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98 lines
2.8 KiB
Plaintext
98 lines
2.8 KiB
Plaintext
UUID Generation Functions
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=========================
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Peter Eisentraut <peter_e@gmx.net>
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This module provides functions to generate universally unique
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identifiers (UUIDs) using one of the several standard algorithms, as
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well as functions to produce certain special UUID constants.
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Installation
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------------
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The extra library required can be found at
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<http://www.ossp.org/pkg/lib/uuid/>.
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UUID Generation
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---------------
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The relevant standards ITU-T Rec. X.667, ISO/IEC 9834-8:2005, and RFC
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4122 specify four algorithms for generating UUIDs, identified by the
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version numbers 1, 3, 4, and 5. (There is no version 2 algorithm.)
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Each of these algorithms could be suitable for a different set of
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applications.
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uuid_generate_v1()
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~~~~~~~~~~~~~~~~~~
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This function generates a version 1 UUID. This involves the MAC
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address of the computer and a time stamp. Note that UUIDs of this
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kind reveal the identity of the computer that created the identifier
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and the time at which it did so, which might make it unsuitable for
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certain security-sensitive applications.
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uuid_generate_v1mc()
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~~~~~~~~~~~~~~~~~~~~
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This function generates a version 1 UUID but uses a random multicast
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MAC address instead of the real MAC address of the computer.
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uuid_generate_v3(namespace uuid, name text)
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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This function generates a version 3 UUID in the given namespace using
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the specified input name. The namespace should be one of the special
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constants produced by the uuid_ns_*() functions shown below. (It
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could be any UUID in theory.) The name is an identifier in the
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selected namespace. For example:
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uuid_generate_v3(uuid_ns_url(), 'http://www.postgresql.org')
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The name parameter will be MD5-hashed, so the cleartext cannot be
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derived from the generated UUID.
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The generation of UUIDs by this method has no random or
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environment-dependent element and is therefore reproducible.
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uuid_generate_v4()
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~~~~~~~~~~~~~~~~~~
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This function generates a version 4 UUID, which is derived entirely
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from random numbers.
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uuid_generate_v5(namespace uuid, name text)
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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This function generates a version 5 UUID, which works like a version 3
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UUID except that SHA-1 is used as a hashing method. Version 5 should
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be preferred over version 3 because SHA-1 is thought to be more secure
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than MD5.
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UUID Constants
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--------------
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uuid_nil()
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A "nil" UUID constant, which does not occur as a real UUID.
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uuid_ns_dns()
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Constant designating the DNS namespace for UUIDs.
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uuid_ns_url()
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Constant designating the URL namespace for UUIDs.
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uuid_ns_oid()
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Constant designating the ISO object identifier (OID) namespace for
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UUIDs. (This pertains to ASN.1 OIDs, unrelated to the OIDs used in
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PostgreSQL.)
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uuid_ns_x500()
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Constant designating the X.500 distinguished name (DN) namespace for
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UUIDs.
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