4 files changed, 90 insertions, 23 deletions
diff --git a/pkg/instance/handler.go b/pkg/instance/handler.go
index f2bc621..95d90a8 100644
--- a/pkg/instance/handler.go
+++ b/pkg/instance/handler.go
@@ -41,9 +41,9 @@ func (a Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	ctx, cancel := context.WithDeadline(r.Context(), now.Add(a.Instance.Deadline))
 	defer cancel()
 
-	if r.Method != a.Method {
+	statusCode = a.verifyMethod(w, r)
+	if statusCode != 0 {
 		glog.Warningf("%s/%s: got HTTP %s, wanted HTTP %s", a.Instance.Prefix, string(a.Endpoint), r.Method, a.Method)
-		http.Error(w, "", http.StatusMethodNotAllowed)
 		return
 	}
 
@@ -54,6 +54,23 @@ func (a Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	}
 }
 
+// verifyMethod checks that an appropriate HTTP method is used.  Error handling
+// is based on RFC 7231, see Sections 6.5.5 (Status 405) and 6.5.1 (Status 400).
+func (h *Handler) verifyMethod(w http.ResponseWriter, r *http.Request) int {
+	if h.Method == r.Method {
+		return 0
+	}
+
+	code := http.StatusBadRequest
+	if ok := h.Instance.checkHTTPMethod(r.Method); ok {
+		w.Header().Set("Allow", h.Method)
+		code = http.StatusMethodNotAllowed
+	}
+
+	http.Error(w, fmt.Sprintf("error=%s", http.StatusText(code)), code)
+	return code
+}
+
 func addLeaf(ctx context.Context, i *Instance, w http.ResponseWriter, r *http.Request) (int, error) {
 	glog.V(3).Info("handling add-entry request")
 	req, err := i.leafRequestFromHTTP(ctx, r)
diff --git a/pkg/instance/handler_test.go b/pkg/instance/handler_test.go
index 8a48860..05388fa 100644
--- a/pkg/instance/handler_test.go
+++ b/pkg/instance/handler_test.go
@@ -76,28 +76,50 @@ func TestHandlers(t *testing.T) {
 	}
 }
 
-// TestServeHTTP checks that invalid HTTP methods are rejected
-func TestServeHTTP(t *testing.T) {
-	i := &Instance{
-		Config: testConfig,
-	}
-	for _, handler := range i.Handlers() {
-		// Prepare invalid HTTP request
-		method := http.MethodPost
-		if method == handler.Method {
-			method = http.MethodGet
-		}
-		url := handler.Endpoint.Path("http://example.com", i.Prefix)
-		req, err := http.NewRequest(method, url, nil)
-		if err != nil {
-			t.Fatalf("must create HTTP request: %v", err)
-		}
-		w := httptest.NewRecorder()
+func TestVerifyMethod(t *testing.T) {
+	badMethod := http.MethodHead
+	instance := Instance{Config: testConfig}
+	for _, handler := range instance.Handlers() {
+		for _, method := range []string{
+			http.MethodGet,
+			http.MethodPost,
+			badMethod,
+		} {
+			url := handler.Endpoint.Path("http://log.example.com", instance.Prefix)
+			req, err := http.NewRequest(method, url, nil)
+			if err != nil {
+				t.Fatalf("must create HTTP request: %v", err)
+			}
 
-		// Check that it is rejected
-		handler.ServeHTTP(w, req)
-		if got, want := w.Code, http.StatusMethodNotAllowed; got != want {
-			t.Errorf("got HTTP code %v but wanted %v for endpoint %q", got, want, handler.Endpoint)
+			w := httptest.NewRecorder()
+			code := handler.verifyMethod(w, req)
+			if got, want := code == 0, handler.Method == method; got != want {
+				t.Errorf("%s %s: got %v but wanted %v: %v", method, url, got, want, err)
+				continue
+			}
+			if code == 0 {
+				continue
+			}
+
+			if method == badMethod {
+				if got, want := code, http.StatusBadRequest; got != want {
+					t.Errorf("%s %s: got status %d, wanted %d", method, url, got, want)
+				}
+				if _, ok := w.Header()["Allow"]; ok {
+					t.Errorf("%s %s: got Allow header, wanted none", method, url)
+				}
+				continue
+			}
+
+			if got, want := code, http.StatusMethodNotAllowed; got != want {
+				t.Errorf("%s %s: got status %d, wanted %d", method, url, got, want)
+			} else if methods, ok := w.Header()["Allow"]; !ok {
+				t.Errorf("%s %s: got no allow header, expected one", method, url)
+			} else if got, want := len(methods), 1; got != want {
+				t.Errorf("%s %s: got %d allowed method(s), wanted %d", method, url, got, want)
+			} else if got, want := methods[0], handler.Method; got != want {
+				t.Errorf("%s %s: got allowed method %s, wanted %s", method, url, got, want)
+			}
 		}
 	}
 }
diff --git a/pkg/instance/instance.go b/pkg/instance/instance.go
index 7ade955..f62922e 100644
--- a/pkg/instance/instance.go
+++ b/pkg/instance/instance.go
@@ -51,6 +51,11 @@ func (i *Instance) Handlers() []Handler {
 	}
 }
 
+// checkHTTPMethod checks if an HTTP method is supported
+func (i *Instance) checkHTTPMethod(m string) bool {
+	return m == http.MethodGet || m == http.MethodPost
+}
+
 func (i *Instance) leafRequestFromHTTP(ctx context.Context, r *http.Request) (*requests.Leaf, error) {
 	var req requests.Leaf
 	if err := req.FromASCII(r.Body); err != nil {
diff --git a/pkg/instance/instance_test.go b/pkg/instance/instance_test.go
new file mode 100644
index 0000000..00d996d
--- /dev/null
+++ b/pkg/instance/instance_test.go
@@ -0,0 +1,23 @@
+package instance
+
+import (
+	"net/http"
+	"testing"
+)
+
+func CheckHTTPMethod(t *testing.T) {
+	var instance Instance
+	for _, table := range []struct {
+		method string
+		wantOK bool
+	}{
+		{wantOK: false, method: http.MethodHead},
+		{wantOK: true, method: http.MethodPost},
+		{wantOK: true, method: http.MethodGet},
+	} {
+		ok := instance.checkHTTPMethod(table.method)
+		if got, want := ok, table.wantOK; got != want {
+			t.Errorf("%s: got %v but wanted %v", table.method, got, want)
+		}
+	}
+}