Re: [Bug-mailfromd] attachment filtering / removal

["Sergey Poznyakoff" <gray@xxxxxxxxxx>]

Hi Marc,

> > 
> > Can you advise on some best practice for rejecting messages having
> > attachments with specific file extensions?
> > 

Use current_message[1] to get the descriptor of the message.  Use
message_count_parts[2] to obtain the number of MIME parts in the
message, and iterate over them.  For each part, obtain its descriptor
using message_get_part[2], and inspect the value of
"Content-Disposition" and "Content-Type" headers using message_find_header[3]
function.  You might need to unfold[4] these values before using them.
In order to get the attachment file name, refer to discussions of these
headers in RFC 1806[5] and 1521[6], correspondingly.

This all should be done in prog eom.  Furthermore, notice that MIME
parts can be nested, so that this process is inherently recursive:
the function that iterates over message parts is supposed to call
itself when it encounters a message part of type "multipart/*".  It
would be wise to limit the recursion depth somehow.  Finally, it is
obvious that the process might be quite resource-consuming: you might
need to tune your stack size[7] in order to silent expansion warning
messages.

Kind regards,
Sergey

[1] https://www.gnu.org.ua/software/mailfromd/manual/Current-Message-Functions.html
[2] https://www.gnu.org.ua/software/mailfromd/manual/MIME-functions.html
[3] https://www.gnu.org.ua/software/mailfromd/manual/Header-functions.html
[4] https://www.gnu.org.ua/software/mailfromd/manual/Mail-header-functions.html
[5] https://www.rfc-editor.org/rfc/rfc1806.html
[6] https://www.rfc-editor.org/rfc/rfc1521
[7] https://www.gnu.org.ua/software/mailfromd/manual/stacksize.html