reject http3 requests that exceeded the header size limit

http3/server.go

@@ -155,6 +155,13 @@ func (s *Server) handleConn(sess quic.Session) {
 	}
 }
 
+func (s *Server) maxHeaderBytes() uint64 {
+	if s.Server.MaxHeaderBytes <= 0 {
+		return http.DefaultMaxHeaderBytes
+	}
+	return uint64(s.Server.MaxHeaderBytes)
+}
+
 // TODO: improve error handling.
 // Most (but not all) of the errors occurring here are connection-level erros.
 func (s *Server) handleRequest(str quic.Stream, decoder *qpack.Decoder) error {
@@ -168,7 +175,10 @@ func (s *Server) handleRequest(str quic.Stream, decoder *qpack.Decoder) error {
 		str.CancelWrite(quic.ErrorCode(errorUnexpectedFrame))
 		return errors.New("expected first frame to be a headers frame")
 	}
-	// TODO: check length
+	if hf.Length > s.maxHeaderBytes() {
+		str.CancelWrite(quic.ErrorCode(errorLimitExceeded))
+		return fmt.Errorf("Headers frame too large: %d bytes (max: %d)", hf.Length, s.maxHeaderBytes())
+	}
 	headerBlock := make([]byte, hf.Length)
 	if _, err := io.ReadFull(str, headerBlock); err != nil {
 		str.CancelWrite(quic.ErrorCode(errorIncompleteRequest))

http3/server_test.go

@@ -181,6 +181,28 @@ var _ = Describe("Server", func() {
 			Expect(hfs).To(HaveKeyWithValue(":status", []string{"200"}))
 		})
 
+		It("errors when the client sends a too large header frame", func() {
+			s.Server.MaxHeaderBytes = 42
+			s.Handler = http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				Fail("Handler should not be called.")
+			})
+
+			requestData := encodeRequest(exampleGetRequest)
+			buf := &bytes.Buffer{}
+			(&dataFrame{Length: 6}).Write(buf) // add a body
+			buf.Write([]byte("foobar"))
+			responseBuf := &bytes.Buffer{}
+			setRequest(append(requestData, buf.Bytes()...))
+			str.EXPECT().Write(gomock.Any()).DoAndReturn(func(p []byte) (int, error) {
+				return responseBuf.Write(p)
+			}).AnyTimes()
+
+			str.EXPECT().CancelWrite(quic.ErrorCode(errorLimitExceeded))
+			err := s.handleRequest(str, qpackDecoder)
+			Expect(err).To(HaveOccurred())
+			Expect(err.Error()).To(ContainSubstring("Headers frame too large"))
+		})
+
 		It("cancels reading when the body of POST request is not read", func() {
 			handlerCalled := make(chan struct{})
 			s.Handler = http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {