go/neo/neonet: Factor-out decode of packet header into pktHeadDecode

Preparatory step before we introduce support for msgpack encoding.

go/neo/neonet/connection.go

@@ -788,10 +788,17 @@ func (nl *NodeLink) serveRecv() {
 		// NOTE if nl.peerLink was just closed by tx->shutdown we'll get ErrNetClosing
 		pkt, err := nl.recvPkt()
 		//fmt.Printf("\n%p recvPkt -> %v, %v\n", nl, pkt, err)
-		if err != nil {
+
+		// pkt.ConnId -> Conn
+		var connId uint32
+		if err == nil {
+			connId, _, _, err = pktDecodeHead(pkt)
+		}
+
 		// on IO error framing over peerLink becomes broken
 		// so we shut down node link and all connections over it.
-
+		// Same if we cannot decode packet header.
+		if err != nil {
 			nl.errMu.Lock()
 			nl.errRecv = err
 			nl.errMu.Unlock()
@@ -800,8 +807,7 @@ func (nl *NodeLink) serveRecv() {
 			return
 		}
 
-		// pkt.ConnId -> Conn
-		connId := packed.Ntoh32(pkt.Header().ConnId)
+
 		accept := false
 
 		nl.connMu.Lock()
@@ -1034,12 +1040,14 @@ func (c *Conn) sendPkt(pkt *pktBuf) error {
 
 func (c *Conn) sendPkt2(pkt *pktBuf) error {
 	// connId must be set to one associated with this connection
-	if pkt.Header().ConnId != packed.Hton32(c.connId) {
+	connID, _, _, err := pktDecodeHead(pkt)
+	if err != nil {
+		panic(fmt.Sprintf("Conn.sendPkt: bad packet: %s", err))
+	}
+	if connID != c.connId {
 		panic("Conn.sendPkt: connId wrong")
 	}
 
-	var err error
-
 	select {
 	case <-c.txdown:
 		return c.errSendShutdown()
@@ -1120,11 +1128,17 @@ func (nl *NodeLink) serveSend() {
 
 // sendPktDirect sends raw packet with appropriate connection ID directly via link.
 func (c *Conn) sendPktDirect(pkt *pktBuf) error {
-	// set pkt connId associated with this connection
-	pkt.Header().ConnId = packed.Hton32(c.connId)
+	// connId must be set to one associated with this connection
+	connID, _, _, err := pktDecodeHead(pkt)
+	if err != nil {
+		panic(fmt.Sprintf("Conn.sendPkt: bad packet: %s", err))
+	}
+	if connID != c.connId {
+		panic("Conn.sendPkt: connId wrong")
+	}
 
 	// NOTE if n.peerLink was just closed by rx->shutdown we'll get ErrNetClosing
-	err := c.link.sendPkt(pkt)
+	err = c.link.sendPkt(pkt)
 	//fmt.Printf("sendPkt -> %v\n", err)
 
 	// on IO error framing over peerLink becomes broken
@@ -1319,7 +1333,22 @@ func pktEncode(connId uint32, msg proto.Msg) *pktBuf {
 	return buf
 }
 
-// TODO msgUnpack
+// pktDecodeHead decodes header of a packet.
+func pktDecodeHead(pkt *pktBuf) (connID uint32, msgCode uint16, payload []byte, err error) {
+	if len(pkt.data) < proto.PktHeaderLen {
+		return 0, 0, nil, fmt.Errorf("packet too short")
+	}
+	pkth := pkt.Header()
+	connID  = packed.Ntoh32(pkth.ConnId)
+	msgCode = packed.Ntoh16(pkth.MsgCode)
+	msgLen := packed.Ntoh32(pkth.MsgLen)
+	payload = pkt.Payload()
+	if len(payload) != int(msgLen) {
+		return 0, 0, nil, fmt.Errorf("len(payload) != msgLen")
+	}
+	return
+}
+
 
 // Recv receives message from the connection.
 func (c *Conn) Recv() (proto.Msg, error) {
@@ -1330,8 +1359,11 @@ func (c *Conn) Recv() (proto.Msg, error) {
 	defer pkt.Free()
 
 	// decode packet
-	pkth := pkt.Header()
-	msgCode := packed.Ntoh16(pkth.MsgCode)
+	_, msgCode, payload, err := pktDecodeHead(pkt)
+	if err != nil {
+		return nil, err
+	}
+
 	msgType := proto.MsgType(msgCode)
 	if msgType == nil {
 		err := fmt.Errorf("invalid msgCode (%d)", msgCode)
@@ -1344,7 +1376,7 @@ func (c *Conn) Recv() (proto.Msg, error) {
 //	msg := reflect.NewAt(msgType, bufAlloc(msgType.Size())
 
 
-	_, err = msg.NEOMsgDecode(pkt.Payload())
+	_, err = msg.NEOMsgDecode(payload)
 	if err != nil {
 		return nil, c.err("decode", err) // XXX "decode:" is already in ErrDecodeOverflow
 	}
@@ -1388,12 +1420,15 @@ func (c *Conn) Expect(msgv ...proto.Msg) (which int, err error) {
 	}
 	defer pkt.Free()
 
-	pkth := pkt.Header()
-	msgCode := packed.Ntoh16(pkth.MsgCode)
+	// decode packet
+	_, msgCode, payload, err := pktDecodeHead(pkt)
+	if err != nil {
+		return -1, err
+	}
 
 	for i, msg := range msgv {
 		if msg.NEOMsgCode() == msgCode {
-			_, err := msg.NEOMsgDecode(pkt.Payload())
+			_, err := msg.NEOMsgDecode(payload)
 			if err != nil {
 				return -1, c.err("decode", err)
 			}

go/neo/neonet/connection_test.go

@@ -136,20 +136,20 @@ func (c *Conn) mkpkt(msgcode uint16, payload []byte) *pktBuf {
 // Verify pktBuf is as expected.
 func (t *T) xverifyPkt(pkt *pktBuf, connid uint32, msgcode uint16, payload []byte) {
 	errv := xerr.Errorv{}
-	h := pkt.Header()
+
+	pktConnID, pktMsgCode, pktPayload, err := pktDecodeHead(pkt)
+	exc.Raiseif(err)
+
 	// TODO include caller location
-	if packed.Ntoh32(h.ConnId) != connid {
-		errv.Appendf("header: unexpected connid %v  (want %v)", packed.Ntoh32(h.ConnId), connid)
-	}
-	if packed.Ntoh16(h.MsgCode) != msgcode {
-		errv.Appendf("header: unexpected msgcode %v  (want %v)", packed.Ntoh16(h.MsgCode), msgcode)
+	if pktConnID != connid {
+		errv.Appendf("header: unexpected connid %v  (want %v)", pktConnID, connid)
 	}
-	if packed.Ntoh32(h.MsgLen) != uint32(len(payload)) {
-		errv.Appendf("header: unexpected msglen %v  (want %v)", packed.Ntoh32(h.MsgLen), len(payload))
+	if pktMsgCode != msgcode {
+		errv.Appendf("header: unexpected msgcode %v  (want %v)", pktMsgCode, msgcode)
 	}
-	if !bytes.Equal(pkt.Payload(), payload) {
+	if !bytes.Equal(pktPayload, payload) {
 		errv.Appendf("payload differ:\n%s",
-			pretty.Compare(string(payload), string(pkt.Payload())))
+			pretty.Compare(string(payload), string(pktPayload)))
 	}
 
 	exc.Raiseif(errv.Err())
@@ -614,8 +614,9 @@ func _TestNodeLink(t *T) {
 
 			gox(wg, func(_ context.Context) {
 				pkt := xrecvPkt(c)
-				n := packed.Ntoh16(pkt.Header().MsgCode)
-				x := replyOrder[n]
+				_, msgCode, _, err := pktDecodeHead(pkt)
+				exc.Raiseif(err)
+				x := replyOrder[msgCode]
 
 				// wait before it is our turn & echo pkt back
 				<-x.start

go/neo/neonet/pkt.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
@@ -28,7 +28,6 @@ import (
 
 	"lab.nexedi.com/kirr/go123/xbytes"
 
-	"lab.nexedi.com/kirr/neo/go/internal/packed"
 	"lab.nexedi.com/kirr/neo/go/neo/proto"
 )
 
@@ -80,32 +79,29 @@ func (pkt *pktBuf) Free() {
 
 // String dumps a packet in human-readable form.
 func (pkt *pktBuf) String() string {
-	if len(pkt.data) < proto.PktHeaderLen {
-		return fmt.Sprintf("(! < PktHeaderLen) % x", pkt.data)
+	connID, msgCode, payload, err := pktDecodeHead(pkt)
+	if err != nil {
+		return fmt.Sprintf("(%s) % x", err, pkt.data)
 	}
 
-	h := pkt.Header()
-	s := fmt.Sprintf(".%d", packed.Ntoh32(h.ConnId))
+	s := fmt.Sprintf(".%d", connID)
 
-	msgCode := packed.Ntoh16(h.MsgCode)
-	msgLen  := packed.Ntoh32(h.MsgLen)
-	data    := pkt.Payload()
 	msgType := proto.MsgType(msgCode)
 	if msgType == nil {
-		s += fmt.Sprintf(" ? (%d) #%d [%d]: % x", msgCode, msgLen, len(data), data)
+		s += fmt.Sprintf(" ? (%d) [%d]: % x", msgCode, len(payload), payload)
 		return s
 	}
 
 	// XXX dup wrt Conn.Recv
 	msg := reflect.New(msgType).Interface().(proto.Msg)
-	n, err := msg.NEOMsgDecode(data)
+	n, err := msg.NEOMsgDecode(payload)
 	if err != nil {
-		s += fmt.Sprintf(" (%s) %v; #%d [%d]: % x", msgType.Name(), err, msgLen, len(data), data)
+		s += fmt.Sprintf(" (%s) %v; [%d]: % x", msgType.Name(), err, len(payload), payload)
 	} else {
 		s += fmt.Sprintf(" %s %v", msgType.Name(), msg) // XXX or %+v better?
 
-		if n < len(data) {
-			tail := data[n:]
+		if n < len(payload) {
+			tail := payload[n:]
 			s += fmt.Sprintf(" ;  [%d]tail: % x", len(tail), tail)
 		}
 	}