notify if icmp cannot be used due to bad StackConfig

ipv4/icmpv4/client.go

@@ -78,6 +78,10 @@ func (client *Client) Reset() {
 	client.responseRing.Reset()
 }
 
+func (client *Client) IncomingEchoCapacity() int {
+	return cap(client.incomingEcho)
+}
+
 func (client *Client) Demux(carrierData []byte, frameOffset int) error {
 	rawdata := carrierData[frameOffset:]
 	ifrm, err := NewFrame(rawdata)

x/xnet/stack-async.go

@@ -334,6 +334,10 @@ func (s *StackAsync) Gateway6() [6]byte {
 // EnableICMP registers an ICMP handler to the stack when enabled is true.
 // If enabled=false the currently registered ICMP handler is unregistered and state reset.
 func (s *StackAsync) EnableICMP(enabled bool) (err error) {
+	if s.icmp.IncomingEchoCapacity() == 0 {
+		err = lneto.ErrInvalidConfig
+		enabled = false // ensure aborted.
+	}
 	if enabled {
 		if s.ip.IsRegistered(lneto.IPProtoICMP) {
 			return nil