I saw a code like this:
$len = strlen($str1);
$str = pack('V', $len) . $str1 . $str2;
What will be the code for doing the reverse thing?
As far, as I understand, the first step would be:
$len = substr($str, 0, 4);
$str = substr($str, 4);
But what is next?
$len = unpack(???);
$str1 = substr($str, 0, $len);
$str2 = substr($str, $len);
I don't quite understand how am I supposed to convert binary $len back to... binary integer? I would use a simple typecast or memory copy in the usual languages, but I am new to PHP.
It's just a case of removing the extra string added here
$str = pack('V', $len) . $str1 . $str2;
and unpacking the rest.
Example:
// your code
$len = strlen($str1);
$str = pack('V', $len) . $str1 . $str2;
// unpacking
$length_of_packed_string = strlen($str) - strlen($str1 . $str2);
$unpacked = unpack('V', substr($str, 0, $length_of_packed_string));
print_r($unpacked);
Note that this returns an array, with your value at index 1 (the only index) - so $unpacked[1]. See the notes section on the unpack manpage for more info on why.