Question

I am trying to implement a very basic system from my C# .NET application that sends the IP address of the machine to authenticate.php on my web server. The php page will check this IP address against a database and either respond back with “yes” or “no”.

It has been a long time since I worked with PHP, and I am a little bit confused. Here is what my .NET function looks like.

public static bool IsAuthenticated()
{
    string sData = getPublicIP();
    Uri uri = new Uri("http://www.mysite.com/authenticate.php");
    if (uri.Scheme == Uri.UriSchemeHttp)
    {
        HttpWebRequest request = (HttpWebRequest)WebRequest.Create(uri);
        request.Method = WebRequestMethods.Http.Post;
        request.ContentLength = sData.Length;
        request.ContentType = "application/x-www-form-urlencoded";

        // POST the data to the authentication page
        StreamWriter writer = new StreamWriter(request.GetRequestStream());
        writer.Write(sData);
        writer.Close();

        // Retrieve response from authentication page
        HttpWebResponse response = (HttpWebResponse)request.GetResponse();
        StreamReader reader = new StreamReader(response.GetResponseStream());
        string sResponse = reader.ReadToEnd();
        response.Close();

        if (sResponse == "yes")
        {
            Console.WriteLine("Authentication was Successful.");
            return true;
        }
        else
        {
            Console.WriteLine("Authentication Failed!");
            return false;
        }
    }
}

So would the POST variable be $_POST[‘sData’]; and how do I respond back to my application with the result?

Answer 1

Assuming the value of sData is (say) “10.1.1.1” then you’re currently not posting proper form data in the first place. The name of the variable isn’t part of the text written by

 writer.Write(sData);

You need to do something like:

 string postData = "ipaddress=" + sData;

and then use the ipaddress form parameter within your PHP.

Note also that you should be giving the binary content length, which may not be the same as the string length in characters. Of course it’s okay if the string here is entirely ASCII, which I’d expect if it’s an IP address… but it’s worth bearing in mind for other uses. (Likewise you would normally need to bear in mind any characters which need special encoding.)

Also note that it would be better to use using statements for the StreamWriter, HttpResponse etc, to make sure that everything gets closed even if an exception is thrown.