man uuid () - Universally Unique Identifier

NAME

OSSP uuid - Universally Unique Identifier

VERSION

OSSP uuid 1.3.2 (06-Dec-2005)

DESCRIPTION

OSSP uuid is a ISO-C:1999 application programming interface (API) and corresponding command line interface (CLI) for the generation of DCE 1.1, ISO/IEC 11578:1996 and RFC 4122 compliant Universally Unique Identifier (UUID). It supports DCE 1.1 variant UUIDs of version 1 (time and node based), version 3 (name based, MD5), version 4 (random number based) and version 5 (name based, SHA-1). Additional API bindings are provided for the languages ISO-:1998, Perl:5 and PHP:4/5. Optional backward compatibility exists for the ISO-C DCE-1.1 and Perl Data::UUID APIs.

UUIDs are 128 bit numbers which are intended to have a high likelihood of uniqueness over space and time and are computationally difficult to guess. They are globally unique identifiers which can be locally generated without contacting a global registration authority. UUIDs are intended as unique identifiers for both mass tagging objects with an extremely short lifetime and to reliably identifying very persistent objects across a network.

This is the ISO-C application programming interface (API) of OSSP uuid.

UUID Binary Representation

According to the DCE 1.1, ISO/IEC 11578:1996 and RFC 4122 standards, a DCE 1.1 variant UUID is a 128 bit number defined out of 7 fields, each field a multiple of an octet in size and stored in network byte order:

  0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 0|                          time_low                             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 1|       time_mid                |         time_hi_and_version   |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 2|clk_seq_hi_res |  clk_seq_low  |         node (0-1)            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 3|                         node (2-5)                            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

An example of a UUID binary representation is the octet stream "CW0xEC 0xB9 0xF3 0x5F 0x44 0x2A 0x11 0xD8 0x8A 0x24 0x00 0x90 0x27 0x2F 0xF7 0x25". The binary representation format is exactly what the OSSP uuid API functions uuid_import() and uuid_export() deal with under CWUUID_FMT_BIN.

UUID ASCII String Representation

According to the DCE 1.1, ISO/IEC 11578:1996 and RFC 4122 standards, a DCE 1.1 variant UUID is represented as an ASCII string consisting of 8 hexadecimal digits followed by a hyphen, then three groups of 4 hexadecimal digits each followed by a hyphen, then 12 hexadecimal digits. Formally, the string representation is defined by the following grammar:

 uuid                   = <time_low> "-" <time_mid> "-"
                          <time_high_and_version> "-"
                          <clock_seq_and_reserved>
                          <clock_seq_low> "-" <node>
 time_low               = 4*<hex_octet>
 time_mid               = 2*<hex_octet>
 time_high_and_version  = 2*<hex_octet>
 clock_seq_and_reserved = <hex_octet>
 clock_seq_low          = <hex_octet>
 node                   = 6*<hex_octet>
 hex_octet              = <hex_digit> <hex_digit>
 hex_digit              = "0"|"1"|"2"|"3"|"4"|"5"|"6"|"7"|"8"|"9"
                         |"a"|"b"|"c"|"d"|"e"|"f"
                         |"A"|"B"|"C"|"D"|"E"|"F"

An example of a UUID string representation is the ASCII string "CW54531d28-402b-11d8-af12-0002a5094c23". The string representation format is exactly what the OSSP uuid API functions uuid_import() and uuid_export() deal with under CWUUID_FMT_STR.

UUID Variants and Versions

A UUID has a variant and version. The variant defines the layout of the UUID. The version defines the content of the UUID. The UUID variant supported in OSSP uuid is the DCE 1.1 variant only. The DCE 1.1 UUID variant versions supported in OSSP uuid are:

Version 1 (time and node based): These are the classical UUIDs, created out of a 60-bit system time, a 14-bit local clock sequence and 48-bit system MAC address. The MAC address can be either the real one of a physical network interface card (NIC) or a random multi-cast MAC address. Version 1 UUIDs are usually used as one-time global unique identifiers.
Version 3 (name based, MD5): These are UUIDs which are based on the 128-bit MD5 message digest of the concatenation of a 128-bit namespace UUID and a name string of arbitrary length. Version 3 UUIDs are usually used for non-unique but repeatable message digest identifiers.
Version 4 (random data based): These are UUIDs which are based on just 128-bit of random data. Version 4 UUIDs are usually used as one-time local unique identifiers.
Version 5 (name based, SHA-1): These are UUIDs which are based on the 160-bit SHA-1 message digest of the concatenation of a 128-bit namespace UUID and a name string of arbitrary length. Version 5 UUIDs are usually used for non-unique but repeatable message digest identifiers.

UUID Uniqueness

Version 1 UUIDs are guaranteed to be unique through combinations of hardware addresses, time stamps and random seeds. There is a reference in the UUID to the hardware (MAC) address of the first network interface card (NIC) on the host which generated the UUID this reference is intended to ensure the UUID will be unique in space as the MAC address of every network card is assigned by a single global authority (IEEE) and is guaranteed to be unique. The next component in a UUID is a timestamp which, as clock always (should) move forward, will be unique in time. Just in case some part of the above goes wrong (the hardware address cannot be determined or the clock moved steps backward), there is a random clock sequence component placed into the UUID as a catch-all for uniqueness.

Version 3 and version 5 UUIDs are guaranteed to be inherently globally unique if the combination of namespace and name used to generate them is unique.

Version 4 UUIDs are not guaranteed to be globally unique, because they are generated out of locally gathered pseudo-random numbers only. Nevertheless there is still a high likelihood of uniqueness over space and time and that they are computationally difficult to guess.

Nil UUID

There is a special Nil UUID consisting of all octets set to zero in the binary representation. It can be used as a special UUID value which does not conflict with real UUIDs.

APPLICATION PROGRAMMING INTERFACE

The ISO-C Application Programming Interface (API) of OSSP uuid consists of the following components.

CONSTANTS

The following constants are provided:

UUID_VERSION: The hexadecimal encoded OSSP uuid version. This allows compile-time checking of the OSSP uuid version. For run-time checking use uuid_version() instead. The hexadecimal encoding for a version "$v.$r$t$l" is calculated with the GNU shtool version command and is (in Perl-style for concise description) "sprintf('0x%x%02x%d%02x', $v, $r, {qw(s 9 . 2 b 1 a 0)}->{$t}, ($t eq 's' ? 99 : $l)), i.e., the version 0.9.6 is encoded as 0x009206".
UUID_LEN_BIN, UUID_LEN_STR: The number of octets of the UUID binary and string representations. Notice that the lengths of the string representation does not include the necessary CWNUL termination character.
UUID_MAKE_V1, UUID_MAKE_V3, UUID_MAKE_V4, UUID_MAKE_V5, UUID_MAKE_MC: The mode bits for use with uuid_make(). The UUID_MAKE_VN specify which UUID version to generate. The UUID_MAKE_MC forces the use of a random multi-cast MAC address instead of the real physical MAC address in version 1 UUIDs.
UUID_RC_OK, UUID_RC_ARG, UUID_RC_MEM, UUID_RC_SYS, UUID_RC_INT, UUID_RC_IMP: The possible numerical return-codes of API functions. The CWUUID_RC_OK indicates success, the others indicate errors. Use uuid_error() to translate them into string versions.
UUID_FMT_BIN, UUID_FMT_STR, UUID_FMT_TXT: The fmt formats for use with uuid_import() and uuid_export(). The UUID_FMT_BIN indicates the UUID binary representation (of length UUID_LEN_BIN), the UUID_FMT_STR indicates the UUID string representation (of length UUID_LEN_STR) and the UUID_FMT_TXT indicates the textual description (of arbitrary length) of a UUID.

FUNCTIONS

The following functions are provided:

uuid_rc_t uuid_create(uuid_t **uuid);: Create a new UUID object and store a pointer to it in CW*uuid. A UUID object consists of an internal representation of a UUID, the internal PRNG and MD5 generator contexts, and cached MAC address and timestamp information. The initial UUID is the Nil UUID.
uuid_rc_t uuid_destroy(uuid_t *uuid);: Destroy UUID object uuid.
uuid_rc_t uuid_clone(const uuid_t *uuid, uuid_t **uuid_clone);: Clone UUID object uuid and store new UUID object in uuid_clone.
uuid_rc_t uuid_isnil(const uuid_t *uuid, int *result);: Checks whether the UUID in uuid is the Nil UUID. If this is the case, it returns true in CW*result. Else it returns false in CW*result.
uuid_rc_t uuid_compare(const uuid_t *uuid, const uuid_t *uuid2, int *result);: Compares the order of the two UUIDs in uuid1 and uuid2 and returns the result in CW*result: CW-1 if uuid1 is smaller than uuid2, CW0 if uuid1 is equal to uuid2 and CW+1 if uuid1 is greater than uuid2.
uuid_rc_t uuid_import(uuid_t *uuid, uuid_fmt_t fmt, const void *data_ptr, size_t data_len);: Imports a UUID uuid from an external representation of format fmt. The data is read from the buffer at data_ptr which contains at least data_len bytes. The format of the external representation is specified by fmt and the minimum expected length in data_len depends on it. Valid values for fmt are UUID_FMT_BIN and UUID_FMT_STR.
uuid_rc_t uuid_export(const uuid_t *uuid, uuid_fmt_t fmt, void **data_ptr, size_t *data_len);: Exports a UUID uuid into an external representation of format fmt. The data is written to the buffer at CW*data_ptr which has to be room for at least CW*data_len bytes. If CW*data_ptr is CWNULL, data_len is ignored as input and a new buffer is allocated and returned in CW*data_ptr (the caller has to free(3) it later on). If data_len is not CWNULL, the number of available bytes at CW*data_ptr has to be provided in CW*data_len and the number of actually written bytes are returned in CW*data_len again. The format of the external representation is specified by fmt and the minimum required length in CW*data_len depends on it. Valid values for fmt are UUID_FMT_BIN, UUID_FMT_STR and UUID_FMT_TXT.
uuid_rc_t uuid_load(uuid_t *uuid, const char *name);: Loads a pre-defined UUID value into the UUID object uuid. The following name arguments are currently known:
name UUID
nil 00000000-0000-0000-0000-000000000000
ns:DNS 6ba7b810-9dad-11d1-80b4-00c04fd430c8
ns:URL 6ba7b811-9dad-11d1-80b4-00c04fd430c8
ns:OID 6ba7b812-9dad-11d1-80b4-00c04fd430c8
ns:X500 6ba7b814-9dad-11d1-80b4-00c04fd430c8: The "CWns:XXX" are names of pre-defined name-space UUIDs for use in the generation of DCE 1.1 version 3 and version 5 UUIDs.
uuid_rc_t uuid_make(uuid_t *uuid, unsigned int mode, ...);: Generates a new UUID in uuid according to mode and optional arguments (dependent on mode). If mode contains the CWUUID_MAKE_V1 bit, a DCE 1.1 variant UUID of version 1 is generated. Then optionally the bit CWUUID_MAKE_MC forces the use of random multi-cast MAC address instead of the real physical MAC address (the default). The UUID is generated out of the 60-bit current system time, a 12-bit clock sequence and the 48-bit MAC address. If mode contains the CWUUID_MAKE_V3 or CWUUID_MAKE_V5 bit, a DCE 1.1 variant UUID of version 3 or 5 is generated and two additional CWNUL-terminated string arguments of type "CWconst char * are expected: first a namespace, given as an internally pre-defined id (currently known are ids CWDNS, CWURL, CWOID, and CWX500") or a UUID in string representation. Second, a name string of arbitrary length. The UUID is generated out of the 128-bit MD5 or 160-bit SHA-1 from the concatenated octet stream of namespace UUID and name string. If mode contains the CWUUID_MAKE_V4 bit, a DCE 1.1 variant UUID of version 4 is generated. The UUID is generated out of 128-bit random data.
char *uuid_error(uuid_rc_t rc);: Returns a constant string representation corresponding to the return-code rc for use in displaying OSSP uuid errors.
unsigned long uuid_version(void);: Returns the hexadecimal encoded OSSP uuid version as compiled into the library object files. This allows run-time checking of the OSSP uuid version. For compile-time checking use CWUUID_VERSION instead.

EXAMPLE

The following shows an example usage of the API. Error handling is omitted for code simplification and has to be re-added for production code.

 /* generate a DCE 1.1 v1 UUID from system environment */
 char *uuid_v1(void)
 {
     uuid_t *uuid;
     char *str;

     uuid_create(&uuid);
     uuid_make(uuid, UUID_MAKE_V1);
     str = NULL;
     uuid_export(uuid, UUID_FMT_STR, (void **)&str, NULL);
     uuid_destroy(uuid);
     return str;
 }

 /* generate a DCE 1.1 v3 UUID from an URL */
 char *uuid_v3(const char *url)
 {
     uuid_t *uuid;
     uuid_t *uuid_ns;
     char *str;

     uuid_create(&uuid);
     uuid_create(&uuid_ns);
     uuid_load(uuid_ns, "ns:URL");
     uuid_make(uuid, UUID_MAKE_V3, uuid_ns, url);
     str = NULL;
     uuid_export(uuid, UUID_FMT_STR, (void **)&str, NULL);
     uuid_destroy(uuid_ns);
     uuid_destroy(uuid);
     return str;
 }

HISTORY

OSSP uuid was implemented in January 2004 by Ralf S. Engelschall <rse@engelschall.com>. It was prompted by the use of UUIDs in the OSSP as and OpenPKG projects. It is a clean room implementation intended to be strictly standards compliant and maximum portable.

cd ~tigrou/pwet.fr/man/linux/Fonctions bibliothèques/ossp/uuid