stream_filter.php

<?php declare(strict_types = 1);

class simple_filter extends php_user_filter {
    function filter($in, $out, &$consumed, $closing) {
        while ($bucket = stream_bucket_make_writeable($in)) {
            $consumed += $bucket->datalen;
            stream_bucket_append($out, $bucket);
        }
        return PSFS_PASS_ON;
    }
}

stream_filter_register("simple", "simple_filter");

file_get_contents("php://filter/read=simple/resource=http://google.com");
// Warning: file_get_contents(): Filter failed to process pre-buffered data in scratchpad.php on line 15