[Dovecot] Size detection/replair does not work with zlib

[Roland Rosenfeld]

Hi!

Usually dovecot auto detects or repairs the size of a maildir
message.  So I can place a message named "foo" in the cur directory
and dovecot uses it.

Now I tried the same with a zlib compressed message but here dovecot
doesn't recognize/repair the size of the message.

When I access this folder via IMAP the connection is diconnected and
in dovecot logs I see the following error messages:

Error: Cached message size smaller than expected (805 < 2666)
Error: Corrupted index cache file /somedir/dovecot.index.cache: Broken physical size for mail UID 23
Error: read() failed: Input/output error (FETCH for mailbox INBOX UID 23)
Disconnected: Internal error occurred. Refer to server log for more information. [2013-12-12 10:54:18] in=321 out=1977

As you can see in the first line, dovecot does know the compressed
size of the file (805) as well as the uncompressed size (2666), but it
isn't able to repair its index for this.

If I modify the setup a little with a standard file naming but with a
wrong file size in S-flag (compressed size instead of uncompressed
size), the log entries become stranger:

Error: Cached message size smaller than expected (805 < 2666)
Error: Maildir filename has wrong S value, renamed the file from /somedir/cur/1386772057.M152553P9709.host,S=805:2, to /somedir/cur/1386772057.M152553P9709.host,S=805:2,

So here dovecot detects the wrong S value, but instead of fixing it by
using the uncompressed size, it renames to the same file name as
before...

All the above was tested with dovecot 2.1.17.
We did a short cross test with 2.2.9 which gives somewhat different
error messages, but also isn't able to detect/repair the
(uncompressed) file size:

Error: Cached message size smaller than expected (805 < 2666)
Error: Corrupted index cache file /somedir/dovecot.index.cache: Broken physical size for mail UID 23
Error: read(zlib(/somedir/cur/foo)) failed: Invalid argument

We also noticed that on both dovecot versions after trying to access
the above file, dovecot.index.cache is always deleted and not
rebuild...

Is all this intended behavior?  It sounds different to the standard
behavior of dovecot, that repairs broken folders if possible...

Ciao
Roland