Implement NopSender (removed by switch to libchan)

Signed-off-by: Solomon Hykes <solomon@docker.com>

beam/nop.go

@@ -0,0 +1,30 @@
+package beam
+
+import (
+	"github.com/docker/libchan"
+	"io"
+)
+
+type NopSender struct{}
+
+func (s NopSender) Send(msg *Message) (Receiver, error) {
+	return NopReceiver{}, nil
+}
+
+func (s NopSender) Close() error {
+	return nil
+}
+
+func (s NopSender) Unwrap() libchan.Sender {
+	return libchan.NopSender{}
+}
+
+type NopReceiver struct{}
+
+func (r NopReceiver) Receive(mode int) (*Message, error) {
+	return nil, io.EOF
+}
+
+func (r NopReceiver) Unwrap() libchan.Receiver {
+	return libchan.NopReceiver{}
+}