Adds the Allow header on 405 response (#776)

context.go

@@ -76,6 +76,7 @@ type Context struct {
 
 	// methodNotAllowed hint
 	methodNotAllowed bool
+	methodsAllowed   []methodTyp // allowed methods in case of a 405
 }
 
 // Reset a routing context to its initial state.

mux.go

@@ -378,11 +378,11 @@ func (mx *Mux) NotFoundHandler() http.HandlerFunc {
 
 // MethodNotAllowedHandler returns the default Mux 405 responder whenever
 // a method cannot be resolved for a route.
-func (mx *Mux) MethodNotAllowedHandler() http.HandlerFunc {
+func (mx *Mux) MethodNotAllowedHandler(methodsAllowed ...methodTyp) http.HandlerFunc {
 	if mx.methodNotAllowedHandler != nil {
 		return mx.methodNotAllowedHandler
 	}
-	return methodNotAllowedHandler
+	return methodNotAllowedHandler(methodsAllowed...)
 }
 
 // handle registers a http.Handler in the routing tree for a particular http method
@@ -445,7 +445,7 @@ func (mx *Mux) routeHTTP(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	if rctx.methodNotAllowed {
-		mx.MethodNotAllowedHandler().ServeHTTP(w, r)
+		mx.MethodNotAllowedHandler(rctx.methodsAllowed...).ServeHTTP(w, r)
 	} else {
 		mx.NotFoundHandler().ServeHTTP(w, r)
 	}
@@ -480,8 +480,14 @@ func (mx *Mux) updateRouteHandler() {
 }
 
 // methodNotAllowedHandler is a helper function to respond with a 405,
-// method not allowed.
-func methodNotAllowedHandler(w http.ResponseWriter, r *http.Request) {
-	w.WriteHeader(405)
-	w.Write(nil)
+// method not allowed. It sets the Allow header with the list of allowed
+// methods for the route.
+func methodNotAllowedHandler(methodsAllowed ...methodTyp) func(w http.ResponseWriter, r *http.Request) {
+	return func(w http.ResponseWriter, r *http.Request) {
+		for _, m := range methodsAllowed {
+			w.Header().Add("Allow", reverseMethodMap[m])
+		}
+		w.WriteHeader(405)
+		w.Write(nil)
+	}
 }

mux_test.go

@@ -392,6 +392,43 @@ func TestMuxNestedNotFound(t *testing.T) {
 	}
 }
 
+func TestMethodNotAllowed(t *testing.T) {
+	r := NewRouter()
+
+	r.Get("/hi", func(w http.ResponseWriter, r *http.Request) {
+		w.Write([]byte("hi, get"))
+	})
+
+	r.Head("/hi", func(w http.ResponseWriter, r *http.Request) {
+		w.Write([]byte("hi, head"))
+	})
+
+	ts := httptest.NewServer(r)
+	defer ts.Close()
+
+	t.Run("Registered Method", func(t *testing.T) {
+		resp, _ := testRequest(t, ts, "GET", "/hi", nil)
+		if resp.StatusCode != 200 {
+			t.Fatal(resp.Status)
+		}
+		if resp.Header.Values("Allow") != nil {
+			t.Fatal("allow should be empty when method is registered")
+		}
+	})
+
+	t.Run("Unregistered Method", func(t *testing.T) {
+		resp, _ := testRequest(t, ts, "POST", "/hi", nil)
+		if resp.StatusCode != 405 {
+			t.Fatal(resp.Status)
+		}
+		allowedMethods := resp.Header.Values("Allow")
+		if len(allowedMethods) != 2 || allowedMethods[0] != "GET" || allowedMethods[1] != "HEAD" {
+			t.Fatal("Allow header should contain 2 headers: GET, HEAD. Received: ", allowedMethods)
+
+		}
+	})
+}
+
 func TestMuxNestedMethodNotAllowed(t *testing.T) {
 	r := NewRouter()
 	r.Get("/root", func(w http.ResponseWriter, r *http.Request) {
@@ -1771,6 +1808,7 @@ func BenchmarkMux(b *testing.B) {
 	mx := NewRouter()
 	mx.Get("/", h1)
 	mx.Get("/hi", h2)
+	mx.Post("/hi-post", h2) // used to benchmark 405 responses
 	mx.Get("/sup/{id}/and/{this}", h3)
 	mx.Get("/sup/{id}/{bar:foo}/{this}", h3)
 
@@ -1787,6 +1825,7 @@ func BenchmarkMux(b *testing.B) {
 	routes := []string{
 		"/",
 		"/hi",
+		"/hi-post",
 		"/sup/123/and/this",
 		"/sup/123/foo/this",
 		"/sharing/z/aBc",                 // subrouter-1

tree.go

@@ -43,6 +43,18 @@ var methodMap = map[string]methodTyp{
 	http.MethodTrace:   mTRACE,
 }
 
+var reverseMethodMap = map[methodTyp]string{
+	mCONNECT: http.MethodConnect,
+	mDELETE:  http.MethodDelete,
+	mGET:     http.MethodGet,
+	mHEAD:    http.MethodHead,
+	mOPTIONS: http.MethodOptions,
+	mPATCH:   http.MethodPatch,
+	mPOST:    http.MethodPost,
+	mPUT:     http.MethodPut,
+	mTRACE:   http.MethodTrace,
+}
+
 // RegisterMethod adds support for custom HTTP method handlers, available
 // via Router#Method and Router#MethodFunc
 func RegisterMethod(method string) {
@@ -454,6 +466,13 @@ func (n *node) findRoute(rctx *Context, method methodTyp, path string) *node {
 							return xn
 						}
 
+						for endpoints := range xn.endpoints {
+							if endpoints == mALL || endpoints == mSTUB {
+								continue
+							}
+							rctx.methodsAllowed = append(rctx.methodsAllowed, endpoints)
+						}
+
 						// flag that the routing context found a route, but not a corresponding
 						// supported method
 						rctx.methodNotAllowed = true
@@ -493,6 +512,13 @@ func (n *node) findRoute(rctx *Context, method methodTyp, path string) *node {
 					return xn
 				}
 
+				for endpoints := range xn.endpoints {
+					if endpoints == mALL || endpoints == mSTUB {
+						continue
+					}
+					rctx.methodsAllowed = append(rctx.methodsAllowed, endpoints)
+				}
+
 				// flag that the routing context found a route, but not a corresponding
 				// supported method
 				rctx.methodNotAllowed = true