XMPP Echo Bot

Do you know that situation, you really really need an XMPP echo bot, but you don’t have access to high-level tools like Python <https://github.com/horazont/aioxmpp>_ to write one? All you have is openssl, bash, dig, stdbuf and sed? Then this tool is for you.

This is an XMPP echo bot written in (mostly) sed. Bash is used to do the pre-authentication setup (look up DNS records, establish TLS via openssl s_client). sed processes the XML stream and handles all interaction with the server on the XMPP level. Yes, this kinda parses XML in sed.

Tested to work against Prosody 0.9.

Usage

::

./echoz.sh [email protected] password

Supported Features

• Off-the-Record messaging
• XEP-0092 (Software Version) <https://xmpp.org/extensions/xep-0092.html>_
• XEP-0199 (XMPP Ping) <https://xmpp.org/extensions/xep-0199.html>_

Testimonials

• This is crazy, I haven't crashed it yet! — Matthew Wild <https://github.com/mwild1>_
• I'm frightened. It's only two steps away from gaining consciousness. — Georg Lukas <https://op-co.de/>_
• I am simultaneously appalled and in awe. wow — Lance <https://github.com/legastero>_
• With Echoz.sed, we were able to reduce our XMPP Echo server costs by 90% compared to our previous TeX-based solution. — Leon
• While simple and limited, sed is sufficiently powerful for a large number of purposes. — Wikipedia <https://en.wikipedia.org/wiki/Sed>_
• oh my god this actually works — Test <xmpp:[email protected]>_

Implementation Details

• We use tr to convert > to \n -- since sed is line (or NUL) based, there’s not really another way to parse XMPP XML (which generally never contains newlines) with sed.
• TLS is handled outside of sed for similar reasons. And to keep my sanity (some people might question whether I still have any bit of sanity left).
• Likewise, SRV lookup and composition of the authentication data is entirely handled in bash. This also means that only PLAIN SASL authentication is supported -- SCRAM requires a level of interactivity which would be extremely hard to achieve in sed (not impossible though; we would "just" have to implement base64 and sha1-hmac in sed).
• Since XMPP is a protocol where the client speaks first, we need to hand sed some initial input to allow it to generate a "line" of output (the stream header). We do that with bash, and use that opportunity to pass some configuration to the sed program (namely JID and authentication string).

Design Considerations

• We considered using xml2 to convert the XML stream into events; however, it turns out that 2xm[ doesn’t like stream resets. Also, using the tr approach also allows us to detect the end of elements, which is useful for various purposes.