don't send CONNECTION_CLOSE if error occurred before sending anything

connection.go

@@ -190,6 +190,7 @@ type connection struct {
 	clientHelloWritten    <-chan *wire.TransportParameters
 	earlyConnReadyChan    chan struct{}
 	handshakeCompleteChan chan struct{} // is closed when the handshake completes
+	sentFirstPacket       bool
 	handshakeComplete     bool
 	handshakeConfirmed    bool
 
@@ -1519,6 +1520,12 @@ func (s *connection) handleCloseError(closeErr *closeError) {
 		s.connIDGenerator.RemoveAll()
 		return
 	}
+	// Don't send out any CONNECTION_CLOSE if this is an error that occurred
+	// before we even sent out the first packet.
+	if s.perspective == protocol.PerspectiveClient && !s.sentFirstPacket {
+		s.connIDGenerator.RemoveAll()
+		return
+	}
 	connClosePacket, err := s.sendConnectionClose(e)
 	if err != nil {
 		s.logger.Debugf("Error sending CONNECTION_CLOSE: %s", err)
@@ -1760,6 +1767,7 @@ func (s *connection) sendPacket() (bool, error) {
 		if err != nil || packet == nil {
 			return false, err
 		}
+		s.sentFirstPacket = true
 		s.logCoalescedPacket(packet)
 		for _, p := range packet.packets {
 			if s.firstAckElicitingPacketAfterIdleSentTime.IsZero() && p.IsAckEliciting() {

connection_test.go

@@ -2477,6 +2477,7 @@ var _ = Describe("Client Connection", func() {
 		conn.packer = packer
 		cryptoSetup = mocks.NewMockCryptoSetup(mockCtrl)
 		conn.cryptoStreamHandler = cryptoSetup
+		conn.sentFirstPacket = true
 	})
 
 	It("changes the connection ID when receiving the first packet from the server", func() {
@@ -2568,6 +2569,25 @@ var _ = Describe("Client Connection", func() {
 		Expect(conn.handleAckFrame(ack, protocol.Encryption1RTT)).To(Succeed())
 	})
 
+	It("doesn't send a CONNECTION_CLOSE when no packet was sent", func() {
+		conn.sentFirstPacket = false
+		tracer.EXPECT().ClosedConnection(gomock.Any())
+		tracer.EXPECT().Close()
+		running := make(chan struct{})
+		cryptoSetup.EXPECT().RunHandshake().Do(func() {
+			close(running)
+			conn.closeLocal(errors.New("early error"))
+		})
+		cryptoSetup.EXPECT().Close()
+		connRunner.EXPECT().Remove(gomock.Any())
+		go func() {
+			defer GinkgoRecover()
+			conn.run()
+		}()
+		Eventually(running).Should(BeClosed())
+		Eventually(areConnsRunning).Should(BeFalse())
+	})
+
 	Context("handling tokens", func() {
 		var mockTokenStore *MockTokenStore
 

integrationtests/self/handshake_test.go

@@ -12,6 +12,7 @@ import (
 	"github.com/lucas-clemente/quic-go"
 	"github.com/lucas-clemente/quic-go/integrationtests/tools/israce"
 	"github.com/lucas-clemente/quic-go/internal/protocol"
+	"github.com/lucas-clemente/quic-go/internal/qerr"
 	"github.com/lucas-clemente/quic-go/logging"
 
 	. "github.com/onsi/ginkgo"
@@ -567,4 +568,37 @@ var _ = Describe("Handshake tests", func() {
 			Expect(token.IsRetryToken).To(BeTrue())
 		})
 	})
+
+	It("doesn't send any packets when generating the ClientHello fails", func() {
+		ln, err := net.ListenUDP("udp", nil)
+		Expect(err).ToNot(HaveOccurred())
+		done := make(chan struct{})
+		packetChan := make(chan struct{})
+		go func() {
+			defer GinkgoRecover()
+			defer close(done)
+			for {
+				_, _, err := ln.ReadFromUDP(make([]byte, protocol.MaxPacketBufferSize))
+				if err != nil {
+					return
+				}
+				packetChan <- struct{}{}
+			}
+		}()
+
+		tlsConf := getTLSClientConfig()
+		tlsConf.NextProtos = []string{""}
+		_, err = quic.DialAddr(
+			fmt.Sprintf("localhost:%d", ln.LocalAddr().(*net.UDPAddr).Port),
+			tlsConf,
+			nil,
+		)
+		Expect(err).To(MatchError(&qerr.TransportError{
+			ErrorCode:    qerr.InternalError,
+			ErrorMessage: "tls: invalid NextProtos value",
+		}))
+		Consistently(packetChan).ShouldNot(Receive())
+		ln.Close()
+		Eventually(done).Should(BeClosed())
+	})
 })