Comments on: Generating UUIDs with CakePHP http://cakebaker.42dh.com/2007/08/20/generating-uuids-with-cakephp/ baking cakes with CakePHP Tue, 31 Jan 2012 15:12:14 +0000 hourly 1 http://wordpress.org/?v=3.3.1 By: cakebaker http://cakebaker.42dh.com/2007/08/20/generating-uuids-with-cakephp/comment-page-1/#comment-98259 cakebaker Mon, 14 Jul 2008 15:00:17 +0000 http://cakebaker.42dh.com/2007/08/20/generating-uuids-with-cakephp/#comment-98259 @Peter: It looks like they use a hash function to generate such IDs, but I don't know which hash function they actually use... @Peter: It looks like they use a hash function to generate such IDs, but I don’t know which hash function they actually use…

]]> By: Peter http://cakebaker.42dh.com/2007/08/20/generating-uuids-with-cakephp/comment-page-1/#comment-97920 Peter Fri, 11 Jul 2008 17:32:07 +0000 http://cakebaker.42dh.com/2007/08/20/generating-uuids-with-cakephp/#comment-97920 Hi, Do you know how YouTube is getting their unique id? http://www.youtube.com/watch?v=_RSaYVgd7yk More hash?? Any help would be appreciated. Thanks. Hi,

Do you know how YouTube is getting their unique id?
http://www.youtube.com/watch?v=_RSaYVgd7yk
More hash??

Any help would be appreciated. Thanks.

]]> By: cakebaker http://cakebaker.42dh.com/2007/08/20/generating-uuids-with-cakephp/comment-page-1/#comment-76708 cakebaker Sun, 23 Mar 2008 16:42:01 +0000 http://cakebaker.42dh.com/2007/08/20/generating-uuids-with-cakephp/#comment-76708 @PD: Thanks for your explanations! @PD: Thanks for your explanations!

]]> By: PD http://cakebaker.42dh.com/2007/08/20/generating-uuids-with-cakephp/comment-page-1/#comment-76432 PD Sat, 22 Mar 2008 18:42:50 +0000 http://cakebaker.42dh.com/2007/08/20/generating-uuids-with-cakephp/#comment-76432 @Yevgeny: It's not that the 36-char format isn't URL safe; it's all ascii letters, numbers, & dashes, so it's inherently URL safe. It's just long. The 22-char format comes from running a few operations on it. First, you do a quick str_replace to pull the "-"'s out. They're always in the same place, so why have them there? Then, you can run "pack('H*',$string)" on the thing, where $string is the result of the str_replace. That will code the ASCII down to a much shorter binary value. However, that binary is most definitely *not* URL safe; it's binary. So, you do a base64_encode on the thing. That results in a new ASCII string, 24 characters in length. The last two characters will always be "==" padding, however, because of the size of the binary you get from pack(). Finally, you can get 22 characters by rtrimming those '=' chars out. All in all, looks kinda like rtrim(base64_encode(pack('H*',r('-','',$uuid))),'=') where $uuid is your original 36-char uuid. None of those opperations are lossy, so you can always reverse back and get the same UUID again: unpack('H*', base64_decode($shortuuid . '==')) will give you back the original UUID, but without the dashes. It's easy enough to put those back in, by chunking that string into groups of 4, and combining the first 2 and last 3 elements of the array, and joining that result with dashes. Or maybe a quick preg_replace. @Yevgeny: It’s not that the 36-char format isn’t URL safe; it’s all ascii letters, numbers, & dashes, so it’s inherently URL safe. It’s just long.

The 22-char format comes from running a few operations on it. First, you do a quick str_replace to pull the “-”‘s out. They’re always in the same place, so why have them there?

Then, you can run “pack(‘H*’,$string)” on the thing, where $string is the result of the str_replace. That will code the ASCII down to a much shorter binary value. However, that binary is most definitely *not* URL safe; it’s binary.

So, you do a base64_encode on the thing. That results in a new ASCII string, 24 characters in length. The last two characters will always be “==” padding, however, because of the size of the binary you get from pack().

Finally, you can get 22 characters by rtrimming those ‘=’ chars out.

All in all, looks kinda like rtrim(base64_encode(pack(‘H*’,r(‘-’,”,$uuid))),’=')
where $uuid is your original 36-char uuid.

None of those opperations are lossy, so you can always reverse back and get the same UUID again:
unpack(‘H*’, base64_decode($shortuuid . ‘==’))
will give you back the original UUID, but without the dashes. It’s easy enough to put those back in, by chunking that string into groups of 4, and combining the first 2 and last 3 elements of the array, and joining that result with dashes. Or maybe a quick preg_replace.

]]> By: cakebaker http://cakebaker.42dh.com/2007/08/20/generating-uuids-with-cakephp/comment-page-1/#comment-10812 cakebaker Tue, 28 Aug 2007 13:23:51 +0000 http://cakebaker.42dh.com/2007/08/20/generating-uuids-with-cakephp/#comment-10812 @Yevgeny: I'm sorry, but I don't know the answer to your question... It's the first time I hear about this 22 character format ;-) @Yevgeny: I’m sorry, but I don’t know the answer to your question… It’s the first time I hear about this 22 character format ;-)

]]> By: Yevgeny Tomenko http://cakebaker.42dh.com/2007/08/20/generating-uuids-with-cakephp/comment-page-1/#comment-10803 Yevgeny Tomenko Tue, 28 Aug 2007 07:19:28 +0000 http://cakebaker.42dh.com/2007/08/20/generating-uuids-with-cakephp/#comment-10803 @cakebaker: I have one question. May be you know that in rails exists plugin that make same thing for ror projects(http://tools.assembla.com/breakout/wiki/FreeSoftware). But it manipulate with 22 length url sage uuid instead of 36 bytes as in cake. So why 22 buty is more url safe than 36? @cakebaker: I have one question. May be you know that in rails exists plugin that make same thing for ror projects(http://tools.assembla.com/breakout/wiki/FreeSoftware).
But it manipulate with 22 length url sage uuid instead of 36 bytes as in cake. So why 22 buty is more url safe than 36?

]]> By: Abhimanyu Grover http://cakebaker.42dh.com/2007/08/20/generating-uuids-with-cakephp/comment-page-1/#comment-10747 Abhimanyu Grover Tue, 21 Aug 2007 03:16:04 +0000 http://cakebaker.42dh.com/2007/08/20/generating-uuids-with-cakephp/#comment-10747 Nice and handy.. Thanks :) Nice and handy.. Thanks :)

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