router: add option to save matched route path

Fixes #139
Fixes #286

Co-authored-by: Julien Schmidt <git@julienschmidt.com>

Author: GeorgeMac

router.go

@@ -122,6 +122,25 @@ func ParamsFromContext(ctx context.Context) Params {
 	return p
 }
 
+type matchKey struct{}
+
+// MatchedRoutePathKey is the request context key under which the handler path
+// match is stored.
+var MatchedRoutePathKey = matchKey{}
+
+// MatchedRoutePathFromContext retrieves the matched route path from the context.
+func MatchedRoutePathFromContext(ctx context.Context) string {
+	p, _ := ctx.Value(MatchedRoutePathKey).(string)
+	return p
+}
+
+func saveMatchedRoutePathToContext(path string, handle Handle) Handle {
+	return func(w http.ResponseWriter, req *http.Request, ps Params) {
+		req = req.WithContext(context.WithValue(req.Context(), MatchedRoutePathKey, path))
+		handle(w, req, ps)
+	}
+}
+
 // Router is a http.Handler which can be used to dispatch requests to different
 // handler functions via configurable routes
 type Router struct {
@@ -130,6 +149,10 @@ type Router struct {
 	paramsPool sync.Pool
 	maxParams  uint16
 
+	// SaveMatchedRoutePathToContext when enabled adds the matched route path
+	// onto the http.Request context before invoking the handler
+	SaveMatchedRoutePathToContext bool
+
 	// Enables automatic redirection if the current route can't be matched but a
 	// handler for the path with (without) the trailing slash exists.
 	// For example if /foo/ is requested but a route only exists for /foo, the
@@ -268,6 +291,10 @@ func (r *Router) Handle(method, path string, handle Handle) {
 		panic("handle must not be nil")
 	}
 
+	if r.SaveMatchedRoutePathToContext {
+		handle = saveMatchedRoutePathToContext(path, handle)
+	}
+
 	if r.trees == nil {
 		r.trees = make(map[string]*node)
 	}

router_test.go

@@ -610,6 +610,32 @@ func TestRouterParamsFromContext(t *testing.T) {
 	}
 }
 
+func TestRouterMatchedRouteFromContext(t *testing.T) {
+	routed := false
+
+	handlerFunc := func(_ http.ResponseWriter, req *http.Request) {
+		// get params from request context
+		route := MatchedRoutePathFromContext(req.Context())
+
+		if route != "/user/:name" {
+			t.Fatalf("Wrong matched route: want /user/:name, got %q", route)
+		}
+
+		routed = true
+	}
+
+	router := New()
+	router.SaveMatchedRoutePathToContext = true
+	router.HandlerFunc(http.MethodGet, "/user/:name", handlerFunc)
+
+	w := new(mockResponseWriter)
+	r, _ := http.NewRequest(http.MethodGet, "/user/gopher", nil)
+	router.ServeHTTP(w, r)
+	if !routed {
+		t.Fatal("Routing failed!")
+	}
+}
+
 type mockFileSystem struct {
 	opened bool
 }