vtece4564-websockets

vtece4564-websockets

This is a fork of the excellent websockets library, created to facilitate use of a patched version that properly supports the threaded WebSocketServer implementation on Windows. A pull request has been submitted to the main project to incorporate the fix in the official distribution.

Unless you're a student of Virginia Tech's ECE 4564 Network Applications Design course in Spring 2023, you almost certainly want to use the official websockets distribution. This distribution will be removed from PyPI in May 2023.

Background

For a senior-level university network apps design course, my students are using the threaded version of WebSocketServer as part of their final project. While the project required their work to run successfully in containers on Linux, many of them use Windows for their development workstation.

We discovered that serve_forever throws an error at startup on Windows due to the use of select.poll as the means to block while waiting for incoming socket connections. The documentation for pollindicates that it is not supported on all platforms, and apparently Windows is one such platform.

We patched WebSocketServer to instead use selectors.DefaultSelector which determines the best supported mechanism for I/O multiplexing on the runtime platform. The functionality is the same, but it works on a wider range of platforms.

After switching to selectors.DefaultSelector, we discovered that Windows also doesn't support I/O multiplexing using pipes or files -- only sockets. we removed the use of os.pipe for the shutdown mechanism. It was redundant anyway -- simply closing the listener socket in the shutdown method is sufficient to cause the selector to return. Subsequently, the call to socket.accept (on the closed listener socket) causes the loop in serve_forever to terminate as expected.

We tested the change on Windows, Mac OS X, and a Linux container, and it seems that it correctly supports all three platforms.