"DrUUID" is an implementation for PHP5 of---and associated API for---the data format described in RFC 4122, A Universally Unique IDentifier (UUID) URN Namespace. It is able to mint new UUIDs, import existing UUIDs, extract information from UUIDs, and compare two UUIDs for bit-exact equality. +
The API is designed to be as simple as possible, with an implementation as accurate as practical given the limits of PHP. All other concerns, including PHP compatibility, efficiency and extensibility are secondary. +
Questions and comments are very welcome, and should be directed to the author via his Web site. +
Behaviour may be erratic with PHP versions earlier than 5.1 due to bugs in string casting for objects. +
The last three points only apply if DrUUID is used in its default configuration; the first point is not a conformance violation, but is sub-optimal. See Section 4 for further details on configuring for optimal accuracy. +
This manual often makes references to binary and hexdecimal strings for input and output. For the sake of simplicity please assume that such strings are always in network order (big-endian). +
For methods accepting a UUID as a argument, the UUID may be: +
UUID object
+ This manual often makes reference to invalid UUIDs. For simplicity this is merely any string more or less than 16 bytes long. DrUUID performs no other validation on UUIDs. +
The core DrUUID API consists of four static methods: UUID::mint(), UUID::import(), UUID::compare() as well as UUID::mintStr(). Of these UUID::mint() and UUID::import() return an instance of the UUID class.
+
UUID UUID::mint( [int version [, ... ]] ) +
The UUID::mint() method generates ("mints", like coinage) a new UUID. It is capable of producing Version 1 (time-based), Version 3 (MD5 hash-based), Version 4 (random) and Version 5 (SHA-1 hash-based) UUIDs. Its argument list is generic: required and optional argument depend upon the specified version to produce.
+
+ UUID UUID::mint( void )
+
+ UUID UUID::mint( 1 [, string node [, string sequence [, string time ]]] )
+
Version 1 UUIDs (the default type) are generated based on the current time and a MAC address (called a node). +
If specified, node should be either an 6-byte binary string or a 12-character hexadecimal string (with or without separators) representing a MAC address. DrUUID does not attempt to detect the host's MAC address. Invalid nodes will throw an exception. +
The sequence argument specifies a clock sequence and should be a two-byte binary string. This should only be used for debugging. Invalid sequences will throw an exception. +
Finally, the time argument may be specified to employ a past or future time (as a Unix timestamp with microseconds like that returned by microtime() for example) instead of the curent time. This should only be used for debugging and never used to generate UUIDs for any purpose but testing. Input which cannot be parsed as a timestamp will throw an exception.
+
UUID UUID::mint( 3, string name, mixed namespace ) +
Version 3 UUIDs are generated based upon a an MD5 hash of an arbitrary name and its associated name-space. For example the name "www.example.com" is within the DNS namespace, much as "Canada" is within a name-space of the world's countries. A name/namespace pair will predictably generate the same UUID. +
The name argument is an arbitrary name and should be in a binary form appropriate for namespace. It is the responsibility of the user to assure the proper conversion to binary form. For many namespaces (like the DNS) the appropriate representation is plain text and therefore no conversion is required. +
The namespace argument is itself a UUID; invalid UUIDs will throw an exception. +
Note that the continued use of Version 3 UUIDs is discouraged: Version 5 UUIDs should be used instead whenever possible. +
UUID UUID::mint( 4 ) +
Version 4 UUIDs are generated from random numbers. Save for embedded version information they are completely random. +
UUID UUID::mint( 5, string name, mixed namespace ) +
Version 5 UUIDs are generated based upon a an SHA-1 hash of an arbitrary name and its associated name-space. For example the name "www.example.com" is within the DNS namespace, much as "Canada" is within a name-space of the world's countries. A name/namespace pair will predictably generate the same UUID. +
The name argument is an arbitrary name and should be in a binary form appropriate for namespace. It is the responsibility of the user to assure the proper conversion to binary form. For many namespaces (like the DNS) the appropriate representation is plain text and therefore no conversion is required. +
The namespace argument is itself a UUID; invalid UUIDs will throw an exception. +
Version 5 UUIDs are preferred over Version 3 UUIDs. +
UUID UUID::import( string uuid ) +
The UUID::import() method imports a UUID string as a UUID object. Invalid UUIDs will throw an exception.
+
bool UUID::compare( mixed uuid1, mixed uuid2 ) +
The UUID::compare() method compares two UUIDs for equivalency. If both UUIDs, as binary numbers, are equal, the method returns TRUE. The method will also return TRUE if neither arguments is a valid UUID.
+
This method is useful for determining if two different UUID representations (eg. canonical string, lowercase hex string, uppercase hex string, binary, URN) are in fact the same UUID. +
string UUID::mintStr( [int version [, ... ] ) +
The UUID::mintStr() method performs the same functions as the UUID::mint() method, but returns the UUID directly as a string in canonical form.
+
UUID objects cannot be instantiated manually; they must be created via UUID::mint() or UUID::import(). When cast to a string a UUID object will be rendered in the canonical string form (eg. 550e8400-e29b-41d4-a716-446655440000). They have no public methods, but do have a number of public properties:
+
PHP has a number of good sources for random numbers available to it, but most are either system-dependent, incur considerable overhead, or both. Consequently DrUUID uses the mt_rand() function to generate random numbers unless instructed to seek an alternative, usually cryptographically secure source. In order to use an alternative source the UUID::initRandom() static method must be invoked.
+
int UUID::initRandom( [int source] ) +
If envoked without arguments, the UUID::initRandom() method will attempt to make use of the best available randomness source; this may nevertheless be mt_rand().
+
An integer constant, source, may be passed to explicitly choose a source. Passing an unknown value will throw an exception; an exception will also be thrown if an explicitly selected source is not available. +
A list of valid source constants is available in Appendix A. +
Note that since the characteristics of any given system can be unpredictably different from those of another, users are encouraged to run their own benchmarks to ascertain whether the performance of both UUID::initRandom() and calls thereafter to UUID::randomBytes() warrant an alternative source's use.
+
For Version 1 UUIDs, a 60-bit timestamp must be generated. On 32-bit systems, this causes PHP to use floating-point arithmetic, which yields inaccurate results, with precision only reliable to the millisecond rather than the microsecond. If either the GMP or BC Math extension is available, DrUUID can make use of it to produce accurate results: +
int UUID::initBignum( [int means] ) +
If envoked without arguments, the UUID::initBignum() method will try to use the fastest means of producing accurate timestamps.
+
An integer constant, means, may be passed to explicitly choose a method. Passing an unknown value will throw an exception; an exception will also be thrown if an explicitly selected method is not available. +
A list of valid means constants is available in Appendix A. +
On 64-bit systems DrUUID will use accurate arithmetic without having to call UUID::initBignum().
+
In order to ensure uniqueness of Version 1 UUIDs, the value of the clock sequence, node ID and last timestamp used should be kept in stable storage for reference. By default DrUUID only keeps these values in memory, but they can also be written to a file: +
void UUID::initStorage( string path ) +
DrUUID will read state from and write state to the file specified by path. If the file specified is not accessible, an exception will be thrown. The default implementation will create a file which does not exist, but will not create folders. +
If access to a file is either impossible or impractical, an API for implementing a custom storage is described in Section 5. If using custom storage, required arguments may be different. +
void UUID::initAccurate( string path ) +
The UUID::initAccurate() method is a shortcut to achieving optimal accuracy. It successively calls UUID::initBignum(), UUID::initRandom(), and UUID::initStorage(). Unlike calling the three methods by themselves, however, UUID::initAccurate() will reject results which will yield inaccurate UUIDs, and will throw an exception accordingly.
+
DrUUID includes a basic implementation of stable storage for Version 1 UUIDs which is consistent with Section 4.2.1 of RFC 4122. This implementation, however, is not especially efficient if UUIDs are expected to be created in bulk in a single session, nor can it write to a back-end other than a file. For more complex requirements, an API is available to allow DrUUID to communicate with alternative storage backends or otherwise tailor the implementation to individual needs. +
void UUID::registerStorage( string class_name [, mixed arg ... ] ) +
The class_name argument must be the name of a defined class which imprements the UUIDStorage interface, described below. Any further arguments will be passed to UUID::initStorage().
+
If no supplementary arguments are passed, UUID::initStorage() must be called before the custom storage may be used.
+
interface UUIDStorage {
+ public function getNode();
+ public function getSequence($timestamp, $node);
+ public function setSequence($sequence);
+ public function setTimestamp($timestamp, $sequence, $node);
+ const maxSequence = 16383; // 00111111 11111111
+}The UUIDStorage interface defines a set of methods which DrUUID will call during the generation of Version 1 UUIDs in a predictable order to query storage and write data. A visualization of the process is available in Appendix C for reference. The order of the method calls is as follows:
+
getNode()
+ setSequence() and skip to Step 7
+ getSequence(), passing the timestamp and node ID
+ setSequence()
+ setTimestamp() to update the stored timestamp, signalling the end of communication
+ The following subsections serve as implementation notes for the interface's methods. +
As DrUUID is unable to retrieve the system's MAC address, it calls the getNode() method, which might implement a means of doing so or retrieve one from storage. If it does return a value, it should be formatted as six bytes, in big-endian order (the reverse of conventional hexdecimal pair representation).
+
The getSequence() method is the heart of the interface, taking as input the target timestamp (as a number of 100ns ticks since the Unix epoch) and the node ID (as a six-byte string). Output should be a two-byte string, with the two most significant bits set to zero.
+
Per Section 4.1.5 of RFC 4122, the clock sequence should be randomized if the node ID changes, and should be incremented if the target timestamp is lower than that in storage. Due to the limits of 32-bit systems and the difficulties inherent in comparing floating-point numbers, the input timestamp is always a string with integer precision. +
This method simply alerts the storage of a new clock sequence, if either the user has supplied a sequence or the storage failed to return a result. Input is a two-byte string; no return value is required. +
The method serves as a marker that communication with the storage is complete and any buffered data may be written to stable storage if appropriate. Input is a string representation of the number of 100ns ticks since the Unix epoch. +
For convenience DrUUID includes a number of class constants, with three distinct groups: +
UUID::initRandom()
+ UUID::initBignum()
+ These groups are documented in this appendix. +
| Constant + | Description + | Value + |
|---|---|---|
UUID::randChoose
+ | For auto-detection. The best available randomness source will be used. + | -1 + |
UUID::randPoor
+ | PHP's mt_rand() function, the lowest common denominator.
+ | 0 + |
UUID::randDev
+ | The /dev/urandom pseudo-device file, available on most Unix-like systems.
+ | 1 + |
UUID::randCAPICOM
+ | COM calls to CAPICOM's GetRandom method, available on Windows prior to Windows 7. + | 2 + |
UUID::randOpenSSL
+ | The openssl_random_pseudo_bytes() function, available since PHP 5.3.0.
+ | 3 + |
UUID::randMcrypt
+ | The mcrypt_create_iv() function.
+ | 4 + |
| Constant + | Description + | Value + |
|---|---|---|
UUID::bigChoose
+ | For auto-detection. Native 64-bit will trump GMP, which will trump BC Math + | -1 + |
UUID::bigNot
+ | No 64-bit integer/bignum support. This will produce inaccurate results. + | 0 + |
UUID::bigNative
+ | Native 64-bit integer support. This is fastest. + | 1 + |
UUID::bigGMP
+ | GNU Multiple Precision library. + | 2 + |
UUID::bigBC
+ | BC Math library. + | 3 + |
| Constant + | Namespace description + | UUID + |
|---|---|---|
UUID::nsDNS
+ | DNS hostnames (eg. "www.example.com") + | 6ba7b810-9dad-11d1-80b4-00c04fd430c8 + |
UUID::nsURL
+ | Any valid URL (eg. "http://www.example.com/example.html") + | 6ba7b811-9dad-11d1-80b4-00c04fd430c8 + |
UUID::nsOID
+ | An ISO Object Identifier + | 6ba7b812-9dad-11d1-80b4-00c04fd430c8 + |
UUID::nsX500
+ | An X.500 Distinguished Name + | 6ba7b814-9dad-11d1-80b4-00c04fd430c8 + |
DrUUID will throw either UUIDException or UUIDStorageException exceptions under various circumstances. Details on these exceptions are below.
+
| Code + | Type + | Description + | Public methods [1] + |
|---|---|---|---|
Notes:
+
| |||
| 0001 | UUIDException | Selected version is invalid or unsupported. + | UUID::mint() + |
| 0002 | UUIDException | Version 2 is unsupported. + | UUID::mint() + |
| 0003 | UUIDException | Input must be a valid UUID. + | UUID::import() + |
| 0101 | UUIDException | Node must be a valid MAC address. + | UUID::mint(1) + |
| 0102 | UUIDException | Clock sequence must be a two-byte binary string. + | UUID::mint(1) + |
| 0103 | UUIDException | Time input was of an unexpected format. + | UUID::mint(1) + |
| 0201 | UUIDException | A name-string is required for Version 3 or 5 UUIDs. + | UUID::mint(3)
+ UUID::mint(5) + |
| 0202 | UUIDException | A valid UUID namespace is required for Version 3 or 5 UUIDs. + | UUID::mint(3)
+ UUID::mint(5) + |
| 0801 | UUIDException | Bignum method is not available. + | UUID::initBignum() + |
| 0802 | UUIDException | Randomness strategy is not available. + | UUID::initRandom() + |
| 0901 | UUIDException | Bignum method not implemented. + | UUID::initBignum() + |
| 0902 | UUIDException | Randomness strategy not implemented. + | UUID::initRandom() + |
| 1001 | UUIDStorageException | Storage class does not exist. + | UUID::registerStorage() + |
| 1002 | UUIDStorageException | Storage class does not implement the UUIDStorage interface. + | UUID::registerStorage() + |
| 1003 | UUIDStorageException | Storage class could not be instantiated with supplied arguments. + | UUID::initStorage()
+ UUID::registerStorage() + UUID::initAccurate() [2] + |
| 1101 | UUIDStorageException | Stable storage is not readable. + | UUID::initStorage()
+ UUID::initAccurate() [2] + |
| 1102 | UUIDStorageException | Stable storage is not writable. + | UUID::initStorage()
+ UUID::initAccurate() [2] + |
| 1201 | UUIDStorageException | Stable storage could not be read. + | UUID::mint(1) + |
| 1202 | UUIDStorageException | Stable storage could not be written. + | UUID::mint(1) + |
| 1203 | UUIDStorageException | Stable storage data is invalid or corrupted. + | UUID::mint(1) + |
| 2001 | UUIDException | 64-bit integer arithmetic is not available. + | UUID::initAccurate() + |
| 2002 | UUIDException | Secure random number generator is not available. + | UUID::initAccurate() + |
| 2003 | UUIDStorageException | Stable storage not available. + | UUID::initAccurate() + |
| 2004 | UUIDStorageException | Storage is invalid. + | UUID::initAccurate() + |
DrUUID and its manual (i.e. this document) were written by J. King. They are both governed by the following license: +
Copyright (c) 2009 J. King + +Permission is hereby granted, free of charge, to any person +obtaining a copy of this software and associated documentation +files (the "Software"), to deal in the Software without +restriction, including without limitation the rights to use, +copy, modify, merge, publish, distribute, sublicense, and/or sell +copies of the Software, and to permit persons to whom the +Software is furnished to do so, subject to the following +conditions: + +The above copyright notice and this permission notice shall be +included in all copies or substantial portions of the Software. + +THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, +EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES +OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND +NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT +HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, +WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING +FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR +OTHER DEALINGS IN THE SOFTWARE.+
This manual's stylesheet was written by Dustin Wilson. It is licensed under the Creative Commons Attribution license (v2.5). +
This software is dedicated to Seung Park. HLN forever! +
UUID::initBignum() method to trigger bignum support
+ UUID::initBignum() may be passed a constant to explicitly choose a strategy
+ UUID::seq() is no longer required. It remains a public method, but is now undocumented
+ UUID::initRandom() are now no-ops
+ UUID::initRandom() may now be passed a constant to explicitly choose a randomness source; it now returns an integer constant representing a source rather than a string
+ UUID::mintStr() method to return canonical strings rather than objects
+ UUID::initAccurate() method as a shortcut to optimal accuracy.
+ UUID::mintTime() [Dave Gardner]
+ UUID::seq() [David Ward]
+ UUID->time now returns a string with a fixed precision
+ UUID::import() is now a no-op
+ UUID::mint(1), as well as the addition of UUID::seq().
+ UUID::import as reported by Sander van Lambalgen.
+ UUID::compare() method. Also allowed input UUIDs to be RFC 4122 URNs.
+ UUID::initRandom() method. See Section 4 for details. As a consequence generating random numbers is now much faster. Acknowledgement to Rubén Marrero for the impulse to implement this.
+ /dev/urandom from being used. Reported by Rubén Marrero.
+