Web API Request is null in ExecuteAsync method of ApiController

Question

I am trying to access the Request property in my ApiController-derived class.

For some reason, Request is null in ExecuteAsync method. I've seen the other questions, so before you ask:

I am not initializing the controller by calling the constructor, it's a regular HTTP POST API call from an external device.
I've tried the same request locally with Fiddler, the behavior is identical.
I am not unit testing.
Before hitting the ExecuteAsync method, my request passes through a delegating handler, and in the delegating handler, my request object exists (I even add some properties without any problem).
At the last line of delegating handler, I call return await base.SendAsync(request, cancellationToken); without a problem and request exists.
Right after than in API controller, HttpContext.Current.Request is not null and accessible without problem.
In API controller, RequestContext is not null and accessible without problem.
In that same line, Request is null.

Why would this occur? I'm on Web API 2.2 (and MVC 5, if relevant).

If possible, can you show your POST API call? It might be that the external device is not forming the request properly. Did you try testing the API with a Postman or any REST client? — Souvik Ghosh
– Souvik Ghosh, Commented Mar 14, 2017 at 9:48
@SouvikGhosh I've just tried with Fiddler upon your comment. Unfortunately, it's still the same. — Can Poyrazoğlu
– Can Poyrazoğlu, Commented Mar 14, 2017 at 9:56
The RequestContext is a part by the Request (can also be obtained by Request.GetRequestContext()). Can you check how the request is created at the client side? Also, you may check HttpContext which can also give you information about individual requests. — Souvik Ghosh
– Souvik Ghosh, Commented Mar 14, 2017 at 10:24
@SouvikGhosh what do you mean by the client side? I've already tried with two different clients, they are regular HTTP requests with nothing special. I'm pretty much sure it's not the client. — Can Poyrazoğlu
– Can Poyrazoğlu, Commented Mar 14, 2017 at 11:00

yonisha · Accepted Answer · 2017-03-18 20:31:01Z

4

+50

This is probably due to the fact that you're trying to access HttpContext while working with async/await.

So, you have two options:

Access the request via the ExecuteAsync method 'HttpControllerContext' parameter - controllerContext.Request.
Make sure your web.config is targeting .NET 4.5 and update appSettings with aspnet:UseTaskFriendlySynchronizationContext set to true.

You can read more here - Using HttpContext Safely After Async in ASP.NET MVC Applications.

To better understand what's going on under the hood, I'd recommend:

Understand what is SynchronizationContext - ExecutionContext vs SynchronizationContext
Understand how it is related to ASP.NET - Understanding the SynchronizationContext in ASP.NET.

In a very very high level: in a synchronous server implementations, where the entire request is processed by the same thread, the execution context is stored using TLS (thread local storage), means HttpContext is available anywhere in your code.

In an asynchronous server implementation (async/await), the request may be processed by several threads, and there's a need to pass the execution context between those threads.

edited Mar 18, 2017 at 20:31

answered Mar 16, 2017 at 23:37

yonisha

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2 Comments

Thiago Custodio Over a year ago

<add key="aspnet:UseTaskFriendlySynchronizationContext" value="true" /> in the web.config

Can Poyrazoğlu Over a year ago

Option 2 seemed easier but it didn't work for some reason (it was still null). Option 1 worked. I'd be happy to learn about the reason though.

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