[NOD-652] Add selected tip and get selected tip messages (#595)

* [NOD-652] Add selectedTip and getSelectedTip messages

* [NOD-652] Remove peerSyncState.isSelectedTipKnown

* [NOD-652] Do nothing on OnSelectedTip if the peer selected tip hasn't changed

* [NOD-652] Handle selected tip message with block handler

* [NOD-652] Add comments

* [NOD-652] go mod tidy

* [NOD-652] Fix TestVersion

* [NOD-652] Use dag.AdjustedTime instead of dag.timeSource.AdjustedTime

* [NOD-652] Create shouldQueryPeerSelectedTips and queueMsgGetSelectedTip functions

* [NOD-652] Change selectedTip to selectedTipHash where needed

* [NOD-652] add minDAGTimeDelay constant

* [NOD-652] add comments

* [NOD-652] Fix names and comments

* [NOD-652] Put msg.reply push in the right place

* [NOD-652] Fix comments and names

blockdag/blocknode.go

@@ -114,7 +114,7 @@ func (dag *BlockDAG) newBlockNode(blockHeader *wire.BlockHeader, parents blockSe
 		parents:            parents,
 		children:           make(blockSet),
 		blueScore:          math.MaxUint64, // Initialized to the max value to avoid collisions with the genesis block
-		timestamp:          dag.timeSource.AdjustedTime().Unix(),
+		timestamp:          dag.AdjustedTime().Unix(),
 		bluesAnticoneSizes: make(map[daghash.Hash]uint32),
 	}
 

blockdag/dag.go

@@ -1274,10 +1274,17 @@ func (dag *BlockDAG) isCurrent() bool {
 	} else {
 		dagTimestamp = selectedTip.timestamp
 	}
-	minus24Hours := dag.timeSource.AdjustedTime().Add(-24 * time.Hour).Unix()
+	minus24Hours := dag.AdjustedTime().Add(-24 * time.Hour).Unix()
 	return dagTimestamp >= minus24Hours
 }
 
+// AdjustedTime returns the adjusted time according to
+// dag.timeSource. See MedianTimeSource.AdjustedTime for
+// more details.
+func (dag *BlockDAG) AdjustedTime() time.Time {
+	return dag.timeSource.AdjustedTime()
+}
+
 // IsCurrent returns whether or not the DAG believes it is current. Several
 // factors are used to guess, but the key factors that allow the DAG to
 // believe it is current are:
@@ -1774,7 +1781,7 @@ func (dag *BlockDAG) SubnetworkID() *subnetworkid.SubnetworkID {
 }
 
 func (dag *BlockDAG) addDelayedBlock(block *util.Block, delay time.Duration) error {
-	processTime := dag.timeSource.AdjustedTime().Add(delay)
+	processTime := dag.AdjustedTime().Add(delay)
 	log.Debugf("Adding block to delayed blocks queue (block hash: %s, process time: %s)", block.Hash().String(), processTime)
 	delayedBlock := &delayedBlock{
 		block:       block,
@@ -1792,7 +1799,7 @@ func (dag *BlockDAG) processDelayedBlocks() error {
 	// Check if the delayed block with the earliest process time should be processed
 	for dag.delayedBlocksQueue.Len() > 0 {
 		earliestDelayedBlockProcessTime := dag.peekDelayedBlock().processTime
-		if earliestDelayedBlockProcessTime.After(dag.timeSource.AdjustedTime()) {
+		if earliestDelayedBlockProcessTime.After(dag.AdjustedTime()) {
 			break
 		}
 		delayedBlock := dag.popDelayedBlock()

blockdag/mining.go

@@ -114,7 +114,7 @@ func (dag *BlockDAG) NextBlockTime() time.Time {
 	// timestamp is truncated to a second boundary before comparison since a
 	// block timestamp does not supported a precision greater than one
 	// second.
-	newTimestamp := dag.timeSource.AdjustedTime()
+	newTimestamp := dag.AdjustedTime()
 	minTimestamp := dag.NextBlockMinimumTime()
 	if newTimestamp.Before(minTimestamp) {
 		newTimestamp = minTimestamp

blockdag/process.go

@@ -251,7 +251,7 @@ func (dag *BlockDAG) maxDelayOfParents(parentHashes []*daghash.Hash) (delay time
 	for _, parentHash := range parentHashes {
 		if delayedParent, exists := dag.delayedBlocks[*parentHash]; exists {
 			isDelayed = true
-			parentDelay := delayedParent.processTime.Sub(dag.timeSource.AdjustedTime())
+			parentDelay := delayedParent.processTime.Sub(dag.AdjustedTime())
 			if parentDelay > delay {
 				delay = parentDelay
 			}

blockdag/validate.go

@@ -435,7 +435,7 @@ func (dag *BlockDAG) checkBlockHeaderSanity(header *wire.BlockHeader, flags Beha
 	// the duration of time that should be waited before the block becomes valid.
 	// This check needs to be last as it does not return an error but rather marks the
 	// header as delayed (and valid).
-	maxTimestamp := dag.timeSource.AdjustedTime().Add(time.Second *
+	maxTimestamp := dag.AdjustedTime().Add(time.Second *
 		time.Duration(int64(dag.TimestampDeviationTolerance)*dag.targetTimePerBlock))
 	if header.Timestamp.After(maxTimestamp) {
 		return header.Timestamp.Sub(maxTimestamp), nil

go.mod

@@ -16,8 +16,8 @@ require (
 	github.com/jrick/logrotate v1.0.0
 	github.com/kr/pretty v0.1.0 // indirect
 	github.com/pkg/errors v0.8.1
-	golang.org/x/crypto v0.0.0-20190426145343-a29dc8fdc734
+	golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550
-	golang.org/x/net v0.0.0-20190613194153-d28f0bde5980 // indirect
+	golang.org/x/net v0.0.0-20190620200207-3b0461eec859 // indirect
 	golang.org/x/sys v0.0.0-20190426135247-a129542de9ae // indirect
 	golang.org/x/text v0.3.2 // indirect
 	gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127 // indirect

go.sum

@@ -34,12 +34,12 @@ github.com/onsi/gomega v1.4.1/go.mod h1:C1qb7wdrVGGVU+Z6iS04AVkA3Q65CEZX59MT0QO5
 github.com/pkg/errors v0.8.1 h1:iURUrRGxPUNPdy5/HRSm+Yj6okJ6UtLINN0Q9M4+h3I=
 github.com/pkg/errors v0.8.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
-golang.org/x/crypto v0.0.0-20190426145343-a29dc8fdc734 h1:p/H982KKEjUnLJkM3tt/LemDnOc1GiZL5FCVlORJ5zo=
+golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550 h1:ObdrDkeb4kJdCP557AjRjq69pTHfNouLtWZG7j9rPN8=
-golang.org/x/crypto v0.0.0-20190426145343-a29dc8fdc734/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
+golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
 golang.org/x/net v0.0.0-20180719180050-a680a1efc54d/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
-golang.org/x/net v0.0.0-20190613194153-d28f0bde5980 h1:dfGZHvZk057jK2MCeWus/TowKpJ8y4AmooUzdBSR9GU=
+golang.org/x/net v0.0.0-20190620200207-3b0461eec859 h1:R/3boaszxrf1GEUWTVDzSKVwLmSJpwZ1yqXm8j0v2QI=
-golang.org/x/net v0.0.0-20190613194153-d28f0bde5980/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
+golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190426135247-a129542de9ae h1:mQLHiymj/JXKnnjc62tb7nD5pZLs940/sXJu+Xp3DBA=

netsync/manager.go

@@ -18,6 +18,7 @@ import (
 	"net"
 	"sync"
 	"sync/atomic"
+	"time"
 )
 
 const (
@@ -32,6 +33,10 @@ const (
 	// maxRequestedTxns is the maximum number of requested transactions
 	// hashes to store in memory.
 	maxRequestedTxns = wire.MaxInvPerMsg
+
+	minGetSelectedTipInterval = time.Minute
+
+	minDAGTimeDelay = time.Minute
 )
 
 // newPeerMsg signifies a newly connected peer to the block handler.
@@ -113,6 +118,12 @@ type pauseMsg struct {
 	unpause <-chan struct{}
 }
 
+type selectedTipMsg struct {
+	selectedTipHash *daghash.Hash
+	peer            *peerpkg.Peer
+	reply           chan struct{}
+}
+
 type requestQueueAndSet struct {
 	queue []*wire.InvVect
 	set   map[daghash.Hash]struct{}
@@ -122,6 +133,8 @@ type requestQueueAndSet struct {
 // about a peer.
 type peerSyncState struct {
 	syncCandidate           bool
+	lastSelectedTipRequest  time.Time
+	isPendingForSelectedTip bool
 	requestQueueMtx         sync.Mutex
 	requestQueues           map[wire.InvType]*requestQueueAndSet
 	requestedTxns           map[daghash.TxID]struct{}
@@ -169,8 +182,7 @@ func (sm *SyncManager) startSync() {
 			continue
 		}
 
-		if !peer.IsSyncCandidate() {
+		if !peer.IsSelectedTipKnown() {
-			state.syncCandidate = false
 			continue
 		}
 
@@ -187,13 +199,38 @@ func (sm *SyncManager) startSync() {
 		sm.requestedBlocks = make(map[daghash.Hash]struct{})
 
 		log.Infof("Syncing to block %s from peer %s",
-			syncPeer.SelectedTip(), syncPeer.Addr())
+			syncPeer.SelectedTipHash(), syncPeer.Addr())
 
-		syncPeer.PushGetBlockLocatorMsg(syncPeer.SelectedTip(), sm.dagParams.GenesisHash)
+		syncPeer.PushGetBlockLocatorMsg(syncPeer.SelectedTipHash(), sm.dagParams.GenesisHash)
 		sm.syncPeer = syncPeer
-	} else {
+		return
-		log.Warnf("No sync peer candidates available")
 	}
+
+	log.Warnf("No sync peer candidates available")
+	if sm.shouldQueryPeerSelectedTips() {
+		for peer, state := range sm.peerStates {
+			if !state.syncCandidate {
+				continue
+			}
+
+			if time.Now().Sub(state.lastSelectedTipRequest) < minGetSelectedTipInterval {
+				continue
+			}
+
+			queueMsgGetSelectedTip(peer, state)
+		}
+	}
+	return
+}
+
+func (sm *SyncManager) shouldQueryPeerSelectedTips() bool {
+	return sm.dag.AdjustedTime().Sub(sm.dag.CalcPastMedianTime()) > minDAGTimeDelay
+}
+
+func queueMsgGetSelectedTip(peer *peerpkg.Peer, state *peerSyncState) {
+	state.lastSelectedTipRequest = time.Now()
+	state.isPendingForSelectedTip = true
+	peer.QueueMessage(wire.NewMsgGetSelectedTip(), nil)
 }
 
 // isSyncCandidate returns whether or not the peer is a candidate to consider
@@ -827,6 +864,23 @@ func (sm *SyncManager) limitHashMap(m map[daghash.Hash]struct{}, limit int) {
 	}
 }
 
+func (sm *SyncManager) handleSelectedTipMsg(msg *selectedTipMsg) {
+	peer := msg.peer
+	selectedTipHash := msg.selectedTipHash
+	state := sm.peerStates[peer]
+	if !state.isPendingForSelectedTip {
+		log.Warnf("Got unrequested selected tip message from %s -- "+
+			"disconnecting", peer.Addr())
+		peer.Disconnect()
+	}
+	state.isPendingForSelectedTip = false
+	if selectedTipHash.IsEqual(peer.SelectedTipHash()) {
+		return
+	}
+	peer.SetSelectedTipHash(selectedTipHash)
+	sm.startSync()
+}
+
 // blockHandler is the main handler for the sync manager. It must be run as a
 // goroutine. It processes block and inv messages in a separate goroutine
 // from the peer handlers so the block (MsgBlock) messages are handled by a
@@ -894,6 +948,10 @@ out:
 				// Wait until the sender unpauses the manager.
 				<-msg.unpause
 
+			case *selectedTipMsg:
+				sm.handleSelectedTipMsg(msg)
+				msg.reply <- struct{}{}
+
 			default:
 				log.Warnf("Invalid message type in block "+
 					"handler: %T", msg)
@@ -992,6 +1050,17 @@ func (sm *SyncManager) QueueInv(inv *wire.MsgInv, peer *peerpkg.Peer) {
 	sm.msgChan <- &invMsg{inv: inv, peer: peer}
 }
 
+// QueueSelectedTipMsg adds the passed selected tip message and peer to the
+// block handling queue. Responds to the done channel argument after it finished
+// handling the message.
+func (sm *SyncManager) QueueSelectedTipMsg(msg *wire.MsgSelectedTip, peer *peerpkg.Peer, done chan struct{}) {
+	sm.msgChan <- &selectedTipMsg{
+		selectedTipHash: msg.SelectedTipHash,
+		peer:            peer,
+		reply:           done,
+	}
+}
+
 // DonePeer informs the blockmanager that a peer has disconnected.
 func (sm *SyncManager) DonePeer(peer *peerpkg.Peer) {
 	// Ignore if we are shutting down.

peer/example_test.go

@@ -23,7 +23,7 @@ func mockRemotePeer() error {
 		UserAgentName:    "peer",  // User agent name to advertise.
 		UserAgentVersion: "1.0.0", // User agent version to advertise.
 		DAGParams:        &dagconfig.SimnetParams,
-		SelectedTip:      fakeSelectedTipFn,
+		SelectedTipHash:  fakeSelectedTipFn,
 	}
 
 	// Accept connections on the simnet port.
@@ -78,7 +78,7 @@ func Example_newOutboundPeer() {
 				verack <- struct{}{}
 			},
 		},
-		SelectedTip: fakeSelectedTipFn,
+		SelectedTipHash: fakeSelectedTipFn,
 	}
 	p, err := peer.NewOutboundPeer(peerCfg, "127.0.0.1:18555")
 	if err != nil {

peer/log.go

@@ -96,7 +96,7 @@ func messageSummary(msg wire.Message) string {
 	switch msg := msg.(type) {
 	case *wire.MsgVersion:
 		return fmt.Sprintf("agent %s, pver %d, selected tip %s",
-			msg.UserAgent, msg.ProtocolVersion, msg.SelectedTip)
+			msg.UserAgent, msg.ProtocolVersion, msg.SelectedTipHash)
 
 	case *wire.MsgVerAck:
 		// No summary.

peer/peer.go

@@ -168,6 +168,14 @@ type MessageListeners struct {
 	// message.
 	OnSendHeaders func(p *Peer, msg *wire.MsgSendHeaders)
 
+	// OnGetSelectedTip is invoked when a peer receives a getSelectedTip kaspa
+	// message.
+	OnGetSelectedTip func()
+
+	// OnSelectedTip is invoked when a peer receives a selectedTip kaspa
+	// message.
+	OnSelectedTip func(p *Peer, msg *wire.MsgSelectedTip)
+
 	// OnRead is invoked when a peer receives a kaspa message. It
 	// consists of the number of bytes read, the message, and whether or not
 	// an error in the read occurred. Typically, callers will opt to use
@@ -186,12 +194,12 @@ type MessageListeners struct {
 
 // Config is the struct to hold configuration options useful to Peer.
 type Config struct {
-	// SelectedTip specifies a callback which provides the selected tip
+	// SelectedTipHash specifies a callback which provides the selected tip
 	// to the peer as needed.
-	SelectedTip func() *daghash.Hash
+	SelectedTipHash func() *daghash.Hash
 
-	// SelectedTip specifies a callback which provides the selected tip
+	// BlockExists determines whether a block with the given hash exists in
-	// to the peer as needed.
+	// the DAG.
 	BlockExists func(*daghash.Hash) bool
 
 	// HostToNetAddress returns the netaddress for the given host. This can be
@@ -341,7 +349,7 @@ type StatsSnap struct {
 	Version         uint32
 	UserAgent       string
 	Inbound         bool
-	SelectedTip    *daghash.Hash
+	SelectedTipHash *daghash.Hash
 	LastPingNonce   uint64
 	LastPingTime    time.Time
 	LastPingMicros  int64
@@ -426,7 +434,7 @@ type Peer struct {
 	statsMtx        sync.RWMutex
 	timeOffset      int64
 	timeConnected   time.Time
-	selectedTip    *daghash.Hash
+	selectedTipHash *daghash.Hash
 	lastPingNonce   uint64    // Set to nonce if we have a pending ping.
 	lastPingTime    time.Time // Time we sent last ping.
 	lastPingMicros  int64     // Time for last ping to return.
@@ -486,7 +494,7 @@ func (p *Peer) StatsSnapshot() *StatsSnap {
 		TimeOffset:      p.timeOffset,
 		Version:         protocolVersion,
 		Inbound:         p.inbound,
-		SelectedTip:    p.selectedTip,
+		SelectedTipHash: p.selectedTipHash,
 		LastPingNonce:   p.lastPingNonce,
 		LastPingMicros:  p.lastPingMicros,
 		LastPingTime:    p.lastPingTime,
@@ -633,22 +641,28 @@ func (p *Peer) ProtocolVersion() uint32 {
 	return protocolVersion
 }
 
-// SelectedTip returns the selected tip of the peer.
+// SelectedTipHash returns the selected tip of the peer.
 //
 // This function is safe for concurrent access.
-func (p *Peer) SelectedTip() *daghash.Hash {
+func (p *Peer) SelectedTipHash() *daghash.Hash {
 	p.statsMtx.RLock()
-	selectedTip := p.selectedTip
+	selectedTipHash := p.selectedTipHash
 	p.statsMtx.RUnlock()
 
-	return selectedTip
+	return selectedTipHash
 }
 
-// IsSyncCandidate returns whether or not this peer is a sync candidate.
+// SetSelectedTipHash sets the selected tip of the peer.
+func (p *Peer) SetSelectedTipHash(selectedTipHash *daghash.Hash) {
+	p.selectedTipHash = selectedTipHash
+}
+
+// IsSelectedTipKnown returns whether or not this peer selected
+// tip is a known block.
 //
 // This function is safe for concurrent access.
-func (p *Peer) IsSyncCandidate() bool {
+func (p *Peer) IsSelectedTipKnown() bool {
-	return !p.cfg.BlockExists(p.selectedTip)
+	return !p.cfg.BlockExists(p.selectedTipHash)
 }
 
 // LastSend returns the last send time of the peer.
@@ -718,7 +732,7 @@ func (p *Peer) WantsHeaders() bool {
 // localVersionMsg creates a version message that can be used to send to the
 // remote peer.
 func (p *Peer) localVersionMsg() (*wire.MsgVersion, error) {
-	selectedTip := p.cfg.SelectedTip()
+	selectedTipHash := p.cfg.SelectedTipHash()
 	theirNA := p.na
 
 	// If we are behind a proxy and the connection comes from the proxy then
@@ -754,7 +768,7 @@ func (p *Peer) localVersionMsg() (*wire.MsgVersion, error) {
 	subnetworkID := p.cfg.SubnetworkID
 
 	// Version message.
-	msg := wire.NewMsgVersion(ourNA, theirNA, nonce, selectedTip, subnetworkID)
+	msg := wire.NewMsgVersion(ourNA, theirNA, nonce, selectedTipHash, subnetworkID)
 	msg.AddUserAgent(p.cfg.UserAgentName, p.cfg.UserAgentVersion,
 		p.cfg.UserAgentComments...)
 
@@ -960,7 +974,7 @@ func (p *Peer) handleRemoteVersionMsg(msg *wire.MsgVersion) error {
 	// Updating a bunch of stats including block based stats, and the
 	// peer's time offset.
 	p.statsMtx.Lock()
-	p.selectedTip = msg.SelectedTip
+	p.selectedTipHash = msg.SelectedTipHash
 	p.timeOffset = msg.Timestamp.Unix() - time.Now().Unix()
 	p.statsMtx.Unlock()
 
@@ -1172,6 +1186,10 @@ func (p *Peer) maybeAddDeadline(pendingResponses map[string]time.Time, msgCmd st
 		// headers.
 		deadline = time.Now().Add(stallResponseTimeout * 3)
 		pendingResponses[wire.CmdHeaders] = deadline
+
+	case wire.CmdGetSelectedTip:
+		// Expects a selected tip message.
+		pendingResponses[wire.CmdSelectedTip] = deadline
 	}
 }
 
@@ -1500,6 +1518,16 @@ out:
 				p.cfg.Listeners.OnSendHeaders(p, msg)
 			}
 
+		case *wire.MsgGetSelectedTip:
+			if p.cfg.Listeners.OnGetSelectedTip != nil {
+				p.cfg.Listeners.OnGetSelectedTip()
+			}
+
+		case *wire.MsgSelectedTip:
+			if p.cfg.Listeners.OnSelectedTip != nil {
+				p.cfg.Listeners.OnSelectedTip(p, msg)
+			}
+
 		default:
 			log.Debugf("Received unhandled message of type %s "+
 				"from %s", rmsg.Command(), p)

peer/peer_test.go

@@ -218,7 +218,7 @@ func TestPeerConnection(t *testing.T) {
 		DAGParams:         &dagconfig.MainnetParams,
 		ProtocolVersion:   wire.ProtocolVersion, // Configure with older version
 		Services:          0,
-		SelectedTip:       fakeSelectedTipFn,
+		SelectedTipHash:   fakeSelectedTipFn,
 	}
 	peer2Cfg := &peer.Config{
 		Listeners:         peer1Cfg.Listeners,
@@ -228,7 +228,7 @@ func TestPeerConnection(t *testing.T) {
 		DAGParams:         &dagconfig.MainnetParams,
 		ProtocolVersion:   wire.ProtocolVersion + 1,
 		Services:          wire.SFNodeNetwork,
-		SelectedTip:       fakeSelectedTipFn,
+		SelectedTipHash:   fakeSelectedTipFn,
 	}
 
 	wantStats1 := peerStats{
@@ -403,7 +403,7 @@ func TestPeerListeners(t *testing.T) {
 		UserAgentComments: []string{"comment"},
 		DAGParams:         &dagconfig.MainnetParams,
 		Services:          wire.SFNodeBloom,
-		SelectedTip:       fakeSelectedTipFn,
+		SelectedTipHash:   fakeSelectedTipFn,
 	}
 	inConn, outConn := pipe(
 		&conn{raddr: "10.0.0.1:16111"},
@@ -528,7 +528,7 @@ func TestPeerListeners(t *testing.T) {
 // TestOutboundPeer tests that the outbound peer works as expected.
 func TestOutboundPeer(t *testing.T) {
 	peerCfg := &peer.Config{
-		SelectedTip: func() *daghash.Hash {
+		SelectedTipHash: func() *daghash.Hash {
 			return &daghash.ZeroHash
 		},
 		UserAgentName:     "peer",
@@ -568,8 +568,8 @@ func TestOutboundPeer(t *testing.T) {
 	<-done
 	p.Disconnect()
 
-	// Test SelectedTip
+	// Test SelectedTipHashAndBlueScore
-	var selectedTip = func() *daghash.Hash {
+	var selectedTipHash = func() *daghash.Hash {
 		hashStr := "14a0810ac680a3eb3f82edc878cea25ec41d6b790744e5daeef"
 		hash, err := daghash.NewHashFromStr(hashStr)
 		if err != nil {
@@ -578,7 +578,7 @@ func TestOutboundPeer(t *testing.T) {
 		return hash
 	}
 
-	peerCfg.SelectedTip = selectedTip
+	peerCfg.SelectedTipHash = selectedTipHash
 	r1, w1 := io.Pipe()
 	c1 := &conn{raddr: "10.0.0.1:16111", Writer: w1, Reader: r1}
 	p1, err := peer.NewOutboundPeer(peerCfg, "10.0.0.1:16111")
@@ -645,7 +645,7 @@ func TestUnsupportedVersionPeer(t *testing.T) {
 		UserAgentComments: []string{"comment"},
 		DAGParams:         &dagconfig.MainnetParams,
 		Services:          0,
-		SelectedTip:       fakeSelectedTipFn,
+		SelectedTipHash:   fakeSelectedTipFn,
 	}
 
 	localNA := wire.NewNetAddressIPPort(

server/p2p/on_block_locator.go

@@ -33,7 +33,7 @@ func (sp *Peer) OnBlockLocator(_ *peer.Peer, msg *wire.MsgBlockLocator) {
 		// This is not a mistake. The invs we desire start from the highest
 		// hash that we know of and end at the highest hash that the peer
 		// knows of.
-		err := sp.Peer.PushGetBlockInvsMsg(highHash, sp.Peer.SelectedTip())
+		err := sp.Peer.PushGetBlockInvsMsg(highHash, sp.Peer.SelectedTipHash())
 		if err != nil {
 			peerLog.Errorf("Failed pushing get blocks message for peer %s: %s",
 				sp, err)

server/p2p/on_get_selected_tip.go

@@ -0,0 +1,11 @@
+package p2p
+
+import (
+	"github.com/kaspanet/kaspad/wire"
+)
+
+// OnGetSelectedTip is invoked when a peer receives a getSelectedTip kaspa
+// message.
+func (sp *Peer) OnGetSelectedTip() {
+	sp.QueueMessage(wire.NewMsgSelectedTip(sp.selectedTipHash()), nil)
+}

server/p2p/on_selected_tip.go

@@ -0,0 +1,14 @@
+package p2p
+
+import (
+	"github.com/kaspanet/kaspad/peer"
+	"github.com/kaspanet/kaspad/wire"
+)
+
+// OnSelectedTip is invoked when a peer receives a selectedTip kaspa
+// message.
+func (sp *Peer) OnSelectedTip(peer *peer.Peer, msg *wire.MsgSelectedTip) {
+	done := make(chan struct{})
+	sp.server.SyncManager.QueueSelectedTipMsg(msg, peer, done)
+	<-done
+}

server/p2p/p2p.go

@@ -296,8 +296,8 @@ func newServerPeer(s *Server, isPersistent bool) *Peer {
 	}
 }
 
-// selectedTip returns the current selected tip
+// selectedTipHash returns the current selected tip hash
-func (sp *Peer) selectedTip() *daghash.Hash {
+func (sp *Peer) selectedTipHash() *daghash.Hash {
 	return sp.server.DAG.SelectedTipHash()
 }
 
@@ -894,7 +894,7 @@ func (s *Server) handleQuery(state *peerState, querymsg interface{}) {
 		shouldMineOnGenesis := true
 		if state.Count() != 0 {
 			shouldMineOnGenesis = state.forAllPeers(func(sp *Peer) bool {
-				if !sp.SelectedTip().IsEqual(s.DAGParams.GenesisHash) {
+				if !sp.SelectedTipHash().IsEqual(s.DAGParams.GenesisHash) {
 					return false
 				}
 				return true
@@ -1046,10 +1046,12 @@ func newPeerConfig(sp *Peer) *peer.Config {
 			OnFilterLoad:      sp.OnFilterLoad,
 			OnGetAddr:         sp.OnGetAddr,
 			OnAddr:            sp.OnAddr,
+			OnGetSelectedTip:  sp.OnGetSelectedTip,
+			OnSelectedTip:     sp.OnSelectedTip,
 			OnRead:            sp.OnRead,
 			OnWrite:           sp.OnWrite,
 		},
-		SelectedTip:       sp.selectedTip,
+		SelectedTipHash:   sp.selectedTipHash,
 		BlockExists:       sp.blockExists,
 		HostToNetAddress:  sp.server.addrManager.HostToNetAddress,
 		Proxy:             config.ActiveConfig().Proxy,

server/rpc/handle_get_peer_info.go

@@ -28,7 +28,7 @@ func handleGetPeerInfo(s *Server, cmd interface{}, closeChan <-chan struct{}) (i
 			Version:     statsSnap.Version,
 			SubVer:      statsSnap.UserAgent,
 			Inbound:     statsSnap.Inbound,
-			SelectedTip: statsSnap.SelectedTip.String(),
+			SelectedTip: statsSnap.SelectedTipHash.String(),
 			BanScore:    int32(p.BanScore()),
 			FeeFilter:   p.FeeFilter(),
 			SyncNode:    statsSnap.ID == syncPeerID,

server/rpc/rpcserverhelp.go

@@ -364,7 +364,7 @@ var helpDescsEnUS = map[string]string{
 
 	// GetChainFromBlockResult help.
 	"getChainFromBlockResult-removedChainBlockHashes": "List chain-block hashes that were removed from the selected parent chain in top-to-bottom order",
-	"getChainFromBlockResult-addedChainBlocks":        "List of ChainBlocks from Virtual.SelectedTip to StartHash (excluding StartHash) ordered bottom-to-top.",
+	"getChainFromBlockResult-addedChainBlocks":        "List of ChainBlocks from Virtual.SelectedTipHashAndBlueScore to StartHash (excluding StartHash) ordered bottom-to-top.",
 	"getChainFromBlockResult-blocks":                  "If includeBlocks=true - contains the contents of all chain and accepted blocks in the AddedChainBlocks. Otherwise - omitted.",
 
 	// GetConnectionCountCmd help.

wire/message.go

@@ -52,6 +52,8 @@ const (
 	CmdFeeFilter       = "feefilter"
 	CmdGetBlockLocator = "getlocator"
 	CmdBlockLocator    = "locator"
+	CmdSelectedTip     = "selectedtip"
+	CmdGetSelectedTip  = "getseltip"
 )
 
 // Message is an interface that describes a kaspa message. A type that
@@ -139,6 +141,12 @@ func makeEmptyMessage(command string) (Message, error) {
 	case CmdFeeFilter:
 		msg = &MsgFeeFilter{}
 
+	case CmdGetSelectedTip:
+		msg = &MsgGetSelectedTip{}
+
+	case CmdSelectedTip:
+		msg = &MsgSelectedTip{}
+
 	default:
 		return nil, errors.Errorf("unhandled command [%s]", command)
 	}

wire/msggetblocklocator.go

@@ -9,8 +9,6 @@ import (
 // MsgGetBlockLocator implements the Message interface and represents a kaspa
 // getlocator message. It is used to request a block locator between start and stop hash.
 // The locator is returned via a locator message (MsgBlockLocator).
-//
-// This message has no payload.
 type MsgGetBlockLocator struct {
 	HighHash *daghash.Hash
 	LowHash  *daghash.Hash

wire/msggetselectedtip.go

@@ -0,0 +1,41 @@
+package wire
+
+import (
+	"io"
+)
+
+// MsgGetSelectedTip implements the Message interface and represents a kaspa
+// getseltip message. It is used to request the selected tip of another peer.
+//
+// This message has no payload.
+type MsgGetSelectedTip struct{}
+
+// KaspaDecode decodes r using the kaspa protocol encoding into the receiver.
+// This is part of the Message interface implementation.
+func (msg *MsgGetSelectedTip) KaspaDecode(r io.Reader, pver uint32) error {
+	return nil
+}
+
+// KaspaEncode encodes the receiver to w using the kaspa protocol encoding.
+// This is part of the Message interface implementation.
+func (msg *MsgGetSelectedTip) KaspaEncode(w io.Writer, pver uint32) error {
+	return nil
+}
+
+// Command returns the protocol command string for the message. This is part
+// of the Message interface implementation.
+func (msg *MsgGetSelectedTip) Command() string {
+	return CmdGetSelectedTip
+}
+
+// MaxPayloadLength returns the maximum length the payload can be for the
+// receiver. This is part of the Message interface implementation.
+func (msg *MsgGetSelectedTip) MaxPayloadLength(pver uint32) uint32 {
+	return 0
+}
+
+// NewMsgGetSelectedTip returns a new kaspa getseltip message that conforms to the
+// Message interface.
+func NewMsgGetSelectedTip() *MsgGetSelectedTip {
+	return &MsgGetSelectedTip{}
+}

wire/msggetselectedtip_test.go

@@ -0,0 +1,87 @@
+// Copyright (c) 2013-2016 The btcsuite developers
+// Use of this source code is governed by an ISC
+// license that can be found in the LICENSE file.
+
+package wire
+
+import (
+	"bytes"
+	"reflect"
+	"testing"
+
+	"github.com/davecgh/go-spew/spew"
+)
+
+// TestGetSelectedTip tests the MsgGetSelectedTip API.
+func TestGetSelectedTip(t *testing.T) {
+	pver := ProtocolVersion
+
+	// Ensure the command is expected value.
+	wantCmd := "getseltip"
+	msg := NewMsgGetSelectedTip()
+	if cmd := msg.Command(); cmd != wantCmd {
+		t.Errorf("NewMsgGetSelectedTip: wrong command - got %v want %v",
+			cmd, wantCmd)
+	}
+
+	// Ensure max payload is expected value.
+	wantPayload := uint32(0)
+	maxPayload := msg.MaxPayloadLength(pver)
+	if maxPayload != wantPayload {
+		t.Errorf("MaxPayloadLength: wrong max payload length for "+
+			"protocol version %d - got %v, want %v", pver,
+			maxPayload, wantPayload)
+	}
+}
+
+// TestGetSelectedTipWire tests the MsgGetSelectedTip wire encode and decode for various
+// protocol versions.
+func TestGetSelectedTipWire(t *testing.T) {
+	msgGetSelectedTip := NewMsgGetSelectedTip()
+	msgGetSelectedTipEncoded := []byte{}
+
+	tests := []struct {
+		in   *MsgGetSelectedTip // Message to encode
+		out  *MsgGetSelectedTip // Expected decoded message
+		buf  []byte             // Wire encoding
+		pver uint32             // Protocol version for wire encoding
+	}{
+		// Latest protocol version.
+		{
+			msgGetSelectedTip,
+			msgGetSelectedTip,
+			msgGetSelectedTipEncoded,
+			ProtocolVersion,
+		},
+	}
+
+	t.Logf("Running %d tests", len(tests))
+	for i, test := range tests {
+		// Encode the message to wire format.
+		var buf bytes.Buffer
+		err := test.in.KaspaEncode(&buf, test.pver)
+		if err != nil {
+			t.Errorf("KaspaEncode #%d error %v", i, err)
+			continue
+		}
+		if !bytes.Equal(buf.Bytes(), test.buf) {
+			t.Errorf("KaspaEncode #%d\n got: %s want: %s", i,
+				spew.Sdump(buf.Bytes()), spew.Sdump(test.buf))
+			continue
+		}
+
+		// Decode the message from wire format.
+		var msg MsgGetSelectedTip
+		rbuf := bytes.NewReader(test.buf)
+		err = msg.KaspaDecode(rbuf, test.pver)
+		if err != nil {
+			t.Errorf("KaspaDecode #%d error %v", i, err)
+			continue
+		}
+		if !reflect.DeepEqual(&msg, test.out) {
+			t.Errorf("KaspaDecode #%d\n got: %s want: %s", i,
+				spew.Sdump(msg), spew.Sdump(test.out))
+			continue
+		}
+	}
+}

wire/msgselectedtip.go

@@ -0,0 +1,53 @@
+package wire
+
+import (
+	"github.com/kaspanet/kaspad/util/daghash"
+	"io"
+)
+
+// MsgSelectedTip implements the Message interface and represents a kaspa
+// selectedtip message. It is used to answer getseltip messages and tell
+// the asking peer what is the selected tip of this peer.
+type MsgSelectedTip struct {
+	// The selected tip hash of the generator of the message.
+	SelectedTipHash *daghash.Hash
+}
+
+// KaspaDecode decodes r using the kaspa protocol encoding into the receiver.
+// This is part of the Message interface implementation.
+func (msg *MsgSelectedTip) KaspaDecode(r io.Reader, pver uint32) error {
+	msg.SelectedTipHash = &daghash.Hash{}
+	err := ReadElement(r, msg.SelectedTipHash)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// KaspaEncode encodes the receiver to w using the kaspa protocol encoding.
+// This is part of the Message interface implementation.
+func (msg *MsgSelectedTip) KaspaEncode(w io.Writer, pver uint32) error {
+	return WriteElement(w, msg.SelectedTipHash)
+}
+
+// Command returns the protocol command string for the message. This is part
+// of the Message interface implementation.
+func (msg *MsgSelectedTip) Command() string {
+	return CmdSelectedTip
+}
+
+// MaxPayloadLength returns the maximum length the payload can be for the
+// receiver. This is part of the Message interface implementation.
+func (msg *MsgSelectedTip) MaxPayloadLength(_ uint32) uint32 {
+	// selected tip hash 32 bytes
+	return daghash.HashSize
+}
+
+// NewMsgSelectedTip returns a new kaspa selectedtip message that conforms to the
+// Message interface.
+func NewMsgSelectedTip(selectedTipHash *daghash.Hash) *MsgSelectedTip {
+	return &MsgSelectedTip{
+		SelectedTipHash: selectedTipHash,
+	}
+}

wire/msgselectedtip_test.go

@@ -0,0 +1,90 @@
+package wire
+
+import (
+	"bytes"
+	"github.com/kaspanet/kaspad/util/daghash"
+	"reflect"
+	"testing"
+
+	"github.com/davecgh/go-spew/spew"
+)
+
+// TestSelectedTip tests the MsgSelectedTip API.
+func TestSelectedTip(t *testing.T) {
+	pver := ProtocolVersion
+
+	// Ensure the command is expected value.
+	wantCmd := "selectedtip"
+	msg := NewMsgSelectedTip(&daghash.ZeroHash)
+	if cmd := msg.Command(); cmd != wantCmd {
+		t.Errorf("NewMsgSelectedTip: wrong command - got %v want %v",
+			cmd, wantCmd)
+	}
+
+	// Ensure max payload is expected value.
+	wantPayload := uint32(32)
+	maxPayload := msg.MaxPayloadLength(pver)
+	if maxPayload != wantPayload {
+		t.Errorf("MaxPayloadLength: wrong max payload length for "+
+			"protocol version %d - got %v, want %v", pver,
+			maxPayload, wantPayload)
+	}
+}
+
+// TestSelectedTipWire tests the MsgSelectedTip wire encode and decode for various
+// protocol versions.
+func TestSelectedTipWire(t *testing.T) {
+	hash := &daghash.Hash{1, 2, 3}
+	msgSelectedTip := NewMsgSelectedTip(hash)
+	msgSelectedTipEncoded := []byte{
+		0x01, 0x02, 0x03, 0x00, 0x00, 0x00, 0x00, 0x00,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+	}
+
+	tests := []struct {
+		in   *MsgSelectedTip // Message to encode
+		out  *MsgSelectedTip // Expected decoded message
+		buf  []byte          // Wire encoding
+		pver uint32          // Protocol version for wire encoding
+	}{
+		// Latest protocol version.
+		{
+			msgSelectedTip,
+			msgSelectedTip,
+			msgSelectedTipEncoded,
+			ProtocolVersion,
+		},
+	}
+
+	t.Logf("Running %d tests", len(tests))
+	for i, test := range tests {
+		// Encode the message to wire format.
+		var buf bytes.Buffer
+		err := test.in.KaspaEncode(&buf, test.pver)
+		if err != nil {
+			t.Errorf("KaspaEncode #%d error %v", i, err)
+			continue
+		}
+		if !bytes.Equal(buf.Bytes(), test.buf) {
+			t.Errorf("KaspaEncode #%d\n got: %s want: %s", i,
+				spew.Sdump(buf.Bytes()), spew.Sdump(test.buf))
+			continue
+		}
+
+		// Decode the message from wire format.
+		var msg MsgSelectedTip
+		rbuf := bytes.NewReader(test.buf)
+		err = msg.KaspaDecode(rbuf, test.pver)
+		if err != nil {
+			t.Errorf("KaspaDecode #%d error %v", i, err)
+			continue
+		}
+		if !reflect.DeepEqual(&msg, test.out) {
+			t.Errorf("KaspaDecode #%d\n got: %s want: %s", i,
+				spew.Sdump(msg), spew.Sdump(test.out))
+			continue
+		}
+	}
+}

wire/msgversion.go

@@ -55,8 +55,8 @@ type MsgVersion struct {
 	// on the wire. This has a max length of MaxUserAgentLen.
 	UserAgent string
 
-	// The selected tip of the generator of the version message.
+	// The selected tip hash of the generator of the version message.
-	SelectedTip *daghash.Hash
+	SelectedTipHash *daghash.Hash
 
 	// Don't announce transactions to peer.
 	DisableRelayTx bool
@@ -137,8 +137,8 @@ func (msg *MsgVersion) KaspaDecode(r io.Reader, pver uint32) error {
 	}
 	msg.UserAgent = userAgent
 
-	msg.SelectedTip = &daghash.Hash{}
+	msg.SelectedTipHash = &daghash.Hash{}
-	err = ReadElement(buf, msg.SelectedTip)
+	err = ReadElement(buf, msg.SelectedTipHash)
 	if err != nil {
 		return err
 	}
@@ -200,7 +200,7 @@ func (msg *MsgVersion) KaspaEncode(w io.Writer, pver uint32) error {
 		return err
 	}
 
-	err = WriteElement(w, msg.SelectedTip)
+	err = WriteElement(w, msg.SelectedTipHash)
 	if err != nil {
 		return err
 	}
@@ -223,21 +223,19 @@ func (msg *MsgVersion) Command() string {
 // MaxPayloadLength returns the maximum length the payload can be for the
 // receiver. This is part of the Message interface implementation.
 func (msg *MsgVersion) MaxPayloadLength(pver uint32) uint32 {
-	// XXX: <= 106 different
-
 	// Protocol version 4 bytes + services 8 bytes + timestamp 16 bytes +
 	// remote and local net addresses + nonce 8 bytes + length of user
-	// agent (varInt) + max allowed useragent length + last block 4 bytes +
+	// agent (varInt) + max allowed useragent length + selected tip hash length +
 	// relay transactions flag 1 byte.
-	return 33 + (maxNetAddressPayload(pver) * 2) + MaxVarIntPayload +
+	return 29 + (maxNetAddressPayload(pver) * 2) + MaxVarIntPayload +
-		MaxUserAgentLen
+		MaxUserAgentLen + daghash.HashSize
 }
 
 // NewMsgVersion returns a new kaspa version message that conforms to the
 // Message interface using the passed parameters and defaults for the remaining
 // fields.
 func NewMsgVersion(me *NetAddress, you *NetAddress, nonce uint64,
-	selectedTip *daghash.Hash, subnetworkID *subnetworkid.SubnetworkID) *MsgVersion {
+	selectedTipHash *daghash.Hash, subnetworkID *subnetworkid.SubnetworkID) *MsgVersion {
 
 	// Limit the timestamp to one second precision since the protocol
 	// doesn't support better.
@@ -249,7 +247,7 @@ func NewMsgVersion(me *NetAddress, you *NetAddress, nonce uint64,
 		AddrMe:          *me,
 		Nonce:           nonce,
 		UserAgent:       DefaultUserAgent,
-		SelectedTip:     selectedTip,
+		SelectedTipHash: selectedTipHash,
 		DisableRelayTx:  false,
 		SubnetworkID:    subnetworkID,
 	}

wire/msgversion_test.go

@@ -23,7 +23,7 @@ func TestVersion(t *testing.T) {
 	pver := ProtocolVersion
 
 	// Create version message data.
-	selectedTip := &daghash.Hash{12, 34}
+	selectedTipHash := &daghash.Hash{12, 34}
 	tcpAddrMe := &net.TCPAddr{IP: net.ParseIP("127.0.0.1"), Port: 16111}
 	me := NewNetAddress(tcpAddrMe, SFNodeNetwork)
 	tcpAddrYou := &net.TCPAddr{IP: net.ParseIP("192.168.0.1"), Port: 16111}
@@ -34,7 +34,7 @@ func TestVersion(t *testing.T) {
 	}
 
 	// Ensure we get the correct data back out.
-	msg := NewMsgVersion(me, you, nonce, selectedTip, nil)
+	msg := NewMsgVersion(me, you, nonce, selectedTipHash, nil)
 	if msg.ProtocolVersion != int32(pver) {
 		t.Errorf("NewMsgVersion: wrong protocol version - got %v, want %v",
 			msg.ProtocolVersion, pver)
@@ -55,9 +55,9 @@ func TestVersion(t *testing.T) {
 		t.Errorf("NewMsgVersion: wrong user agent - got %v, want %v",
 			msg.UserAgent, DefaultUserAgent)
 	}
-	if !msg.SelectedTip.IsEqual(selectedTip) {
+	if !msg.SelectedTipHash.IsEqual(selectedTipHash) {
-		t.Errorf("NewMsgVersion: wrong selected tip - got %s, want %s",
+		t.Errorf("NewMsgVersion: wrong selected tip hash - got %s, want %s",
-			msg.SelectedTip, selectedTip)
+			msg.SelectedTipHash, selectedTipHash)
 	}
 	if msg.DisableRelayTx {
 		t.Errorf("NewMsgVersion: disable relay tx is not false by "+
@@ -106,10 +106,10 @@ func TestVersion(t *testing.T) {
 
 	// Ensure max payload is expected value.
 	// Protocol version 4 bytes + services 8 bytes + timestamp 16 bytes +
-	// remote and local net addresses + nonce 8 bytes + length of user agent
+	// remote and local net addresses + nonce 8 bytes + length of user
-	// (varInt) + max allowed user agent length + last block 4 bytes +
+	// agent (varInt) + max allowed useragent length + selected tip hash length +
 	// relay transactions flag 1 byte.
-	wantPayload := uint32(366)
+	wantPayload := uint32(394)
 	maxPayload := msg.MaxPayloadLength(pver)
 	if maxPayload != wantPayload {
 		t.Errorf("MaxPayloadLength: wrong max payload length for "+
@@ -323,7 +323,7 @@ var baseVersion = &MsgVersion{
 	},
 	Nonce:           123123, // 0x1e0f3
 	UserAgent:       "/kaspadtest:0.0.1/",
-	SelectedTip: &daghash.Hash{0x12, 0x34},
+	SelectedTipHash: &daghash.Hash{0x12, 0x34},
 }
 
 // baseVersionEncoded is the wire encoded bytes for baseVersion using protocol
@@ -373,7 +373,7 @@ var baseVersionWithRelayTx = &MsgVersion{
 	},
 	Nonce:           123123, // 0x1e0f3
 	UserAgent:       "/kaspadtest:0.0.1/",
-	SelectedTip: &daghash.Hash{0x12, 0x34},
+	SelectedTipHash: &daghash.Hash{0x12, 0x34},
 }
 
 // baseVersionWithRelayTxEncoded is the wire encoded bytes for