Networking

HPACK

Header compression for HTTP/2.

In plain terms

RFC 7541. Static + dynamic Huffman tables. A repeated 200-byte User-Agent header collapses to one byte after the first send.

Origin

RFC 7541 (2015). HTTP/2 needed header compression that resisted CRIME-style attacks (which had killed gzipped TLS in 2012). HPACK uses Huffman tables but only over headers, not body.

Where it shows up in production

Every HTTP/2 server h2load benchmarks show typical 80-90% header size reduction on repeated requests.

On Semicolony

Simulator http2 streams

Sources & further reading

RFC RFC 7541 — HPACK

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