XML response from asp page

I have been trying to send xml message from php to asp and output response to my php page using CURL but having no luck in receiving any response. This is what I have tried:

<?php
$url = "https://someweb.asp";
$post_string = "xmlmessage=<?xml version='1.0' encoding='UTF-8'?> 
<abc>
<UserId>123</UserId> 
</abc>";

//$header  = "POST HTTPS/1.0 \r\n";
$header = "Content-type: text/xml \r\n";
$header .= "Conte开发者_JAVA技巧nt-length: ".strlen($post_string)." \r\n";
$header .= "Content-transfer-encoding: text \r\n";
$header .= "Connection: close \r\n\r\n"; 
$header .= $post_string;

$ch = curl_init($url);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0); 
curl_setopt($ch, CURLOPT_URL,$url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_TIMEOUT, 4);
curl_setopt($ch, CURLOPT_CUSTOMREQUEST, $header);

$output = curl_exec($ch);
$info = curl_getinfo($ch);

if ($output == false || $info['http_code'] != 200) {
  $output = "No cURL data returned for $url [". $info['http_code']. "]";
  if (curl_error($ch))
    $output .= "\n". curl_error($ch);
  }
else
    {curl_close($ch);}

echo $output;
?>

Can anyone please guide me where i am wrong?

Don't build a custom request for a simple POST. CURL is perfectly capable of doing a post without all those shenanigans:

$xml = <<<EOL
<?xml version='1.0' encoding='UTF-8'?> 
<abc>
<UserId>123</UserId> 
</abc>
EOL;

$ch = curl_init($url);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, array('xmlmessage' => $xml));
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_TIMEOUT, 4);

$result = curl_exec($ch);
if ($result === FALSE) {
    die(curl_error($ch));
}

echo $result

$post_string = "xmlmessage=<?xml version='1.0' encoding='UTF-8'?> 
<abc>
<UserId>123</UserId> 
</abc>";

swap the double and single quotes

$post_string = 'xmlmessage=<?xml version="1.0" encoding="UTF-8"?> 
<abc>
<UserId>123</UserId> 
</abc>';

single quotes are not valid in xml markup