API to return matched router path

[jehiah]

I would like to propose an API that returns the exact router path that's been matched. There are multiple situations where having the router path available would be beneficial like logging, rate limiting, etc because it will have less cardinality than the full URL with dynamic parameters.

Given the following example

r = httprouter.New()
r.GET("/user/:name", func(w http.ResponseWriter, r *http.Request, _ httprouter.Params) {
    fmt.Println("no way to get '/user/:name' here")
})

I'd like to store the state of the full route being matched in each node of the match tree and add a router.LookupRoute() (to avoid a backwards incompatible change to Lookup()) so that you can re-parse the request path and find which route matched. I'm open to other naming suggestions, or if you'd rather make a breaking change to Lookup and add the return value there.

r = httprouter.New()
r.GET("/user/:name", func(w http.ResponseWriter, r *http.Request, _ httprouter.Params) {
    _, matchedRoute, _, _ := r.LookupRoute(r.Method, r.URL.Path)
    fmt.Printf("matched %q for %q", matchedRoute, r.URL.Path)
})

[jharlap]

My $0.02: Love the idea, and have a totally hack logger in place that this would make a million times better, but maybe it could just be a new method on Params that just returns a string?

[jehiah]

@jharlap because Params is an array I don't see how we can add this context there in a backwards compatible fashion.

[kpurdon]

missmatc > mismatch

[jehiah]

you know me. always trying to sneak in some typos.

[kpurdon]

@julienschmidt hoping to get some feedback on this! Thanks!

[apriendeau]

@julienschmidt This is really a much needed feature. Can you please provide some sort of feedback here?

[laplaceon]

I have a fork with this feature here: https://github.com/laplaceon/httprouter. You can see it in action here: https://github.com/laplaceon/polyhedron.

[alexanderheldt]

@julienschmidt Could you please take a look at this again? Having this would be really great when measuring endpoints with prometheus. 🙏

[GeorgeMac]

I only saw this PR after I started to open mine, but I took a slightly different stab at this as well. Mine doesn't effect the Lookup method signature and exposes the route to your handlers through the request context.
If anyone is interested: #286
My usecase is enriching my trace data with router path matches in middleware.

[jehiah]

@julienschmidt do you have any feedback on this or #286?

I'd be happy to take any design or implementation feedback and update this PR. This has been very useful for me since i've opened this PR a few years ago and i'd love to contribute this upstream.

[julienschmidt]

I gave some feedback over here: #286 (comment)