nethernet: Fix packet truncation and listener blocking forever (#24)

* Fix packet truncation and listener blocking forever

* simplify

Author: HashimTheArab

discovery/listener.go

@@ -253,8 +253,8 @@ func (l *Listener) Responses() map[uint64][]byte {
 
 // listen continuously reads packets received in the conn and calls handlePacket.
 func (l *Listener) listen() {
+	b := make([]byte, maxUDPPacketSize)
 	for {
-		b := make([]byte, 1024)
 		n, addr, err := l.conn.ReadFrom(b)
 		if err != nil {
 			if !errors.Is(err, net.ErrClosed) {
@@ -269,6 +269,9 @@ func (l *Listener) listen() {
 	}
 }
 
+// maxUDPPacketSize is 65,535 bytes, the maximum UDP payload size.
+const maxUDPPacketSize = 65535
+
 // write writes the packet to the destination address using the network ID of Listener.
 func (l *Listener) write(pk Packet, addr net.Addr) error {
 	b := Marshal(pk, l.conf.NetworkID)

listener.go

@@ -460,6 +460,10 @@ func (l *Listener) handleConn(conn *Conn, d *description, channelsReady <-chan s
 		}
 
 		select {
+		case <-ctx.Done():
+			err = ctx.Err()
+		case <-conn.ctx.Done():
+			err = context.Cause(conn.ctx)
 		case <-l.closed:
 			_ = conn.Close()
 		case l.incoming <- conn: