accept_lang.nx

accept_lang.nx -- parse HTTP Accept-Language header. RFC 7231 §5.3.5. Clients send a comma-separated list of language tags with optional quality values: Accept-Language: en-US,en;q=0.9,fr;q=0.8,*;q=0.1 We parse this into a sorted array of (tag, quality_thousandths) and expose a lookup helper that picks the best match from a server-supported-languages list. Quality values: - Default q = 1.0 if omitted - Range 0.0..1.0; anything else clamped - Stored as integer thousandths (0..1000) to avoid FP math Sorting: higher quality first; ties preserve input order (stable). Caller walks sorted list first-match against their supported set. Invariants: AL1 Zero-alloc: offsets into caller's buffer. AL2 \"*\" wildcard accepted as a language tag; it matches any language that hasn't been explicitly excluded. AL3 Language tag byte ranges preserved as-is (case-sensitive in the buffer); caller does ASCII-lowercase compare if they need RFC-correct case-insensitive matching.