Issue

HTTP Status Code Tag incorrect on root span

The issue occurs when the ASP.NET application calls System.Web.HttpServerUtility.TransferRequest. When this happens, the end-user of the site does not see any redirects, but internally IIS initiates a second request through the Integrated pipeline. This means there are two aspnet.request spans: one for the initial request, and one for the transferred request. While the parent relationship is correct, the root span is assigned a http.status_code tag of 200, whereas the inner span has the correct code (what the end-user sees in the HTTP response).

MVC scope not closed on error

There is also a second issue that was discovered while testing this fix: when there is an error in the processing of an MVC action, the AspNetMvc integration returns from the System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeAction method with Tracer.ActiveScope still returning the MVC span. This leads to new spans becoming children of the MVC span up until the ASP.NET pipeline signals the end of the request and we close the MVC span.

Fix

HTTP Status Code Tag incorrect on root span

The order of the HttpModule callbacks for the two requests (initial and transferred) is as follows:

- initial.BeginRequest
- transferred.BeginRequest
- transferred.EndRequest
- initial.EndRequest

The solution for the http.status_code tag is to modify the EndRequest callback to only set http-related tags once. When transferred.EndRequest is handled, we take the correct HTTP status code and apply it to both its span and the root span. Then, when initial.EndRequest is called, we see that the HTTP status code tag has already been set so we don't update them.

This commit shows the snapshot changes from applying the fix: b122aaf

Note: This solution seemed like the best solution because the HttpContext is not shared between the two requests, so the only way to share information between the two requests is with existing objects or with AsyncLocal storage.

MVC scope not closed on error

The solution for the MVC scope issue is to reset the active scope to its parent before leaving the AspNetMvc integration. While this could be done several ways, my approach is to overwrite the FinishOnClose bool and set it to false so we can close the Scope before exiting the method. The span will remain unfinished and will be finished when the request ends and we set the correct HTTP tags.

This commit shows the snapshot changes from applying the fix, which makes the second aspnet.request span a child of the first aspnet.request span, NOT the first aspnet-mvc.request span: ecf88d8

Testing

Tests are added to ensure that the root-span's http.status_code tag matches the HTTP response in the following scenarios:

• AspNetMvc4
• AspNetMvc5
• WebApi2 (ASP.NET only, not OWIN)