curl not working on certain networks - php

Question

I seem to be facing a weird problem. I have a PHP script in laptop (running under wamp) which uses 'curl' and works perfectly fine at work. But when at home and connected to my ISP, the same
script fails to return any data. Even a sample code like below fails:
$ch = curl_init("http://www.yahoo.com/");
curl_setopt($ch, CURLOPT_URL, "http://www.example.com/");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLINFO_HEADER_OUT, true);
curl_exec($ch);
var_dump(curl_getinfo($ch));
curl_getinfo dows not provide any clues to further debug. The HTTP CODE is zero. Do I need to add any headers>
I am able to access example.com through the browser, so no network issues I guess. curl_err and curl_errno is null.
<pre>
array (size=22)
'url' => string 'http://www.example.com/' (length=23)
'content_type' => null
'http_code' => int 0
'header_size' => int 0
'request_size' => int 0
'filetime' => int -1
'ssl_verify_result' => int 0
'redirect_count' => int 0
'total_time' => float 0
'namelookup_time' => float 0
'connect_time' => float 0
'pretransfer_time' => float 0
'size_upload' => float 0
'size_download' => float 0
'speed_download' => float 0
'speed_upload' => float 0
'download_content_length' => float -1
'upload_content_length' => float -1
'starttransfer_time' => float 0
'redirect_time' => float 0
'certinfo' =>
array (size=0)
empty
'redirect_url' => string '' (length=0)
</pre>
null
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Answer 1

After thinking this through I think this is what you should do:
Ensure you can connect to the site from PHP:
<?php
$urlNoHttp = 'www.example.com'; // try 'example.com', too
$hostIP = gethostbyname($urlNoHttp);
var_dump($hostIP);
If it does not get the IP you have connection issues, so proceed to point 2.
Otherwise - it's not the network issues, it's curl setting itself - try point 3 and following.
Try pinging/wget'ting your destination from command line (ping www.example.com). If you get responses - your host is reachable for your OS and not the PHP, so
If you got the IP - then try reading about curl_setopt() int PHP docs. I'd start with setting proper HTTP headers (like Content-type, User-Agent, non-empty body to the request etc.). Also, try adding curl_setopt($c, CURLOPT_FRESH_CONNECT, 1); which forces not using a cached version of the url.
If it's still not working - try mixing in some proxy options, like curl_setopt($c, CURLOPT_HTTPPROXYTUNNEL, TRUE); to force "transparcence" of proxies, if there are any.
Generally you have to figure out what changes when you switch network environments. You have to know if there are any proxies involved, some strange NAT systems or maybe your router's firewall has some strange settings, that assume this kind of request as insecure and block it.
Hope this helps.