TUN-6716: Document limitation of Windows ICMP proxy

ingress/icmp_windows.go

@@ -262,6 +262,9 @@ func (ip *icmpProxy) Serve(ctx context.Context) error {
 	return ctx.Err()
 }
 
+// Request sends an ICMP echo request and wait for a reply or timeout.
+// The async version of Win32 APIs take a callback whose memory is not garbage collected, so we use the synchronous version.
+// It's possible that a slow request will block other requests, so we set the timeout to only 1s.
 func (ip *icmpProxy) Request(pk *packet.ICMP, responder packet.FunnelUniPipe) error {
 	if pk == nil {
 		return errPacketNil

packet/router.go

@@ -11,7 +11,7 @@ import (
 type ICMPRouter interface {
 	// Serve starts listening for responses to the requests until context is done
 	Serve(ctx context.Context) error
-	// Request sends an ICMP message
+	// Request sends an ICMP message. Implementations should not modify pk after the function returns.
 	Request(pk *ICMP, responder FunnelUniPipe) error
 }