Explode a string where the explode condition is bunch of specific characters - php

Question

I'm looking for a way to explode a string. For example, I have the following string: (we don't count the beginning - 0x)
0xa9059xbb000000000000000000000000fc7a5f48a1a1b3f48e7dcb1f23a1ea24199af4d00000000000000000000000000000000000000000000000000000000000054368
which is actually an ETH transaction input. I need to explode this string into 3 parts. Imagine 1 bunch of zeros is actually a single space and these spaces define the gates where the string should be exploded.
How can I do that?

Answer 1

preg_split()
This function uses a regular expression to split a string.
So in this example at two or more 0 in a row:
$arr = preg_split('/[0]{2,}/', $string);
print_r($arr);
echo PHP_EOL;
This will output the following:
Array
(
[0] => a9059xbb
[1] => fc7a5f48a1a1b3f48e7dcb1f23a1ea24199af4d
[2] => 54368
)
Be aware that you will have problems if a message itself has a 00 in it. Assuming it is used as a null-byte for "end of string", this will not happen, though.
preg_match()
This is an example using regular expressions. You can split at arbitrary points.
$string = 'a9059xbb000000000000000000000000fc7a5f48a1a1b3f48e7dcb1f23a1ea24199af4d00000000000000000000000000000000000000000000000000000000000054368';
print_r($string);
echo PHP_EOL;
$res = preg_match('/(.{4})(.{32})(.{32})/', $string, $matches);
print_r($matches);
echo PHP_EOL;
This outputs:
a9059xbb000000000000000000000000fc7a5f48a1a1b3f48e7dcb1f23a1ea24199af4d00000000000000000000000000000000000000000000000000000000000054368
Array
(
[0] => a9059xbb000000000000000000000000fc7a5f48a1a1b3f48e7dcb1f23a1ea24199a
[1] => a905
[2] => 9xbb000000000000000000000000fc7a
[3] => 5f48a1a1b3f48e7dcb1f23a1ea24199a
)
As you can see /(.{4})(.{32})(.{32})/ will find 4 bytes, then 32 and after that 32 again. Capturing groups are made with () around what you want to find. They appear in the $matches array (0 is always the whole string found).
In case you want to ignore certain parts you can express that as well:
/(.{4})9x(.{32}).{4}(.{32})/
This changes the found string:
Array
(
[0] => a9059xbb000000000000000000000000fc7a5f48a1a1b3f48e7dcb1f23a1ea24199af4d000
[1] => a905
[2] => bb000000000000000000000000fc7a5f
[3] => a1b3f48e7dcb1f23a1ea24199af4d000
)
Links
PHP documentation for the mentioned functions:
https://www.php.net/manual/en/function.preg-split.php
https://www.php.net/manual/en/book.pcre.php
Play around with the second regular expression using this demo:
https://regex101.com/r/pfZtH8/1

Answer 2

If you will always explode them at the same points (4 bytes(8 hexadecimal digits), 32 bytes(64 hexadecimal digits), 32 bytes(64 hexadecimal digits)), you could use substr().
$input = "0xa9059xbb000000000000000000000000fc7a5f48a1a1b3f48e7dcb1f23a1ea24199af4d00000000000000000000000000000000000000000000000000000000000054368";
$first = substr($input,2,8);
$second = substr($input,10,64);
$third = substr($input,74,64);
print_r($first);
print "<br>";
print_r($second);
print "<br>";
print_r($third);
print "<br>";
this outputs:
a9059xbb
000000000000000000000000fc7a5f48a1a1b3f48e7dcb1f23a1ea24199af4d0
0000000000000000000000000000000000000000000000000000000000054368