inmem: Implement `Copy`, `ReceiveFrom` and `SendTo`

* Copy is the beam equivalent of `io.Copy`
* `ReceiveFrom` is the beam equivalent of `io.ReadFrom`
* `SendTo` is the beam equivalent of `io.WriteTo`

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

inmem/copy.go

@@ -0,0 +1,53 @@
+package inmem
+
+import (
+	"io"
+	"fmt"
+)
+
+type ReceiverFrom interface {
+	ReceiveFrom(Receiver) (int, error)
+}
+
+type SenderTo interface {
+	SendTo(Sender) (int, error)
+}
+
+func Copy(dst Sender, src Receiver) (int, error) {
+	if senderTo, ok := src.(SenderTo); ok {
+		return senderTo.SendTo(dst)
+	}
+	if receiverFrom, ok := dst.(ReceiverFrom); ok {
+		return receiverFrom.ReceiveFrom(src)
+	}
+	var (
+		n int
+	)
+	for {
+		msg, r, w, err := src.Receive(R|W)
+		if err == io.EOF {
+			break
+		}
+		if r != nil {
+			// FIXME: spawn goroutines to shuttle messages for each
+			// level of nested sender/receiver.
+			r.Close()
+			return n, fmt.Errorf("operation not supported")
+		}
+		if w != nil {
+			// FIXME: spawn goroutines to shuttle messages for each
+			// level of nested sender/receiver.
+			w.Close()
+			return n, fmt.Errorf("operation not supported")
+		}
+		if err != nil {
+			return n, err
+		}
+		if _, _, err := dst.Send(msg, 0); err != nil {
+			return n, err
+		}
+		n++
+	}
+	return n, nil
+}
+

inmem/inmem.go

@@ -1,6 +1,7 @@
 package inmem
 
 import (
+	"fmt"
 	"io"
 	"sync"
 )
@@ -18,7 +19,7 @@ type Receiver interface {
 type Message struct {
 	Name string
 	Args []string
-	Data string
+	Data []byte
 }
 
 const (
@@ -53,6 +54,33 @@ type pipeMessage struct {
 	in  *PipeReceiver
 }
 
+func (p *pipe) psend(pmsg *pipeMessage) error {
+	var err error
+	// One writer at a time.
+	p.wl.Lock()
+	defer p.wl.Unlock()
+
+	p.l.Lock()
+	defer p.l.Unlock()
+	p.pmsg = pmsg
+	p.rwait.Signal()
+	for {
+		if p.pmsg == nil {
+			break
+		}
+		if p.rerr != nil {
+			err = p.rerr
+			break
+		}
+		if p.werr != nil {
+			err = io.ErrClosedPipe
+		}
+		p.wwait.Wait()
+	}
+	p.pmsg = nil // in case of rerr or werr
+	return err
+}
+
 func (p *pipe) send(msg *Message, mode int) (in *PipeReceiver, out *PipeSender, err error) {
 	// Prepare the message
 	pmsg := &pipeMessage{msg: msg}
@@ -76,28 +104,7 @@ func (p *pipe) send(msg *Message, mode int) (in *PipeReceiver, out *PipeSender,
 			}
 		}()
 	}
-	// One writer at a time.
-	p.wl.Lock()
-	defer p.wl.Unlock()
-
-	p.l.Lock()
-	defer p.l.Unlock()
-	p.pmsg = pmsg
-	p.rwait.Signal()
-	for {
-		if p.pmsg == nil {
-			break
-		}
-		if p.rerr != nil {
-			err = p.rerr
-			break
-		}
-		if p.werr != nil {
-			err = io.ErrClosedPipe
-		}
-		p.wwait.Wait()
-	}
-	p.pmsg = nil // in case of rerr or werr
+	err = p.psend(pmsg)
 	return
 }
 
@@ -164,7 +171,7 @@ type PipeReceiver struct {
 	p *pipe
 }
 
-func (r *PipeReceiver) Receive(mode int) (*Message, *PipeReceiver, *PipeSender, error) {
+func (r *PipeReceiver) Receive(mode int) (*Message, Receiver, Sender, error) {
 	return r.p.receive(mode)
 }
 
@@ -183,10 +190,49 @@ type PipeSender struct {
 	p *pipe
 }
 
-func (w *PipeSender) Send(msg *Message, mode int) (*PipeReceiver, *PipeSender, error) {
+func (w *PipeSender) Send(msg *Message, mode int) (Receiver, Sender, error) {
 	return w.p.send(msg, mode)
 }
 
+func (w *PipeSender) ReceiveFrom(src Receiver, mode int) (int, error) {
+	var n int
+	for {
+		msg, msgr, msgw, err := src.Receive(mode)
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return n, err
+		}
+		pmsg := &pipeMessage{msg: msg}
+		if msgr != nil {
+			if pmsgr, ok := msgr.(*PipeReceiver); ok {
+				pmsg.in = pmsgr
+			} else {
+				// FIXME: if we're not receiving from a PipeReceiver,
+				// we need to create a new pipe and shuttle messages through it
+				// in a new goroutine.
+				return n, fmt.Errorf("operation not supported")
+			}
+		}
+		if msgw != nil {
+			if pmsgw, ok := msgw.(*PipeSender); ok {
+				pmsg.out = pmsgw
+			} else {
+				// FIXME: if we're not sending to a PipeSender,
+				// we need to create a new pipe and shuttle messages through it
+				// in a new goroutine.
+				return n, fmt.Errorf("operation not supported")
+			}
+		}
+		if err := w.p.psend(pmsg); err != nil {
+			return n, err
+		}
+		n++
+	}
+	return n, nil
+}
+
 func (w *PipeSender) Close() error {
 	return w.CloseWithError(nil)
 }