Native OPTIONS handling

Fixes  #98

router.go

diff --git a/router.go b/router.go
index 5d6c81c..f18a678 100644
--- a/router.go
+++ b/router.go
@@ -138,6 +138,10 @@
 	// handler.
 	HandleMethodNotAllowed bool
 
+	// If enabled, the router automatically replies to OPTIONS requests.
+	// Custom OPTIONS handlers take priority over automatic replies.
+	HandleOPTIONS bool
+
 	// Configurable http.Handler which is called when no matching route is
 	// found. If it is not set, http.NotFound is used.
 	NotFound http.Handler
@@ -167,6 +171,7 @@
 		RedirectTrailingSlash:  true,
 		RedirectFixedPath:      true,
 		HandleMethodNotAllowed: true,
+		HandleOPTIONS:          true,
 	}
 }
 
@@ -288,15 +293,35 @@
 	return nil, nil, false
 }
 
+func (r *Router) allowed(path, reqMethod string) (allow string) {
+	for method := range r.trees {
+		// Skip the requested method - we already tried this one
+		if method == reqMethod || method == "OPTIONS" {
+			continue
+		}
+
+		handle, _, _ := r.trees[method].getValue(path)
+		if handle != nil {
+			// add request method to list of allowed methods
+			if len(allow) == 0 {
+				allow = method
+			} else {
+				allow += ", " + method
+			}
+		}
+	}
+	return
+}
+
 // ServeHTTP makes the router implement the http.Handler interface.
 func (r *Router) ServeHTTP(w http.ResponseWriter, req *http.Request) {
 	if r.PanicHandler != nil {
 		defer r.recv(w, req)
 	}
 
-	if root := r.trees[req.Method]; root != nil {
-		path := req.URL.Path
+	path := req.URL.Path
 
+	if root := r.trees[req.Method]; root != nil {
 		if handle, ps, tsr := root.getValue(path); handle != nil {
 			handle(w, req, ps)
 			return
@@ -333,37 +358,46 @@
 		}
 	}
 
-	// Handle 405
-	if r.HandleMethodNotAllowed {
-		var allow string
-		for method := range r.trees {
-			// Skip the requested method - we already tried this one
-			if method == req.Method || method == "OPTIONS" {
-				continue
-			}
+	if req.Method == "OPTIONS" {
+		// Handle OPTIONS requests
+		if r.HandleOPTIONS {
+			var allow string
+			if path == "*" { // server OPTIONS
+				for method := range r.trees {
+					if method == "OPTIONS" {
+						continue
+					}
 
-			handle, _, _ := r.trees[method].getValue(req.URL.Path)
-			if handle != nil {
-				// add request method to list of allowed methods
-				if len(allow) == 0 {
-					allow = method
-				} else {
-					allow += ", " + method
+					// add request method to list of allowed methods
+					if len(allow) == 0 {
+						allow = method
+					} else {
+						allow += ", " + method
+					}
 				}
+			} else { // path OPTIONS
+				allow = r.allowed(path, req.Method)
+			}
+			if len(allow) > 0 {
+				w.Header().Set("Allow", allow)
+				return
 			}
 		}
-
-		if len(allow) > 0 {
-			w.Header().Set("Allow", allow)
-			if r.MethodNotAllowed != nil {
-				r.MethodNotAllowed.ServeHTTP(w, req)
-			} else {
-				http.Error(w,
-					http.StatusText(http.StatusMethodNotAllowed),
-					http.StatusMethodNotAllowed,
-				)
+	} else {
+		// Handle 405
+		if r.HandleMethodNotAllowed {
+			if allow := r.allowed(path, req.Method); len(allow) > 0 {
+				w.Header().Set("Allow", allow)
+				if r.MethodNotAllowed != nil {
+					r.MethodNotAllowed.ServeHTTP(w, req)
+				} else {
+					http.Error(w,
+						http.StatusText(http.StatusMethodNotAllowed),
+						http.StatusMethodNotAllowed,
+					)
+				}
+				return
 			}
-			return
 		}
 	}
 

router_test.go

diff --git a/router_test.go b/router_test.go
index 265bd55..db57740 100644
--- a/router_test.go
+++ b/router_test.go
@@ -216,6 +216,96 @@
 	}
 }
 
+func TestRouterOPTIONS(t *testing.T) {
+	handlerFunc := func(_ http.ResponseWriter, _ *http.Request, _ Params) {}
+
+	router := New()
+	router.POST("/path", handlerFunc)
+
+	// test not allowed
+	// * (server)
+	r, _ := http.NewRequest("OPTIONS", "*", nil)
+	w := httptest.NewRecorder()
+	router.ServeHTTP(w, r)
+	if !(w.Code == http.StatusOK) {
+		t.Errorf("OPTIONS handling failed: Code=%d, Header=%v", w.Code, w.Header())
+	} else if allow := w.Header().Get("Allow"); allow != "POST" {
+		t.Error("unexpected Allow header value: " + allow)
+	}
+
+	// path
+	r, _ = http.NewRequest("OPTIONS", "/path", nil)
+	w = httptest.NewRecorder()
+	router.ServeHTTP(w, r)
+	if !(w.Code == http.StatusOK) {
+		t.Errorf("OPTIONS handling failed: Code=%d, Header=%v", w.Code, w.Header())
+	} else if allow := w.Header().Get("Allow"); allow != "POST" {
+		t.Error("unexpected Allow header value: " + allow)
+	}
+
+	r, _ = http.NewRequest("OPTIONS", "/doesnotexist", nil)
+	w = httptest.NewRecorder()
+	router.ServeHTTP(w, r)
+	if !(w.Code == http.StatusNotFound) {
+		t.Errorf("OPTIONS handling failed: Code=%d, Header=%v", w.Code, w.Header())
+	}
+
+	// add another method
+	router.GET("/path", handlerFunc)
+
+	// test again
+	// * (server)
+	r, _ = http.NewRequest("OPTIONS", "*", nil)
+	w = httptest.NewRecorder()
+	router.ServeHTTP(w, r)
+	if !(w.Code == http.StatusOK) {
+		t.Errorf("OPTIONS handling failed: Code=%d, Header=%v", w.Code, w.Header())
+	} else if allow := w.Header().Get("Allow"); allow != "POST, GET" && allow != "GET, POST" {
+		t.Error("unexpected Allow header value: " + allow)
+	}
+
+	// path
+	r, _ = http.NewRequest("OPTIONS", "/path", nil)
+	w = httptest.NewRecorder()
+	router.ServeHTTP(w, r)
+	if !(w.Code == http.StatusOK) {
+		t.Errorf("OPTIONS handling failed: Code=%d, Header=%v", w.Code, w.Header())
+	} else if allow := w.Header().Get("Allow"); allow != "POST, GET" && allow != "GET, POST" {
+		t.Error("unexpected Allow header value: " + allow)
+	}
+
+	// custom handler
+	var custom bool
+	router.OPTIONS("/path", func(w http.ResponseWriter, r *http.Request, _ Params) {
+		custom = true
+	})
+
+	// test again
+	// * (server)
+	r, _ = http.NewRequest("OPTIONS", "*", nil)
+	w = httptest.NewRecorder()
+	router.ServeHTTP(w, r)
+	if !(w.Code == http.StatusOK) {
+		t.Errorf("OPTIONS handling failed: Code=%d, Header=%v", w.Code, w.Header())
+	} else if allow := w.Header().Get("Allow"); allow != "POST, GET" && allow != "GET, POST" {
+		t.Error("unexpected Allow header value: " + allow)
+	}
+	if custom {
+		t.Error("custom handler called on *")
+	}
+
+	// path
+	r, _ = http.NewRequest("OPTIONS", "/path", nil)
+	w = httptest.NewRecorder()
+	router.ServeHTTP(w, r)
+	if !(w.Code == http.StatusOK) {
+		t.Errorf("OPTIONS handling failed: Code=%d, Header=%v", w.Code, w.Header())
+	}
+	if !custom {
+		t.Error("custom handler not called")
+	}
+}
+
 func TestRouterNotAllowed(t *testing.T) {
 	handlerFunc := func(_ http.ResponseWriter, _ *http.Request, _ Params) {}