[Python-Dev] Buildbot timing out - test suite failure (original) (raw)

[Python-Dev] Buildbot timing out - test suite failure - test_socket issue with UDP6?

Chris Angelico rosuav at gmail.com
Wed Jan 27 07:47:33 EST 2016

On Wed, Jan 27, 2016 at 8:39 PM, Victor Stinner <victor.stinner at gmail.com> wrote:

2016-01-23 7:03 GMT+01:00 Chris Angelico <rosuav at gmail.com>:

Running just that test file:

$ ./python Lib/test/testsocket.py ... chomp lots of lines ... testRecvmsgPeek (main.RecvmsgUDP6Test) ... seems to indicate that the stall is due to IPv6 and UDP. The VM should have full IPv6 support, although my ISPs don't carry IPv6 traffic, so it won't be able to reach the internet proper; but it should be able to do all manner of local tests. Try to apply attached patch and run: $ ./python -m test -v -m testRecvmsgPeek testsocket (...) testRecvmsgPeek (test.testsocket.RecvmsgUDP6Test) ... CLI SOCK <socket.socket fd=5, family=AddressFamily.AFINET6,_ _type=SocketKind.SOCKDGRAM, proto=0, laddr=('::1', 44347, 0, 0)> SERV SOCK <socket.socket fd=4, family=AddressFamily.AFINET6,_ _type=SocketKind.SOCKDGRAM, proto=0, laddr=('::1', 40488, 0, 0)> CLI SOCK ('::1', 44347, 0, 0) SERV SOCK ('::1', 40488, 0, 0) ok testRecvmsgPeek (test.testsocket.RecvmsgIntoUDP6Test) ... CLI SOCK <socket.socket fd=5, family=AddressFamily.AFINET6,_ _type=SocketKind.SOCKDGRAM, proto=0, laddr=('::1', 52721, 0, 0)> SERV SOCK <socket.socket fd=4, family=AddressFamily.AFINET6,_ _type=SocketKind.SOCKDGRAM, proto=0, laddr=('::1', 43967, 0, 0)> CLI SOCK ('::1', 52721, 0, 0) SERV SOCK ('::1', 43967, 0, 0) ok (...) As you can see: the test uses the local loopback interface. Inet6TestBase.host is "::1".

Confirmed. It does two tests of IPv4 which run just fine, and then:

testRecvmsgPeek (test.test_socket.RecvmsgUDP6Test) ... CLI SOCK <socket.socket fd=5, family=AddressFamily.AF_INET6, type=SocketKind.SOCK_DGRAM, proto=0, laddr=('::1', 47518, 0, 0)> CLI SOCK ('::1', 47518, 0, 0) SERV SOCK <socket.socket fd=4, family=AddressFamily.AF_INET6, type=SocketKind.SOCK_DGRAM, proto=0, laddr=('::1', 42421, 0, 0)> SERV SOCK ('::1', 42421, 0, 0)

and hangs until I interrupt it.

You can try to run a UDP server using netcat: "nc -l -u ::1 12345". Keep the command running in a terminal, and then run in a different terminal: "echo abc | nc -u ::1 12345". You should receive abc in the server.

(Oddly, the default netcat-traditional doesn't seem to support this, but installing netcat-openbsd adds IPv6 support.)

Yep, and that works flawlessly. It's nothing weird about that particular port, either - nc can use 42421 without a problem.

After digging through test_socket.py for over an hour (the MRO for RecvmsgUDP6Test is enormous!!), I've boiled the issue down to this:

import socket MSG = b'asdf qwer zxcv' serv = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM) serv.bind(("::1", 0)) cli = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM) cli.bind(("::1", 0)) cli.sendto(MSG, serv.getsockname()) print(serv.recvmsg(len(MSG) - 3, 0, socket.MSG_PEEK)) print(serv.recvmsg(len(MSG), 0, socket.MSG_PEEK)) print(serv.recvmsg(len(MSG)))

On my main system, this produces three lines of output: the first has truncated text, the second has full text, and the third also has full text. This proves that MSG_PEEK is working correctly. On the buildbot, though, the first one stalls out. Commenting that line out produces correct results - peek the full data, then read it, and all is well.

Any idea why partial read on a datagram socket would sometimes stall?

ChrisA

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