Workaround for HttpContext.HideRequestResponse being internal? Detect if HttpContext.Request is really available?

Question

We're migrating an application to use IIS7 integrated mode. In library code that is designed to work either within the context of an HTTP request or not, we commonly have code like this:

if (HttpContext.Current != null &&
    HttpContext.Current.Request != null) {

    // do something with HttpContext.Current.Request

} else {

    // do equivalent thing without HttpContext..

}

But in IIS7 integrated mode the check for HttpContext.Current.Request throws an exception whenever this code is called from Application_Start.

protected void Application_Start(object sender, EventArgs e)
{
    SomeLibrary.DoSomethingWithHttpContextCurrentDetection();
}

Results in:

System.Web.HttpException: Request is not available in this context

How can I detect whether the request is really available without wrapping these calls in an exception handler and taking action based on whether an exception is generated or not.

Looking at HttpContext in Reflector I see it has an internal bool HideRequestResponse field but it's internal so I can only get to it with reflection and that's fragile. Is there a more official/approved way to determine if it's ok to call HttpContext.Request?

This blog post about the subject says not to use HttpContext, but how, in generic library code, can you determine if it's ok to use HttpContext?

http://mvolo.com/iis7-integrated-mode-request-is-not-available-in-this-context-exception-in-applicationstart/

I'm using the work-around mentioned there which is to use Application_BeginRequest and an initialized field to only initialize once as part of BeginRequest, but that has to be done in every calling application whereas I'd prefer to make the library code more robust and handle this situation regardless of where it's called from.

Answer 1

I would refactor your code to this:

if (IsRequestAvailable())
{
    // do something with HttpContext.Current.Request...
}
else
{
    // do equivalent thing without HttpContext...
}

public Boolean IsRequestAvailable()
{
    if (HttpContext.Current == null)
        return false;

    try
    {
        if (HttpContext.Current.Request == null)
            return false;
    }
    catch (System.Web.HttpException ex)
    {
        #if DEBUG
            // Testing exception to a magic string not the best practice but
            // it works for this demo.
            if (ex.Message == "Request is not available in this context")
                return false;

            throw;
        #else
            return false;
        #endif
    }

    return true;
}

Your question asked not to use exception handling (I assume for performance reasons) and my answer does. However, by changing your code from using "If (HttpContext.Current != null && HttpContext.Current.Request != null)" to "If (IsRequestAvailable())" you only have one place to change the code when you find an answer how not to use exception handling.

Answer 2

I'm afraid the answer is that you can't get what you want - Microsoft sees this case as an 'exceptional circumstance' and so it will throw an exception.

You can use reflection as you describe in your answer but you don't want to and so are limited by the API that Microsoft have provided, for better or for worse.

If you do decide to use reflection, of note is the HttpApplication.InitInternal method which is what sets the HideRequestResponse flag.

Hope that helps. I would suggest you file a report with Microsoft Connect.

Answer 3

You should not even use Request (or Response) in the Application_Start since application could be started without a request. So in the future your application won't even run when other parts of framework stop providing the Request object.

If you want to just hack it temporarily, you could use Reflection (if you have above-medium trust) or catching an exception (even though you don't want to) and store the result in a static variable or possibly use a static HttpContext wrapper:

Also you could use HttpRuntime.UsingIntegratedPipeline.

So the best approach is remove the dependance of your classes on HttpContext when they are being initialized or not initalize them in appstart.

What is your reasoning to use Request in the app start anyway? For statistics? Or just telling the user he woke the application?

Edited with code to explain better:

public static class ContextWrapper
{
    public static HttpRequest Request
    {
        get
        {
            HttpContext context = HttpContext.Current;
            if (context == null) return null;

            if (HttpRuntime.UsingIntegratedPipeline)
            {
                try { return context.Request; }
                catch (HttpException e) { /* Consume or log e*/ return null; }
                // Do not use message comparison - .NET translates messages for multi-culture environments.
            }

            return context.Request;
        }
    }
}

And in code:

if (ContextWrapper.Request != null) //...

Or a user-controlled faster way:

public static class ContextWrapper2
{
    public static bool IsIis7IntegratedAppStart { get; set; }

    public static HttpRequest Request
    {
        get
        {
            if (ContextWrapper2.IsIis7IntegratedAppStart) return null;

            HttpContext context = HttpContext.Current;
            if (context == null) return null;

            return context.Request;
        }
    }
}

And in app start:

protected void Application_Start(object sender, EventArgs e)
{
    yourLibraryNamespace.ContextWrapper2.IsIis7IntegratedAppStart = true;
    //...
    yourLibraryNamespace.yourClass.Init();
    //...
    yourLibraryNamespace.ContextWrapper2.IsIis7IntegratedAppStart = false;
}

You could note this behaviour in your documentation and all should be well. AppStart-like context should be the only place where you get such an exception.

You could also implement IDisposable on a member and use it in appStart with the using statement so you do not forget to set IsIis7IntegratedAppStart = false.