Question

I’m fetching a URL but that’s filtered in some countries. I was looking for a way to configure cURL to use client proxy.

I mean proxy that has been set in browser or connection.

Any other solution is appreciated that could solve the problem and determine if website is filtered or not.

Answer 1

For libcurl, use CURLOPT_PROXY:

http://curl.haxx.se/libcurl/c/curl_easy_setopt.html#CURLOPTPROXY

For the curl command line tool, use option –proxy host:port.

Both the library and the command line tool respect the environment variables http_proxy, ftp_proxy, all_proxy, so that’s another option.

Edit:
If you want to use the client’s proxy on the server – this won’t work reliably.
First, you would need to determine client’s proxy settings via javascript – which might work.
Second, you would need to use that proxy to make a request on the server – this will certainly not work reliably, as the client’s proxy might be in a local network (not accessible from outside), require authentication etc.

An option would be to make a client request via JavaScript (AJAX) and verify the result – which is a somewhat questionable approach, as you are making requests from your client’s computers to possibly blocked (illegal?) sites. Better don’t do that.