transport: Make error-handling for bad HTTP method consistent between HTTP/2 server transport and handler server transport (#6989)

Author: jhump

internal/transport/handler_server.go

@@ -51,14 +51,10 @@ import (
 // inside an http.Handler, or writes an HTTP error to w and returns an error.
 // It requires that the http Server supports HTTP/2.
 func NewServerHandlerTransport(w http.ResponseWriter, r *http.Request, stats []stats.Handler) (ServerTransport, error) {
-	if r.ProtoMajor != 2 {
-		msg := "gRPC requires HTTP/2"
-		http.Error(w, msg, http.StatusBadRequest)
-		return nil, errors.New(msg)
-	}
-	if r.Method != "POST" {
+	if r.Method != http.MethodPost {
+		w.Header().Set("Allow", http.MethodPost)
 		msg := fmt.Sprintf("invalid gRPC request method %q", r.Method)
-		http.Error(w, msg, http.StatusBadRequest)
+		http.Error(w, msg, http.StatusMethodNotAllowed)
 		return nil, errors.New(msg)
 	}
 	contentType := r.Header.Get("Content-Type")
@@ -69,6 +65,11 @@ func NewServerHandlerTransport(w http.ResponseWriter, r *http.Request, stats []s
 		http.Error(w, msg, http.StatusUnsupportedMediaType)
 		return nil, errors.New(msg)
 	}
+	if r.ProtoMajor != 2 {
+		msg := "gRPC requires HTTP/2"
+		http.Error(w, msg, http.StatusHTTPVersionNotSupported)
+		return nil, errors.New(msg)
+	}
 	if _, ok := w.(http.Flusher); !ok {
 		msg := "gRPC requires a ResponseWriter supporting http.Flusher"
 		http.Error(w, msg, http.StatusInternalServerError)

internal/transport/handler_server_test.go

@@ -50,15 +50,6 @@ func (s) TestHandlerTransport_NewServerHandlerTransport(t *testing.T) {
 		check       func(*serverHandlerTransport, *testCase) error
 	}
 	tests := []testCase{
-		{
-			name: "http/1.1",
-			req: &http.Request{
-				ProtoMajor: 1,
-				ProtoMinor: 1,
-			},
-			wantErr:     "gRPC requires HTTP/2",
-			wantErrCode: http.StatusBadRequest,
-		},
 		{
 			name: "bad method",
 			req: &http.Request{
@@ -67,7 +58,7 @@ func (s) TestHandlerTransport_NewServerHandlerTransport(t *testing.T) {
 				Header:     http.Header{},
 			},
 			wantErr:     `invalid gRPC request method "GET"`,
-			wantErrCode: http.StatusBadRequest,
+			wantErrCode: http.StatusMethodNotAllowed,
 		},
 		{
 			name: "bad content type",
@@ -81,6 +72,17 @@ func (s) TestHandlerTransport_NewServerHandlerTransport(t *testing.T) {
 			wantErr:     `invalid gRPC request content-type "application/foo"`,
 			wantErrCode: http.StatusUnsupportedMediaType,
 		},
+		{
+			name: "http/1.1",
+			req: &http.Request{
+				ProtoMajor: 1,
+				ProtoMinor: 1,
+				Method:     "POST",
+				Header:     http.Header{"Content-Type": []string{"application/grpc"}},
+			},
+			wantErr:     "gRPC requires HTTP/2",
+			wantErrCode: http.StatusHTTPVersionNotSupported,
+		},
 		{
 			name: "not flusher",
 			req: &http.Request{