[Dovecot] Plugin architecture

[Philipp Brüll]

Hi,

I'm currently developing a scrambler plugin which should be used to 
store the mails encrypted on the disk. It uses a special ostream for 
encryption and an istream for decryption.

The idea is, that if a mail arrives via LMTP it goes through the ostream 
and is written encrypted to disk. If an mail is accessed via IMAP, the 
istream is used to decrypt the data from disk.

That all works fine, but if I add the zlib plugin it all gets mixed up. 
For some reason, the lmtp process tries to read something from disk 
using the chain of istreams. That behaviour is a little bit bizzare to 
me, because my understanding is, that the zlib plugin at this point 
should only write (compressed) data to disk.

Why is the istream used here? And what is read? If I remove zlib from 
the configuration again, it all works as expected.

The dovecot version is 2.1.17.

Best regards,
Philipp