In Part 1 of this series, we explored a high-level overview of reverse proxies and dived deep into connection management. This post shifts our focus to the intricate world of HTTP handling within a reverse proxy.
Deep Dive into HTTP Handling
At a high level, the HTTP workflow from a proxy’s perspective might seem straightforward:
Receive the request from the client Parse and sanitize the request Uses different requst metadata (path, headers, cookies) to select an upstream host Manipulates the requests as needed Send the request to the selected upstream Read the response from the upstream Sanitize the response Forward response to the client
While many standard libraries support these steps, making them work reliably at scale, and meeting strict security and compliance requirements, is surprisingly complex. From malformed requests and malicious attacks to browser quirks, this layer becomes a battleground for performance, correctness, and resilience.
What Makes It Complex
Challenges in HTTP parsing
The Evolution of the HTTP Protocol
Over the years, http spec has significantly evolved. It started with simple request lines like GET /index.html in HTTP/0.9 , moved to newline-separated headers and persistent connections in HTTP/1.1 , and later adopted full binary framing and multiplexing in HTTP/2 .
Each new version brought added features, redefined earlier assumptions, and introduced additional complexity. These changes require continual updates to existing systems, libraries, and tooling.
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