go/neo/neonet: MessagePack support for link layer (draft)

This patch adds support for serializing packet frames with M encoding on
the wire. To do so it follows rules defined in

    	nexedi/neoppod@9d0bf97a
    	( nexedi/neoppod!11 )

Server handshake is reworked to autodetect client's preferred encoding.
Client always prefers 'N' for now.

go/neo/neonet/connection.go

@@ -100,9 +100,11 @@ import (
 
 	"lab.nexedi.com/kirr/neo/go/internal/packed"
 	"lab.nexedi.com/kirr/neo/go/internal/xio"
+	"lab.nexedi.com/kirr/neo/go/neo/internal/msgpack"
 	"lab.nexedi.com/kirr/neo/go/neo/proto"
 
 	"github.com/someonegg/gocontainer/rbuf"
+	"github.com/tinylib/msgp/msgp"
 
 	"lab.nexedi.com/kirr/go123/xbytes"
 )
@@ -123,7 +125,7 @@ import (
 // It is safe to use NodeLink from multiple goroutines simultaneously.
 type NodeLink struct {
 	peerLink net.Conn       // raw conn to peer
-	enc      proto.Encoding // protocol encoding in use ('N')
+	enc      proto.Encoding // protocol encoding in use ('N' or 'M')
 
 	connMu     sync.Mutex
 	connTab    map[uint32]*Conn // connId -> Conn associated with connId
@@ -153,6 +155,8 @@ type NodeLink struct {
 	closed   atomic32	// whether Close was called
 
 	rxbufN      rbuf.RingBuf      // buffer for reading from peerLink (N encoding)
+	rxbufM      *msgp.Reader      // ----//---- (M encoding)
+	rxbufMlimit *io.LimitedReader // limiter inserted inbetween rxbufM and peerLink
 
 	// scheduling optimization: whenever serveRecv sends to Conn.rxq
 	// receiving side must ack here to receive G handoff.
@@ -261,7 +265,9 @@ const (
 //
 // Though it is possible to wrap just-established raw connection into NodeLink,
 // users should always use Handshake which performs protocol handshaking first.
-func newNodeLink(conn net.Conn, enc proto.Encoding, role _LinkRole) *NodeLink {
+//
+// rxbuf if != nil indicates what was already read-buffered from conn.
+func newNodeLink(conn net.Conn, enc proto.Encoding, role _LinkRole, rxbuf *xbufReader) *NodeLink {
 	var nextConnId uint32
 	switch role &^ linkFlagsMask {
 	case _LinkServer:
@@ -283,6 +289,27 @@ func newNodeLink(conn net.Conn, enc proto.Encoding, role _LinkRole) *NodeLink {
 //		axdown:     make(chan struct{}),
 		down:       make(chan struct{}),
 	}
+
+	if rxbuf == nil {
+		rxbuf = newXBufReader(conn, 0)
+	}
+	switch enc {
+	case 'N':
+		// rxbufN <- rxbufM (what was preread)
+		b, err := rxbuf.Next(rxbuf.Buffered())
+		if err != nil {
+			panic(err) // must not fail
+		}
+		nl.rxbufN.Write(b)
+
+	case 'M':
+		nl.rxbufM        = &msgp.Reader{R: rxbuf.Reader}
+		nl.rxbufMlimit   = &rxbuf.Limit
+		nl.rxbufMlimit.N = 0 // reads will fail unless .N is explicitly reset
+	default:
+		panic("bug")
+	}
+
 	if role&linkNoRecvSend == 0 {
 		nl.serveWg.Add(2)
 		go nl.serveRecv()
@@ -1190,6 +1217,7 @@ var ErrPktTooBig = errors.New("packet too big")
 func (nl *NodeLink) recvPkt() (pkt *pktBuf, err error) {
 	switch nl.enc {
 	case 'N': pkt, err = nl.recvPktN()
+	case 'M': pkt, err = nl.recvPktM()
 	default:  panic("bug")
 	}
 
@@ -1272,6 +1300,25 @@ func (nl *NodeLink) recvPktN() (*pktBuf, error) {
 	return pkt, nil
 }
 
+func (nl *NodeLink) recvPktM() (*pktBuf, error) {
+	pkt := pktAlloc(4096)
+	mraw := msgp.Raw(pkt.data)
+
+	// limit size of one packet to proto.PktMaxSize
+	// we don't care if it will be slightly more with what is already buffered
+	nl.rxbufMlimit.N = proto.PktMaxSize
+
+	err := mraw.DecodeMsg(nl.rxbufM)
+	if err != nil {
+		if nl.rxbufMlimit.N <= 0 {
+			err = ErrPktTooBig
+		}
+		return nil, err
+	}
+	pkt.data = []byte(mraw)
+	return pkt, nil
+}
+
 
 // ---- for convenience: Conn -> NodeLink & local/remote link addresses  ----
 
@@ -1343,6 +1390,7 @@ func (c *Conn) err(op string, e error) error {
 func pktEncode(e proto.Encoding, connId uint32, msg proto.Msg) *pktBuf {
 	switch e {
 	case 'N': return pktEncodeN(connId, msg)
+	case 'M': return pktEncodeM(connId, msg)
 	default:  panic("bug")
 	}
 }
@@ -1351,6 +1399,7 @@ func pktEncode(e proto.Encoding, connId uint32, msg proto.Msg) *pktBuf {
 func pktDecodeHead(e proto.Encoding, pkt *pktBuf) (connID uint32, msgCode uint16, payload []byte, err error) {
 	switch e {
 	case 'N': connID, msgCode, payload, err = pktDecodeHeadN(pkt)
+	case 'M': connID, msgCode, payload, err = pktDecodeHeadM(pkt)
 	default:  panic("bug")
 	}
 
@@ -1391,6 +1440,52 @@ func pktDecodeHeadN(pkt *pktBuf) (connID uint32, msgCode uint16, payload []byte,
 	return
 }
 
+func pktEncodeM(connId uint32, msg proto.Msg) *pktBuf {
+	const enc = proto.Encoding('M')
+
+	// [3](connID, msgCode, argv)
+	msgCode := proto.MsgCode(msg)
+	hroom := msgpack.ArrayHeadSize(3)   +
+		 msgpack.Uint32Size(connId) +
+		 msgpack.Uint16Size(msgCode)
+	l := enc.MsgEncodedLen(msg)
+
+	buf := pktAlloc(hroom + l)
+
+	b := buf.data
+	i := 0
+	i += msgpack.PutArrayHead (b[i:], 3)
+	i += msgpack.PutUint32    (b[i:], connId)
+	i += msgpack.PutUint16    (b[i:], msgCode)
+	if i != hroom {
+		panic("bug")
+	}
+	enc.MsgEncode(msg, b[hroom:])
+	return buf
+}
+
+func pktDecodeHeadM(pkt *pktBuf) (connID uint32, msgCode uint16, payload []byte, err error) {
+	b := pkt.data
+	sz, b, err := msgp.ReadArrayHeaderBytes(b)
+	if err != nil {
+		return 0, 0, nil, err
+	}
+	if sz != 3 {
+		return 0, 0, nil, fmt.Errorf("expected [3]tuple, got [%d]tuple", sz)
+	}
+
+	connID, b, err = msgp.ReadUint32Bytes(b)
+	if err != nil {
+		return 0, 0, nil, fmt.Errorf("connID: %s", err)
+	}
+
+	msgCode, b, err = msgp.ReadUint16Bytes(b)
+	if err != nil {
+		return 0, 0, nil, fmt.Errorf("msgCode: %s", err)
+	}
+
+	return connID, msgCode, b, nil
+}
 
 // Recv receives message from the connection.
 func (c *Conn) Recv() (proto.Msg, error) {

go/neo/neonet/connection_test.go

@@ -39,6 +39,8 @@ import (
 	"lab.nexedi.com/kirr/neo/go/neo/proto"
 	"lab.nexedi.com/kirr/neo/go/zodb"
 
+	"github.com/tinylib/msgp/msgp"
+
 	"github.com/kylelemons/godebug/pretty"
 	"github.com/pkg/errors"
 )
@@ -52,7 +54,7 @@ type T struct {
 // Verify tests f for all possible environments.
 func Verify(t *testing.T, f func(*T)) {
 	// for each encoding
-	for _, enc := range []proto.Encoding{'N'} {
+	for _, enc := range []proto.Encoding{'N', 'M'} {
 		t.Run(fmt.Sprintf("enc=%c", enc), func(t *testing.T) {
 			f(&T{t, enc})
 		})
@@ -63,6 +65,7 @@ func Verify(t *testing.T, f func(*T)) {
 func (t *T) bin(data string) []byte {
 	switch t.enc {
 	case 'N': return []byte(data)
+	case 'M': return msgp.AppendBytes(nil, []byte(data))
 	default:  panic("bug")
 	}
 }
@@ -139,6 +142,15 @@ func _mkpkt(enc proto.Encoding, connid uint32, msgcode uint16, payload []byte) *
 		copy(pkt.PayloadN(), payload)
 		return pkt
 
+	case 'M':
+		var b []byte
+		b = msgp.AppendArrayHeader (b, 3)
+		b = msgp.AppendUint32      (b, connid)
+		b = msgp.AppendUint16      (b, msgcode)
+		// NOTE payload is assumed to be valid msgpack-encoded object.
+		b = append                 (b, payload...)
+		return &pktBuf{b}
+
 	default:
 		panic("bug")
 	}
@@ -195,8 +207,8 @@ func tdelay() {
 // create NodeLinks connected via net.Pipe; messages are encoded via t.enc.
 func (t *T) _nodeLinkPipe(flags1, flags2 _LinkRole) (nl1, nl2 *NodeLink) {
 	node1, node2 := net.Pipe()
-	nl1 = newNodeLink(node1, t.enc, _LinkClient|flags1)
-	nl2 = newNodeLink(node2, t.enc, _LinkServer|flags2)
+	nl1 = newNodeLink(node1, t.enc, _LinkClient|flags1, nil)
+	nl2 = newNodeLink(node2, t.enc, _LinkServer|flags2, nil)
 	return nl1, nl2
 }
 

go/neo/neonet/misc.go

-// Copyright (C) 2016-2018  Nexedi SA and Contributors.
+// Copyright (C) 2016-2021  Nexedi SA and Contributors.
 //                          Kirill Smelkov <kirr@nexedi.com>
 //
 // This program is free software: you can Use, Study, Modify and Redistribute
@@ -20,7 +20,13 @@
 package neonet
 // syntax sugar for atomic load/store to raise signal/noise in logic
 
-import "sync/atomic"
+import (
+	"io"
+	"sync/atomic"
+
+	"github.com/philhofer/fwd"
+)
+
 
 type atomic32 struct {
 	v int32	// struct member so `var a atomic32; if a == 0 ...` does not work
@@ -37,3 +43,16 @@ func (a *atomic32) Set(v int32) {
 func (a *atomic32) Add(δ int32) int32 {
 	return atomic.AddInt32(&a.v, δ)
 }
+
+
+// xbufReader provides fwd.Reader with io.LimitedReader inserted underneath it.
+type xbufReader struct {
+	*fwd.Reader
+	Limit       io.LimitedReader // .Reader reads through .limit
+}
+
+func newXBufReader(r io.Reader, n int64) *xbufReader {
+	rxbuf := &xbufReader{Limit: io.LimitedReader{R: r, N: n}}
+	rxbuf.Reader = fwd.NewReader(&rxbuf.Limit)
+	return rxbuf
+}

go/neo/neonet/newlink.go

@@ -21,12 +21,14 @@ package neonet
 // link establishment
 
 import (
+	"bytes"
 	"context"
-	"encoding/binary"
 	"fmt"
 	"io"
 	"net"
 
+	"github.com/tinylib/msgp/msgp"
+
 	"lab.nexedi.com/kirr/go123/xerr"
 	"lab.nexedi.com/kirr/go123/xnet"
 	"lab.nexedi.com/kirr/neo/go/internal/xcontext"
@@ -41,7 +43,7 @@ import (
 // do not have such uses.
 
 func _HandshakeClient(ctx context.Context, conn net.Conn) (*NodeLink, error) {
-	return handshakeClient(ctx, conn, proto.Version)
+	return handshakeClient(ctx, conn, proto.Version, proto.Encoding('N'))
 }
 
 func _HandshakeServer(ctx context.Context, conn net.Conn) (*NodeLink, error) {
@@ -72,52 +74,54 @@ func (e *_HandshakeError) Unwrap() error { return e.Err }
 // handshakeClient implements client-side NEO protocol handshake just after raw
 // connection between 2 nodes was established.
 //
-// Client indicates its version to server.
+// Client indicates its version and preferred encoding, but accepts any
+// encoding chosen to use by server.
 //
 // On success raw connection is returned wrapped into NodeLink.
 // On error raw connection is closed.
-func handshakeClient(ctx context.Context, conn net.Conn, version uint32) (*NodeLink, error) {
-	err := _handshakeClient(ctx, conn, version)
+func handshakeClient(ctx context.Context, conn net.Conn, version uint32, encPrefer proto.Encoding) (*NodeLink, error) {
+	enc, rxbuf, err := _handshakeClient(ctx, conn, version, encPrefer)
 	if err != nil {
 		return nil, err
 	}
-	enc := proto.Encoding('N')
-	return newNodeLink(conn, enc, _LinkClient), nil
+	return newNodeLink(conn, enc, _LinkClient, rxbuf), nil
 }
 
 // handshakeServer implements server-side NEO protocol handshake just after raw
 // connection between 2 nodes was established.
 //
-// Server verifies that its version matches Client.
+// Server verifies that its version matches Client and accepts client preferred encoding.
 //
 // On success raw connection is returned wrapped into NodeLink.
 // On error raw connection is closed.
 func handshakeServer(ctx context.Context, conn net.Conn, version uint32) (*NodeLink, error) {
-	err := _handshakeServer(ctx, conn, version)
+	enc, rxbuf, err := _handshakeServer(ctx, conn, version)
 	if err != nil {
 		return nil, err
 	}
-	enc := proto.Encoding('N')
-	return newNodeLink(conn, enc, _LinkServer), nil
+	return newNodeLink(conn, enc, _LinkServer, rxbuf), nil
 }
 
-func _handshakeClient(ctx context.Context, conn net.Conn, version uint32) (err error) {
+func _handshakeClient(ctx context.Context, conn net.Conn, version uint32, encPrefer proto.Encoding) (enc proto.Encoding, rxbuf *xbufReader, err error) {
 	defer func() {
 		if err != nil {
 			err = &_HandshakeError{_LinkClient, conn.LocalAddr(), conn.RemoteAddr(), err}
 		}
 	}()
 
+	rxbuf = newXBufReader(conn, /*any non-small limit*/1024)
+
+	var peerEnc proto.Encoding
 	err = xcontext.WithCloseOnErrCancel(ctx, conn, func() error {
 		// tx client hello
-		err := txHello("tx hello", conn, version)
+		err := txHello("tx hello", conn, version, encPrefer)
 		if err != nil {
 			return err
 		}
 
 		// rx server hello reply
 		var peerVer uint32
-		peerVer, err = rxHello("rx hello reply", conn)
+		peerEnc, peerVer, err = rxHello("rx hello reply", rxbuf)
 		if err != nil {
 			return err
 		}
@@ -130,24 +134,29 @@ func _handshakeClient(ctx context.Context, conn net.Conn, version uint32) (err e
 		return nil
 	})
 	if err != nil {
-		return err
+		return 0, nil, err
 	}
 
-	return nil
+	// use peer encoding (server should return the same, but we are ok if
+	// it asks to switch to different)
+	return peerEnc, rxbuf, nil
 }
 
-func _handshakeServer(ctx context.Context, conn net.Conn, version uint32) (err error) {
+func _handshakeServer(ctx context.Context, conn net.Conn, version uint32) (enc proto.Encoding, rxbuf *xbufReader, err error) {
 	defer func() {
 		if err != nil {
 			err = &_HandshakeError{_LinkServer, conn.LocalAddr(), conn.RemoteAddr(), err}
 		}
 	}()
 
+	rxbuf = newXBufReader(conn, /*any non-small limit*/1024)
+
+	var peerEnc proto.Encoding
 	err = xcontext.WithCloseOnErrCancel(ctx, conn, func() error {
 		// rx client hello
 		var peerVer uint32
 		var err     error
-		peerVer, err = rxHello("rx hello", conn)
+		peerEnc, peerVer, err = rxHello("rx hello", rxbuf)
 		if err != nil {
 			return err
 		}
@@ -156,7 +165,7 @@ func _handshakeServer(ctx context.Context, conn net.Conn, version uint32) (err e
 		//
 		// do it before version check so that client can also detect "version
 		// mismatch" instead of just getting "disconnect".
-		err = txHello("tx hello reply", conn, version)
+		err = txHello("tx hello reply", conn, version, peerEnc)
 		if err != nil {
 			return err
 		}
@@ -169,19 +178,43 @@ func _handshakeServer(ctx context.Context, conn net.Conn, version uint32) (err e
 		return nil
 	})
 	if err != nil {
-		return err
+		return 0, nil, err
 	}
 
-	return nil
+	return peerEnc, rxbuf, nil
 }
 
-func txHello(errctx string, conn net.Conn, version uint32) (err error) {
+// handshake hello:
+//
+// - 00 00 00 <ver>	for 'N' encoding, and
+// - 92 c4 03 NEO ...	for 'M' encoding (= msgpack of (b"NEO", <ver>))
+//
+// the first byte is different from TLS handshake (0x16).
+
+func txHello(errctx string, conn net.Conn, version uint32, enc proto.Encoding) (err error) {
 	defer xerr.Context(&err, errctx)
 
-	var b [4]byte
-	binary.BigEndian.PutUint32(b[:], version) // XXX -> hton32 ?
+	var b []byte
+	switch enc {
+	case 'N':
+		// 00 00 00 <v>
+		b = make([]byte, 4)
+		if version > 0xff {
+			panic("encoding N supports versions only in range [0, 0xff]")
+		}
+		b[3] = uint8(version)
+
+	case 'M':
+		// (b"NEO", <V>) encoded as msgpack (= 92 c4 03 NEO int(<V>))
+		b = msgp.AppendArrayHeader(b, 2)       // 92
+		b = msgp.AppendBytes(b, []byte("NEO")) // c4 03 NEO
+		b = msgp.AppendUint32(b, version)      // u?intX version
+
+	default:
+		panic("bug")
+	}
 
-	_, err = conn.Write(b[:])
+	_, err = conn.Write(b)
 	if err != nil {
 		return err
 	}
@@ -189,18 +222,52 @@ func txHello(errctx string, conn net.Conn, version uint32) (err error) {
 	return nil
 }
 
-func rxHello(errctx string, conn net.Conn) (version uint32, err error) {
+func rxHello(errctx string, rx *xbufReader) (enc proto.Encoding, version uint32, err error) {
 	defer xerr.Context(&err, errctx)
 
-	var b [4]byte
-	_, err = io.ReadFull(conn, b[:])
+	b := make([]byte, 4)
+	_, err = io.ReadFull(rx, b)
 	err = xio.NoEOF(err)
 	if err != nil {
-		return 0, err
+		return 0, 0, err
+	}
+
+	var peerEnc proto.Encoding
+	var peerVer uint32
+	badMagic := false
+	switch {
+	case bytes.Equal(b[:3], []byte{0,0,0}):
+		peerEnc = 'N'
+		peerVer = uint32(b[3])
+
+	case bytes.Equal(b, []byte{0x92, 0xc4, 3, 'N'}): // start of "fixarray<2> bin8 'N | EO' ...
+		b = append(b, []byte{0,0}...)
+		_, err = io.ReadFull(rx, b[4:])
+		err = xio.NoEOF(err)
+		if err != nil {
+			return 0, 0, err
+		}
+		if !bytes.Equal(b[4:], []byte{'E','O'}) {
+			badMagic = true
+			break
+		}
+
+		peerEnc = 'M'
+		rxM := msgp.Reader{R: rx.Reader}
+		peerVer, err = rxM.ReadUint32()
+		if err != nil {
+			return 0, 0, fmt.Errorf("M: recv peer version: %s", err) // XXX + "read magic" ctx
+		}
+
+	default:
+		badMagic = true
+	}
+
+	if badMagic {
+		return 0, 0, fmt.Errorf("invalid magic %x", b)
 	}
 
-	peerVer := binary.BigEndian.Uint32(b[:]) // XXX -> ntoh32 ?
-	return peerVer, nil
+	return peerEnc, peerVer, nil
 }
 
 

go/neo/neonet/newlink_test.go

@@ -28,18 +28,25 @@ import (
 
 	"lab.nexedi.com/kirr/go123/exc"
 	"lab.nexedi.com/kirr/go123/xsync"
+	"lab.nexedi.com/kirr/neo/go/neo/proto"
 )
 
-// _xhandshakeClient handshakes as client.
-func _xhandshakeClient(ctx context.Context, c net.Conn, version uint32) {
-	err := _handshakeClient(ctx, c, version)
+// _xhandshakeClient handshakes as client with encPrefer encoding and verifies that server accepts it.
+func _xhandshakeClient(ctx context.Context, c net.Conn, version uint32, encPrefer proto.Encoding) {
+	enc, _, err := _handshakeClient(ctx, c, version, encPrefer)
 	exc.Raiseif(err)
+	if enc != encPrefer {
+		exc.Raisef("enc (%c) != encPrefer (%c)", enc, encPrefer)
+	}
 }
 
-// _xhandshakeServer handshakes as server.
-func _xhandshakeServer(ctx context.Context, c net.Conn, version uint32) {
-	err := _handshakeServer(ctx, c, version)
+// _xhandshakeServer handshakes as server and verifies negotiated encoding to be encOK.
+func _xhandshakeServer(ctx context.Context, c net.Conn, version uint32, encOK proto.Encoding) {
+	enc, _, err := _handshakeServer(ctx, c, version)
 	exc.Raiseif(err)
+	if enc != encOK {
+		exc.Raisef("enc (%c) != encOK (%c)", enc, encOK)
+	}
 }
 
 func TestHandshake(t *testing.T) {
@@ -51,10 +58,10 @@ func _TestHandshake(t *T) {
 	p1, p2 := net.Pipe()
 	wg := xsync.NewWorkGroup(bg)
 	gox(wg, func(ctx context.Context) {
-		_xhandshakeClient(ctx, p1, 1)
+		_xhandshakeClient(ctx, p1, 1, t.enc)
 	})
 	gox(wg, func(ctx context.Context) {
-		_xhandshakeServer(ctx, p2, 1)
+		_xhandshakeServer(ctx, p2, 1, t.enc)
 	})
 	xwait(wg)
 	xclose(p1)
@@ -65,10 +72,10 @@ func _TestHandshake(t *T) {
 	var err1, err2 error
 	wg = xsync.NewWorkGroup(bg)
 	gox(wg, func(ctx context.Context) {
-		err1 = _handshakeClient(ctx, p1, 1)
+		_, _, err1 = _handshakeClient(ctx, p1, 1, t.enc)
 	})
 	gox(wg, func(ctx context.Context) {
-		err2 = _handshakeServer(ctx, p2, 2)
+		_, _, err2 = _handshakeServer(ctx, p2, 2)
 	})
 	xwait(wg)
 	xclose(p1)
@@ -89,7 +96,7 @@ func _TestHandshake(t *T) {
 	var err error
 	wg = xsync.NewWorkGroup(bg)
 	gox(wg, func(ctx context.Context) {
-		err = _handshakeClient(ctx, p1, 1)
+		_, _, err = _handshakeClient(ctx, p1, 1, t.enc)
 	})
 	gox(wg, func(_ context.Context) {
 		xclose(p2)
@@ -109,7 +116,7 @@ func _TestHandshake(t *T) {
 		xclose(p1)
 	})
 	gox(wg, func(ctx context.Context) {
-		err = _handshakeServer(ctx, p2, 1)
+		_, _, err = _handshakeServer(ctx, p2, 1)
 	})
 	xwait(wg)
 	xclose(p2)
@@ -124,7 +131,7 @@ func _TestHandshake(t *T) {
 	ctx, cancel := context.WithCancel(bg)
 	wg = xsync.NewWorkGroup(ctx)
 	gox(wg, func(ctx context.Context) {
-		err = _handshakeClient(ctx, p1, 1)
+		_, _, err = _handshakeClient(ctx, p1, 1, t.enc)
 	})
 	tdelay()
 	cancel()
@@ -142,7 +149,7 @@ func _TestHandshake(t *T) {
 	ctx, cancel = context.WithCancel(bg)
 	wg = xsync.NewWorkGroup(ctx)
 	gox(wg, func(ctx context.Context) {
-		err = _handshakeServer(ctx, p2, 1)
+		_, _, err = _handshakeServer(ctx, p2, 1)
 	})
 	tdelay()
 	cancel()

go/neo/proto/proto.go

@@ -75,8 +75,7 @@ import (
 
 const (
 	// The protocol version must be increased whenever upgrading a node may require
-	// to upgrade other nodes. It is encoded as a 4-bytes big-endian integer and
-	// the high order byte 0 is different from TLS Handshake (0x16).
+	// to upgrade other nodes.
 	Version = 6
 
 	// length of packet header in 'N'-encoding