Fix traceback to correctly deal with source port already in use errors

[Scott Kitterman]

[Impact]

 * Causes random tracebacks on DNS lookups when break functionality of packages that use the module. In the case the bug was filed for, the impact would be a postfix server returning servfail and deferring message traffic.

 * The code represents a missed change for the port from python to python3.

[Test Case]

 * This bug only happens when multiple DNS queries attempt to use the same port at the same time. It's very difficult to reproduce and as far as I know impossible to do it consistently. The attached script demonstrates the new code working and the old code failing. That and code inspection are the best ways to verify this.

[Regression Potential]

 * Regression potential is nil.

Note: This is an extract from a private bug.

Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/DNS/Base.py", line 192, in getSource
self.s.bind(('', source_port))
OSError: [Errno 98] Address already in use

During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/usr/bin/policyd-spf", line 662, in <module>
instance_dict, configData, peruser)
File "/usr/bin/policyd-spf", line 508, in _spfcheck
res = spf.check2(ip, sender, helo)
File "/usr/lib/python3/dist-packages/spf.py", line 363, in check2
receiver=receiver,timeout=timeout,verbose=verbose,querytime=querytime).check()
File "/usr/lib/python3/dist-packages/spf.py", line 607, in check
spf = self.dns_spf(self.d)
File "/usr/lib/python3/dist-packages/spf.py", line 1179, in dns_spf
a = [t for t in self.dns_txt(domain) if RE_SPF.match(t)]
File "/usr/lib/python3/dist-packages/spf.py", line 1227, in dns_txt
dns_list = self.dns(domainname, rr)
File "/usr/lib/python3/dist-packages/spf.py", line 1357, in dns
for k, v in DNSLookup(name, qtype, self.strict, timeout):
File "/usr/lib/python3/dist-packages/spf.py", line 193, in DNSLookup
resp = req.req()
File "/usr/lib/python3/dist-packages/DNS/Base.py", line 238, in req
self.sendUDPRequest(server)
File "/usr/lib/python3/dist-packages/DNS/Base.py", line 263, in sendUDPRequest
self.conn()
File "/usr/lib/python3/dist-packages/DNS/Base.py", line 199, in conn
self.getSource()
File "/usr/lib/python3/dist-packages/DNS/Base.py", line 196, in getSource
if msg[0] != 98: raise
TypeError: 'OSError' object is not subscriptable
warning: missing attribute action in input from private/policyd-spf
warning: command /usr/bin/policyd-spf exit status 1

Note that the policy server exiting non-zero will intefere with mail delivery.

[Scott Kitterman (kitterman)]

Fixed upstream in 3.1.0 and in trunk for the 3.0 branch for if that's ever released again.

[Scott Kitterman (kitterman)]

Low priority for pre-14.04 due to lack of rdepends likely to have significant usage.

[Chris J Arges (arges)]

Hello Scott, or anyone else affected,

Accepted py3dns into trusty-proposed. The package will build now and be available at http://launchpad.net/ubuntu/+source/py3dns/3.0.4-1ubuntu1 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, and change the tag from verification-needed to verification-done. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed. In either case, details of your testing will help us make a better decision.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance!

[Scott Kitterman (kitterman)]

I ran the upstream pypolicyd-spf test suite multiple times with the new package and was unable to reproduce the error (in the past I was able to at least intermittently reproduce it with the test suite) and confirmed via code inspection that the installed package has the correct change.

[Scott Kitterman (kitterman)]

The verification of the Stable Release Update for py3dns has completed successfully and the package has now been released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regresssions.

[Launchpad Janitor (janitor)]

This bug was fixed in the package py3dns - 3.0.4-1ubuntu1

---------------
py3dns (3.0.4-1ubuntu1) trusty-proposed; urgency=medium

  * Backport fix from 3.1/trunk to correctly deal with source port already in
    use errors (LP: #1318264)
 -- Scott Kitterman <email address hidden> Sat, 10 May 2014 20:42:17 -0400