I have a server that listens for WebSocket connections on port 80, using Twisted and Autobahn. I want to have it also serve static HTML pages, for when the client doesn't want to use a WebSocket. Is it possible to do both things at the same time, using Twisted and Autobahn?
Sure, have a look here and here. You can run Twisted Web and add a Autobahn based WebSocket Twisted Web resource on a path. You can add any number of Twisted Web resources into your resource tree.
Briefly the technique is to start your WebSocketServerFactory manually by invoking startFactory(), then wrap it within a autobahn.twisted.resource.WebSocketResource resource, which you can then register with putChild anywhere within a Twisted Web hierarchy.