go/*: Adapt to xnet.Networker changes wrt Listen and cancellation

See

	kirr/go123@3354b401
and

	kirr/go123@b03d65ff

The wrapping logic in LinkListener goes away because Accept from xnet
now supports cancellation.

go/neo/neonet/newlink.go

@@ -147,8 +147,8 @@ func DialLink(ctx context.Context, net xnet.Networker, addr string) (*NodeLink,
 // ListenLink starts listening on laddr for incoming connections and wraps them as NodeLink.
 //
 // The listener accepts only those connections that pass NEO protocol handshake.
-func ListenLink(net xnet.Networker, laddr string) (LinkListener, error) {
-	rawl, err := net.Listen(laddr)
+func ListenLink(ctx context.Context, net xnet.Networker, laddr string) (LinkListener, error) {
+	rawl, err := net.Listen(ctx, laddr)
 	if err != nil {
 		return nil, err
 	}
@@ -160,82 +160,30 @@ func ListenLink(net xnet.Networker, laddr string) (LinkListener, error) {
 // net.Listener and wraps them as NodeLink.
 //
 // The listener accepts only those connections that pass NEO protocol handshake.
-func NewLinkListener(inner net.Listener) LinkListener {
-	l := &linkListener{
-		l:       inner,
-		acceptq: make(chan linkAccepted),
-		closed:  make(chan struct{}),
-	}
-	go l.run()
-	return l
+func NewLinkListener(inner xnet.Listener) LinkListener {
+	return &linkListener{l: inner}
 }
 
-// LinkListener is net.Listener adapted to return handshaked NodeLink on Accept.
+// LinkListener is xnet.Listener adapted to return handshaked NodeLink on Accept.
 type LinkListener interface {
-	// from net.Listener:
+	// from xnet.Listener:
 	Close() error
 	Addr() net.Addr
 
 	// Accept returns new incoming connection wrapped into NodeLink.
 	// It accepts only those connections which pass NEO protocol handshake.
-	Accept() (*NodeLink, error)
+	Accept(ctx context.Context) (*NodeLink, error)
 }
 
 // linkListener implements LinkListener.
 type linkListener struct {
-	l       net.Listener
-	acceptq chan linkAccepted
-	closed  chan struct{}
-}
-
-type linkAccepted struct {
-	link *NodeLink
-	err  error
-}
-
-func (l *linkListener) Close() error {
-	err := l.l.Close()
-	close(l.closed)
-	return err
-}
-
-func (l *linkListener) run() {
-	// context that cancels when listener stops
-	runCtx, runCancel := context.WithCancel(context.Background())
-	defer runCancel()
-
-	for {
-		// stop on close
-		select {
-		case <-l.closed:
-			return
-		default:
-		}
-
-		// XXX add backpressure on too much incoming connections without client .Accept ?
-		conn, err := l.l.Accept()
-		go l.accept(runCtx, conn, err)
-	}
+	l       xnet.Listener
 }
 
-func (l *linkListener) accept(ctx context.Context, conn net.Conn, err error) {
-	link, err := l.accept1(ctx, conn, err)
-
-	select {
-	case l.acceptq <- linkAccepted{link, err}:
-		// ok
-
-	case <-l.closed:
-		// shutdown
-		if link != nil {
-			link.Close()
-		}
-	}
-}
-
-func (l *linkListener) accept1(ctx context.Context, conn net.Conn, err error) (*NodeLink, error) {
+func (l *linkListener) Accept(ctx context.Context) (*NodeLink, error) {
 	// XXX err ctx?
 
+	conn, err := l.l.Accept(ctx)
 	if err != nil {
 		return nil, err
 	}
@@ -249,18 +197,5 @@ func (l *linkListener) accept1(ctx context.Context, conn net.Conn, err error) (*
 	return link, nil
 }
 
-func (l *linkListener) Accept() (*NodeLink, error) {
-	select {
-	case <-l.closed:
-		// we know raw listener is already closed - return proper error about it
-		_, err := l.l.Accept()
-		return nil, err
-
-	case a := <-l.acceptq:
-		return a.link, a.err
-	}
-}
-
-func (l *linkListener) Addr() net.Addr {
-	return l.l.Addr()
-}
+func (l *linkListener) Close() error   { return l.l.Close() }
+func (l *linkListener) Addr() net.Addr { return l.l.Addr()  }