http3: add client trace support (#4749)

Since the QUIC connection establishment process includes TLS handshake logic,
Connect and TLS handshake are called in the following order:

ConnectStart -> TLSHandshakeStart -> TLSHandshakeDone -> ConnectDone.

Notice: Wait100Continue not implemented as quic-go doesn't support handling
Expect: 100-continue.

http3/ip_addr.go

@@ -0,0 +1,48 @@
+package http3
+
+import (
+	"net"
+	"strings"
+)
+
+// An addrList represents a list of network endpoint addresses.
+// Copy from [net.addrList] and change type from [net.Addr] to [net.IPAddr]
+type addrList []net.IPAddr
+
+// isIPv4 reports whether addr contains an IPv4 address.
+func isIPv4(addr net.IPAddr) bool {
+	return addr.IP.To4() != nil
+}
+
+// isNotIPv4 reports whether addr does not contain an IPv4 address.
+func isNotIPv4(addr net.IPAddr) bool { return !isIPv4(addr) }
+
+// forResolve returns the most appropriate address in address for
+// a call to ResolveTCPAddr, ResolveUDPAddr, or ResolveIPAddr.
+// IPv4 is preferred, unless addr contains an IPv6 literal.
+func (addrs addrList) forResolve(network, addr string) net.IPAddr {
+	var want6 bool
+	switch network {
+	case "ip":
+		// IPv6 literal (addr does NOT contain a port)
+		want6 = strings.ContainsRune(addr, ':')
+	case "tcp", "udp":
+		// IPv6 literal. (addr contains a port, so look for '[')
+		want6 = strings.ContainsRune(addr, '[')
+	}
+	if want6 {
+		return addrs.first(isNotIPv4)
+	}
+	return addrs.first(isIPv4)
+}
+
+// first returns the first address which satisfies strategy, or if
+// none do, then the first address of any kind.
+func (addrs addrList) first(strategy func(net.IPAddr) bool) net.IPAddr {
+	for _, addr := range addrs {
+		if strategy(addr) {
+			return addr
+		}
+	}
+	return addrs[0]
+}