cURL WRITEFUNCTION callback with anonymous function and closures

I am using cURL's option for CURLOPT_WRITEFUNCTION to specify a callback to handle when data comes in from a cURL request.

$serverid=5;
$ch=curl_init();
curl_setopt($ch, CURLOPT_URL, 'http://www.whatever.com');
curl_setopt(
    $ch, 
    CURLOPT_WRITEFUNCTION, 
    function ($ch, $string) { 
        return readCallback($ch, $string, $serverid);
    }
);
curl_exec($ch);

function readCallback($ch, $string, $serverid) {
    echo "Server #", $serverid, "  |  ", $string;
    return strlen($string);
}

I want to use an anonymous function to call my own function that actuall does work (readCallback()) so that I can include the server ID associated with the request 开发者_开发百科($serverid). How can I properly utilize closures so that when cURL hits my callback anonymous function, that the anonymous function knows that it was originally defined with $serverid=5 and can call readCallback() appropriately?

I will eventually be using this with ParalellCurl and a common callback, which is why it is necessary to have an anonymous function call my callback with the ID.

If you would like to have access to $serverid inside your anonymous function, you have to tell PHP that you want to use that variable. Like this:

/*
 * I replaced the simple $serverid var to $serverIdHolder because
 * 'use' passes the variable by value, so it won't change inside
 * your anonymous function that way. But if you pass a reference
 * to an object, then you are able to see always the current needed value.
 */
$serverIdHolder = new stdClass;
$serverIdHolder->id = 5;

$ch=curl_init();
curl_setopt($ch, CURLOPT_URL, 'http://www.whatever.com');
curl_setopt(
    $ch, 
    CURLOPT_WRITEFUNCTION, 
    function ($ch, $string) use ($serverIdHolder) { 
        return readCallback($ch, $string, $serverIdHolder->id);
    }
);
curl_exec($ch);

function readCallback($ch, $string, $serverid) {
    echo "Server #", $serverid, "  |  ", $string;
    return strlen($string);
}