Priority: A pure-Python HTTP/2 Priority implementation

Priority is a pure-Python implementation of the priority logic for HTTP/2, set out in RFC 7540 Section 5.3 (Stream Priority). This logic allows for clients to express a preference for how the server allocates its (limited) resources to the many outstanding HTTP requests that may be running over a single HTTP/2 connection.

Specifically, this Python implementation uses a variant of the implementation used in the excellent H2O project. This original implementation is also the inspiration for nghttp2’s priority implementation, and generally produces a very clean and even priority stream. The only notable changes from H2O’s implementation are small modifications to allow the priority implementation to work cleanly as a separate implementation, rather than being embedded in a HTTP/2 stack directly.