Merge pull request #43 from libp2p/fix/multi-bucket

fix: when the target bucket is empty or low, pull from all other buckets

go.mod

@@ -8,3 +8,5 @@ require (
 	github.com/minio/sha256-simd v0.0.0-20190131020904-2d45a736cd16
 	github.com/multiformats/go-multihash v0.0.10
 )
+
+go 1.13

table.go

@@ -238,32 +238,51 @@ func (rt *RoutingTable) NearestPeer(id ID) peer.ID {
 
 // NearestPeers returns a list of the 'count' closest peers to the given ID
 func (rt *RoutingTable) NearestPeers(id ID, count int) []peer.ID {
+	// This is the number of bits _we_ share with the key. All peers in this
+	// bucket share cpl bits with us and will therefore share at least cpl+1
+	// bits with the given key. +1 because both the target and all peers in
+	// this bucket differ from us in the cpl bit.
 	cpl := CommonPrefixLen(id, rt.local)
 
 	// It's assumed that this also protects the buckets.
 	rt.tabLock.RLock()
 
-	// Get bucket at cpl index or last bucket
-	var bucket *Bucket
+	// Get bucket index or last bucket
 	if cpl >= len(rt.Buckets) {
 		cpl = len(rt.Buckets) - 1
 	}
-	bucket = rt.Buckets[cpl]
 
 	pds := peerDistanceSorter{
-		peers:  make([]peerDistance, 0, 3*rt.bucketsize),
+		peers:  make([]peerDistance, 0, count+rt.bucketsize),
 		target: id,
 	}
-	pds.appendPeersFromList(bucket.list)
-	if pds.Len() < count {
-		// In the case of an unusual split, one bucket may be short or empty.
-		// if this happens, search both surrounding buckets for nearby peers
-		if cpl > 0 {
-			pds.appendPeersFromList(rt.Buckets[cpl-1].list)
-		}
-		if cpl < len(rt.Buckets)-1 {
-			pds.appendPeersFromList(rt.Buckets[cpl+1].list)
+
+	// Add peers from the target bucket (cpl+1 shared bits).
+	pds.appendPeersFromList(rt.Buckets[cpl].list)
+
+	// If we're short, add peers from buckets to the right until we have
+	// enough. All buckets to the right share exactly cpl bits (as opposed
+	// to the cpl+1 bits shared by the peers in the cpl bucket).
+	//
+	// Unfortunately, to be completely correct, we can't just take from
+	// buckets until we have enough peers because peers because _all_ of
+	// these peers will be ~2**(256-cpl) from us.
+	//
+	// However, we're going to do that anyways as it's "good enough"
+
+	for i := cpl + 1; i < len(rt.Buckets) && pds.Len() < count; i++ {
+		pds.appendPeersFromList(rt.Buckets[i].list)
 	}
+
+	// If we're still short, add in buckets that share _fewer_ bits. We can
+	// do this bucket by bucket because each bucket will share 1 fewer bit
+	// than the last.
+	//
+	// * bucket cpl-1: cpl-2 shared bits.
+	// * bucket cpl-2: cpl-3 shared bits.
+	// ...
+	for i := cpl - 1; i >= 0 && pds.Len() < count; i-- {
+		pds.appendPeersFromList(rt.Buckets[i].list)
 	}
 	rt.tabLock.RUnlock()
 

table_test.go

@@ -12,6 +12,8 @@ import (
 
 // Test basic features of the bucket struct
 func TestBucket(t *testing.T) {
+	t.Parallel()
+
 	b := newBucket()
 
 	peers := make([]peer.ID, 100)
@@ -49,6 +51,8 @@ func TestBucket(t *testing.T) {
 }
 
 func TestGenRandPeerID(t *testing.T) {
+	t.Parallel()
+
 	nBuckets := 21
 	local := test.RandPeerIDFatal(t)
 	m := pstore.NewMetrics()
@@ -95,6 +99,8 @@ func TestGenRandPeerID(t *testing.T) {
 }
 
 func TestTableCallbacks(t *testing.T) {
+	t.Parallel()
+
 	local := test.RandPeerIDFatal(t)
 	m := pstore.NewMetrics()
 	rt := NewRoutingTable(10, ConvertPeerID(local), time.Hour, m)
@@ -141,6 +147,8 @@ func TestTableCallbacks(t *testing.T) {
 
 // Right now, this just makes sure that it doesnt hang or crash
 func TestTableUpdate(t *testing.T) {
+	t.Parallel()
+
 	local := test.RandPeerIDFatal(t)
 	m := pstore.NewMetrics()
 	rt := NewRoutingTable(10, ConvertPeerID(local), time.Hour, m)
@@ -165,6 +173,8 @@ func TestTableUpdate(t *testing.T) {
 }
 
 func TestTableFind(t *testing.T) {
+	t.Parallel()
+
 	local := test.RandPeerIDFatal(t)
 	m := pstore.NewMetrics()
 	rt := NewRoutingTable(10, ConvertPeerID(local), time.Hour, m)
@@ -183,6 +193,8 @@ func TestTableFind(t *testing.T) {
 }
 
 func TestTableEldestPreferred(t *testing.T) {
+	t.Parallel()
+
 	local := test.RandPeerIDFatal(t)
 	m := pstore.NewMetrics()
 	rt := NewRoutingTable(10, ConvertPeerID(local), time.Hour, m)
@@ -212,6 +224,8 @@ func TestTableEldestPreferred(t *testing.T) {
 }
 
 func TestTableFindMultiple(t *testing.T) {
+	t.Parallel()
+
 	local := test.RandPeerIDFatal(t)
 	m := pstore.NewMetrics()
 	rt := NewRoutingTable(20, ConvertPeerID(local), time.Hour, m)
@@ -229,10 +243,136 @@ func TestTableFindMultiple(t *testing.T) {
 	}
 }
 
+func assertSortedPeerIdsEqual(t *testing.T, a, b []peer.ID) {
+	t.Helper()
+	if len(a) != len(b) {
+		t.Fatal("slices aren't the same length")
+	}
+	for i, p := range a {
+		if p != b[i] {
+			t.Fatalf("unexpected peer %d", i)
+		}
+	}
+}
+
+func TestTableFindMultipleBuckets(t *testing.T) {
+	t.Parallel()
+
+	local := test.RandPeerIDFatal(t)
+	localID := ConvertPeerID(local)
+	m := pstore.NewMetrics()
+
+	rt := NewRoutingTable(5, localID, time.Hour, m)
+
+	peers := make([]peer.ID, 100)
+	for i := 0; i < 100; i++ {
+		peers[i] = test.RandPeerIDFatal(t)
+		rt.Update(peers[i])
+	}
+
+	targetID := ConvertPeerID(peers[2])
+
+	closest := SortClosestPeers(rt.ListPeers(), targetID)
+	targetCpl := CommonPrefixLen(localID, targetID)
+
+	// Split the peers into closer, same, and further from the key (than us).
+	var (
+		closer, same, further []peer.ID
+	)
+	var i int
+	for i = 0; i < len(closest); i++ {
+		cpl := CommonPrefixLen(ConvertPeerID(closest[i]), targetID)
+		if targetCpl >= cpl {
+			break
+		}
+	}
+	closer = closest[:i]
+
+	var j int
+	for j = len(closer); j < len(closest); j++ {
+		cpl := CommonPrefixLen(ConvertPeerID(closest[j]), targetID)
+		if targetCpl > cpl {
+			break
+		}
+	}
+	same = closest[i:j]
+	further = closest[j:]
+
+	// should be able to find at least 30
+	// ~31 (logtwo(100) * 5)
+	found := rt.NearestPeers(targetID, 20)
+	if len(found) != 20 {
+		t.Fatalf("asked for 20 peers, got %d", len(found))
+	}
+
+	// We expect this list to include:
+	// * All peers with a common prefix length > than the CPL between our key
+	//   and the target (peers in the target bucket).
+	// * Then a subset of the peers with the _same_ CPL (peers in buckets to the right).
+	// * Finally, other peers to the left of the target bucket.
+
+	// First, handle the peers that are _closer_ than us.
+	if len(found) <= len(closer) {
+		// All of our peers are "closer".
+		assertSortedPeerIdsEqual(t, found, closer[:len(found)])
+		return
+	}
+	assertSortedPeerIdsEqual(t, found[:len(closer)], closer)
+
+	// We've worked through closer peers, let's work through peers at the
+	// "same" distance.
+	found = found[len(closer):]
+
+	// Next, handle peers that are at the same distance as us.
+	if len(found) <= len(same) {
+		// Ok, all the remaining peers are at the same distance.
+		// unfortunately, that means we may be missing peers that are
+		// technically closer.
+
+		// Make sure all remaining peers are _somewhere_ in the "closer" set.
+		pset := peer.NewSet()
+		for _, p := range same {
+			pset.Add(p)
+		}
+		for _, p := range found {
+			if !pset.Contains(p) {
+				t.Fatalf("unexpected peer %s", p)
+			}
+		}
+		return
+	}
+	assertSortedPeerIdsEqual(t, found[:len(same)], same)
+
+	// We've worked through closer peers, let's work through the further
+	// peers.
+	found = found[len(same):]
+
+	// All _further_ peers will be correctly sorted.
+	assertSortedPeerIdsEqual(t, found, further[:len(found)])
+
+	// Finally, test getting _all_ peers. These should be in the correct
+	// order.
+
+	// Ok, now let's try finding all of them.
+	found = rt.NearestPeers(ConvertPeerID(peers[2]), 100)
+	if len(found) != rt.Size() {
+		t.Fatalf("asked for %d peers, got %d", rt.Size(), len(found))
+	}
+
+	// We should get _all_ peers in sorted order.
+	for i, p := range found {
+		if p != closest[i] {
+			t.Fatalf("unexpected peer %d", i)
+		}
+	}
+}
+
 // Looks for race conditions in table operations. For a more 'certain'
 // test, increase the loop counter from 1000 to a much higher number
 // and set GOMAXPROCS above 1
 func TestTableMultithreaded(t *testing.T) {
+	t.Parallel()
+
 	local := peer.ID("localPeer")
 	m := pstore.NewMetrics()
 	tab := NewRoutingTable(20, ConvertPeerID(local), time.Hour, m)