http://stackoverflow.com/questions/2647170/curl-vs-fopen-vs-fsocketopen
http://stackoverflow.com/questions/2644624/php-curl-get-http-code-not-whole-document/2644663#2644663
http://stackoverflow.com/questions/2539926/validate-links-with-php/2539983#2539983
原文：http://www.cnblogs.com/lein-wang/p/4553936.html