ASP.NET Web API Logging Inbound Request Content - asp.net-mvc

Question

I’m trying to log out Web API Request Content – i.e. the json string. I implemented an ITraceWriter class (example) and configured it so that Web API calls it in the pipeline. But if I read the request.Content or copy into to a stream to read it is not available for the method resulting in a null model. This post talks about that issue a little. Anyone have experience logging out inbound Web API request content and know what the best approach is?
Thanks
Update A
I created a simple sample Web API project to rule out anything in my project and I still see that the model will be null because of logging. I simply test a few times in a row by posting via Fidder and see my model comes in null. With breakpoints in place, it might work which is why I think there is a sync/timing issue. Any thoughts on how to get this to work?
Header:
User-Agent: Fiddler
Host: localhost:56824
Content-Type: application/json
Content-Length: 22
Body:
{
"A":1,"B":"test"
}
Here's the code:
Controller:
public class ValuesController : ApiController
{
[HttpPost]
public void Post(ValuesModel model)
{
if (model == null)
{
Debug.WriteLine("model was null!");
}
else
{
Debug.WriteLine("model was NOT null!");
}
}
}
Model:
public class ValuesModel
{
public int A { get; set; }
public string B { get; set; }
}
Logger:
public class APITraceLogger : DelegatingHandler
{
protected override System.Threading.Tasks.Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, System.Threading.CancellationToken cancellationToken)
{
if (request.Content != null)
{
// This can cause model to be null
request.Content.ReadAsStringAsync().ContinueWith(s =>
{
string requestText = s.Result;
Debug.WriteLine(requestText);
});
// and so can this
//request.Content.ReadAsByteArrayAsync()
// .ContinueWith((task) =>
// {
// string requestText = System.Text.UTF8Encoding.UTF8.GetString(task.Result);
// Debug.WriteLine(requestText);
// });
}
// Execute the request, this does not block
var response = base.SendAsync(request, cancellationToken);
// TODO:
// Once the response is processed asynchronously, log the response data
// to the database
return response;
}
}
Wiring up logger in WebApiConfig class:
config.MessageHandlers.Add(new APITraceLogger());
Update B
It seems like it is now working if I change the logger to the following code adding the await, async and returning the result. Seems like something I'm not understanding in the async code or truly a timing issue or something.
public class APITraceLogger : DelegatingHandler
{
protected async override System.Threading.Tasks.Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, System.Threading.CancellationToken cancellationToken)
{
if (request.Content != null)
{
// This does seem to work - is it because it is synchronous? Is this a potential problem?
var requestText = await request.Content.ReadAsStringAsync();
Debug.WriteLine(requestText);
}
// Execute the request, this does not block
var response = base.SendAsync(request, cancellationToken);
// TODO:
// Once the response is processed asynchronously, log the response data
// to the database
return response.Result;
}
}

Answer 1

As Filip mentions in that post ReadAsStringAsync or ReadAsByteArrayAsync methods buffer the request content internally. This means that even if your incoming request's stream type is a non-buffered stream, you could safely do a ReadAsStringAsync/ReadAsByteArrayAsync at a message handler for example, and also expect the model binding to work fine.
By default, a request's stream is buffered in both webhost and selfhost cases. But if you would like to check if using ReadAsStringAsync/ReadAsByteArrayAsync and model biding works fine even in non-buffered mode, you can do the following to force non-buffered mode:
public class CustomBufferPolicySelector : WebHostBufferPolicySelector
{
public override bool UseBufferedInputStream(object hostContext)
{
//NOTE: by default, the request stream is always in buffered mode.
//return base.UseBufferedInputStream(hostContext);
return false;
}
}
config.Services.Replace(typeof(IHostBufferPolicySelector), new CustomBufferPolicySelector());
Just FYI...the above policy selector works only for Web Host currently. If you would like to do a similar test in SelfHost, then do the following:
//NOTE: by default, the transfer mode is TransferMode.Buffered
config.TransferMode = System.ServiceModel.TransferMode.StreamedRequest;
After Update B of the post above:
You could modify your handler like below:
public class LoggingHandler : DelegatingHandler
{
protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
{
if (request.Content != null)
{
string requestContent = await request.Content.ReadAsStringAsync();
}
HttpResponseMessage response = await base.SendAsync(request, cancellationToken);
if (response.Content != null)
{
string responseContent = await response.Content.ReadAsStringAsync();
}
return response;
}
}