[Dovecot] Passing info from mail process to mail_filter plugin script?

[Timo Sirainen]

On 21.9.2013, at 20.32, Charles Cazabon <charlesc-dovecot at pyropus.ca> wrote:

> The mail_filter plugin allows you to pass messages through an external
> script/command on the way into and out of the Maildir/mbox/etc mail store.
> With the recent/new version of the plugin, this seems to work correctly.
> 
> However, my mail-filter script (for filtering messages on the way from the
> mail store through the IMAP process to a remote client) needs some extra info
> from the IMAP mail process.  I'm having difficulty figuring out how this can
> be accomplished.
> 
> Ideally, I'd like to pass another open file descriptor (opened in the IMAP
> process) to the script, but I'm not sure if this is possible.  Opening the
> file in the IMAP main.c fails, presumably due to file descriptor limits, but I
> don't see where restrict_fd_limit() is called there.

imap process communicates with the mail_filter process via UNIX socket. It would be possible to pass a file descriptor, but it would need motifications to both the mail-filter/[io]stream-ext-filter.c and to src/util/script.c to use fd_send() and fd_recv().

Without modifications the only way to pass data is via the plugin { mail_filter } parameters, such as the %u expanding to username in the example. If you want some other parameters that don't exist in %variables (they get expanded immediately when the imap process starts), you need to modify for example mail-filter-plugin.c where it passes muser->args and muser->out_args to [io]_stream_create_ext_filter().