Curl giving 503 Service Unavailable in response - php

Question

My URL "www.example.com" is working in browser but when I get response via curl of URL "www.example.com" I get 503 service unavailable response.
I used the following code:
$url = 'http://www.example.com';
$curl_handle = curl_init();
curl_setopt($curl_handle, CURLOPT_URL, $url);
curl_setopt($curl_handle, CURLOPT_CONNECTTIMEOUT, 0);
curl_setopt($curl_handle, CURLOPT_TIMEOUT, 0);
curl_setopt($curl_handle, CURLOPT_SSL_VERIFYPEER, FALSE);
curl_setopt($curl_handle, CURLOPT_USERAGENT, $_SERVER['HTTP_USER_AGENT']);
curl_setopt($curl_handle, CURLOPT_FOLLOWLOCATION, 1);
curl_setopt($curl_handle, CURLOPT_RETURNTRANSFER, TRUE);
$JsonResponse = curl_exec($curl_handle);
$http_code = curl_getinfo($curl_handle);
print_r($http_code);die;

Answer 1

I'm pretty sure the remote server requires specific HTTP headers (cookies for example), like a session token or a language preference.
You have to analyze the HTTP traffic sent from your browser to the remote server and find the required HTTP headers yourself. I recommend a tool like Fiddler.
An example:
GET / HTTP/1.1
Host: www.example.com
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:27.0) Gecko/20100101 Firefox/27.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Cookie: foo=bar
Connection: keep-alive
Assuming the remote server requires clients to send a cookie with the name foo, he will probably send you a 503 or 400 error message in the case you omit it. You have to send the cookie from cURL as well in order to get a successful response, acting like a regular client.