PHP implementation Recursive crawl Web page class instance

Specifically as follows:

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<?php class crawler{Private $_depth=5 Private $_urls=array (), function extract_links ($url) {if (! $this->_started {$this->_started=1; $curr _depth=0} else{$curr _depth++} if ($curr _depth< $this->_depth) {$data =file_get_contents ($url); if (Preg_match_all (?: HTTP|HTTPS):///(?: www.) * (?: [A-za-z0-9_-]{1,15}.+[a-za-z0-9_]{1,}) {1,} (?: [a-za-z0-9_/.-?&:%,!;] *)/', $data, $urls) {foreach ($urls 12[0] as $k => $v) {$check =get_headers ($v, 1); if (Strstr ($v, $url) && $ check[0]== ' http/1.1 OK ' &&!array_search ($v, $this->_urls) && $curr _depth< $this->_depth) {$this->_urls[]= $v; $this->extract_links ($v);} }} return $this->_urls; }}?>