how to pass data to JSON server using cURL with POST

Question

Update: the site I'm scraping has provided me with another way to get the data I need, so I am no longer having this problem. However I am still interested in a solution for educational reasons.

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I want to use cURL to pass data to a JSON server via POST.

I'm not sure how to format the variables for the cURL.

this doesn't work (returns null):

define('POSTVARS', 'json='.urlencode('{"cid":"2623","strQuery":"","strValues":"undefined","currentPage":"0","pageSize":"-1","pageSort":"-1","countryId":"2","maxResultCount":""}'));

nor does this

define('POSTVARS', "json=%7B'cid'%3A'2623'%2C%20'strQuery'%3A''%2C%20'strValues'%3A'undefined'%2C%20'currentPage'%3A'0'%2C%20'pageSize'%3A'-1'%2C'pageSort'%3A'-1'%2C'countryId'%3A'2'%2C'maxResultCount'%3A''%7D=");

As per Post JSON using Curl I am setting the header with

curl_setopt($ch, CURLOPT_HTTPHEADERS,array('Content-Type: application/json'));

My script works for regular POST variables, but not when I try to pass data to a JSON server, and I am wondering if I have misformatted the data or must provide some other additional parameter.

full code of my attempt (formatting is kind of broken below, I pasted the full script here https://docs.google.com/document/d/1hokE6-oMtcs3MBgPUzPwJvZIWNABc3XjOO2IzbpxDF4/edit?hl=en&authkey=CKXcnv8C ):

function get_url( $url,  $javascript_loop = 0, $timeout = 5 )
{
    $cookie = tempnam ("/tmp", "CURLCOOKIE");
    $ch = curl_init(POSTURL);
    curl_setopt( $ch, CURLOPT_USERAGENT, "Mozilla/5.0 (Windows; U; Windows NT 5.1; rv:1.7.3) Gecko/20041001 Firefox/0.10.1" );
    curl_setopt( $ch, CURLOPT_URL, $url );
    curl_setopt( $ch, CURLOPT_COOKIEJAR, $cookie );
    curl_setopt( $ch, CURLOPT_FOLLOWLOCATION, true );
    curl_setopt( $ch, CURLOPT_ENCODING, "" );
    curl_setopt( $ch, CURLOPT_RETURNTRANSFER, true );
    curl_setopt( $ch, CURLOPT_AUTOREFERER, true );
    curl_setopt( $ch, CURLOPT_SSL_VERIFYPEER, false );    # required for https urls
    curl_setopt( $ch, CURLOPT_CONNECTTIMEOUT, $timeout );
    curl_setopt( $ch, CURLOPT_TIMEOUT, $timeout );
    curl_setopt( $ch, CURLOPT_MAXREDIRS, 10 );

$postvars=<<<HEREDOC
{'cid':'2623', 'strQuery':"", 'strValues':'undefined', 'currentPage':'0', 'pageSize':'-1','pageSort':'-1','countryId':'2','maxResultCount':''}


HEREDOC;

curl_setopt($ch, CURLOPT_POST      ,1);
curl_setopt($ch, CURLOPT_POSTFIELDS    ,$postvars);
curl_setopt($ch, CURLOPT_HEADER      ,0);  // DO NOT RETURN HTTP HEADERS 

$arr = array();
array_push($arr, 'Content-Type: application/json; charset=utf-8');
curl_setopt($ch, CURLOPT_HTTPHEADER, $arr);

$content = curl_exec( $ch );
$response = curl_getinfo( $ch );
curl_close ( $ch );

if ($response['http_code'] == 301 || $response['http_code'] == 302)
{
    ini_set("user_agent", "Mozilla/5.0 (Windows; U; Windows NT 5.1; rv:1.7.3) Gecko/20041001 Firefox/0.10.1");

    if ( $headers = get_headers($response['url']) )
    {
        foreach( $headers as $value )
        {
            if ( substr( strtolower($value), 0, 9 ) == "location:" )
                return get_url( trim( substr( $value, 9, strlen($value) ) ) );
        }
    }
}

if (    ( preg_match("/>[[:space:]]+window\.location\.replace\('(.*)'\)/i", $content, $value) || preg_match("/>[[:space:]]+window\.location\=\"(.*)\"/i", $content, $value) ) &&
        $javascript_loop < 5
)
{
    return get_url( $value[1], $javascript_loop+1 );
}
else
{
    return array( $content, $response );
}


}

// set url
$url="http://us.asos.com/services/srvWebCategory.asmx/GetWebCategories";

$output = get_url($url);

print_r($output);