smtp-strangler

This is an implementation of the Strangler Fig pattern for any SMTP server program that can run under inetd(8) or tcpserver(1).

In this environment, client requests arrive on stdin and server responses go to stdout.

io_strangler.py sits in the command chain just before the server program. It passes requests to the server and returns responses to the client. This is pretty boring. But since it's written in Python, not idiosyncratic old C, it's pretty easy to start handling certain requests in a new way.

Not exactly like this image (by Christopher J. Wells, here), but almost:

Setup

0. Have macOS, Linux, or another Unix-like system

• The legacy code to be strangled is a Unix command-line program
• Windows Subsystem for Linux might work; if you try, please let me know

1. Get the old C program to be strangled

 $ cd .../where/you/put/source/trees
 $ git clone https://github.com/schmonz/mess822
 $ cd mess822
 $ git checkout smtp-strangler
 $ make ofmipd

2. Get this Python Strangler Fig code

 $ cd .../where/you/put/source/trees
 $ git clone https://github.com/schmonz/smtp-strangler

3. Configure PyCharm Community Edition

• Python interpreter for this project: any 3.x or 2.7
• Right-click and run tests.py: it should run without errors, skipping all tests
• Right-click and run io_strangler.py
  • Run -> Edit Configurations -> Parameters needs to be .../where/you/put/source/trees/mess822/ofmipd
• Run io_strangler.py again and it should work interactively (try HELP, WORD UP, QUIT)