Curl 400 error when using UserAgent - php

Question

Why i'm getting sometimes this error?
**Bad Request**
Your browser sent a request that this server could not understand.
Apache Server at control.digitalcoding.com Port 80
When
$UserAgent = "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/535.11 (KHTML, like Gecko) Chrome/17.0.963.56 Safari/535.11";
everything works fine, but not with
Opera/7.52 (Windows NT 5.1; U) [en]
Mozilla/5.0 (Windows; U; Windows NT 5.1; rv:1.7.3) Gecko/20041001 Firefox/0.10.1
Mozilla/5.0 (Windows NT 6.1; rv:10.0.1) Gecko/20100101 Firefox/10.0.1
for example. What is the problem?
HtmlReciever.php
<?php
if(empty($_GET["Link"]))
{
echo "empty";
die;
}
$LinkToFetch = urldecode($_GET["Link"]);
$UserAgent = urldecode($_GET["UserAgent"]);
function iscurlinstalled()
{
if (in_array ('curl', get_loaded_extensions()))
{
return true;
}
else
{
return false;
}
}
// If curl is instaled
if(iscurlinstalled()==true)
{
$ch = curl_init($LinkToFetch);
curl_setopt($ch, CURLOPT_USERAGENT,$UserAgent);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_BINARYTRANSFER, true);
$HtmlCode = curl_exec($ch);
curl_close($ch);
}
else
{
$HtmlCode = file_get_contents($LinkToFetch);
}
echo $HtmlCode;
?>
I must say that i'm running RecieverHtml.php from another .php with GET like this
http://127.0.0.1/reciever/RecieverHtml.php?Link=http%3A%2F%2Fwww.digitalcoding.com%2Ftools%2Fdetect-browser-settings.html&UserAgent=Mozilla%2F5.0+%28Windows+NT+6.1%3B+rv%3A10.0.1%29+Gecko%2F20100101+Firefox%2F10.0.1%0D%0A

Answer 1

This depends on the server your request is sent to. If the server checks the user agent and allows only requests that match a limited/incomplete/outdated list of common browser user agents, the server might return a generic 400 status code.
If you don't have control over the server and want your script to work, use the user agent that works and forget about the others. The user agent you provide with your request is "wrong" anyway, as it is not Chrome doing the actual request but your server running your PHP script.
EDIT:
You can also pass the user agent of the browser that requests your PHP script by using the following code:
curl_setopt($ch, CURLOPT_USERAGENT, $_REQUEST['HTTP_USER_AGENT']);
Just keep in mind that the value might be empty or exotic (like. Lynx/2.8.8dev.3 libwww-FM/2.14 SSL-MM/1.4.1) and be rejected by the server.