fix: udp dial support ip4p (#1377)

component/resolver/ip4p.go

@@ -0,0 +1,37 @@
+package resolver
+
+import (
+	"net"
+	"net/netip"
+	"strconv"
+
+	"github.com/metacubex/mihomo/log"
+)
+
+var (
+	ip4PEnable bool
+)
+
+func GetIP4PEnable() bool {
+	return ip4PEnable
+}
+
+func SetIP4PEnable(enableIP4PConvert bool) {
+	ip4PEnable = enableIP4PConvert
+}
+
+// kanged from https://github.com/heiher/frp/blob/ip4p/client/ip4p.go
+
+func LookupIP4P(addr netip.Addr, port string) (netip.Addr, string) {
+	if ip4PEnable {
+		ip := addr.AsSlice()
+		if ip[0] == 0x20 && ip[1] == 0x01 &&
+			ip[2] == 0x00 && ip[3] == 0x00 {
+			addr = netip.AddrFrom4([4]byte{ip[12], ip[13], ip[14], ip[15]})
+			port = strconv.Itoa(int(ip[10])<<8 + int(ip[11]))
+			log.Debugln("Convert IP4P address %s to %s", ip, net.JoinHostPort(addr.String(), port))
+			return addr, port
+		}
+	}
+	return addr, port
+}