根据URL中的RSS构建Magpie对象。

原型

fetch_rss( string $url )

参数

$url (string) (Required) 用于检索Feed的网址

返回值

(bool|MagpieRSS)  失败或失败

源文件

路径:wp-includes/rss.php

<?php
...
function fetch_rss ($url) {
	// initialize constants
	init();
	if ( !isset($url) ) {
		// error("fetch_rss called without a url");
		return false;
	}
	// if cache is disabled
	if ( !MAGPIE_CACHE_ON ) {
		// fetch file, and parse it
		$resp = _fetch_remote_file( $url );
		if ( is_success( $resp->status ) ) {
			return _response_to_rss( $resp );
		}
		else {
			// error("Failed to fetch $url and cache is off");
			return false;
		}
	}
	// else cache is ON
	else {
		// Flow
		// 1. check cache
		// 2. if there is a hit, make sure it's fresh
		// 3. if cached obj fails freshness check, fetch remote
		// 4. if remote fails, return stale object, or error
		$cache = new RSSCache( MAGPIE_CACHE_DIR, MAGPIE_CACHE_AGE );
		if (MAGPIE_DEBUG and $cache->ERROR) {
			debug($cache->ERROR, E_USER_WARNING);
		}
		$cache_status 	 = 0;		// response of check_cache
		$request_headers = array(); // HTTP headers to send with fetch
		$rss 			 = 0;		// parsed RSS object
		$errormsg		 = 0;		// errors, if any
		if (!$cache->ERROR) {
			// return cache HIT, MISS, or STALE
			$cache_status = $cache->check_cache( $url );
		}
		// if object cached, and cache is fresh, return cached obj
		if ( $cache_status == 'HIT' ) {
			$rss = $cache->get( $url );
			if ( isset($rss) and $rss ) {
				$rss->from_cache = 1;
				if ( MAGPIE_DEBUG > 1) {
				debug("MagpieRSS: Cache HIT", E_USER_NOTICE);
			}
				return $rss;
			}
		}
		// else attempt a conditional get
		// set up headers
		if ( $cache_status == 'STALE' ) {
			$rss = $cache->get( $url );
			if ( isset($rss->etag) and $rss->last_modified ) {
				$request_headers['If-None-Match'] = $rss->etag;
				$request_headers['If-Last-Modified'] = $rss->last_modified;
			}
		}
		$resp = _fetch_remote_file( $url, $request_headers );
		if (isset($resp) and $resp) {
			if ($resp->status == '304' ) {
				// we have the most current copy
				if ( MAGPIE_DEBUG > 1) {
					debug("Got 304 for $url");
				}
				// reset cache on 304 (at minutillo insistent prodding)
				$cache->set($url, $rss);
				return $rss;
			}
			elseif ( is_success( $resp->status ) ) {
				$rss = _response_to_rss( $resp );
				if ( $rss ) {
					if (MAGPIE_DEBUG > 1) {
						debug("Fetch successful");
					}
					// add object to cache
					$cache->set( $url, $rss );
					return $rss;
				}
			}
			else {
				$errormsg = "Failed to fetch $url. ";
				if ( $resp->error ) {
					# compensate for Snoopy's annoying habbit to tacking
					# on 'n'
					$http_error = substr($resp->error, 0, -2);
					$errormsg .= "(HTTP Error: $http_error)";
				}
				else {
					$errormsg .=  "(HTTP Response: " . $resp->response_code .')';
				}
			}
		}
		else {
			$errormsg = "Unable to retrieve RSS file for unknown reasons.";
		}
		// else fetch failed
		// attempt to return cached object
		if ($rss) {
			if ( MAGPIE_DEBUG ) {
				debug("Returning STALE object for $url");
			}
			return $rss;
		}
		// else we totally failed
		// error( $errormsg );
		return false;
	} // end if ( !MAGPIE_CACHE_ON ) {
} // end fetch_rss()
...
?>

其他

英文文档:https://developer.wordpress.org/reference/functions/fetch_rss/