HPACK Decoder

The HPACK decoder accepts a base64-encoded HPACK block and reconstructs the list of header fields by simulating the HPACK decoding process. It maintains the static and dynamic header tables, applies indexing rules, and emits headers in the original order. The implementation follows RFC 7541 semantics for indexed and literal representations, including optional Huffman coding of string literals when present.
It computes per-header size contributions, tracks dynamic table updates, and reports current table capacity and used space. The output is a structured list of name-value pairs, with header names normalized to lower-case to reflect RFC conventions. The tool can operate in strict mode (validating every bite) or in a permissive mode that tolerates minor non-conformances for debugging.
This tool benefits developers debugging HTTP/2 traffic, QA engineers validating encoder/decoder compatibility, and security researchers assessing header behavior. Its value lies in exposing dynamic table changes, per-header size accounting, and precise decoding traces without requiring a full client implementation.
Core features include base64 input, optional dynamic table size override, decoded header list as name-value pairs, dynamic table state, and a decoding summary. Optional advanced views reveal step-by-step decoding decisions and table updates for deeper analysis.