eth, p2p: remove EncodeMsg from p2p.MsgWriter

...and make it a top-level function instead.

The original idea behind having EncodeMsg in the interface was that
implementations might be able to encode RLP data to their underlying
writer directly instead of buffering the encoded data. The encoder
will buffer anyway, so that doesn't matter anymore.

Given the recent problems with EncodeMsg (copy-pasted implementation
bug) I'd rather implement once, correctly.

eth/protocol.go

@@ -140,7 +140,7 @@ func (self *ethProtocol) handle() error {
 			return self.protoError(ErrDecode, "->msg %v: %v", msg, err)
 		}
 		hashes := self.chainManager.GetBlockHashesFromHash(request.Hash, request.Amount)
-		return self.rw.EncodeMsg(BlockHashesMsg, ethutil.ByteSliceToInterface(hashes)...)
+		return p2p.EncodeMsg(self.rw, BlockHashesMsg, ethutil.ByteSliceToInterface(hashes)...)
 
 	case BlockHashesMsg:
 		// TODO: redo using lazy decode , this way very inefficient on known chains
@@ -185,7 +185,7 @@ func (self *ethProtocol) handle() error {
 				break
 			}
 		}
-		return self.rw.EncodeMsg(BlocksMsg, blocks...)
+		return p2p.EncodeMsg(self.rw, BlocksMsg, blocks...)
 
 	case BlocksMsg:
 		msgStream := rlp.NewStream(msg.Payload)
@@ -298,12 +298,12 @@ func (self *ethProtocol) handleStatus() error {
 
 func (self *ethProtocol) requestBlockHashes(from []byte) error {
 	self.peer.Debugf("fetching hashes (%d) %x...\n", blockHashesBatchSize, from[0:4])
-	return self.rw.EncodeMsg(GetBlockHashesMsg, interface{}(from), uint64(blockHashesBatchSize))
+	return p2p.EncodeMsg(self.rw, GetBlockHashesMsg, interface{}(from), uint64(blockHashesBatchSize))
 }
 
 func (self *ethProtocol) requestBlocks(hashes [][]byte) error {
 	self.peer.Debugf("fetching %v blocks", len(hashes))
-	return self.rw.EncodeMsg(GetBlocksMsg, ethutil.ByteSliceToInterface(hashes)...)
+	return p2p.EncodeMsg(self.rw, GetBlocksMsg, ethutil.ByteSliceToInterface(hashes)...)
 }
 
 func (self *ethProtocol) protoError(code int, format string, params ...interface{}) (err *protocolError) {

eth/protocol_test.go

@@ -41,10 +41,6 @@ func (self *testMsgReadWriter) WriteMsg(msg p2p.Msg) error {
 	return nil
 }
 
-func (self *testMsgReadWriter) EncodeMsg(code uint64, data ...interface{}) error {
-	return self.WriteMsg(p2p.NewMsg(code, data...))
-}
-
 func (self *testMsgReadWriter) ReadMsg() (p2p.Msg, error) {
 	msg, ok := <-self.in
 	if !ok {

p2p/message.go

@@ -71,14 +71,11 @@ type MsgReader interface {
 }
 
 type MsgWriter interface {
-	// WriteMsg sends an existing message.
-	// The Payload reader of the message is consumed.
+	// WriteMsg sends a message. It will block until the message's
+	// Payload has been consumed by the other end.
+	//
 	// Note that messages can be sent only once.
 	WriteMsg(Msg) error
-
-	// EncodeMsg writes an RLP-encoded message with the given
-	// code and data elements.
-	EncodeMsg(code uint64, data ...interface{}) error
 }
 
 // MsgReadWriter provides reading and writing of encoded messages.
@@ -87,6 +84,12 @@ type MsgReadWriter interface {
 	MsgWriter
 }
 
+// EncodeMsg writes an RLP-encoded message with the given code and
+// data elements.
+func EncodeMsg(w MsgWriter, code uint64, data ...interface{}) error {
+	return w.WriteMsg(NewMsg(code, data...))
+}
+
 var magicToken = []byte{34, 64, 8, 145}
 
 func writeMsg(w io.Writer, msg Msg) error {
@@ -209,11 +212,6 @@ func (p *MsgPipeRW) WriteMsg(msg Msg) error {
 	return ErrPipeClosed
 }
 
-// EncodeMsg is a convenient shorthand for sending an RLP-encoded message.
-func (p *MsgPipeRW) EncodeMsg(code uint64, data ...interface{}) error {
-	return p.WriteMsg(NewMsg(code, data...))
-}
-
 // ReadMsg returns a message sent on the other end of the pipe.
 func (p *MsgPipeRW) ReadMsg() (Msg, error) {
 	if atomic.LoadInt32(p.closed) == 0 {

p2p/message_test.go

@@ -75,8 +75,8 @@ func TestDecodeRealMsg(t *testing.T) {
 func ExampleMsgPipe() {
 	rw1, rw2 := MsgPipe()
 	go func() {
-		rw1.EncodeMsg(8, []byte{0, 0})
-		rw1.EncodeMsg(5, []byte{1, 1})
+		EncodeMsg(rw1, 8, []byte{0, 0})
+		EncodeMsg(rw1, 5, []byte{1, 1})
 		rw1.Close()
 	}()
 
@@ -100,7 +100,7 @@ loop:
 		rw1, rw2 := MsgPipe()
 		done := make(chan struct{})
 		go func() {
-			if err := rw1.EncodeMsg(1); err == nil {
+			if err := EncodeMsg(rw1, 1); err == nil {
 				t.Error("EncodeMsg returned nil error")
 			} else if err != ErrPipeClosed {
 				t.Error("EncodeMsg returned wrong error: got %v, want %v", err, ErrPipeClosed)

p2p/peer_test.go

@@ -126,10 +126,10 @@ func TestPeerProtoEncodeMsg(t *testing.T) {
 		Name:   "a",
 		Length: 2,
 		Run: func(peer *Peer, rw MsgReadWriter) error {
-			if err := rw.EncodeMsg(2); err == nil {
+			if err := EncodeMsg(rw, 2); err == nil {
 				t.Error("expected error for out-of-range msg code, got nil")
 			}
-			if err := rw.EncodeMsg(1, "foo", "bar"); err != nil {
+			if err := EncodeMsg(rw, 1, "foo", "bar"); err != nil {
 				t.Errorf("write error: %v", err)
 			}
 			return nil

p2p/protocol.go

@@ -119,22 +119,22 @@ func (bp *baseProtocol) loop(quit <-chan error) error {
 
 	getPeersTick := time.NewTicker(10 * time.Second)
 	defer getPeersTick.Stop()
-	err := bp.rw.EncodeMsg(getPeersMsg)
+	err := EncodeMsg(bp.rw, getPeersMsg)
 
 	for err == nil {
 		select {
 		case err = <-quit:
 			return err
 		case <-getPeersTick.C:
-			err = bp.rw.EncodeMsg(getPeersMsg)
+			err = EncodeMsg(bp.rw, getPeersMsg)
 		case event := <-activity.Chan():
 			ping.Reset(pingTimeout)
 			lastActive = event.(time.Time)
 		case t := <-ping.C:
 			if lastActive.Add(pingTimeout * 2).Before(t) {
 				err = newPeerError(errPingTimeout, "")
 			} else if lastActive.Add(pingTimeout).Before(t) {
-				err = bp.rw.EncodeMsg(pingMsg)
+				err = EncodeMsg(bp.rw, pingMsg)
 			}
 		}
 	}
@@ -164,7 +164,7 @@ func (bp *baseProtocol) handle(rw MsgReadWriter) error {
 		return discRequestedError(reason[0])
 
 	case pingMsg:
-		return bp.rw.EncodeMsg(pongMsg)
+		return EncodeMsg(bp.rw, pongMsg)
 
 	case pongMsg:
 
@@ -177,7 +177,7 @@ func (bp *baseProtocol) handle(rw MsgReadWriter) error {
 		//
 		// TODO: add event mechanism to notify baseProtocol for new peers
 		if len(peers) > 0 {
-			return bp.rw.EncodeMsg(peersMsg, peers...)
+			return EncodeMsg(bp.rw, peersMsg, peers...)
 		}
 
 	case peersMsg:

p2p/protocol_test.go

@@ -93,7 +93,7 @@ func TestBaseProtocolDisconnect(t *testing.T) {
 		if err := expectMsg(rw2, handshakeMsg); err != nil {
 			t.Error(err)
 		}
-		err := rw2.EncodeMsg(handshakeMsg,
+		err := EncodeMsg(rw2, handshakeMsg,
 			baseProtocolVersion,
 			"",
 			[]interface{}{},
@@ -106,7 +106,7 @@ func TestBaseProtocolDisconnect(t *testing.T) {
 		if err := expectMsg(rw2, getPeersMsg); err != nil {
 			t.Error(err)
 		}
-		if err := rw2.EncodeMsg(discMsg, DiscQuitting); err != nil {
+		if err := EncodeMsg(rw2, discMsg, DiscQuitting); err != nil {
 			t.Error(err)
 		}