custom_base64_decode

custom_base64_decode.php

<?php

function custom_base64_decode($input) {
    $base64_chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
    $output = '';
    
    // Remove padding characters and replace invalid characters
    $input = str_replace(['-', '_'], ['+', '/'], $input);
    $input = rtrim($input, '=');

    $bitstream = '';
  
    foreach (str_split($input) as $char) {
        $position = strpos($base64_chars, $char);
        if ($position === false) {
            throw new InvalidArgumentException("Invalid Base64 character: {$char}");
        }
        $bitstream .= str_pad(decbin($position), 6, '0', STR_PAD_LEFT);
    }
    
    $bytes = str_split($bitstream, 8);
    foreach ($bytes as $byte) {
        if (strlen($byte) === 8) {
            $output .= chr(bindec($byte));
        }
    }
    
    return $output;
}

// Example usage
$encoded = base64_encode("Hello World");
$decoded = custom_base64_decode($encoded);
echo $decoded;