serialization when moving a site, explained?

  • When I first started working with WordPress, I did what many others do. Work locally on MAMP and then move to an actual live environment. I would dump the database, search and replace URLs and then import to the live site.

    I eventually learned that is no good due to serialization issues so I started using the WP DB script.

    All well and good, but the thing is, I never had any issues before hand and I moved a lot of site like that. Can someone please explain why and how using the former method can be a problem?

Viewing 3 replies - 1 through 3 (of 3 total)

  • If you look carefully at a serialized array or object you will notice that some of the values in the serialized string represent the length of the other values in the string. For example:

    array(2) {
  [0]=>
  string(4) "bird"
  [1]=>
  string(3) "dog"
}
a:2:{i:0;s:4:"bird";i:1;s:3:"dog";}

    Notice the number immediately preceding the animal type? That is a count of the characters in that value. Also, notice the ‘s’ before preceding the number. That is the type– string. If you search and replace a serialized array, it may not unserialize correctly because those values don’t match the string they are supposed to refer to. For example:

    $s = 'a:2:{i:0;s:4:"bird";i:1;s:3:"dog";}';
var_dump(unserialize($s));

$s = 'a:2:{i:0;s:4:"falcon";i:1;s:3:"dog";}';
var_dump(unserialize($s));

$s = 'a:2:{i:0;s:8:"bird";i:1;s:3:"dog";}';
var_dump(unserialize($s));

    The first is correct and will unserialize to the same array as we started with. They other two, which I have edited carelessly, unserialize to false. The are just strings though, and if you know what you are doing you can edit them. This will unserialize correctly because I edited both the value and the ‘length’:

    $s = 'a:2:{i:0;s:6:"falcon";i:1;s:3:"dog";}';
var_dump(unserialize($s));
    Thread Starter justinwhall

    (@jwind)

    Got it. I think. So the problem is really, for instance, a URL to an image that is stored within an array.

    URL one may be 10 characters long…
    URL two is 12 characters long…

    Any URL, not just for an image, and don’t forget that it break the entire serialize string not just part of it.

Viewing 3 replies - 1 through 3 (of 3 total)
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