Response-compression middleware.

Negotiates the client's Accept-Encoding against the registered livery_codec codecs and compresses eligible responses, setting Content-Encoding and a cache-correct Vary: Accept-Encoding. gzip and deflate are built in (OTP zlib); brotli/zstd become available when their apps register a codec. Configure as a stack entry {livery_compress, Config} where every key is optional:

• codecs — list of codec modules in server-preference order (default livery_codec:registered()); restricts/overrides the set.
• min_size — minimum {full, _} body size to compress (default 1024).
• types — compressible Content-Type prefixes (default text and the common structured types).

Negotiation

A coding is acceptable iff its Accept-Encoding q-value is > 0 (by exact name or *; q=0 rejects). Among acceptable codings the SERVER preference order wins; client q-weights are only an accept/reject filter. With no acceptable coding the response is sent uncompressed (identity); identity;q=0 is deliberately treated as identity, not a 406.

Scope

Only {full, _} (>= min_size) and {chunked, _} bodies with a compressible Content-Type and no existing Content-Encoding are eligible. SSE, file, empty, and upgrade bodies pass through unchanged.