From 96dad6b6f6f8db88cca7496665016152272881cb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?P=C3=A9ter=20Szil=C3=A1gyi?= <peterke@gmail.com>
Date: Sun, 11 Feb 2018 14:43:56 +0200
Subject: [PATCH] eth/downloader: don't require state for ancestor lookups

---
 eth/downloader/downloader.go      | 11 ++++++-----
 eth/downloader/downloader_test.go | 11 +++--------
 2 files changed, 9 insertions(+), 13 deletions(-)

diff --git a/eth/downloader/downloader.go b/eth/downloader/downloader.go
index 3870f10b91..7ede530a94 100644
--- a/eth/downloader/downloader.go
+++ b/eth/downloader/downloader.go
@@ -173,8 +173,8 @@ type LightChain interface {
 type BlockChain interface {
 	LightChain
 
-	// HasBlockAndState verifies block and associated states' presence in the local chain.
-	HasBlockAndState(common.Hash, uint64) bool
+	// HasBlock verifies a block's presence in the local chain.
+	HasBlock(common.Hash, uint64) bool
 
 	// GetBlockByHash retrieves a block from the local chain.
 	GetBlockByHash(common.Hash) *types.Block
@@ -582,7 +582,6 @@ func (d *Downloader) findAncestor(p *peerConnection, height uint64) (uint64, err
 	// Figure out the valid ancestor range to prevent rewrite attacks
 	floor, ceil := int64(-1), d.lightchain.CurrentHeader().Number.Uint64()
 
-	p.log.Debug("Looking for common ancestor", "local", ceil, "remote", height)
 	if d.mode == FullSync {
 		ceil = d.blockchain.CurrentBlock().NumberU64()
 	} else if d.mode == FastSync {
@@ -591,6 +590,8 @@ func (d *Downloader) findAncestor(p *peerConnection, height uint64) (uint64, err
 	if ceil >= MaxForkAncestry {
 		floor = int64(ceil - MaxForkAncestry)
 	}
+	p.log.Debug("Looking for common ancestor", "local", ceil, "remote", height)
+
 	// Request the topmost blocks to short circuit binary ancestor lookup
 	head := ceil
 	if head > height {
@@ -646,7 +647,7 @@ func (d *Downloader) findAncestor(p *peerConnection, height uint64) (uint64, err
 					continue
 				}
 				// Otherwise check if we already know the header or not
-				if (d.mode == FullSync && d.blockchain.HasBlockAndState(headers[i].Hash(), headers[i].Number.Uint64())) || (d.mode != FullSync && d.lightchain.HasHeader(headers[i].Hash(), headers[i].Number.Uint64())) {
+				if (d.mode == FullSync && d.blockchain.HasBlock(headers[i].Hash(), headers[i].Number.Uint64())) || (d.mode != FullSync && d.lightchain.HasHeader(headers[i].Hash(), headers[i].Number.Uint64())) {
 					number, hash = headers[i].Number.Uint64(), headers[i].Hash()
 
 					// If every header is known, even future ones, the peer straight out lied about its head
@@ -711,7 +712,7 @@ func (d *Downloader) findAncestor(p *peerConnection, height uint64) (uint64, err
 				arrived = true
 
 				// Modify the search interval based on the response
-				if (d.mode == FullSync && !d.blockchain.HasBlockAndState(headers[0].Hash(), headers[0].Number.Uint64())) || (d.mode != FullSync && !d.lightchain.HasHeader(headers[0].Hash(), headers[0].Number.Uint64())) {
+				if (d.mode == FullSync && !d.blockchain.HasBlock(headers[0].Hash(), headers[0].Number.Uint64())) || (d.mode != FullSync && !d.lightchain.HasHeader(headers[0].Hash(), headers[0].Number.Uint64())) {
 					end = check
 					break
 				}
diff --git a/eth/downloader/downloader_test.go b/eth/downloader/downloader_test.go
index d94d55f114..cb671a7df4 100644
--- a/eth/downloader/downloader_test.go
+++ b/eth/downloader/downloader_test.go
@@ -221,14 +221,9 @@ func (dl *downloadTester) HasHeader(hash common.Hash, number uint64) bool {
 	return dl.GetHeaderByHash(hash) != nil
 }
 
-// HasBlockAndState checks if a block and associated state is present in the testers canonical chain.
-func (dl *downloadTester) HasBlockAndState(hash common.Hash, number uint64) bool {
-	block := dl.GetBlockByHash(hash)
-	if block == nil {
-		return false
-	}
-	_, err := dl.stateDb.Get(block.Root().Bytes())
-	return err == nil
+// HasBlock checks if a block is present in the testers canonical chain.
+func (dl *downloadTester) HasBlock(hash common.Hash, number uint64) bool {
+	return dl.GetBlockByHash(hash) != nil
 }
 
 // GetHeader retrieves a header from the testers canonical chain.