http3: allow re-dialing of connection after a dial error (#4573)

* http3: do not cache dial error

* add an integration test

* http3: add a unit test for dial failures

---------

Co-authored-by: 世界 <i@sekai.icu>

http3/roundtrip.go

@@ -166,6 +166,7 @@ func (r *RoundTripper) RoundTripOpt(req *http.Request, opt RoundTripOpt) (*http.
 	}
 
 	if cl.dialErr != nil {
+		r.removeClient(hostname)
 		return nil, cl.dialErr
 	}
 	defer cl.useCount.Add(-1)
@@ -258,6 +259,7 @@ func (r *RoundTripper) getClient(ctx context.Context, hostname string, onlyCache
 	select {
 	case <-cl.dialing:
 		if cl.dialErr != nil {
+			delete(r.clients, hostname)
 			return nil, false, cl.dialErr
 		}
 		select {

http3/roundtrip_test.go

@@ -265,6 +265,37 @@ var _ = Describe("RoundTripper", func() {
 			Expect(count).To(Equal(1))
 		})
 
+		It("redials a connection if dialing failed", func() {
+			cl1 := NewMockSingleRoundTripper(mockCtrl)
+			clientChan <- cl1
+
+			req1, err := http.NewRequest("GET", "https://quic-go.net/foo.html", nil)
+			Expect(err).ToNot(HaveOccurred())
+			req2, err := http.NewRequest("GET", "https://quic-go.net/bar.html", nil)
+			Expect(err).ToNot(HaveOccurred())
+
+			testErr := errors.New("handshake error")
+			conn := mockquic.NewMockEarlyConnection(mockCtrl)
+			var count int
+			rt.Dial = func(context.Context, string, *tls.Config, *quic.Config) (quic.EarlyConnection, error) {
+				count++
+				if count == 1 {
+					return nil, testErr
+				}
+				return conn, nil
+			}
+			handshakeChan := make(chan struct{})
+			close(handshakeChan)
+			conn.EXPECT().HandshakeComplete().Return(handshakeChan).MaxTimes(2)
+			cl1.EXPECT().RoundTrip(req2).Return(&http.Response{Request: req2}, nil)
+			_, err = rt.RoundTrip(req1)
+			Expect(err).To(MatchError(testErr))
+			rsp, err := rt.RoundTrip(req2)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(rsp.Request).To(Equal(req2))
+			Expect(count).To(Equal(2))
+		})
+
 		It("immediately removes a clients when a request errored", func() {
 			cl1 := NewMockSingleRoundTripper(mockCtrl)
 			clientChan <- cl1