment:

Better than trying to detect IPv6 compatibility beforehand would probably to 
recognize the error and simply ignore it.

Note: errno 99 is EADDRNOTAVAIL.

Something like this could work (untested):

diff --git a/Lib/asyncio/base_events.py b/Lib/asyncio/base_events.py
index 33b8f48..413161a 100644
--- a/Lib/asyncio/base_events.py
+++ b/Lib/asyncio/base_events.py
@@ -1038,6 +1038,11 @@ class BaseEventLoop(events.AbstractEventLoop):
 try:
 sock.bind(sa)
 except OSError as err:
+if err.errno == errno.EADDRNOTAVAIL:
+# See bpo-30945
+sockets.pop()
+sock.close()
+continue
 raise OSError(err.errno, 'error while attempting '
   'to bind on address %r: %s'
   % (sa, err.strerror.lower())) from None

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nosy: +pitrou
versions: +Python 3.7 -Python 3.4

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[issue30945] loop.create_server does not detect if the interface is IPv6 enabled

[Cecile Tonglet]

New submission from Cecile Tonglet:

The IPv6 detection in asyncio.base_events.create_server only detect if IPv6 is 
available instead of checking if the interface can actually support it.

I noticed that by using Python in a Docker container (example code to reproduce 
in attachment):


docker run -it --rm -v /tmp/test_ipv6.py:/src/test_ipv6.py python:3.6 python 
/src/test_ipv6.py


Will result in:


Traceback (most recent call last):
  File "/usr/local/lib/python3.6/asyncio/base_events.py", line 1043, in 
create_server
sock.bind(sa)
OSError: [Errno 99] Cannot assign requested address

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/src/test_ipv6.py", line 11, in 
server = loop.run_until_complete(server_creation)
  File "/usr/local/lib/python3.6/asyncio/base_events.py", line 466, in 
run_until_complete
return future.result()
  File "/usr/local/lib/python3.6/asyncio/base_events.py", line 1047, in 
create_server
% (sa, err.strerror.lower()))
OSError: [Errno 99] error while attempting to bind on address ('::1', 27015, 0, 
0): cannot assign requested address


By default Docker containers have only IPv4 enabled:


1: lo:  mtu 65536 qdisc noqueue state UNKNOWN group 
default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
   valid_lft forever preferred_lft forever
38: eth0@if39:  mtu 1500 qdisc noqueue state 
UP group default 
link/ether 02:42:ac:11:00:02 brd ff:ff:ff:ff:ff:ff
inet 172.17.0.2/16 scope global eth0
   valid_lft forever preferred_lft forever


I believe this detection mechanism should rely on the interface requested. I 
found this on the web for Python 2 that manage to get the info per interface: 
https://pastebin.com/VEnhF1Ht but it's using an external library.

However if you change the hostname to 127.0.0.1 it works normally.

--
components: asyncio
files: test_ipv6.py
messages: 298474
nosy: cecton, yselivanov
priority: normal
severity: normal
status: open
title: loop.create_server does not detect if the interface is IPv6 enabled
type: behavior
versions: Python 3.4, Python 3.5, Python 3.6
Added file: http://bugs.python.org/file47019/test_ipv6.py

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