fix: if cache best is nil, return chain head

chain/events/events.go

@@ -35,6 +35,7 @@ type eventAPI interface {
 	ChainNotify(context.Context) (<-chan []*api.HeadChange, error)
 	ChainGetBlockMessages(context.Context, cid.Cid) (*api.BlockMessages, error)
 	ChainGetTipSetByHeight(context.Context, abi.ChainEpoch, types.TipSetKey) (*types.TipSet, error)
+	ChainHead(context.Context) (*types.TipSet, error)
 	StateGetReceipt(context.Context, cid.Cid, types.TipSetKey) (*types.MessageReceipt, error)
 	ChainGetTipSet(context.Context, types.TipSetKey) (*types.TipSet, error)
 
@@ -57,7 +58,7 @@ type Events struct {
 func NewEvents(ctx context.Context, api eventAPI) *Events {
 	gcConfidence := 2 * build.ForkLengthThreshold
 
-	tsc := newTSCache(gcConfidence, api.ChainGetTipSetByHeight)
+	tsc := newTSCache(gcConfidence, api)
 
 	e := &Events{
 		api: api,

chain/events/events_called.go

@@ -307,7 +307,10 @@ func (e *hcEvents) onHeadChanged(check CheckFunc, hnd EventHandler, rev RevertHa
 	defer e.lk.Unlock()
 
 	// Check if the event has already occurred
-	ts := e.tsc.best()
+	ts, err := e.tsc.best()
+	if err != nil {
+		return 0, xerrors.Errorf("error getting best tipset: %w", err)
+	}
 	done, more, err := check(ts)
 	if err != nil {
 		return 0, xerrors.Errorf("called check error (h: %d): %w", ts.Height(), err)

chain/events/events_height.go

@@ -4,6 +4,8 @@ import (
 	"context"
 	"sync"
 
+	"golang.org/x/xerrors"
+
 	"github.com/filecoin-project/specs-actors/actors/abi"
 	"go.opencensus.io/trace"
 
@@ -152,8 +154,12 @@ func (e *heightEvents) ChainAt(hnd HeightHandler, rev RevertHandler, confidence
 
 	e.lk.Lock() // Tricky locking, check your locks if you modify this function!
 
-	bestH := e.tsc.best().Height()
+	best, err := e.tsc.best()
+	if err != nil {
+		return xerrors.Errorf("error getting best tipset: %w", err)
+	}
 
+	bestH := best.Height()
 	if bestH >= h+abi.ChainEpoch(confidence) {
 		ts, err := e.tsc.getNonNull(h)
 		if err != nil {
@@ -172,7 +178,11 @@ func (e *heightEvents) ChainAt(hnd HeightHandler, rev RevertHandler, confidence
 		}
 
 		e.lk.Lock()
-		bestH = e.tsc.best().Height()
+		best, err = e.tsc.best()
+		if err != nil {
+			return xerrors.Errorf("error getting best tipset: %w", err)
+		}
+		bestH = best.Height()
 	}
 
 	defer e.lk.Unlock()

chain/events/events_test.go

@@ -46,6 +46,10 @@ type fakeCS struct {
 	sub func(rev, app []*types.TipSet)
 }
 
+func (fcs *fakeCS) ChainHead(ctx context.Context) (*types.TipSet, error) {
+	panic("implement me")
+}
+
 func (fcs *fakeCS) ChainGetTipSet(ctx context.Context, key types.TipSetKey) (*types.TipSet, error) {
 	return fcs.tipsets[key], nil
 }
@@ -110,7 +114,11 @@ func (fcs *fakeCS) makeTs(t *testing.T, parents []cid.Cid, h abi.ChainEpoch, msg
 
 func (fcs *fakeCS) ChainNotify(context.Context) (<-chan []*api.HeadChange, error) {
 	out := make(chan []*api.HeadChange, 1)
-	out <- []*api.HeadChange{{Type: store.HCCurrent, Val: fcs.tsc.best()}}
+	best, err := fcs.tsc.best()
+	if err != nil {
+		return nil, err
+	}
+	out <- []*api.HeadChange{{Type: store.HCCurrent, Val: best}}
 
 	fcs.sub = func(rev, app []*types.TipSet) {
 		notif := make([]*api.HeadChange, len(rev)+len(app))
@@ -174,7 +182,8 @@ func (fcs *fakeCS) advance(rev, app int, msgs map[int]cid.Cid, nulls ...int) { /
 
 	var revs []*types.TipSet
 	for i := 0; i < rev; i++ {
-		ts := fcs.tsc.best()
+		ts, err := fcs.tsc.best()
+		require.NoError(fcs.t, err)
 
 		if _, ok := nullm[int(ts.Height())]; !ok {
 			revs = append(revs, ts)
@@ -196,7 +205,9 @@ func (fcs *fakeCS) advance(rev, app int, msgs map[int]cid.Cid, nulls ...int) { /
 			continue
 		}
 
-		ts := fcs.makeTs(fcs.t, fcs.tsc.best().Key().Cids(), fcs.h, mc)
+		best, err := fcs.tsc.best()
+		require.NoError(fcs.t, err)
+		ts := fcs.makeTs(fcs.t, best.Key().Cids(), fcs.h, mc)
 		require.NoError(fcs.t, fcs.tsc.add(ts))
 
 		if hasMsgs {

chain/events/tscache.go

@@ -9,7 +9,10 @@ import (
 	"github.com/filecoin-project/lotus/chain/types"
 )
 
-type tsByHFunc func(context.Context, abi.ChainEpoch, types.TipSetKey) (*types.TipSet, error)
+type tsCacheAPI interface {
+	ChainGetTipSetByHeight(context.Context, abi.ChainEpoch, types.TipSetKey) (*types.TipSet, error)
+	ChainHead(context.Context) (*types.TipSet, error)
+}
 
 // tipSetCache implements a simple ring-buffer cache to keep track of recent
 // tipsets
@@ -18,10 +21,10 @@ type tipSetCache struct {
 	start int
 	len   int
 
-	storage tsByHFunc
+	storage tsCacheAPI
 }
 
-func newTSCache(cap abi.ChainEpoch, storage tsByHFunc) *tipSetCache {
+func newTSCache(cap abi.ChainEpoch, storage tsCacheAPI) *tipSetCache {
 	return &tipSetCache{
 		cache: make([]*types.TipSet, cap),
 		start: 0,
@@ -94,7 +97,7 @@ func (tsc *tipSetCache) getNonNull(height abi.ChainEpoch) (*types.TipSet, error)
 func (tsc *tipSetCache) get(height abi.ChainEpoch) (*types.TipSet, error) {
 	if tsc.len == 0 {
 		log.Warnf("tipSetCache.get: cache is empty, requesting from storage (h=%d)", height)
-		return tsc.storage(context.TODO(), height, types.EmptyTSK)
+		return tsc.storage.ChainGetTipSetByHeight(context.TODO(), height, types.EmptyTSK)
 	}
 
 	headH := tsc.cache[tsc.start].Height()
@@ -114,14 +117,18 @@ func (tsc *tipSetCache) get(height abi.ChainEpoch) (*types.TipSet, error) {
 
 	if height < tail.Height() {
 		log.Warnf("tipSetCache.get: requested tipset not in cache, requesting from storage (h=%d; tail=%d)", height, tail.Height())
-		return tsc.storage(context.TODO(), height, tail.Key())
+		return tsc.storage.ChainGetTipSetByHeight(context.TODO(), height, tail.Key())
 	}
 
 	return tsc.cache[normalModulo(tsc.start-int(headH-height), clen)], nil
 }
 
-func (tsc *tipSetCache) best() *types.TipSet {
+func (tsc *tipSetCache) best() (*types.TipSet, error) {
-	return tsc.cache[tsc.start]
+	best := tsc.cache[tsc.start]
+	if best == nil {
+		return tsc.storage.ChainHead(context.TODO())
+	}
+	return best, nil
 }
 
 func normalModulo(n, m int) int {

chain/events/tscache_test.go

@@ -13,10 +13,7 @@ import (
 )
 
 func TestTsCache(t *testing.T) {
-	tsc := newTSCache(50, func(context.Context, abi.ChainEpoch, types.TipSetKey) (*types.TipSet, error) {
+	tsc := newTSCache(50, &tsCacheAPIFailOnStorageCall{t: t})
-		t.Fatal("storage call")
-		return &types.TipSet{}, nil
-	})
 
 	h := abi.ChainEpoch(75)
 
@@ -43,7 +40,12 @@ func TestTsCache(t *testing.T) {
 
 	for i := 0; i < 9000; i++ {
 		if i%90 > 60 {
-			if err := tsc.revert(tsc.best()); err != nil {
+			best, err := tsc.best()
+			if err != nil {
+				t.Fatal(err, "; i:", i)
+				return
+			}
+			if err := tsc.revert(best); err != nil {
 				t.Fatal(err, "; i:", i)
 				return
 			}
@@ -55,11 +57,21 @@ func TestTsCache(t *testing.T) {
 
 }
 
+type tsCacheAPIFailOnStorageCall struct {
+	t *testing.T
+}
+
+func (tc *tsCacheAPIFailOnStorageCall) ChainGetTipSetByHeight(ctx context.Context, epoch abi.ChainEpoch, key types.TipSetKey) (*types.TipSet, error) {
+	tc.t.Fatal("storage call")
+	return &types.TipSet{}, nil
+}
+func (tc *tsCacheAPIFailOnStorageCall) ChainHead(ctx context.Context) (*types.TipSet, error) {
+	tc.t.Fatal("storage call")
+	return &types.TipSet{}, nil
+}
+
 func TestTsCacheNulls(t *testing.T) {
-	tsc := newTSCache(50, func(context.Context, abi.ChainEpoch, types.TipSetKey) (*types.TipSet, error) {
+	tsc := newTSCache(50, &tsCacheAPIFailOnStorageCall{t: t})
-		t.Fatal("storage call")
-		return &types.TipSet{}, nil
-	})
 
 	h := abi.ChainEpoch(75)
 
@@ -91,7 +103,9 @@ func TestTsCacheNulls(t *testing.T) {
 	add()
 	add()
 
-	require.Equal(t, h-1, tsc.best().Height())
+	best, err := tsc.best()
+	require.NoError(t, err)
+	require.Equal(t, h-1, best.Height())
 
 	ts, err := tsc.get(h - 1)
 	require.NoError(t, err)
@@ -109,9 +123,17 @@ func TestTsCacheNulls(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, h-8, ts.Height())
 
-	require.NoError(t, tsc.revert(tsc.best()))
+	best, err = tsc.best()
-	require.NoError(t, tsc.revert(tsc.best()))
+	require.NoError(t, err)
-	require.Equal(t, h-8, tsc.best().Height())
+	require.NoError(t, tsc.revert(best))
+
+	best, err = tsc.best()
+	require.NoError(t, err)
+	require.NoError(t, tsc.revert(best))
+
+	best, err = tsc.best()
+	require.NoError(t, err)
+	require.Equal(t, h-8, best.Height())
 
 	h += 50
 	add()
@@ -120,3 +142,27 @@ func TestTsCacheNulls(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, h-1, ts.Height())
 }
+
+type tsCacheAPIStorageCallCounter struct {
+	t                      *testing.T
+	chainGetTipSetByHeight int
+	chainHead              int
+}
+
+func (tc *tsCacheAPIStorageCallCounter) ChainGetTipSetByHeight(ctx context.Context, epoch abi.ChainEpoch, key types.TipSetKey) (*types.TipSet, error) {
+	tc.chainGetTipSetByHeight++
+	return &types.TipSet{}, nil
+}
+func (tc *tsCacheAPIStorageCallCounter) ChainHead(ctx context.Context) (*types.TipSet, error) {
+	tc.chainHead++
+	return &types.TipSet{}, nil
+}
+
+func TestTsCacheEmpty(t *testing.T) {
+	// Calling best on an empty cache should just call out to the chain API
+	callCounter := &tsCacheAPIStorageCallCounter{t: t}
+	tsc := newTSCache(50, callCounter)
+	_, err := tsc.best()
+	require.NoError(t, err)
+	require.Equal(t, 1, callCounter.chainHead)
+}