Workerman\WebServer::sendFile PHP Method

    public static function sendFile($connection, $file_path)
    {
        // Check 304.
        $info = stat($file_path);
        $modified_time = $info ? date('D, d M Y H:i:s', $info['mtime']) . ' GMT' : '';
        if (!empty($_SERVER['HTTP_IF_MODIFIED_SINCE']) && $info) {
            // Http 304.
            if ($modified_time === $_SERVER['HTTP_IF_MODIFIED_SINCE']) {
                // 304
                Http::header('HTTP/1.1 304 Not Modified');
                // Send nothing but http headers..
                $connection->close('');
                return;
            }
        }
        // Http header.
        if ($modified_time) {
            $modified_time = "Last-Modified: {$modified_time}\r\n";
        }
        $file_size = filesize($file_path);
        $file_info = pathinfo($file_path);
        $extension = isset($file_info['extension']) ? $file_info['extension'] : '';
        $file_name = isset($file_info['filename']) ? $file_info['filename'] : '';
        $header = "HTTP/1.1 200 OK\r\n";
        if (isset(self::$mimeTypeMap[$extension])) {
            $header .= "Content-Type: " . self::$mimeTypeMap[$extension] . "\r\n";
        } else {
            $header .= "Content-Type: application/octet-stream\r\n";
            $header .= "Content-Disposition: attachment; filename=\"{$file_name}\"\r\n";
        }
        $header .= "Connection: keep-alive\r\n";
        $header .= $modified_time;
        $header .= "Content-Length: {$file_size}\r\n\r\n";
        $trunk_limit_size = 1024 * 1024;
        if ($file_size < $trunk_limit_size) {
            return $connection->send($header . file_get_contents($file_path), true);
        }
        $connection->send($header, true);
        // Read file content from disk piece by piece and send to client.
        $connection->fileHandler = fopen($file_path, 'r');
        $do_write = function () use($connection) {
            // Send buffer not full.
            while (empty($connection->bufferFull)) {
                // Read from disk.
                $buffer = fread($connection->fileHandler, 8192);
                // Read eof.
                if ($buffer === '' || $buffer === false) {
                    return;
                }
                $connection->send($buffer, true);
            }
        };
        // Send buffer full.
        $connection->onBufferFull = function ($connection) {
            $connection->bufferFull = true;
        };
        // Send buffer drain.
        $connection->onBufferDrain = function ($connection) use($do_write) {
            $connection->bufferFull = false;
            $do_write();
        };
        $do_write();
    }