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Ben Ramsey
69 lines
2.4 KiB
ReStructuredText
69 lines
2.4 KiB
ReStructuredText
.. _rfc4122.version3:
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===========================
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Version 3: Name-based (MD5)
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===========================
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.. attention::
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`RFC 4122`_ states, "If backward compatibility is not an issue, SHA-1 is
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preferred." As a result, the use of :ref:`version 5 UUIDs
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<rfc4122.version5>` is preferred over version 3 UUIDs, unless you have a
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specific use-case for version 3 UUIDs.
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.. note::
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To learn about name-based UUIDs, read the section :ref:`rfc4122.version5`.
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Version 3 UUIDs behave exactly the same as :ref:`version 5 UUIDs
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<rfc4122.version5>`. The only difference is the hashing algorithm used to
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generate the UUID.
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Version 3 UUIDs use `MD5`_ as the hashing algorithm for combining
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the namespace and the name.
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Due to the use of a different hashing algorithm, version 3 UUIDs generated with
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any given namespace and name will differ from version 5 UUIDs generated using
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the same namespace and name.
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As an example, let's take a look at generating a version 3 UUID using the same
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namespace and name used in ":ref:`rfc4122.version5.url-example`."
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.. code-block:: php
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:caption: Generate a version 3, name-based UUID for a URL
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:name: rfc4122.version3.url-example
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use Ramsey\Uuid\Uuid;
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$uuid = Uuid::uuid3(Uuid::NAMESPACE_URL, 'https://www.php.net');
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Even though the namespace and name are the same, the version 3 UUID generated
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will always be ``3f703955-aaba-3e70-a3cb-baff6aa3b28f``.
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Likewise, we can use the custom namespace we created in
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":ref:`rfc4122.version5.create-namespace`" to generate a version 3 UUID, but the
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result will be different from the version 5 UUID with the same custom namespace
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and name.
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.. code-block:: php
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:caption: Use a custom namespace to create version 3, name-based UUIDs
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:name: rfc4122.version3.custom-example
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use Ramsey\Uuid\Uuid;
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const WIDGET_NAMESPACE = '4bdbe8ec-5cb5-11ea-bc55-0242ac130003';
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$uuid = Uuid::uuid3(WIDGET_NAMESPACE, 'widget/1234567890');
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With this custom namespace, the version 3 UUID for the name "widget/1234567890"
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will always be ``53564aa3-4154-3ca5-ac90-dba59dc7d3cb``.
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.. tip::
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Version 3 UUIDs generated in ramsey/uuid are instances of UuidV3. Check out
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the :php:class:`Ramsey\\Uuid\\Rfc4122\\UuidV3` API documentation to learn
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more about what you can do with a UuidV3 instance.
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.. _RFC 4122: https://tools.ietf.org/html/rfc4122
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.. _MD5: https://en.wikipedia.org/wiki/MD5
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