blockchain: Refactor to use new chain view.

This refactors and simplifies the code in blockchain to use the new more
efficient chain views.

An overview of the logic changes are as follows:

- Remove inMainChain from block nodes since that can now be efficiently
  determined by using the chain view
- Track the best chain via a chain view instead of a single block node
  - Use the tip of the best chain view everywhere bestNode was used
  - Update chain view tip instead of updating best node
- Remove height map and associated lock in favor of chain view
  - Use chain view NodeByHeight everywhere height map was used
- Change reorg logic to use more efficient chain view fork finding logic
- Change block locator code over to use more efficient chain view logic
  - Remove now unused block-index-based block locator code
  - Move BlockLocator definition to chain.go
  - Move BlockLocatorFromHash and LatestBlockLocator to chain.go
    - Update both to use more efficient chain view logic
- Rework several functions to use chain view for main chain detection
  - fetchMainChainBlockByNode
  - BlockByHeight
  - MainChainHasBlock
  - findPreviousCheckpoint
  - IsCheckpointCandidate

blockchain/accept.go

@@ -179,7 +179,7 @@ func (b *BlockChain) maybeAcceptBlock(block *dcrutil.Block, flags BehaviorFlags)
 
 	// Fetching a stake node could enable a new DoS vector, so restrict
 	// this only to blocks that are recent in history.
-	if newNode.height < b.bestNode.height-minMemoryNodes {
+	if newNode.height < b.bestChain.Tip().height-minMemoryNodes {
 		newNode.stakeNode, err = b.fetchStakeNode(newNode)
 		if err != nil {
 			return 0, err
@@ -205,7 +205,7 @@ func (b *BlockChain) maybeAcceptBlock(block *dcrutil.Block, flags BehaviorFlags)
 	// Notify the caller that the new block was accepted into the block
 	// chain.  The caller would typically want to react by relaying the
 	// inventory to other peers.
-	bestHeight := b.bestNode.height
+	bestHeight := b.bestChain.Tip().height
 	b.chainLock.Unlock()
 	b.sendNotification(NTBlockAccepted, &BlockAcceptedNtfnsData{
 		BestHeight: bestHeight,

blockchain/agendas_test.go

@@ -108,7 +108,7 @@ func testLNFeaturesDeployment(t *testing.T, params *chaincfg.Params, deploymentV
 
 	curTimestamp := time.Now()
 	bc := newFakeChain(params)
-	node := bc.bestNode
+	node := bc.bestChain.Tip()
 	for _, test := range tests {
 		for i := uint32(0); i < test.numNodes; i++ {
 			node = newFakeNode(node, int32(deploymentVer),
@@ -122,7 +122,7 @@ func testLNFeaturesDeployment(t *testing.T, params *chaincfg.Params, deploymentV
 					Bits:    yesChoice.Bits | 0x01,
 				})
 			}
-			bc.bestNode = node
+			bc.bestChain.SetTip(node)
 			curTimestamp = curTimestamp.Add(time.Second)
 		}
 

blockchain/blockindex.go

@@ -113,11 +113,6 @@ type blockNode struct {
 	// methods on blockIndex once the node has been added to the index.
 	status blockStatus
 
-	// inMainChain denotes whether the block node is currently on the
-	// the main chain or not.  This is used to help find the common
-	// ancestor when switching chains.
-	inMainChain bool
-
 	// stakeNode contains all the consensus information required for the
 	// staking system.  The node also caches information required to add or
 	// remove stake nodes, so that the stake node itself may be pruneable

blockchain/blockindex_test.go

@@ -34,9 +34,10 @@ func TestBlockNodeHeader(t *testing.T) {
 	// values.
 	params := &chaincfg.SimNetParams
 	bc := newFakeChain(params)
+	tip := bc.bestChain.Tip()
 	testHeader := wire.BlockHeader{
 		Version:      1,
-		PrevBlock:    bc.bestNode.hash,
+		PrevBlock:    tip.hash,
 		MerkleRoot:   *mustParseHash("09876543210987654321"),
 		StakeRoot:    *mustParseHash("43210987654321098765"),
 		VoteBits:     0x03,
@@ -54,7 +55,7 @@ func TestBlockNodeHeader(t *testing.T) {
 		ExtraData:    [32]byte{0xbb},
 		StakeVersion: 5,
 	}
-	node := newBlockNode(&testHeader, bc.bestNode)
+	node := newBlockNode(&testHeader, tip)
 	bc.index.AddNode(node)
 
 	// Ensure reconstructing the header for the node produces the same header
@@ -154,11 +155,11 @@ func TestCalcPastMedianTime(t *testing.T) {
 		// Create a synthetic chain with the correct number of nodes and the
 		// timestamps as specified by the test.
 		bc := newFakeChain(params)
-		node := bc.bestNode
+		node := bc.bestChain.Tip()
 		for _, timestamp := range test.timestamps {
 			node = newFakeNode(node, 0, 0, 0, time.Unix(timestamp, 0))
 			bc.index.AddNode(node)
-			bc.bestNode = node
+			bc.bestChain.SetTip(node)
 		}
 
 		// Ensure the median time is the expected value.
@@ -177,7 +178,7 @@ func TestCalcPastMedianTime(t *testing.T) {
 func TestChainTips(t *testing.T) {
 	params := &chaincfg.SimNetParams
 	bc := newFakeChain(params)
-	genesis := bc.bestNode
+	genesis := bc.bestChain.NodeByHeight(0)
 
 	// Construct a synthetic simnet chain consisting of the following structure.
 	// 0 -> 1 -> 2  -> 3  -> 4