This appservice is designed to make matrix room data public. These rooms must explicitly have a world_visible history visibilty state event. In addition, the appservice virtual user must be explicitly invited to every room that is to be made public. To add another layer of permissions, these rooms must have a custom state event of type commune.room.public with content set to public: true.

In other words, simply running this appservice alongside a matrix homeserver will not leak any room data. All access rules must be explicitly set beforehand.

The appservice cannot read events from rooms it hasn't been invited to. The routing middleware handler enforces this on every API route.

It also explicitly rejects joining and accessing DM rooms, and rooms with E2EE enabled.

The API surface provided by this appservice are a subset of GET requests from the matrix client-server-api. There is no way for the appservice to send new events or modify existing events in rooms that it has access to.

The endpoints are the absolutely necessary ones needed to build a public rendering of the chatroom view - these include room messages, room state, individual events, threads, space hierarchies, event relationships and media.

The full list of API routes can be found here.

A homeserver running this appservice can make remote federated rooms on other homeservers publicly available too, with checks in place to ensure it doesn't happen accidentally or without permission. The appservice has a configuration option that allows only local users to invite the public appservice - meaning users on homeserver B cannot invite homeserver A's appservice user to rooms on the remote homeserver.

Additionally, federated homeserver domains can be whitelisted to ensure only a limited set of remote rooms are publicly accessible.

The appservice membership and join code controls most of the mechanism behind these rules.

This code has not been audited or reviewed by external parties yet, so this document should be viewed as a preliminary outline of all the measures taken to ensure good and necessary security practice. We're hoping to have help with this when possible, and will update the code as is necessary.