EuroPython 2022 - How I wrote a Python client for HTTP/3 proxies - presented by Miloslav Pojman [Wicklow Hall 1 on 2022-07-14] MASQUE (https://tools.ietf.org/id/draft-schinazi-masque-01.html) (Multiplexed Application Substrate over QUIC Encryption) is a draft of a new protocol that allows running proxy or VPN services indistinguishable from HTTPS servers. Akamai built a managed proxy service based on the MASQUE protocol to provide egress proxy (https://www.akamai.com/blog/cloud/powering-and-protecting-online-privacy-icloud-private-relay) for iCloud Private Relay. While working on the proxy at Akamai, I wrote a Python client for testing the proxy service. The MASQUE protocol can tunnel traffic through HTTP/3 or HTTP/2, but common Python libraries only support HTTP/1.1. The tunneled traffic can use any protocol on top of TCP or UDP, including all HTTP versions, so MASQUE can be proxied through MASQUE for onion routing. In this talk, I will show that the MASQUE proxy design is simple and yet client implementations are complex. To put everything into context, I will recap how HTTP proxies operate and how HTTP versions differ. I will highlight lessons learned from designing a low-level HTTP client using Python asyncio. This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License http://creativecommons.org/licenses/by-nc-sa/4.0/