Make python-memcache work on memcache restarts

[Tarek Ziadé]

If you try this scenario, the lib will fail because the socket is closed on dead servers, even if those servers are back :

>>> import memcache
>>> c = memcache.Client(['127.0.0.1:11211'])
>>> c.set('1', 'ok'); c.get('1')
True
'ok'

<RESTART MEMCACHE SERVER HERE AND WAIT MORE THAN 30 SECONDS>
>>> c.get('1')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/tarek/dev/hg.mozilla.org/server-full-again/lib/python2.6/site-packages/python_memcached-1.45-py2.6.egg/memcache.py", line 779, in get
    return self._get('get', key)
  File "/home/tarek/dev/hg.mozilla.org/server-full-again/lib/python2.6/site-packages/python_memcached-1.45-py2.6.egg/memcache.py", line 762, in _get
    rkey, flags, rlen, = self._expectvalue(server)
  File "/home/tarek/dev/hg.mozilla.org/server-full-again/lib/python2.6/site-packages/python_memcached-1.45-py2.6.egg/memcache.py", line 874, in _expectvalue
    if line[:5] == 'VALUE':
TypeError: 'NoneType' object is unsubscriptable

My patch prevents this by resending the query once if the socket is found close. This makes python-memcached working fine when the memcache server is restarted.

Note that the patch includes changes from https://bugs.launchpad.net/python-memcached/+bug/726654 because I wrote both of them when testing this.

[Tarek Ziadé (tziade)]

rewriting a cleaner patch

[Tarek Ziadé (tziade)]

Here's a cleaner attempt

It raises a _ConnectionDeadError if the socket gets closed, and _get and _set retry the command once before marking the server dead.

I am not sure what to do in set_multi, get_multi though

[Hugo Beauzée-Luyssen (chouquette)]

This fixes the issue for me.
Thanks for the patch !

[Neganov Alexandr (ikkeps)]

This works for me too, except for cases when memcached server occasionally stops (In some OSes socket.sendall(..) may not raise an exception if server is down). Here is fixed patch for 1.47 version of python-memcached.

[Sean Reifschneider (jafo)]

Committed ikkeps patch as r45. Thanks everyone!