[Dovecot] (Single instance) attachment storage

[Timo Sirainen]

On Mon, 2010-07-19 at 16:24 +0100, Timo Sirainen wrote:
> Code status
> -----------
> 
> Initial version of the attachment reading/writing code is already done
> and works (lacks some error handling and probably performance
> optimizations). The SIS plugin code is also started and should be
> working soon.

The initial version can be tested here:
http://hg.dovecot.org/dovecot-2.0-sis/

It should work with sdbox, but the settings parsing is causing mdbox to
crash at startup. I need to figure out some way to fix that.

You can enable it by setting e.g.:

dbox_attachment_dir = ~/dbox/attachments

By default is does SIS, but if you want only external attachment
storage, you can set:

dbox_attachment_fs = posix

(default is dbox_attachment_fs = sis posix)

TODO has:

 - attachments can generate very long metadata lines. input stream reading
   them probably has a limit..
 - save attachments base64-decoded
 - if attachment stream is too small/long, log an error
     - if file is completely empty, maybe show it as spaces? this could be
       useful for deleting viruses by truncating their files to zero bytes
 - delayed deduplication daemon?

Perhaps the settings troubles could be solved simply by making the code
to be common for all storage backends, even though currently only dbox
would use it. Then the setting names would be mail_attachment_fs and
mail_attachment_dir.