Freedom: Cache UDP resolve result

proxy/freedom/freedom.go

@@ -346,6 +346,12 @@ type PacketWriter struct {
 	*Handler
 	context.Context
 	UDPOverride net.Destination
+
+	// Dest of udp packets might be a domain, we will resolve them to IP
+	// But resolver will return a random one if the domain has many IPs
+	// Resulting in these packets being sent to many different IPs randomly
+	// So, cache and keep the resolve result
+	resolvedUDPAddr map[string]*net.UDPAddr
 }
 
 func (w *PacketWriter) WriteMultiBuffer(mb buf.MultiBuffer) error {
@@ -364,13 +370,19 @@ func (w *PacketWriter) WriteMultiBuffer(mb buf.MultiBuffer) error {
 			if w.UDPOverride.Port != 0 {
 				b.UDP.Port = w.UDPOverride.Port
 			}
-			if w.Handler.config.hasStrategy() && b.UDP.Address.Family().IsDomain() {
+			var destAddr *net.UDPAddr
-				ip := w.Handler.resolveIP(w.Context, b.UDP.Address.Domain(), nil)
+			if w.resolvedUDPAddr == nil {
-				if ip != nil {
+				if w.Handler.config.hasStrategy() && b.UDP.Address.Family().IsDomain() {
-					b.UDP.Address = ip
+					ip := w.Handler.resolveIP(w.Context, b.UDP.Address.Domain(), nil)
+					if ip != nil {
+						b.UDP.Address = ip
+					}
 				}
+				destAddr, _ = net.ResolveUDPAddr("udp", b.UDP.NetAddr())
+				w.resolvedUDPAddr[b.UDP.NetAddr()] = destAddr
+			} else {
+				destAddr = w.resolvedUDPAddr[b.UDP.NetAddr()]
 			}
-			destAddr, _ := net.ResolveUDPAddr("udp", b.UDP.NetAddr())
 			if destAddr == nil {
 				b.Release()
 				continue