PHP : Sometimes CURL not return any content - php

Question

When I try to get content using CURL but many time does not return any value..
Note : I am tested on same URL
CURL CODE
function curltest($url){
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_HEADER, 0);
$agents = array(
'Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:7.0.1) Gecko/20100101 Firefox/7.0.1',
'Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1.9) Gecko/20100508 SeaMonkey/2.0.4',
'Mozilla/5.0 (Windows; U; MSIE 7.0; Windows NT 6.0; en-US)',
'Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10_6_7; da-dk) AppleWebKit/533.21.1 (KHTML, like Gecko) Version/5.0.5 Safari/533.21.1'
);
curl_setopt($ch,CURLOPT_USERAGENT,$agents[array_rand($agents)]);
$header[0] = "Accept: text/xml,application/xml,application/xhtml+xml,";
$header[0] .= "text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5";
$header[] = "Cache-Control: max-age=0";
$header[] = "Connection: keep-alive";
$header[] = "Keep-Alive: 10";
$header[] = "Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7";
$header[] = "Accept-Language: en-us,en;q=0.5";
$header[] = "Pragma: ";
curl_setopt($ch, CURLOPT_HTTPHEADER, $header);
curl_setopt($ch, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_1_1); // ADD THIS
curl_setopt ($ch, CURLOPT_CONNECTTIMEOUT, 20);
curl_setopt($ch, CURLOPT_TIMEOUT, 10);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
curl_setopt($ch,CURLOPT_ENCODING, '');
$output = curl_exec($ch);
if(curl_errno($ch)){
curl_close($ch);
$output = file_get_contents($url);
}
return $output;
}
Please give any suggestion OR tell me if any changes required in above code

Answer 1

see here to get all options in curl php curl options. Different sites using different type of client validation. If your curl fails to valid there site, it may return nothing.