Decompiling Interactive Fiction
A couple of weeks ago a friend of mine pointed me to the web-based interactive fiction piece called Aisle. As I played it, I immediately started wondering how I could get a text blob of all the possible paths instead of trying to figure out all the actions required to input into the interpreter.
Finding the Source
% sed -e "s/processBase64Zcode('//g" Aisle.z5.js \ | sed -e "s/');//g" \ | base64 --decode > Aisle.z5
At first I did this without output redirection, and it flooded my terminal with binary control characters, essentially frying it. I killed the tmux window, and started again, this time looking to see if the file type was known.
% file Aisle.z5 Aisle.z5: Infocom (Z-machine 5, Release 1 / Serial 990528)
A quick search on Infocom and Z-Machine, shows that Z-Machine was developed for interactive fiction in 1979 for Infocom text adventure games, of which Zork was the first and where the Z comes from. There’s a whole lot of interesting history online about Z-Machine if anyone wants to know more (spoiler: it’s related to UCSD Pascal P-Machine).
Now that the raw source was available, the next step was actually finding useful text. A search found an open source tool called Frotz that can play these files, and the next thing I know I have Aisle running in a terminal and it works just like it does in the browser.
Some addition searches didn’t really uncover much on how to de-compile a Z-Machine file. Nothing in the Debian repos, and some additional man pages for Frotz didn’t lead to much.
Finally I found Z-Code Tools. There was no compiled binaries for Linux, and if there were, they probably don’t work anymore on a newer version of Linux. I downloaded the source and a make later made the binaries magically appear. The freshly compiled txd tool finally yielded the results I wanted:
% ./txd /var/tmp/Aisle.z5 | grep gnocchi | head -5 gnocchiyou S139: "You pick up a bag of gnocchi and turn it over. The doughy balls weigh your eyes; gnocchi, women, a woman, statues, a slow motion crash of flesh on show her some gnocchi and then you eat it and live happily ever after." intelligent. Leaving the gnocchi you walk over and drop to a knee. "Will you
I put the full text dump of Aisle into a gist if anyone is interested in taking a look.
There are many other tools included in ztools that can provide additional information, such as listing a dictionary of available actions and commands.
Interactive fiction is just more than a big blob of text. Since the early days of Z-Machine, these stories have not only included fascinating stories, but also puzzles and other methods of fully immersing a reader. Fully exploring and creating Z-Machine and Interactive fiction is best left to to the experts if you’d like to learn more.
It also appears the Z-code Tools are not packaged in Debian, and this may be a fun project to do sometime.