Error in converting .NET Rest Client code into PHP

I have a working .NET REST client code. I need to convert the .NET code into PHP. After a lot of time spent to convert the code I have no clue on how to proceed further. The relevant code in .NET is as below:

Public Function GetDemographicDetail(ByVal UID As Decimal) As DataSet
    Dim DsResult As New DataSet
    Dim proxyobject As WebProxy = New WebProxy("http://proxyserver:80/", True)
    'Variable to hold the XML file.
    Dim sample As String

    'URL of the Webservice.
    Dim serviceBaseUrl As String = "http://srdh.punjab.gov.in:80/searchservice/searchservice/searchService"

    Dim req As WebRequest = WebRequest.Create(serviceBaseUrl)

    req.Proxy = proxyobject
    Dim resourceUrl As String = ""
    Dim method As String = "POST"
    Dim Result As String

    'Fetch the UID's in Dataset.
    Dim Photo() As Byte
    Dim DOB As String
    Dim DOY As String
    'Generate the XML file attaching UID No.

    If IsNumeric(RTrim(UID.ToString())) And (RTrim(UID.ToString().Length = 12)) Then
        sample = "<advanceSearchParameters xmlns=""http://uidai.gov.in/SRDH/SearchResults"" xmlns:i=""http://www.w3.org/2001/XMLSchema-instance""><uid>" & UID & "</uid><userId>user</userId><password>pass</password></advanceSearchParameters>"

        'Hit webservice and save the result in "Result"
        Result = UseHttpWebApproach(serviceBaseUrl, resourceUrl, method, sample)

    End If
    Retu DsResult
End Function

Private Function UseHttpWebApproach(ByVal serviceUrl As String, ByVal resourceUrl As String, ByVal method As String, ByVal xmlRequestBody As String) As String

    Dim responseMessage As String = Nothing
    Dim request = TryCast(WebRequest.Create(String.Concat(serviceUrl)), HttpWebRequest)
    If request IsNot Nothing Then
        request.ContentType = "application/xml"
        request.Method = method
    End If

    If method = "POST" AndAlso xmlRequestBody IsNot Nothing Then
        Dim requestBodyBytes As Byte() = ASCIIEncoding.UTF8.GetBytes(xmlRequestBody.ToString())
        request.ContentLength = requestBodyBytes.Length
        Using postStream As Stream = request.GetRequestStream()
            postStream.Write(requestBodyBytes, 0, requestBodyBytes.Length)
        End Using
    End If
    If request IsNot Nothing Then
        Dim response = TryCast(request.GetResponse(), HttpWebResponse)
        If response.StatusCode = HttpStatusCode.OK Then
            Dim responseStream As Stream = response.GetResponseStream()
            If responseStream IsNot Nothing Then
                Dim reader = New StreamReader(responseStream)

                responseMessage = reader.ReadToEnd()
            End If
        Else
            responseMessage = response.StatusDescription
        End If
    End If
    Retu responseMessage

End Function

The following is the converted code into PHP:

    <?php
    //Store your XML Request in a variable

$input_xml = '<advanceSearchParameters xmlns="http://uidai.gov.in/SRDH/SearchResults" xmlns:i="http://www.w3.org/2001/XMLSchema-instance"><uid>823631843375</uid><userId>user</userId><password>pass</password></advanceSearchParameters>';

 $url = "http://srdh.punjab.gov.in:80/searchservice/searchservice/searchService";

 $header_data = array(
        "Content-Type: application/xml",
    );
    //setting the curl parameters.
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_HTTPHEADER, $header_data);
    curl_setopt($ch, CURLOPT_POST, count($input_xml));
    // Following line is compulsory to add as it is
    curl_setopt($ch, CURLOPT_POSTFIELDS,
                "xmlRequest=" . $input_xml);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 300);

    //curl_setopt($ch, CURLOPT_VERBOSE, true);
    //curl_setopt($ch, CURLOPT_STDERR, fopen(diame(__FILE__).'/errorlog.txt', 'a'));


    echo $data = curl_exec($ch);
    curl_close($ch);

    //convert the XML result into array
    $array_data = json_decode(json_encode(simplexml_load_string($data)), true);

    print_r('<pre>');
    print_r($array_data);
    print_r('</pre>');

 ?>

The output xml for the above php code is that I get as output is:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?><srdhSearchResults xmlns="http://uidai.gov.in/SRDH/SearchResults"/><pre>Array
(
)
</pre>

whereas the expected output should be an xml record retued from the server.

Please guide as to what I may be doing wrong. Note: The useame and password have been changed as the above url is a live one and a test user credentials caot be provided.