Question

I created a message handler which will log the request and the response. ideally I want to

public class LoggingMessageHandler : DelegatingHandler
{
    protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        LogRequest(request);

        return base.SendAsync(request, cancellationToken).ContinueWith(task =>
        {
            var response = task.Result;

            LogResponse(response);

            return response;
        });
    }

    private void LogRequest(HttpRequestMessage request)
    {
        var writer = request.GetConfiguration().Services.GetTraceWriter();
        var content = request.Content;

        (content ?? new StringContent("")).ReadAsStringAsync().ContinueWith(x =>
        {
            writer.Trace(request, "request", System.Web.Http.Tracing.TraceLevel.Info, t =>
            {
                t.Message = x.Result;
            });
        });
    }

    private void LogResponse(HttpResponseMessage response)
    {
        var request = response.RequestMessage;
        var writer = request.GetConfiguration().Services.GetTraceWriter();
        var content = response.Content;

        (content ?? new StringContent("")).ReadAsStringAsync().ContinueWith(x =>
        {
            writer.Trace(request, "response", System.Web.Http.Tracing.TraceLevel.Info, t => 
            {
                t.Status = response.StatusCode;
                t.Message = x.Result;
            });
        });
    }
}

and here is my client code.

public ActionResult Index()
{
    var profile = Client.GetAsync("Vendor").Result.EnsureSuccessStatusCode().Content.ReadAsAsync<VendorProfileModel>().Result;
    return View(profile);
}

Logging appears to be working. However, when this handler is registered my client code returns an empty object. If I remove this handler the model is successfully read from the response and displayed on screen.

Is there a way to read the content and display the results on the client?

Answer 1

after a few more days for digging around on the net I finally found the root problem and a solution. First the problem:

1. everything in webapi is async
2. my action uses Controller.User which in turn is calling Thread.CurrentPrinciple
3. I am using ITraceWriter as my logging abstraction

apparently there is a bug in the ITraceWriter mechanicism where the current profile is not propagated across threads. therefore, i loose the principle when i get to my controller action. therefore, my query returns an empty result, rather than a fully populated result.

solution: don’t use ITraceWriter to log messages. It would have been nice to use the built in mechanics, but that doesn’t work. here is the link to the same issue which provides more detail/context.

https://aspnetwebstack.codeplex.com/workitem/237