read_mime_header safety

Hello,

I'm writing a mail filter for qmail-qfilter in OCaml that uses read_mime_header
to parse just the header of the message and perform logic based on the header
field values. qmail-qfilter passes incoming email messages to it's filter
programs on stdin, and qmail-qfilter reads the message output from the filter
program's stdout so the modified message can be passed to the next filter
program or qmail-queue.

My #1 concern with this OCaml filter program I'm writing is ultimate
reliability. If read_mime_header fails to parse the header properly, I want to
execute a default action. I will have two possible default actions at this point:
  1.) Allow the message through
  2.) Block the message entirely

And I'll make this configurable at run time via a config file.

So, given the following code to read the header:

  let ch = new Netchannels.input_channel (stdin) in
  let stream = new Netstream.input_stream ch in
  let header = Netmime.read_mime_header stream in

If read_mime_header throws an exception and I catch the exception and the
program is configured to allow the message through on error conditions, how do I
reset ch to the beginning of stdin so I can pass the message to stdout in it's
entirety?

Thanks!

--
Jesse Guardiani
Programmer / Sys Admin
[email protected]



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