How to base64-decode large files in PHP

Question

My PHP web application has an API that can recieve reasonably large files (up to 32 MB) which are base64 encoded. The goal is to write these files somewhere on my filesystem

Answer 1

Even though this has an accepted answer, I have a different suggestion.

If you are pulling the data from an API, you should not store the entire payload in a variable. Using curl or other HTTP fetchers you can automatically store your data in a file.

Assuming you are fetching the data through a simple GET url:

$url = 'http://www.example.com/myfile.base64';
$target = 'localfile.data';

$rhandle = fopen($url,'r');
stream_filter_append($rhandle, 'convert.base64-decode');

$whandle = fopen($target,'w');

stream_copy_to_stream($rhandle,$whandle);
fclose($rhandle);
fclose($whandle);

Benefits:

• Should be faster (less copying of huge variables)
• Very little memory overhead

If you must grab the data from a temporary variable, I can suggest this approach:

$data = 'your base64 data';
$target = 'localfile.data';

$whandle = fopen($target,'w');
stream_filter_append($whandle, 'convert.base64-decode',STREAM_FILTER_WRITE);

fwrite($whandle,$data);

fclose($whandle);

Answer 2

Decode the data in smaller chunks. Four characters of Base64 data equal three bytes of “Base256” data.

So you could group each 1024 characters and decode them to 768 octets of binary data:

$chunkSize = 1024;
$src = fopen('base64.data', 'rb');
$dst = fopen('binary.data', 'wb');
while (!feof($src)) {
    fwrite($dst, base64_decode(fread($src, $chunkSize)));
}
fclose($dst);
fclose($src);