WP_HTTP_Proxy::send_through_proxy

		// Malformed URL, can not process, but this could mean ssl, so let through anyway.
		if ( false === $check ) {
			return true;
		}

		$home = parse_url( get_option( 'siteurl' ) );

		/**
		 * Filters whether to preempt sending the request through the proxy.
		 *
		 * Returning false will bypass the proxy; returning true will send
		 * the request through the proxy. Returning null bypasses the filter.
		 *
		 * @since 3.5.0
		 *
		 * @param bool|null $override Whether to send the request through the proxy. Default null.
		 * @param string    $uri      URL of the request.
		 * @param array     $check    Associative array result of parsing the request URL with `parse_url()`.
		 * @param array     $home     Associative array result of parsing the site URL with `parse_url()`.
		 */
		$result = apply_filters( 'pre_http_send_through_proxy', null, $uri, $check, $home );
		if ( ! is_null( $result ) ) {
			return $result;
		}

		if ( 'localhost' === $check['host'] || ( isset( $home['host'] ) && $home['host'] === $check['host'] ) ) {
			return false;
		}

		if ( ! defined( 'WP_PROXY_BYPASS_HOSTS' ) ) {
			return true;
		}

		static $bypass_hosts   = null;
		static $wildcard_regex = array();
		if ( null === $bypass_hosts ) {
			$bypass_hosts = preg_split( '|,\s*|', WP_PROXY_BYPASS_HOSTS );

			if ( false !== strpos( WP_PROXY_BYPASS_HOSTS, '*' ) ) {
				$wildcard_regex = array();
				foreach ( $bypass_hosts as $host ) {
					$wildcard_regex[] = str_replace( '\*', '.+', preg_quote( $host, '/' ) );
				}
				$wildcard_regex = '/^(' . implode( '|', $wildcard_regex ) . ')$/i';
			}
		}

		if ( ! empty( $wildcard_regex ) ) {
			return ! preg_match( $wildcard_regex, $check['host'] );
		} else {
			return ! in_array( $check['host'], $bypass_hosts, true );
		}
	}
}