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.::uuid(3) |
Universally Unique Identifier |
.::uuid(3) |
OSSP uuid - Universally Unique Identifier
OSSP uuid 1.6.2 (04-Jul-2008)
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.
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.
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;
}
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
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.
uuid(1), uuid-config(1), OSSP::uuid(3).
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