uuid5.nx

uuid5.nx -- UUIDv5 (SHA-1 namespace + name -> UUID). RFC 4122 §4.3. Produces a DETERMINISTIC 128-bit UUID from a namespace UUID + an arbitrary name. Same (ns, name) always yields the same UUID. Used for: - stable IDs derived from URLs (content hashing) - deterministic object IDs in distributed systems - test fixture IDs that don't drift between runs - git-style content addressing without exposing the hash Algorithm: hash = SHA-1(namespace_uuid_bytes || name_bytes) uuid[0..16] = hash[0..16] (take first 16 bytes) uuid[6] = (uuid[6] & 0x0F) | 0x50 (version = 5) uuid[8] = (uuid[8] & 0x3F) | 0x80 (variant = RFC 4122) The RFC defines four standard namespace UUIDs for DNS, URL, OID, and X.500 -- we expose them as byte constants. Callers needing their own namespace mint a v4 UUID (uuid_v4_bytes) once and reuse it forever. Invariants: U5 1 Output is 16 bytes (not the hyphenated string; use uuid_format from uuid.nx to get the string form). U5 2 Deterministic: pure function of (ns, name). U5 3 Byte-for-byte compatible with Python's uuid.uuid5, Node's uuid library, java.util.UUID.nameUUIDFromBytes.