http: add allow func

For further extendability

etcdserver/etcdhttp/http.go

@@ -204,7 +204,7 @@ func (h Handler) serveKeys(ctx context.Context, w http.ResponseWriter, r *http.R
 // TODO: rethink the format of machine list because it is not json format.
 func (h Handler) serveMachines(w http.ResponseWriter, r *http.Request) {
 	if r.Method != "GET" && r.Method != "HEAD" {
-		w.WriteHeader(http.StatusMethodNotAllowed)
+		allow(w, "GET", "HEAD")
 		return
 	}
 	urls := make([]string, 0)
@@ -349,3 +349,9 @@ func waitForEvent(ctx context.Context, w http.ResponseWriter, wa store.Watcher)
 		return nil, ctx.Err()
 	}
 }
+
+// allow writes response for the case that Method Not Allowed
+func allow(w http.ResponseWriter, m ...string) {
+	w.Header().Set("Allow", strings.Join(m, ","))
+	http.Error(w, "Method Not Allowed", http.StatusMethodNotAllowed)
+}

etcdserver/etcdhttp/http_test.go

@@ -363,7 +363,7 @@ func TestV2MachinesEndpoint(t *testing.T) {
 	defer s.Close()
 
 	for _, tt := range tests {
-		req, _ := http.NewRequest(tt.method, s.URL + machinesPrefix, nil)
+		req, _ := http.NewRequest(tt.method, s.URL+machinesPrefix, nil)
 		resp, err := http.DefaultClient.Do(req)
 		if err != nil {
 			t.Fatal(err)
@@ -385,7 +385,7 @@ func TestServeMachines(t *testing.T) {
 	h.serveMachines(writer, req)
 	w := "http://localhost:8080, http://localhost:8081, http://localhost:8082"
 	if g := writer.Body.String(); g != w {
-		t.Errorf("data = %s, want %s", g, w)
+		t.Errorf("body = %s, want %s", g, w)
 	}
 	if writer.Code != http.StatusOK {
 		t.Errorf("header = %d, want %d", writer.Code, http.StatusOK)