1 files changed, 105 insertions, 56 deletions

diff --git a/p2p/discover/table.go b/p2p/discover/table.go
index 972bc1077..66afa52ea 100644
--- a/p2p/discover/table.go
+++ b/p2p/discover/table.go
@@ -44,6 +44,10 @@ const (
 
 	maxBondingPingPongs = 16
 	maxFindnodeFailures = 5
+
+	autoRefreshInterval = 1 * time.Hour
+	seedCount           = 30
+	seedMaxAge          = 5 * 24 * time.Hour
 )
 
 type Table struct {
@@ -52,6 +56,10 @@ type Table struct {
 	nursery []*Node           // bootstrap nodes
 	db      *nodeDB           // database of known nodes
 
+	refreshReq chan struct{}
+	closeReq   chan struct{}
+	closed     chan struct{}
+
 	bondmu    sync.Mutex
 	bonding   map[NodeID]*bondproc
 	bondslots chan struct{} // limits total number of active bonding processes
@@ -93,11 +101,14 @@ func newTable(t transport, ourID NodeID, ourAddr *net.UDPAddr, nodeDBPath string
 		db, _ = newNodeDB("", Version, ourID)
 	}
 	tab := &Table{
-		net:       t,
-		db:        db,
-		self:      newNode(ourID, ourAddr.IP, uint16(ourAddr.Port), uint16(ourAddr.Port)),
-		bonding:   make(map[NodeID]*bondproc),
-		bondslots: make(chan struct{}, maxBondingPingPongs),
+		net:        t,
+		db:         db,
+		self:       newNode(ourID, ourAddr.IP, uint16(ourAddr.Port), uint16(ourAddr.Port)),
+		bonding:    make(map[NodeID]*bondproc),
+		bondslots:  make(chan struct{}, maxBondingPingPongs),
+		refreshReq: make(chan struct{}),
+		closeReq:   make(chan struct{}),
+		closed:     make(chan struct{}),
 	}
 	for i := 0; i < cap(tab.bondslots); i++ {
 		tab.bondslots <- struct{}{}
@@ -105,6 +116,7 @@ func newTable(t transport, ourID NodeID, ourAddr *net.UDPAddr, nodeDBPath string
 	for i := range tab.buckets {
 		tab.buckets[i] = new(bucket)
 	}
+	go tab.refreshLoop()
 	return tab
 }
 
@@ -163,10 +175,12 @@ func randUint(max uint32) uint32 {
 
 // Close terminates the network listener and flushes the node database.
 func (tab *Table) Close() {
-	if tab.net != nil {
-		tab.net.close()
+	select {
+	case <-tab.closed:
+		// already closed.
+	case tab.closeReq <- struct{}{}:
+		<-tab.closed // wait for refreshLoop to end.
 	}
-	tab.db.close()
 }
 
 // Bootstrap sets the bootstrap nodes. These nodes are used to connect
@@ -183,7 +197,7 @@ func (tab *Table) Bootstrap(nodes []*Node) {
 		tab.nursery = append(tab.nursery, &cpy)
 	}
 	tab.mutex.Unlock()
-	tab.refresh()
+	tab.requestRefresh()
 }
 
 // Lookup performs a network search for nodes close
@@ -210,9 +224,9 @@ func (tab *Table) Lookup(targetID NodeID) []*Node {
 	result := tab.closest(target, bucketSize)
 	tab.mutex.Unlock()
 
-	// If the result set is empty, all nodes were dropped, refresh
+	// If the result set is empty, all nodes were dropped, refresh.
 	if len(result.entries) == 0 {
-		tab.refresh()
+		tab.requestRefresh()
 		return nil
 	}
 
@@ -257,56 +271,86 @@ func (tab *Table) Lookup(targetID NodeID) []*Node {
 	return result.entries
 }
 
-// refresh performs a lookup for a random target to keep buckets full, or seeds
-// the table if it is empty (initial bootstrap or discarded faulty peers).
-func (tab *Table) refresh() {
-	seed := true
+func (tab *Table) requestRefresh() {
+	select {
+	case tab.refreshReq <- struct{}{}:
+	case <-tab.closed:
+	}
+}
 
-	// If the discovery table is empty, seed with previously known nodes
-	tab.mutex.Lock()
-	for _, bucket := range tab.buckets {
-		if len(bucket.entries) > 0 {
-			seed = false
-			break
+func (tab *Table) refreshLoop() {
+	defer func() {
+		tab.db.close()
+		if tab.net != nil {
+			tab.net.close()
 		}
-	}
-	tab.mutex.Unlock()
+		close(tab.closed)
+	}()
 
-	// If the table is not empty, try to refresh using the live entries
-	if !seed {
-		// The Kademlia paper specifies that the bucket refresh should
-		// perform a refresh in the least recently used bucket. We cannot
-		// adhere to this because the findnode target is a 512bit value
-		// (not hash-sized) and it is not easily possible to generate a
-		// sha3 preimage that falls into a chosen bucket.
-		//
-		// We perform a lookup with a random target instead.
-		var target NodeID
-		rand.Read(target[:])
-
-		result := tab.Lookup(target)
-		if len(result) == 0 {
-			// Lookup failed, seed after all
-			seed = true
+	timer := time.NewTicker(autoRefreshInterval)
+	var done chan struct{}
+	for {
+		select {
+		case <-timer.C:
+			if done == nil {
+				done = make(chan struct{})
+				go tab.doRefresh(done)
+			}
+		case <-tab.refreshReq:
+			if done == nil {
+				done = make(chan struct{})
+				go tab.doRefresh(done)
+			}
+		case <-done:
+			done = nil
+		case <-tab.closeReq:
+			if done != nil {
+				<-done
+			}
+			return
 		}
 	}
+}
 
-	if seed {
-		// Pick a batch of previously know seeds to lookup with
-		seeds := tab.db.querySeeds(10)
-		for _, seed := range seeds {
-			glog.V(logger.Debug).Infoln("Seeding network with", seed)
-		}
-		nodes := append(tab.nursery, seeds...)
+// doRefresh performs a lookup for a random target to keep buckets
+// full. seed nodes are inserted if the table is empty (initial
+// bootstrap or discarded faulty peers).
+func (tab *Table) doRefresh(done chan struct{}) {
+	defer close(done)
+
+	// The Kademlia paper specifies that the bucket refresh should
+	// perform a lookup in the least recently used bucket. We cannot
+	// adhere to this because the findnode target is a 512bit value
+	// (not hash-sized) and it is not easily possible to generate a
+	// sha3 preimage that falls into a chosen bucket.
+	// We perform a lookup with a random target instead.
+	var target NodeID
+	rand.Read(target[:])
+	result := tab.Lookup(target)
+	if len(result) > 0 {
+		return
+	}
 
-		// Bond with all the seed nodes (will pingpong only if failed recently)
-		bonded := tab.bondall(nodes)
-		if len(bonded) > 0 {
-			tab.Lookup(tab.self.ID)
+	// The table is empty. Load nodes from the database and insert
+	// them. This should yield a few previously seen nodes that are
+	// (hopefully) still alive.
+	seeds := tab.db.querySeeds(seedCount, seedMaxAge)
+	seeds = tab.bondall(append(seeds, tab.nursery...))
+	if glog.V(logger.Debug) {
+		if len(seeds) == 0 {
+			glog.Infof("no seed nodes found")
+		}
+		for _, n := range seeds {
+			age := time.Since(tab.db.lastPong(n.ID))
+			glog.Infof("seed node (age %v): %v", age, n)
 		}
-		// TODO: the Kademlia paper says that we're supposed to perform
-		// random lookups in all buckets further away than our closest neighbor.
 	}
+	tab.mutex.Lock()
+	tab.stuff(seeds)
+	tab.mutex.Unlock()
+
+	// Finally, do a self lookup to fill up the buckets.
+	tab.Lookup(tab.self.ID)
 }
 
 // closest returns the n nodes in the table that are closest to the
@@ -373,8 +417,9 @@ func (tab *Table) bond(pinged bool, id NodeID, addr *net.UDPAddr, tcpPort uint16
 	}
 	// If the node is unknown (non-bonded) or failed (remotely unknown), bond from scratch
 	var result error
-	if node == nil || fails > 0 {
-		glog.V(logger.Detail).Infof("Bonding %x: known=%v, fails=%v", id[:8], node != nil, fails)
+	age := time.Since(tab.db.lastPong(id))
+	if node == nil || fails > 0 || age > nodeDBNodeExpiration {
+		glog.V(logger.Detail).Infof("Bonding %x: known=%t, fails=%d age=%v", id[:8], node != nil, fails, age)
 
 		tab.bondmu.Lock()
 		w := tab.bonding[id]
@@ -435,13 +480,17 @@ func (tab *Table) pingpong(w *bondproc, pinged bool, id NodeID, addr *net.UDPAdd
 // ping a remote endpoint and wait for a reply, also updating the node
 // database accordingly.
 func (tab *Table) ping(id NodeID, addr *net.UDPAddr) error {
-	// Update the last ping and send the message
 	tab.db.updateLastPing(id, time.Now())
 	if err := tab.net.ping(id, addr); err != nil {
 		return err
 	}
-	// Pong received, update the database and return
 	tab.db.updateLastPong(id, time.Now())
+
+	// Start the background expiration goroutine after the first
+	// successful communication. Subsequent calls have no effect if it
+	// is already running. We do this here instead of somewhere else
+	// so that the search for seed nodes also considers older nodes
+	// that would otherwise be removed by the expiration.
 	tab.db.ensureExpirer()
 	return nil
 }