Bug: parse the wrong ServerName from addr

[chaosmatrix]

quic-go/transport.go

Lines 176 to 184 in f633dca

	// If no ServerName is set, infer the ServerName from the hostname we're connecting to.
	if tlsConf.ServerName == "" {
	if hostname == "" {
	if udpAddr, ok := addr.(*net.UDPAddr); ok {
	hostname = udpAddr.IP.String()
	}
	}
	tlsConf.ServerName = hostname
	}

Test case:

// env:
//  go1.21.0
// github.com/quic-go/quic-go v0.38.0
func TestQUICTLS(t *testing.T) {
	quicConf := &quic.Config{
		HandshakeIdleTimeout:    5 * time.Second,
		DisablePathMTUDiscovery: true,
	}

	tlsConf := &tls.Config{
		NextProtos: []string{"h3"},
	}

	//tlsConf.ServerName = "quic.nginx.org."

	addr := "quic.nginx.org:443"

	_, err := quic.DialAddr(context.TODO(), addr, tlsConf, quicConf)
	if err != nil {
		t.Error(err)
	}

}

The result is:

--- FAIL: TestQUICTLS (0.64s)
    example_test.go:30: CRYPTO_ERROR 0x12a (local): tls: failed to verify certificate: x509: certificate is valid for quic.nginx.org, not quic.nginx.org:443
FAIL
exit status 1

one way to fix it:

if tlsConf.ServerName == "" {
	if i := strings.LastIndex(hostname, ":"); i > 0 {
		tlsConf.ServerName = hostname[:i]
	} else {
		tlsConf.ServerName = hostname
	}
}

[marten-seemann]

I see the bug. However, the fix is not correct, it would try to break split IPv6 addresses.

[marten-seemann]

@chaosmatrix Could you try out #4046 please? A review would also be appreciated :)

If this fixes your problem, we could cut a patch release today or tomorrow.

[chaosmatrix]

It fixes my problem, thanks.