XUDP protocol: Add Global ID & UoT Migration

The first UoT protocol that supports UoT Migration
Thank @yuhan6665 for testing

transport/pipe/impl.go

@@ -37,6 +37,7 @@ type pipe struct {
 	readSignal  *signal.Notifier
 	writeSignal *signal.Notifier
 	done        *done.Instance
+	errChan     chan error
 	option      pipeOption
 	state       state
 }
@@ -92,6 +93,8 @@ func (p *pipe) ReadMultiBuffer() (buf.MultiBuffer, error) {
 		select {
 		case <-p.readSignal.Wait():
 		case <-p.done.Wait():
+		case err = <-p.errChan:
+			return nil, err
 		}
 	}
 }

transport/pipe/pipe.go

@@ -59,6 +59,7 @@ func New(opts ...Option) (*Reader, *Writer) {
 		readSignal:  signal.NewNotifier(),
 		writeSignal: signal.NewNotifier(),
 		done:        done.New(),
+		errChan:     make(chan error, 1),
 		option: pipeOption{
 			limit: -1,
 		},

transport/pipe/reader.go

@@ -25,3 +25,17 @@ func (r *Reader) ReadMultiBufferTimeout(d time.Duration) (buf.MultiBuffer, error
 func (r *Reader) Interrupt() {
 	r.pipe.Interrupt()
 }
+
+// ReturnAnError makes ReadMultiBuffer return an error, only once.
+func (r *Reader) ReturnAnError(err error) {
+	r.pipe.errChan <- err
+}
+
+// Recover catches an error set by ReturnAnError, if exists.
+func (r *Reader) Recover() (err error) {
+	select {
+	case err = <-r.pipe.errChan:
+	default:
+	}
+	return
+}