Add round-robin implementation (#66)

* add handler.encapsulateNode

* implement round robin handler approach

* simplify round robin implementation

* leave TODO

* internet.node touch up

* fix conflict resolve f-up

* replace certain ErrShortBuffer with ErrTruncatedFrame error

ipv4/icmpv4/client.go

@@ -54,6 +54,7 @@ func (client *Client) Configure(cfg ClientConfig) error {
 	}
 	client.connid++
 	internal.SliceReuse(&client.outgoingEcho, cfg.ResponseQueueLimit)
+	internal.SliceReuse(&client.incomingEcho, cfg.ResponseQueueLimit)
 	client.responseRing = internal.Ring{Buf: cfg.ResponseQueueBuffer}
 	client.magic = cfg.HashSeed
 	client.id = cfg.ID
@@ -101,6 +102,10 @@ func (client *Client) Demux(carrierData []byte, frameOffset int) error {
 	}
 	switch tp {
 	case TypeEcho:
+		free := cap(client.incomingEcho) - len(client.incomingEcho)
+		if free == 0 {
+			return lneto.ErrExhausted
+		}
 		// We received a ping request; not handled client-side.
 		efrm := FrameEcho{Frame: ifrm}
 		data := efrm.Data()
@@ -227,6 +232,10 @@ func (client *Client) PingStart(remoteAddr [4]byte, pattern []byte, size uint16)
 	} else if remoteAddr == [4]byte{} {
 		return 0, lneto.ErrZeroDestination
 	}
+	free := cap(client.outgoingEcho) - len(client.outgoingEcho)
+	if free == 0 {
+		return 0, lneto.ErrExhausted
+	}
 	key = client.magichash(pattern, int(size)) & keyHashBits
 	v := internal.SliceReclaim(&client.outgoingEcho)
 	v.key = key

ipv4/icmpv4/icmpv4.go

@@ -59,7 +59,7 @@ const (
 
 func NewFrame(buf []byte) (Frame, error) {
 	if len(buf) < sizeHeader {
-		return Frame{}, lneto.ErrShortBuffer
+		return Frame{}, lneto.ErrTruncatedFrame
 	}
 	return Frame{buf: buf}, nil
 }