Source 
  File: wp-includes/class-wp-simplepie-file.php 
 public function __construct( $url, $timeout = 10, $redirects = 5, $headers = null, $useragent = null, $force_fsockopen = false ) {
		$this->url       = $url;
		$this->timeout   = $timeout;
		$this->redirects = $redirects;
		$this->headers   = $headers;
		$this->useragent = $useragent;
		$this->method = SIMPLEPIE_FILE_SOURCE_REMOTE;
		if ( preg_match( '/^http(s)?:\/\//i', $url ) ) {
			$args = array(
				'timeout'     => $this->timeout,
				'redirection' => $this->redirects,
			);
			if ( ! empty( $this->headers ) ) {
				$args['headers'] = $this->headers;
			}
			if ( SIMPLEPIE_USERAGENT != $this->useragent ) { // Use default WP user agent unless custom has been specified.
				$args['user-agent'] = $this->useragent;
			}
			$res = wp_safe_remote_request( $url, $args );
			if ( is_wp_error( $res ) ) {
				$this->error   = 'WP HTTP Error: ' . $res->get_error_message();
				$this->success = false;
			} else {
				$this->headers     = wp_remote_retrieve_headers( $res );
				$this->body        = wp_remote_retrieve_body( $res );
				$this->status_code = wp_remote_retrieve_response_code( $res );
			}
		} else {
			$this->error   = '';
			$this->success = false;
		}
	}