3.1 KiB
Epicyon Software Architecture
Anti-scale principle
In general, methods have been preferred which do not vertically scale. This includes the decision not to use a database, and the way that the inbox is processed. Lack of scalability also simplifies the design.
Being hostile towards the common notion of scaling means that this system will be of no interest to "big tech" and can't easily be used within extractive economic models without needing a substantial rewrite.
This system should however be able to scale rhizomatically with the deployment of many small instances federated together.
No Javascript
This is so that the system can be accessed and used normally with javascript in the web browser turned off. If you want to have good security then this is useful, since lack of javascript greatly reduces the attack surface and constrains adversaries to a limited number of vectors.
High level architecture
The main modules are epicyon.py and daemon.py. epicyon.py is the commandline interface and daemon.py is the http server.
The daemon runs the inbox queue in a separate thread (see inbox.py) and the inbox queue processes incoming ActivityPub posts one at a time in a strictly serial fashion. Doing it this way means minimum potential for any parallelism/locking issues. It also means that the inbox queue is not highly scalable, but that's ok for a system which is only intended to have a few users per instance.
All ActivityPub posts are stored as text files, and there is no database as such other than the filesystem itself. Think of it as being like an email server. Each post is a json file stored in accounts/nick@domain/inbox or accounts/nick@domain/outbox. To avoid parsing problems slashes are replaced by hashes within the ActivityPub post filename. The filename for each post is the same as its ActivityPub id.
Themes security
It is possible to include arbitrary CSS within a custom theme. To avoid security problems the CSS is sanitized before being used. Scripts or import references to other CSS files are not permitted.
The way that the theming system was designed is in order to avoid problems similar to Wordpress, in which an adversary will create an attactive looking theme which contains an expolit. The discovery of exploits then leads to a centralizing dynamic where there is a single "official" themes website or app store. With Epicyon, themes should always be safe to use no matter where they were downloaded from. There should be nothing Turing complete within a theme.
Notifications
There are no notifications in the conventional sense. That is, there is no streaming API or linkage to browser notifications. Instead when significant events occur these create text files which can then be detected by other systems via polling.
See scripts/epicyon-notifications for an example of a script which could be run in a cron job to then send notifications via XMPP or Matrix.