Fix handling of servers that return UIDs in some FETCH responses

closes #22

from pistore in OfflineIMAP #22:

When an IMAP flag update is performed for multiple messages, some IMAP
servers (e.g. Exchange) return the UID attribute only for some of the
FETCH untagged responses, as shown in the following log:

21:19.04 > DCKF8 UID STORE 66050,50613,52164,40043,40055,25874 +FLAGS
(\Deleted)
21:19.36 < * 35 FETCH (FLAGS (\Seen \Deleted) UID 25874)
21:19.36 < * 321 FETCH (FLAGS (\Seen \Deleted))
21:19.57 < * 322 FETCH (FLAGS (\Seen \Deleted))
21:19.57 < * 560 FETCH (FLAGS (\Seen \Deleted))
21:19.57 < * 581 FETCH (FLAGS (\Seen \Deleted) UID 52164)
21:19.62 < * 1022 FETCH (FLAGS (\Seen \Deleted))
21:19.62 < DCKF8 OK STORE completed.

Function IMAPFolder.processmessagesflags is able to manage the servers
which return the UID and the servers which do not return it, but is
not able to deal with the mixed behavior shown above.

The problem is that the fragment of function
IMAPFolder.processmessagesflags that handles the responses with UID
attribute uses variable flags to store the list of flags of the
message in the IMAP format ("flags = attributehashFLAGS?"), while the
fragment that handles the responses without UID expects variable
"flags" to contain the list of modified flags passed to the function
in Maildir format ("self.messagelist[uid]flags?.append(flag)").

As a consequence, the wrong list of flags is used for the messages
without UID, leading to the addition of "strange" flags to the Maildir
messages:

Syncing messages IMAP[INBOX] -> Maildir[.]
Adding flags   to 4 messages  on Maildir[.]
Adding flags e to 4 messages  on Maildir[.]
Adding flags d to 4 messages  on Maildir[.]
Adding flags ) to 4 messages  on Maildir[.]
Adding flags ( to 4 messages  on Maildir[.]
Adding flags l to 4 messages  on Maildir[.]
Adding flags n to 4 messages  on Maildir[.]
Adding flags t to 4 messages  on Maildir[.]
Adding flags \ to 4 messages  on Maildir[.]
Adding flags D to 4 messages  on Maildir[.]
Deleting flags T to 4 messages on Maildir[.]
Adding flags   to 4 messages  on LocalStatus[.]
Adding flags e to 4 messages  on LocalStatus[.]
Adding flags d to 4 messages  on LocalStatus[.]
Adding flags ) to 4 messages  on LocalStatus[.]
Adding flags ( to 4 messages  on LocalStatus[.]
Adding flags l to 4 messages  on LocalStatus[.]
Adding flags n to 4 messages  on LocalStatus[.]
Adding flags t to 4 messages  on LocalStatus[.]
Adding flags \ to 4 messages  on LocalStatus[.]
Adding flags D to 4 messages  on LocalStatus[.]
Deleting flags T to 4 messages on LocalStatus[.]

Fix: use a different variable to store IMAP flags when managing
messages corresponding to responses with UID attribute, e.g.:

*** IMAP.py.orig        Wed Aug 22 18:23:17 2007
--- IMAP.py     Wed Aug 22 18:22:38 2007
*************** class IMAPFolder(BaseFolder):
*** 340,348 ****
              if not ('UID' in attributehash and 'FLAGS' in
              attributehash):
                  # Compensate for servers that don't return a UID
                  attribute.
                  continue
!             flags = attributehash['FLAGS']
              uid = long(attributehash['UID'])
!             self.messagelist[uid]['flags'] =
imaputil.flagsimap2maildir(flags)
              try:
                  needupdate.remove(uid)
              except ValueError:          # Let it slide if it's not
              in the list
--- 340,348 ----
              if not ('UID' in attributehash and 'FLAGS' in
              attributehash):
                  # Compensate for servers that don't return a UID
                  attribute.
                  continue
!             lflags = attributehash['FLAGS']
              uid = long(attributehash['UID'])
!             self.messagelist[uid]['flags'] =
imaputil.flagsimap2maildir(lflags)
              try:
                  needupdate.remove(uid)
              except ValueError:          # Let it slide if it's not
              in the list

02/03/08 14:04:35 changed by js

    * attachment flags-fix.patch added.

Delete 02/03/08 14:05:24 changed by js �

Unfortunately I have to fetch some of my mail from an Exchange server
(Microsoft Exchange Server 2003 IMAP4rev1 server version 6.5.7638.1)
and I can confirm that the analysis of the problem is correct, and the
patch given here fixes the problem.

Looking at the code of the processmessagesflags() method I think it
generally is a bug that the "flags" parameter is reused as a local
variable, since the final "for uid in needupdate:" loop needs the
original value of "flags". This only worked by accident.

I'm attaching a unidiff version of the patch which applies cleanly
against Debian unstable's offlineimap 5.99.4.

offlineimap/folder/IMAP.py

@@ -410,9 +410,9 @@ class IMAPFolder(BaseFolder):
             if not ('UID' in attributehash and 'FLAGS' in attributehash):
                 # Compensate for servers that don't return a UID attribute.
                 continue
-            flags = attributehash['FLAGS']
+            lflags = attributehash['FLAGS']
             uid = long(attributehash['UID'])
-            self.messagelist[uid]['flags'] = imaputil.flagsimap2maildir(flags)
+            self.messagelist[uid]['flags'] = imaputil.flagsimap2maildir(lflags)
             try:
                 needupdate.remove(uid)
             except ValueError:          # Let it slide if it's not in the list