package uuidm

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Universally unique identifiers (UUIDs).

Uuidm implements 128 bits universally unique identifiers version 3, 5 (name based with MD5, SHA-1 hashing) and 4 (random based) according to RFC 4122.



type t

The type for UUIDs.

val v3 : t -> string -> t

v3 ns n is a V3 UUID (named based with MD5 hashing) named by n and namespaced by ns.

val v5 : t -> string -> t

v5 ns n is a V5 UUID (named based with SHA-1 hashing) named by n and namespaced by ns.

val v4 : bytes -> t

v4 b is a V4 UUID (random based) that uses the first 16 bytes of b for randomness. Be aware that most of these 128 bits are seen literally in the result.

val v4_gen : Stdlib.Random.State.t -> unit -> t

v4_gen seed is a function that generates random V4 UUIDs (random based) with the given seed.

Warning. Sequences of UUIDs generated using Stdlib.Random are suitably random but predictable by an observer. If that is an issue for you, use v4 with random bytes generated by a CSPRNG.

Informally deprecated

This interface is informally deprecated: it seems many people are using Uuidm.v `V4 in practice. For new code prefer one of the creation functions above.

type version = [
  1. | `V3 of t * string

    Name based with MD5 hashing

  2. | `V4

    Random based

  3. | `V5 of t * string

    Name based with SHA-1 hasing


The type for UUID versions and generation parameters.

  • `V3 and `V5 specify a namespace and a name for the generation.
  • `V4 is random based with a private state seeded with Stdlib.Random.State.make_self_init. Use v4_gen to specify your own seed. Use v4 to specify your own randomness.

    Warning. The sequence resulting from repeatedly calling v `V4 is random but predictable see v4_gen.

val v : version -> t

v version is an UUID of the given version.


val nil : t

nil is the nil UUID.

val ns_dns : t

ns_dns is the DNS namespace UUID.

val ns_url : t

ns_url is the URL namespace UUID.

val ns_oid : t

ns_oid is the ISO OID namespace UUID.

val ns_X500 : t

ns_dn is the X.500 DN namespace UUID.


val equal : t -> t -> bool

equal u u' is true iff u and u' are equal.

val compare : t -> t -> int

compare u u' totally orders u and u'.

Standard binary format

This is the binary format mandated by RFC 4122.

val of_bytes : ?pos:int -> string -> t option

of_bytes pos s is the UUID represented by the 16 bytes starting at pos (defaults to 0) in s. The result is None if the string is not long enough.

val to_bytes : t -> string

to_bytes u is u as a 16 bytes long string.

Mixed-endian binary format

This is the binary format in which the three first fields of UUIDs (which are oblivious to this module) are read and written in little-endian. This corresponds to how UEFI or Microsoft formats UUIDs.

val of_mixed_endian_bytes : ?pos:int -> string -> t option

of_mixed_endian_bytes is like of_bytes but decodes the mixed endian serialization.

val to_mixed_endian_bytes : t -> string

to_mixed_endian_bytes is like to_bytes but encodes the mixed endian serialization.

US-ASCII format

val of_string : ?pos:int -> string -> t option

of_string pos s converts the substring of s starting at pos (defaults to 0) of the form "XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX" where X is a lower or upper case hexadecimal number to an UUID. The result is None if a parse error occurs.

val to_string : ?upper:bool -> t -> string

to_string u is u as a string of the form "XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX" where X is a lower (or upper if upper is true) case hexadecimal number.


val pp : Stdlib.Format.formatter -> t -> unit

pp ppf u formats a representation based on to_string of u on ppf.

val pp_string : ?upper:bool -> Stdlib.Format.formatter -> t -> unit

pp_string ?upper ppf u formats u on ppf like to_string would do.


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