perf: optionally omit the Route from the request context

Optionally save 3 allocations worth 448B per request with no vars.

```
$ go test -benchmem -benchtime 5000000x -bench BenchmarkMuxSimple
goos: linux
goarch: amd64
pkg: github.com/gorilla/mux
cpu: Intel(R) Core(TM) i7-8550U CPU @ 1.80GHz
BenchmarkMuxSimple/default-8                             5000000               349.3 ns/op           496 B/op          4 allocs/op
BenchmarkMuxSimple/omit_route_from_ctx-8                 5000000               157.8 ns/op            48 B/op          1 allocs/op
PASS
ok      github.com/gorilla/mux  2.556s

$ go test -benchmem -benchtime 5000000x -bench BenchmarkMuxSimple
goos: linux
goarch: amd64
pkg: github.com/gorilla/mux
cpu: Intel(R) Core(TM) i7-8550U CPU @ 1.80GHz
BenchmarkMuxSimple/default-8                             5000000               354.7 ns/op           496 B/op          4 allocs/op
BenchmarkMuxSimple/omit_route_from_ctx-8                 5000000               160.8 ns/op            48 B/op          1 allocs/op
PASS
ok      github.com/gorilla/mux  2.602s

$ go test -benchmem -benchtime 5000000x -bench BenchmarkMuxSimple
goos: linux
goarch: amd64
pkg: github.com/gorilla/mux
cpu: Intel(R) Core(TM) i7-8550U CPU @ 1.80GHz
BenchmarkMuxSimple/default-8                             5000000               376.4 ns/op           496 B/op          4 allocs/op
BenchmarkMuxSimple/omit_route_from_ctx-8                 5000000               168.1 ns/op            48 B/op          1 allocs/op
PASS
ok      github.com/gorilla/mux  2.745s
```

```
$ go test -benchmem -benchtime 5000000x -bench BenchmarkPopulateContext
goos: linux
goarch: amd64
pkg: github.com/gorilla/mux
cpu: Intel(R) Core(TM) i7-8550U CPU @ 1.80GHz
BenchmarkPopulateContext/no_populated_vars-8             5000000               381.6 ns/op           496 B/op          4 allocs/op
BenchmarkPopulateContext/empty_var-8                     5000000               913.6 ns/op           928 B/op          9 allocs/op
BenchmarkPopulateContext/populated_vars-8                5000000               914.0 ns/op           912 B/op          8 allocs/op
BenchmarkPopulateContext/omit_route_/static-8            5000000               168.6 ns/op            48 B/op          1 allocs/op
BenchmarkPopulateContext/omit_route_/dynamic-8           5000000               827.4 ns/op           880 B/op          8 allocs/op
PASS
ok      github.com/gorilla/mux  16.049s
```

Signed-off-by: Jakob Ackermann <das7pad@outlook.com>

bench_test.go

@@ -26,11 +26,30 @@ func BenchmarkMuxSimple(b *testing.B) {
 	handler := func(w http.ResponseWriter, r *http.Request) {}
 	router.HandleFunc("/status", handler)
 
-	request, _ := http.NewRequest("GET", "/status", nil)
-	b.ReportAllocs()
-	b.ResetTimer()
-	for i := 0; i < b.N; i++ {
-		router.ServeHTTP(nil, request)
+	testCases := []struct {
+		name                 string
+		omitRouteFromContext bool
+	}{
+		{
+			name:                 "default",
+			omitRouteFromContext: false,
+		},
+		{
+			name:                 "omit route from ctx",
+			omitRouteFromContext: true,
+		},
+	}
+	for _, tc := range testCases {
+		b.Run(tc.name, func(b *testing.B) {
+			router.OmitRouteFromContext(tc.omitRouteFromContext)
+
+			request, _ := http.NewRequest("GET", "/status", nil)
+			b.ReportAllocs()
+			b.ResetTimer()
+			for i := 0; i < b.N; i++ {
+				router.ServeHTTP(nil, request)
+			}
+		})
 	}
 }
 

mux.go

@@ -85,6 +85,9 @@ type routeConf struct {
 	// will not redirect
 	skipClean bool
 
+	// If true, the http.Request context will not contain the Route.
+	omitRouteFromContext bool
+
 	// Manager for the variables from host and path.
 	regexp routeRegexpGroup
 
@@ -190,7 +193,14 @@ func (r *Router) ServeHTTP(w http.ResponseWriter, req *http.Request) {
 	var handler http.Handler
 	if r.Match(req, &match) {
 		handler = match.Handler
-		req = requestWithRouteAndVars(req, match.Route, match.Vars)
+		if handler == nil {
+			// The default handlers do not make use of the context values.
+		} else if r.omitRouteFromContext {
+			// Only populate the match vars (if any) into the context.
+			req = requestWithVars(req, match.Vars)
+		} else {
+			req = requestWithRouteAndVars(req, match.Route, match.Vars)
+		}
 	}
 
 	if handler == nil && match.MatchErr == ErrMethodMismatch {
@@ -252,6 +262,14 @@ func (r *Router) SkipClean(value bool) *Router {
 	return r
 }
 
+// OmitRouteFromContext defines the behavior of omitting the Route from the
+//   http.Request context.
+// CurrentRoute will yield nil with this option.
+func (r *Router) OmitRouteFromContext(value bool) *Router {
+	r.omitRouteFromContext = value
+	return r
+}
+
 // UseEncodedPath tells the router to match the encoded original path
 // to the routes.
 // For eg. "/path/foo%2Fbar/to" will match the path "/path/{var}/to".

mux_test.go

@@ -2914,18 +2914,20 @@ func TestGetVarNames(t *testing.T) {
 }
 
 func getPopulateContextTestCases() []struct {
-	name             string
-	path             string
-	wantVar          string
-	wantStaticRoute  bool
-	wantDynamicRoute bool
+	name                 string
+	path                 string
+	omitRouteFromContext bool
+	wantVar              string
+	wantStaticRoute      bool
+	wantDynamicRoute     bool
 } {
 	return []struct {
-		name             string
-		path             string
-		wantVar          string
-		wantStaticRoute  bool
-		wantDynamicRoute bool
+		name                 string
+		path                 string
+		omitRouteFromContext bool
+		wantVar              string
+		wantStaticRoute      bool
+		wantDynamicRoute     bool
 	}{
 		{
 			name:            "no populated vars",
@@ -2938,12 +2940,27 @@ func getPopulateContextTestCases() []struct {
 			path:             "/dynamic/",
 			wantVar:          "",
 			wantDynamicRoute: true,
-		}, {
+		},
+		{
 			name:             "populated vars",
 			path:             "/dynamic/foo",
 			wantVar:          "foo",
 			wantDynamicRoute: true,
 		},
+		{
+			name:                 "omit route /static",
+			path:                 "/static",
+			omitRouteFromContext: true,
+			wantVar:              "",
+			wantStaticRoute:      false,
+		},
+		{
+			name:                 "omit route /dynamic",
+			path:                 "/dynamic/",
+			omitRouteFromContext: true,
+			wantVar:              "",
+			wantDynamicRoute:     false,
+		},
 	}
 }
 
@@ -2953,6 +2970,7 @@ func TestPopulateContext(t *testing.T) {
 		t.Run(tc.name, func(t *testing.T) {
 			matched := false
 			r := NewRouter()
+			r.OmitRouteFromContext(tc.omitRouteFromContext)
 			var static *Route
 			var dynamic *Route
 			fn := func(w http.ResponseWriter, r *http.Request) {
@@ -2996,6 +3014,7 @@ func BenchmarkPopulateContext(b *testing.B) {
 		b.Run(tc.name, func(b *testing.B) {
 			matched := false
 			r := NewRouter()
+			r.OmitRouteFromContext(tc.omitRouteFromContext)
 			fn := func(w http.ResponseWriter, r *http.Request) {
 				matched = true
 				w.WriteHeader(http.StatusNoContent)