From 295c0861c408faef2832f754006fc922c9bc7fd4 Mon Sep 17 00:00:00 2001
From: Jeromy <jeromyj@gmail.com>
Date: Wed, 10 Jun 2020 22:15:46 -0700
Subject: [PATCH] fix chain index seeking through long ranges of null rounds

---
 chain/store/index.go      | 12 +++++--
 chain/store/index_test.go | 76 +++++++++++++++++++++++++++++++++++++++
 chain/types/mock/chain.go |  7 +++-
 3 files changed, 91 insertions(+), 4 deletions(-)
 create mode 100644 chain/store/index_test.go

diff --git a/chain/store/index.go b/chain/store/index.go
index 15d5d7025..8747c79c6 100644
--- a/chain/store/index.go
+++ b/chain/store/index.go
@@ -97,9 +97,15 @@ func (ci *ChainIndex) fillCache(tsk types.TipSetKey) (*lbEntry, error) {
 
 	rheight -= ci.skipLength
 
-	skipTarget, err := ci.walkBack(parent, rheight)
-	if err != nil {
-		return nil, err
+	var skipTarget *types.TipSet
+	if parent.Height() < rheight {
+		skipTarget = parent
+
+	} else {
+		skipTarget, err = ci.walkBack(parent, rheight)
+		if err != nil {
+			return nil, xerrors.Errorf("fillCache walkback: %w", err)
+		}
 	}
 
 	lbe := &lbEntry{
diff --git a/chain/store/index_test.go b/chain/store/index_test.go
new file mode 100644
index 000000000..6b97a8614
--- /dev/null
+++ b/chain/store/index_test.go
@@ -0,0 +1,76 @@
+package store_test
+
+import (
+	"bytes"
+	"context"
+	"testing"
+
+	"github.com/filecoin-project/lotus/chain/gen"
+	"github.com/filecoin-project/lotus/chain/store"
+	"github.com/filecoin-project/lotus/chain/types/mock"
+	"github.com/filecoin-project/specs-actors/actors/abi"
+	datastore "github.com/ipfs/go-datastore"
+	syncds "github.com/ipfs/go-datastore/sync"
+	blockstore "github.com/ipfs/go-ipfs-blockstore"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestIndexSeeks(t *testing.T) {
+	cg, err := gen.NewGenerator()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	gencar, err := cg.GenesisCar()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	gen := cg.Genesis()
+
+	ctx := context.TODO()
+
+	nbs := blockstore.NewBlockstore(syncds.MutexWrap(datastore.NewMapDatastore()))
+	cs := store.NewChainStore(nbs, syncds.MutexWrap(datastore.NewMapDatastore()), nil)
+
+	_, err = cs.Import(bytes.NewReader(gencar))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	cur := mock.TipSet(gen)
+	if err := cs.PutTipSet(ctx, mock.TipSet(gen)); err != nil {
+		t.Fatal(err)
+	}
+	cs.SetGenesis(gen)
+
+	for i := 0; i < 100; i++ {
+		nextts := mock.TipSet(mock.MkBlock(cur, 1, 1))
+
+		if err := cs.PutTipSet(ctx, nextts); err != nil {
+			t.Fatal(err)
+		}
+		cur = nextts
+	}
+
+	skip := mock.MkBlock(cur, 1, 1)
+	skip.Height += 50
+
+	skipts := mock.TipSet(skip)
+
+	if err := cs.PutTipSet(ctx, skipts); err != nil {
+		t.Fatal(err)
+	}
+
+	ts, err := cs.GetTipsetByHeight(ctx, skip.Height-10, skipts, false)
+	if err != nil {
+		t.Fatal(err)
+	}
+	assert.Equal(t, abi.ChainEpoch(151), ts.Height())
+
+	ts2, err := cs.GetTipsetByHeight(ctx, 90, skipts, false)
+	if err != nil {
+		t.Fatal(err)
+	}
+	assert.Equal(t, abi.ChainEpoch(90), ts2.Height())
+}
diff --git a/chain/types/mock/chain.go b/chain/types/mock/chain.go
index 5154ab115..00d0eecc9 100644
--- a/chain/types/mock/chain.go
+++ b/chain/types/mock/chain.go
@@ -49,6 +49,11 @@ func MkBlock(parents *types.TipSet, weightInc uint64, ticketNonce uint64) *types
 		panic(err)
 	}
 
+	pstateRoot := c
+	if parents != nil {
+		pstateRoot = parents.Blocks()[0].ParentStateRoot
+	}
+
 	var pcids []cid.Cid
 	var height abi.ChainEpoch
 	weight := types.NewInt(weightInc)
@@ -72,7 +77,7 @@ func MkBlock(parents *types.TipSet, weightInc uint64, ticketNonce uint64) *types
 		ParentWeight:          weight,
 		Messages:              c,
 		Height:                height,
-		ParentStateRoot:       c,
+		ParentStateRoot:       pstateRoot,
 		BlockSig:              &crypto.Signature{Type: crypto.SigTypeBLS, Data: []byte("boo! im a signature")},
 	}
 }