C# - Get Response from WebRequest and handle status codes

Question

I am writing an updatesystem for .NET-applications and at the moment I am stuck. I try to get a file on a remote server and its content. For that I want to use a HttpWebRequest to get the content and the status code if the operation fails.

I built a function that contains a switch-query and each part asks the status code and does an action then.

This looks like the following:

public void AskStatusCode(int code)
{
  switch (code)
  {
  case 404:
     // Do an action
     break;

  case 405:
     // Do an action
     break;
  }
}

Ok, that is it. Now I created a HttpWebRequest and a HttpWebResponse.

HttpWebRequest requestChangelog = (HttpWebRequest)HttpWebRequest.Create(url);
requestChangelog.Method = "GET";

HttpWebResponse changelogResponse = (HttpWebResponse)requestChangelog.GetResponse();

// Now call the function and set the status code of the response as parameter.
AskStatusCode((int)changelogResponse.StatusCode);

So, the theory should work, but it does not. It will not do any actions I put in the "case"-block for a special status code.

I removed the file from the remote server to test if it will execute the case-block for code "404", but it always shows me an exception (remote server answered 404), but not that what I wanted this status code to handle with.

So, my question is, why is this not working? The types are integers and I casted the status code to an Int32 as well, as you could see...

To your info: After the status code had been checked and if it is ok, I want to read the content with a stream reader and the ResponseStream.

Help would be appreciated. Excuse me, if you did not understand that, I tried to say it as clear as I could.

Answer 1

You have to check whether the response failed because of a server error (the WebException provides a WebResponse) or not. Maybe this will help you:

        HttpWebResponse response = null;

        try
        {
            HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create("http://www.google.com/thisisadeadlink");
            request.Method = "GET";

            response = (HttpWebResponse)request.GetResponse();

            StreamReader sr = new StreamReader(response.GetResponseStream());
            Console.Write(sr.ReadToEnd());
        }
        catch (WebException e)
        {
            if (e.Status == WebExceptionStatus.ProtocolError)
            {
                response = (HttpWebResponse)e.Response;
                Console.Write("Errorcode: {0}", (int)response.StatusCode);
            }
            else
            {
                Console.Write("Error: {0}", e.Status);
            }
        }
        finally
        {
            if (response != null)
            {
                response.Close();
            }
        }

Answer 2

StatusCodes in the range of 4xx and 5xx throw a WebException which is why the code is never reaching the switch statement.

You need to handle this exception in your code:

HttpWebRequest requestChangelog = null;
HttpWebResponse changelogResponse = null;

try
{
    requestChangelog = (HttpWebRequest)HttpWebRequest.Create(url);
    requestChangelog.Method = "GET";

    changelogResponse = (HttpWebResponse)requestChangelog.GetResponse();
}
catch (WebException we)
{
    //handle the error
}

AskStatusCode((int)changelogResponse.StatusCode);

If you are only interested in checking error status codes then you would move the AskStatusCode() call inside of the catch block.