Jon Udell

In an earlier installment of the azure+elmcity series I griped about some inconsistencies in how the .NET Framework deals with HTTP:

The .NET equivalent to Python’s httplib, for example, is the HttpWebRequest/HttpWebResponse pair. But these APIs differ from those provided by httplib in a couple of ways that annoy me.

First, there’s an inconsistency in the way headers are handled. You get and set most headers using the Headers collection. But you get and set a few special ones, like Content-Type and Content-Length, using special named properties.

Second, status codes are handled inconsistently. Most responses return status codes. But for codes in the 4xx series, an exception is thrown.

To me these behaviors are quirks that make it trickier to use RESTful interfaces.

The exceptions, in particular, make it much harder to write tests. When I test the method that puts a blog into the Azure blob store, for example, I expect success, and here’s how I express that expectation:

Assert.AreEqual(HttpStatusCode.Created, response.normal_status);

But when I test the method that creates a public container, I expect failure if the container already exists. Here’s how I express that expectation:

Assert.AreEqual(WebExceptionStatus.ProtocolError, response.exception_status);

In order to deal with successes and failures in uniform way, I created an http_response_struct that encapsulates both, and a method that performs a web request and returns a structure of that type.

The code, in its current form, appears below. I present it here for two reasons. First, because it may be of value to others. But second, because others have surely done this in better and more general ways. I’m hoping this entry will attract pointers to some other simple but effective implementations of this idea.

public struct http_response_struct
  {
  public HttpStatusCode normal_status;
  public WebExceptionStatus exception_status;
  public string message;
  public byte[] data;
  public string data_as_string;
  public Dictionary<string, string> headers;

  public http_response_struct(HttpStatusCode normal_status,
      WebExceptionStatus exception_status, string message, byte[] data,
      string data_as_string, Dictionary<string, string> headers)
    {
    this.normal_status = normal_status;
    this.exception_status = exception_status;
    this.message = message;
    this.data = data;
    this.data_as_string = data_as_string;
    this.headers = headers;
    }
  }

public static http_response_struct DoHttpWebRequest(HttpWebRequest request,
    byte[] data)
  {
  request.AllowAutoRedirect = true;
  HttpStatusCode normal_status;
  WebExceptionStatus exception_status;
  string message = "";
  request.ContentLength = 0;
  Dictionary<string, string> headers = new Dictionary<string, string>();

  if (data != null && data.Length > 0)
    {
    request.ContentLength = data.Length;
    var bw = new BinaryWriter(request.GetRequestStream());
    bw.Write(data);
    bw.Flush();
    bw.Close();
    }

  byte[] return_data = new byte[0];
  string return_data_as_string = "";

  try
    {
    HttpWebResponse response = (HttpWebResponse)request.GetResponse();
    normal_status = response.StatusCode;
    exception_status = new WebExceptionStatus();
    message = response.StatusDescription;
    foreach (string key in response.Headers.Keys)
      headers[key] = response.Headers[key];
    get_response_data(request, ref return_data, ref return_data_as_string,
      response);
    response.Close();
    }
  catch (WebException e)
    {
    exception_status = e.Status;
    normal_status = new HttpStatusCode();
    message = string.Format("{0} {1}", exception_status.ToString(),
      e.Message);
    get_response_data(request, ref return_data, ref return_data_as_string,
      (HttpWebResponse) e.Response);
    string logmsg = string.Format("DoHttpRequest ({0}): {1}", request.RequestUri,
      message);
    write_log_message(logmsg);
    }

  return new http_response_struct(normal_status, exception_status,
    message, return_data, return_data_as_string, headers);
  }