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List:       ruby-talk
Subject:    Re: simple smtp server
From:       "Francis Cianfrocca" <garbagecat10 () gmail ! com>
Date:       2006-10-31 22:13:38
Message-ID: 3a94cf510610311413k13f0af99i89699714c560ed4 () mail ! gmail ! com
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On 10/30/06, mmalaidini@gmail.com <mmalaidini@gmail.com> wrote:
>
> Hello folks,
>
> I'd like to understand if anybody has ever written a very simple smtp
> server (supporting SSL authentication). I'd like to write an stmp proxy
> for my own personal usage and I'm trying to understand where to start.
>
> TIA
> MM
>
>
>

I've written SMTP servers several times in Ruby and in C++. You're not too
specific about the point of the exercise. Are you looking to learn about
network programming and SMTP in particular? Or are you looking for a quick
solution to a narrowly-defined problem?

I would start by reading RFC-821 and RFC-822. SMTP is a very old protocol,
designed long before the dominance of IP and of TCP, and written to be
usable interactively by humans at a command prompt as well as by automatic
agents. It's very simple to understand but deceptively difficult to
implement, so don't underrate it. It's not like more modern protocols that
may appear to have more functionality but are actually less complex
grammatically and easier to implement.

Keep the parsing of message headers (RFC-822) separate in your mind from the
protocol state machine (RFC-821). The creators of SMTP (one of whom was the
late, great Jon Postel) were wise to split it into two documents. Headers
can be dealt with easily enough in Ruby with regular expressions but the
protocol stream is best dealt with as a FSM.

Look at the EventMachine library for a framework that will relieve you of
the need to deal with all of the network and server-architecture headaches.
You still have to deal with SMTP, although at some future point EventMachine
should have built-in support for SMTP (as does Twisted, EM's older brother
in the Python world).

Good luck.


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