Implement change_message_uid

Previously, assigning a new UID to a mapped IMAP or Maildir repository
was done by loading the "local" item, saving it under a new UID and
deleting the old one. This involved lots of disk activity for nothing
more than an effective file rename in Maildirs, and lots of network
usage in the MappedUID cases.

We do this on every upload from a local to a remote item, so that can
potentially be quite expensive. This patch lets backends that support it
(Maildir, MappedUID) efficiently rename the file rather than having to
read the mail content, write it out as a new file and delete the old
file. This speeds up uploads from Maildir and the MappedUID server.

Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>

offlineimap/folder/Maildir.py

@@ -273,7 +273,7 @@ class MaildirFolder(BaseFolder):
         if rtime != None:
             os.utime(os.path.join(tmpdir, messagename), (rtime, rtime))
 
-        self.messagelist[uid] = {'flags': set(),
+        self.messagelist[uid] = {'flags': flags,
                                  'filename': os.path.join('tmp', messagename)}
         # savemessageflags moves msg to 'cur' or 'new' as appropriate
         self.savemessageflags(uid, flags)
@@ -284,25 +284,25 @@ class MaildirFolder(BaseFolder):
         return self.messagelist[uid]['flags']
 
     def savemessageflags(self, uid, flags):
+        """Sets the specified message's flags to the given set.
+
+        This function moves the message to the cur or new subdir,
+        depending on the Seen flag."""
+        # TODO: This function could be improved to only parse the
+        # filenames if the flags actually changed.
         oldfilename = self.messagelist[uid]['filename']
-        dir_prefix, newname = os.path.split(oldfilename)
-        tmpdir = os.path.join(self.getfullname(), 'tmp')
-        if 'S' in flags:
-            # If a message has been seen, it goes into the cur
-            # directory.  CR debian#152482
-            dir_prefix = 'cur'
-        else:
-            dir_prefix = 'new'
-
-        # Strip off existing infostring (preserving small letter flags, that
+        dir_prefix, filename = os.path.split(oldfilename)
+        # If a message has been seen, it goes into 'cur'
+        dir_prefix = 'cur' if 'S' in flags else 'new'
+        # Strip off existing infostring (preserving small letter flags that
         # dovecot uses)
-        infomatch = self.flagmatchre.search(newname)
+        infomatch = self.flagmatchre.search(filename)
         if infomatch:
-            newname = newname[:-len(infomatch.group())] #strip off
+            filename = filename[:-len(infomatch.group())] #strip off
         infostr = '%s2,%s' % (self.infosep, ''.join(sorted(flags)))
-        newname += infostr
+        filename += infostr
+        newfilename = os.path.join(dir_prefix, filename)
 
-        newfilename = os.path.join(dir_prefix, newname)
         if (newfilename != oldfilename):
             try:
                 os.rename(os.path.join(self.getfullname(), oldfilename),
@@ -315,10 +315,26 @@ class MaildirFolder(BaseFolder):
             self.messagelist[uid]['flags'] = flags
             self.messagelist[uid]['filename'] = newfilename
 
-        # By now, the message had better not be in tmp/ land!
-        final_dir, final_name = os.path.split(self.messagelist[uid]['filename'])
-        assert final_dir != 'tmp'
+    def change_message_uid(self, uid, new_uid):
+        """Change the message from existing uid to new_uid
 
+        This will not update the statusfolder UID, you need to do that yourself.
+        :param new_uid: (optional) If given, the old UID will be changed
+            to a new UID. The Maildir backend can implement this as an efficient
+            rename."""
+        if not uid in self.messagelist:
+            raise OfflineImapError("Cannot change unknown Maildir UID %s" % uid)
+        if uid == new_uid: return
+
+        oldfilename = self.messagelist[uid]['filename']
+        dir_prefix, filename = os.path.split(oldfilename)
+        flags = self.getmessageflags(uid)
+        filename = self.new_message_filename(new_uid, flags)
+        os.rename(os.path.join(self.getfullname(), oldfilename),
+                  os.path.join(self.getfullname(), dir_prefix, filename))
+        self.messagelist[new_uid] = self.messagelist[uid]
+        del self.messagelist[uid]
+        
     def deletemessage(self, uid):
         """Unlinks a message file from the Maildir.