Simple way to calculate Response length in MVC4

Question

I was trying to calculate the length of a HTTP Response. Seems the stream doesn't want to play. (no read allowed. and the Content-Length doesn't seem set) I was hoping to simply call some length property on the HttpContent response. I have since googled and seen what looks to me like convoluted solutions around filters which I don't understand. Is it possible to access the length (content itself is option extra ) If not I would appreciate a link to an example for 'mvc4/.net 4.5 filter' included that I should work though till I do understand. :-)

   public override void Init()
    {
        base.Init();
        EndRequest += new EventHandler(EndRequestHandler);
    }
    public void EndRequestHandler(object sender, EventArgs e) {
        var     admService = new AdminServices();
        admService.HTTPTrace(Context);
    }


 public void HTTPTrace(HttpContext httpContext) {
        try {
            var eventTrace = new MasterEventTrace();
            eventTrace.RemoteAddress = req.UserHostAddress;
            eventTrace.RequestLengthBytes = req.ContentLength;

          //  var targetMemoryStream = new MemoryStream();
          //   res.OutputStream.CopyTo(targetMemoryStream);
            int len;
            int.TryParse(res.Headers["Content-Length"], out len );
            eventTrace.StatusCode = res.StatusCode;
            eventTrace.ResponseLengthBytes = len;    // <<<<<<< HOW to calculate this

EDIT: Based on Darin's response I got this working, Thank You Darin I made a few tweaks to suit the situation, but otherwise as suggested. It shows a little more from Global.asax.cs, and logging the Request and Response info as required.

//Global.asax.cs
  public override void Init()        {
        base.Init();
        BeginRequest += new EventHandler(BeginRequestHandler);
        EndRequest += new EventHandler(EndRequestHandler);
    }

   public void EndRequestHandler(object sender, EventArgs e)
    {
        var adminService = new AdminServices();
        var handler = Context.Response.Filter as ResponseStreamHandler;
        adminService.HTTPTrace(Context, handler);
    }

    public void BeginRequestHandler(object sender, EventArgs e)
    {
        BootStrapUnauthentiated();
        Context.Response.Filter = new ResponseStreamHandler(Context.Response.Filter);
    }

 public void HTTPTrace(HttpContext httpContext, ResponseStreamHandler responseStreamFilter)
    {
        try {
            var _ILuwMaster = BosGlobal.BGA.ILuwMaster();

            var req = httpContext.Request;
            var res = httpContext.Response;
            var eventTrace = new MasterEventTrace();
            eventTrace.EventName =  req.RequestType  +":"+ req.Url.LocalPath;
            eventTrace.EventDateTime = BosGlobal.BGA.Calendar.Now;
            eventTrace.RemoteAddress = req.UserHostAddress;
            eventTrace.RequestLengthBytes = req.ContentLength;
            eventTrace.ResponseLengthBytes = responseStreamFilter.ResponseSize;   //<<<<<<HERE
            eventTrace.StatusCode = res.StatusCode;
            // save trace entry in DB
            _ILuwMaster.GetRepository<MasterEventTrace>().Add(eventTrace);
            _ILuwMaster.Commit();
        }
        catch (Exception ex ) {} // DONT KILL Live traffic when logging errors occur
    }

 public class ResponseStreamHandler : MemoryStream {
    private readonly Stream _responseStream;
    public long ResponseSize { get; private set; } 
    public ResponseStreamHandler(Stream responseStream) {
        this._responseStream = responseStream;
        ResponseSize = 0;
    }

    public override void Write(byte[] buffer, int offset, int count) {
        this.ResponseSize += count;
        this._responseStream.Write(buffer, offset, count);
    }

    public override void Flush() {
      base.Flush();
    }
}

Answer 1

You could write a custom Response filter:

public class ResponseLengthCalculatingStream: MemoryStream
{
    private readonly Stream responseStream;
    private long responseSize = 0;
    public ResponseLengthCalculatingStream(Stream responseStream)
    {
        this.responseStream = responseStream;
    }

    public override void Write(byte[] buffer, int offset, int count)
    {
        this.responseSize += count;
        this.responseStream.Write(buffer, offset, count);
    }

    public override void Flush()
    {
        var responseSize = this.responseSize;
        // Here you know the size of the response ...
        base.Flush();
    }
}

and register it in your Global.asax:

protected void Application_BeginRequest()
{
    Context.Response.Filter = new ResponseLengthCalculatingStream(Context.Response.Filter);
}

And if you wanted to apply this filter only on particular controller actions you could write a custom action filter instead of applying it in the BeginRequest event in Global.asax:

public class ResponseLengthCapturingAttribute: ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        var response = filterContext.HttpContext.Response;
        response.Filter = new ResponseLengthCalculatingStream(response.Filter);
    }
}

and then all that's left is decorate the controller action with the corresponding action filter:

[ResponseLengthCapturing]
public ActionResult Index()
{
    ...
    return View();
}