.::uuid(3) Universally Unique Identifier .::uuid(3)NAME
OSSP uuid - Universally Unique Identifier
VERSION
OSSP uuid 1.6.2 (04-Jul-2008)
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 IETF 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-C++: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 IETF 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:
[4]
version
-->| |<--
| |
| | [16]
[32] [16] | |time_hi
time_low time_mid | _and_version
|<---------------------------->||<------------>||<------------>|
| MSB || || | |
| / || || | |
|/ || || | |
+------++------++------++------++------++------++------++------+~~
| 15 || 14 || 13 || 12 || 11 || 10 |####9 || 8 |
| MSO || || || || || |#### || |
+------++------++------++------++------++------++------++------+~~
7654321076543210765432107654321076543210765432107654321076543210
~~+------++------++------++------++------++------++------++------+
##* 7 || 6 || 5 || 4 || 3 || 2 || 1 || 0 |
##* || || || || || || || LSO |
~~+------++------++------++------++------++------++------++------+
7654321076543210765432107654321076543210765432107654321076543210
| | || || /|
| | || || / |
| | || || LSB |
|<---->||<---->||<-------------------------------------------->|
|clk_seq clk_seq node
|_hi_res _low [48]
|[5-6] [8]
| |
-->| |<--
variant
[2-3]
An example of a UUID binary representation is the octet stream 0xF8
0x1D 0x4F 0xAE 0x7D 0xEC 0x11 0xD0 0xA7 0x65 0x00 0xA0 0xC9 0x1E 0x6B
0xF6. The binary representation format is exactly what the OSSP uuid
API functions uuid_import() and uuid_export() deal with under
UUID_FMT_BIN.
UUID ASCII String Representation
According to the DCE 1.1, ISO/IEC 11578:1996 and IETF 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_high_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_high_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
"f81d4fae-7dec-11d0-a765-00a0c91e6bf6". The string representation
format is exactly what the OSSP uuid API functions uuid_import() and
uuid_export() deal with under UUID_FMT_STR.
Notice: a corresponding URL can be generated out of a ASCII string
representation of an UUID by prefixing with "urn:uuid:" as in
"urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6".
UUID Single Integer Value Representation
According to the ISO/IEC 11578:1996 and ITU-T Rec. X.667 standards, a
DCE 1.1 variant UUID can be also represented as a single integer value
consisting of a decimal number with up to 39 digits.
An example of a UUID single integer value representation is the decimal
number "329800735698586629295641978511506172918". The string
representation format is exactly what the OSSP uuid API functions
uuid_import() and uuid_export() deal with under UUID_FMT_SIV.
Notice: a corresponding ISO OID can be generated under the
"{joint-iso-itu-t(2)uuid(25)}" arc out of a single integer value
representation of a UUID by prefixing with "2.25.". An example OID is
"2.25.329800735698586629295641978511506172918". Additionally, an URL
can be generated by further prefixing with "urn:oid:" as in
"urn:oid:2.25.329800735698586629295641978511506172918".
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, UUID_LEN_SIV
The number of octets of the UUID binary and string representations.
Notice that the lengths of the string representation (UUID_LEN_STR)
and the lengths of the single integer value representation
(UUID_LEN_SIV) does not include the necessary NUL 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
UUID_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_SIV, 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), the UUID_FMT_SIV indicates
the UUID single integer value representation (of maximum length
UUID_LEN_SIV) 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 *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 *result. Else it returns false in
*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 *result: -1 if uuid1 is smaller than uuid2, 0 if
uuid1 is equal to uuid2 and +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, UUID_FMT_STR and UUID_FMT_SIV.
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.
Valid values for fmt are UUID_FMT_BIN, UUID_FMT_STR, UUID_FMT_SIV
and UUID_FMT_TXT.
The data is written to the buffer whose location is obtained by
dereferencing data_ptr after a "cast" to the appropriate pointer-
to-pointer type. Hence the generic pointer argument data_ptr is
expected to be a pointer to a "pointer of a particular type", i.e.,
it has to be of type "unsigned char **" for UUID_FMT_BIN and "char
**" for UUID_FMT_STR, UUID_FMT_SIV and UUID_FMT_TXT.
The buffer has to be room for at least *data_len bytes. If the
value of the pointer after "casting" and dereferencing data_ptr is
NULL, data_len is ignored as input and a new buffer is allocated
and returned in the pointer after "casting" and dereferencing
data_ptr (the caller has to free(3) it later on).
If data_len is not NULL, the number of available bytes in the
buffer has to be provided in *data_len and the number of actually
written bytes are returned in *data_len again. The minimum required
buffer length depends on the external representation as specified
by fmt and is at least UUID_LEN_BIN for UUID_FMT_BIN, UUID_LEN_STR
for UUID_FMT_STR and UUID_LEN_SIV for UUID_FMT_SIV. For
UUID_FMT_TXT a buffer of unspecified length is required and hence
it is recommended to allow OSSP uuid to allocate the buffer as
necessary.
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 "ns: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 UUID_MAKE_V1 bit, a DCE 1.1 variant UUID of
version 1 is generated. Then optionally the bit UUID_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 UUID_MAKE_V3 or UUID_MAKE_V5 bit, a DCE 1.1
variant UUID of version 3 or 5 is generated and two additional
arguments are expected: first, a namespace UUID object (uuid_t *).
Second, a name string of arbitrary length (const char *). 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 UUID_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 UUID_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, &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, &str, NULL);
uuid_destroy(uuid_ns);
uuid_destroy(uuid);
return str;
}
SEE ALSO
The following are references to UUID documentation and specifications:
· A Universally Unique IDentifier (UUID) URN Namespace, P. Leach, M.
Mealling, R. Salz, IETF RFC-4122, July 2005, 32 pages,
http://www.ietf.org/rfc/rfc4122.txt
· Information Technology -- Open Systems Interconnection (OSI),
Procedures for the operation of OSI Registration Authorities:
Generation and Registration of Universally Unique Identifiers
(UUIDs) and their Use as ASN.1 Object Identifier Components,
ISO/IEC 9834-8:2004 / ITU-T Rec. X.667, 2004, December 2004, 25
pages, http://www.itu.int/ITU-T/studygroups/com17/oid/X.667-E.pdf
· DCE 1.1: Remote Procedure Call, appendix Universally Unique
Identifier, Open Group Technical Standard Document Number C706,
August 1997, 737 pages, (supersedes C309 DCE: Remote Procedure Call
8/1994, which was basis for ISO/IEC 11578:1996 specification),
http://www.opengroup.org/publications/catalog/c706.htm
· Information technology -- Open Systems Interconnection (OSI),
Remote Procedure Call (RPC), ISO/IEC 11578:1996, August 2001, 570
pages, (CHF 340,00), http://www.iso.ch/cate/d2229.html
· HTTP Extensions for Distributed Authoring (WebDAV), section 6.4.1
Node Field Generation Without the IEEE 802 Address, IETF RFC-2518,
February 1999, 94 pages, http://www.ietf.org/rfc/rfc2518.txt
· DCE 1.1 compliant UUID functions, FreeBSD manual pages uuid(3) and
uuidgen(2),
http://www.freebsd.org/cgi/man.cgi?query=uuid&manpath=FreeBSD+6.0-RELEASE
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.
SEE ALSOuuid(1), uuid-config(1), OSSP::uuid(3).
04-Jul-2008 OSSP uuid 1.6.2 .::uuid(3)
