Not possible to set the span operation name to the matched route

[krosen040]

We would like to be able to set the span operation name to the matched gin route, however currently this is difficult. For example, if there is a route /user/:name, and a request is made to /user/foo, we would like to set the span name to the former.

The default span operation name is HTTP + method, e.g. HTTP GET. It's possible to override this default using the OperationNameFunc option, which gives access to the http.Request object, however I don't think that can be used to get the matched route (it's obviously possible to get the path, but that could contain path parameters, which we want to avoid).

As a side note, the gorilla/mux Opentracing middleware implementation defaults to the matched route as the operation name, see https://github.com/opentracing-contrib/go-gorilla/blob/3ee496ae11d5bebfd34703cee4efa29e0439a33d/gorilla/server.go#L35, which I think makes more sense than just the HTTP method used.

[stuart-mclaren-hpe]

Is it possible to get from the request -> context -> FullPath()?

gin-gonic/gin#748
gin-gonic/gin#1826

[krosen040]

FullPath() is what we want to use, however the Context() method on http.Request gives context.Context, not gin.Context, so it's not possible to do so.

[stuart-mclaren-hpe]

Ok, I understand.

Are you thinking about proposing a patch?

[krosen040]

I'd like to, but I'm not sure what that would look like and still keep everything backwards compatible.

[stuart-mclaren-hpe]

Yeah, I agree backwards compatible is important.

A simple option would be to add a gin.fullpath Tag, the same way ext.HTTPUrl.Set sets the http.url Tag -- for example on line 88. But I'm not sure that's exactly what you want.

It would be possible to put gin.fullpath in the request context so it would be available in opNameFunc, eg via a function such as ginhttp.GetFullpath(r). But I'm not keen on duplicating stuff that's already in the gin context that the request context is a subset of; and it also feels a bit "loose".

We could potentially add a new, "extended" flavour of OperationNameFunc, eg OperationNameExtFunc which would have access to a limited set of attributes (eg fullpath) in addition to the request object.

func OperationNameExtFunc(f func(r *http.Request, attrs *Attributes) string) MWOption {

The original function could be left for backwards compatibility.
What do you think?