base64_decode

If you want to save data that is derived from a Javascript canvas.toDataURL() function, you have to convert blancs into plusses. If you do not do that, the decoded data is corrupted:<?php
  $encodedData = str_replace(' ','+',$encodedData);$decocedData= base64_decode($encodedData);
?>

I had some trouble trying to let base64_decode decode base64-strings longuer than ~5c chars.

The base64-decoding function is a homomorphism between modulo 4 and modulo 3-length segmented strings. That motivates a divide and conquer approach: Split the encoded string into substrings counting modulo 4 chars, then decode each substring and concatenate all of them.

Then instead of<?php $decoded = base64_decode($encoded); ?>
for big $encoded strings, it's saver to use<?php
$decoded = "";
for ($i=0; $i< ceil(strlen($encoded)/256); $i++)$decoded= $decoded.base64_decode(substr($encoded,$i*256,256));
?>
where 256 can be replaced by a sufficiently small modulo 4 natural.

This function suppors "base64url" as described in Section 5 of RFC 4648, "Base 64 Encoding with URL and Filename Safe Alphabet"<?php
    functionbase64url_decode($base64url)
    {$base64= strtr($base64url, '-_', '+/');$plainText= base64_decode($base64);
        return ($plainText);
    }?>

Base64 for URL parameters/filenames, that adhere to RFC 4648.
Defauls to dropping the padding on encode since it's not required for decoding, and keeps the URL free of % encodings.<?php
functionbase64url_encode($data, $pad= null) {$data= str_replace(array('+', '/'), array('-', '_'), base64_encode($data));
    if (!$pad) {$data= rtrim($data, '=');
    }
    return$data;
}
function base64url_decode($data) {
    returnbase64_decode(str_replace(array('-', '_'), array('+', '/'), $data));
}

Note, that padding characters are not limited to "=". any character(s) at the end of the string that cannot be decoded will be interpreted as padding. if $strict is set to true, of course padding characters are limited to base64 characters.

examples:<?php
// $strict = false;$str= 'VGhpcyBpcyBhbiBlbmNvZGVcIHN0cmluZw==';
echo base64_decode($str); // This is an encoded string$str= 'VGhpcyBpcyBhbiBlbmNvZGVcIHN0cmluZw';
echo base64_decode($str); // This is an encoded string$str= 'VGhpcyBpcyBhbiBlbmNvZGVcIHN0cmluZwA';
echo base64_decode($str); // This is an encoded string$str= 'VGhpcyBpcyBhbiBlbmNvZGVcIHN0cmluZwA=';
echo base64_decode($str); // This is an encoded string

// $strict = true;$str= 'VGhpcyBpcyBhbiBlbmNvZGVcIHN0cmluZw==';
echo base64_decode($str, true); // This is an encoded string$str= 'VGhpcyBpcyBhbiBlbmNvZGVcIHN0cmluZw';
echo base64_decode($str, true); // This is an encoded string$str= 'VGhpcyBpcyBhbiBlbmNvZGVcIHN0cmluZwA';
echo base64_decode($str, true); // This is an encoded string$str= 'VGhpcyBpcyBhbiBlbmNvZGVcIHN0cmluZwA=';
echo base64_decode($str, true); // This is an encoded string?>