koel/app/Services/Streamers/PHPStreamer.php

<?php

namespace App\Services\Streamers;

class PHPStreamer extends Streamer implements DirectStreamerInterface
{
    /**
     * Stream the current song using the most basic PHP method: readfile()
     * Credits: DaveRandom @ http://stackoverflow.com/a/4451376/794641.
     */
    public function stream(): void
    {
        $range = $this->getRange();
        $start = null;
        $end = null;
        $fileSize = filesize($this->song->path);

        if ($range) {
            list($param, $range) = explode('=', $range);

            // Bad request - range unit is not 'bytes'
            abort_unless(strtolower(trim($param)) === 'bytes', 400);

            $range = explode(',', $range);
            $range = explode('-', $range[0]); // We only deal with the first requested range

            // Bad request - 'bytes' parameter is not valid
            abort_unless(count($range) === 2, 400);

            $start = (int) $range[0];

            if (!$range[0]) {
                // First number missing, return last $range[1] bytes
                $end = (int) $range[1];
            } elseif (!$range[1]) {
                $end = $fileSize - 1;
            } else {
                // Both numbers present, return specific range
                $end = (int) $range[1];

                if ($end >= $fileSize) {
                    $end = $fileSize - 1;
                }
            }

            $partial = $start > 0 || $end < $fileSize - 1;
            $length = $end - $start + 1;
        } else {
            $length = filesize($this->song->path);
            $partial = false;
        }

        // Send standard headers
        header("Content-Type: {$this->contentType}");
        header("Content-Length: $length");
        header('Last-Modified: ' . gmdate('D, d M Y H:i:s T', filemtime($this->song->path)));
        header('Content-Disposition: attachment; filename="' . basename($this->song->path) . '"');
        header('Accept-Ranges: bytes');

        // if requested, send extra headers and part of file...
        if ($partial) {
            header('HTTP/1.1 206 Partial Content');
            header("Content-Range: bytes $start-$end/$fileSize");

            // Error out if we can't read the file
            abort_unless($fp = fopen($this->song->path, 'r'), 500);

            if ($start) {
                fseek($fp, $start);
            }

            while ($length) {
                // Read in blocks of 8KB so we don't chew up memory on the server
                $read = ($length > 8192) ? 8192 : $length;
                $length -= $read;
                echo fread($fp, $read);
            }

            fclose($fp);
        } else {
            readfile($this->song->path);
        }

        exit;
    }

    private function getRange():? string
    {
        if (getenv('HTTP_RANGE')) {
            // IIS/Some Apache versions
            return (string) getenv('HTTP_RANGE');
        }

        if (function_exists('apache_request_headers') && $apache = apache_request_headers()) {
            // Try Apache again
            foreach ($apache as $header => $val) {
                if (strtolower($header) === 'range') {
                    return (string) $val;
                }
            }
        }

        return null;
    }
}