Implementing IRequestIdentifierFeature

[Praburaj]

Using code from HttpListener codebase to generate trace ids just to be consistent with other code.

Depends on aspnet/HttpAbstractions#210.

@Tratcher @GrabYourPitchforks

[Eilon]

What am I missing here? Why unsafe pointer arithmetic?

[Tratcher]

HttpListener has this exact code and somebody was asking about it the other day. Nobody knows.

[Eilon]

I honestly don't even understand it. Why the 1 +? But ultimately why not just grab the RequestId directly?

[Praburaj]

unsafe is because it has memory pointer operations. I heard from @GrabYourPitchforks that the RequestId is a memory address and traditionally IIS and HttpListener has been overlaying this memory address on a base Guid instead of generating a random Guid for every request (as Guid generation is expensive and it can be in such critical code paths).

IIS code : http://wincode//View.aspx?File=%2F%2Fdepot%2Ffbl_srv2_iis%2Finetsrv%2Fiis%2Fiisrearc%2Fiis70%2Fcore%2Fw3context.cxx%236&SDPort=inetsrvdepot.sys-ntgroup.ntdev.microsoft.com%3A2009&Catalog=fbl_srv2_iis%28dev%29&Query=gettraceactivityid
HttpListener code: http://referencesource.microsoft.com/#System/net/System/Net/HttpListenerRequest.cs,333

[Eilon]

So this is to "share" the memory with IIS for the same GUID? Copying a few bytes is really that expensive?

[Eilon]

Yeah I think that's fine. I just don't understand why it's doing crazy pointer math instead of just copying the value. The value doesn't change during the request, right?

[Eilon]

Basically my question is, why isn't the code this:

return (Guid)Request.RequestId;

(Or whatever would compile - I don't know the types.)

[Praburaj]

@GrabYourPitchforks - I didn't see a GUID being part of the request structure HTTP_REQUEST_V2 https://github.com/aspnet/WebListener/blob/fc6b855f422a8039e39d757e66429fa6845f281e/src/Microsoft.Net.Http.Server/NativeInterop/UnsafeNativeMethods.cs#L657 and https://github.com/aspnet/WebListener/blob/fc6b855f422a8039e39d757e66429fa6845f281e/src/Microsoft.Net.Http.Server/NativeInterop/UnsafeNativeMethods.cs#L634 itself. This looks like the data from native layer. Is it possible to to get the GUID from HTTP.SYS?

[GrabYourPitchforks]

HTTP.SYS doesn't surface the tracing id as a first-class value. You can calculate it from the request id by following the same steps as in the IIS code you linked to above.

[Praburaj]

@Eilon @GrabYourPitchforks Updated the PR by using the same base guid as HTTP.SYS and logic similar to IIS in generating the tracing id.

[Praburaj]

@Eilon @GrabYourPitchforks is this change good to go! Could you sign off if its good?

[Eilon]

Looks to me.