Handle OPTIONS HTTP requests correctly.

Fixes https://github.com/prometheus/prometheus/issues/1346

vendor/github.com/prometheus/common/route/route.go

@@ -75,6 +75,11 @@ func (r *Router) Get(path string, h http.HandlerFunc) {
 	r.rtr.GET(r.prefix+path, handle(h))
 }
 
+// Options registers a new OPTIONS route.
+func (r *Router) Options(path string, h http.HandlerFunc) {
+	r.rtr.OPTIONS(r.prefix+path, handle(h))
+}
+
 // Del registers a new DELETE route.
 func (r *Router) Del(path string, h http.HandlerFunc) {
 	r.rtr.DELETE(r.prefix+path, handle(h))

vendor/vendor.json

@@ -174,8 +174,8 @@
 		},
 		{
 			"path": "github.com/prometheus/common/route",
-			"revision": "4fdc91a58c9d3696b982e8a680f4997403132d44",
-			"revisionTime": "2015-10-26T12:04:34+01:00"
+			"revision": "14ca1097bbe21584194c15e391a9dab95ad42a59",
+			"revisionTime": "2016-01-25T23:57:51+01:00"
 		},
 		{
 			"path": "github.com/prometheus/procfs",

web/api/legacy/api.go

@@ -34,6 +34,12 @@ type API struct {
 
 // Register registers the handler for the various endpoints below /api.
 func (api *API) Register(router *route.Router) {
+	// List all the endpoints here instead of using a wildcard route because we
+	// would otherwise handle /api/v1 as well.
+	router.Options("/query", handle("options", api.Options))
+	router.Options("/query_range", handle("options", api.Options))
+	router.Options("/metrics", handle("options", api.Options))
+
 	router.Get("/query", handle("query", api.Query))
 	router.Get("/query_range", handle("query_range", api.QueryRange))
 	router.Get("/metrics", handle("metrics", api.Metrics))

web/api/legacy/query.go

@@ -31,7 +31,7 @@ import (
 // Enables cross-site script calls.
 func setAccessControlHeaders(w http.ResponseWriter) {
 	w.Header().Set("Access-Control-Allow-Headers", "Accept, Authorization, Content-Type, Origin")
-	w.Header().Set("Access-Control-Allow-Methods", "GET")
+	w.Header().Set("Access-Control-Allow-Methods", "GET, OPTIONS")
 	w.Header().Set("Access-Control-Allow-Origin", "*")
 	w.Header().Set("Access-Control-Expose-Headers", "Date")
 }
@@ -61,6 +61,12 @@ func parseDuration(d string) (time.Duration, error) {
 	return time.Duration(dFloat * float64(time.Second/time.Nanosecond)), nil
 }
 
+// Options handles OPTIONS requests to /api/... endpoints.
+func (api *API) Options(w http.ResponseWriter, r *http.Request) {
+	setAccessControlHeaders(w)
+	w.WriteHeader(http.StatusNoContent)
+}
+
 // Query handles the /api/query endpoint.
 func (api *API) Query(w http.ResponseWriter, r *http.Request) {
 	setAccessControlHeaders(w)

web/api/v1/api.go

@@ -38,6 +38,13 @@ const (
 	errorBadData            = "bad_data"
 )
 
+var corsHeaders = map[string]string{
+	"Access-Control-Allow-Headers":  "Accept, Authorization, Content-Type, Origin",
+	"Access-Control-Allow-Methods":  "GET, OPTIONS",
+	"Access-Control-Allow-Origin":   "*",
+	"Access-Control-Expose-Headers": "Date",
+}
+
 type apiError struct {
 	typ errorType
 	err error
@@ -56,10 +63,9 @@ type response struct {
 
 // Enables cross-site script calls.
 func setCORS(w http.ResponseWriter) {
-	w.Header().Set("Access-Control-Allow-Headers", "Accept, Authorization, Content-Type, Origin")
-	w.Header().Set("Access-Control-Allow-Methods", "GET")
-	w.Header().Set("Access-Control-Allow-Origin", "*")
-	w.Header().Set("Access-Control-Expose-Headers", "Date")
+	for h, v := range corsHeaders {
+		w.Header().Set(h, v)
+	}
 }
 
 type apiFunc func(r *http.Request) (interface{}, *apiError)
@@ -91,8 +97,10 @@ func (api *API) Register(r *route.Router) {
 			setCORS(w)
 			if data, err := f(r); err != nil {
 				respondError(w, err, data)
-			} else {
+			} else if data != nil {
 				respond(w, data)
+			} else {
+				w.WriteHeader(http.StatusNoContent)
 			}
 		})
 		return prometheus.InstrumentHandler(name, httputil.CompressionHandler{
@@ -100,6 +108,8 @@ func (api *API) Register(r *route.Router) {
 		})
 	}
 
+	r.Options("/*path", instr("options", api.options))
+
 	r.Get("/query", instr("query", api.query))
 	r.Get("/query_range", instr("query_range", api.queryRange))
 
@@ -114,6 +124,10 @@ type queryData struct {
 	Result     model.Value     `json:"result"`
 }
 
+func (api *API) options(r *http.Request) (interface{}, *apiError) {
+	return nil, nil
+}
+
 func (api *API) query(r *http.Request) (interface{}, *apiError) {
 	var ts model.Time
 	if t := r.FormValue("time"); t != "" {
@@ -255,7 +269,7 @@ func (api *API) dropSeries(r *http.Request) (interface{}, *apiError) {
 
 func respond(w http.ResponseWriter, data interface{}) {
 	w.Header().Set("Content-Type", "application/json")
-	w.WriteHeader(200)
+	w.WriteHeader(http.StatusOK)
 
 	b, err := json.Marshal(&response{
 		Status: statusSuccess,

web/api/v1/api_test.go

@@ -503,3 +503,32 @@ func TestParseDuration(t *testing.T) {
 		}
 	}
 }
+
+func TestOptionsMethod(t *testing.T) {
+	r := route.New()
+	api := &API{}
+	api.Register(r)
+
+	s := httptest.NewServer(r)
+	defer s.Close()
+
+	req, err := http.NewRequest("OPTIONS", s.URL+"/any_path", nil)
+	if err != nil {
+		t.Fatalf("Error creating OPTIONS request: %s", err)
+	}
+	client := &http.Client{}
+	resp, err := client.Do(req)
+	if err != nil {
+		t.Fatalf("Error executing OPTIONS request: %s", err)
+	}
+
+	if resp.StatusCode != http.StatusNoContent {
+		t.Fatalf("Expected status %d, got %d", http.StatusNoContent, resp.StatusCode)
+	}
+
+	for h, v := range corsHeaders {
+		if resp.Header.Get(h) != v {
+			t.Fatalf("Expected %q for header %q, got %q", v, h, resp.Header.Get(h))
+		}
+	}
+}