multi: Rework old fork rejection logic.

blockchain/chain.go

@@ -135,18 +135,19 @@ type BlockChain struct {
 	// The following fields are set when the instance is created and can't
 	// be changed afterwards, so there is no need to protect them with a
 	// separate mutex.
-	assumeValid      chainhash.Hash
-	latestCheckpoint *chaincfg.Checkpoint
-	deploymentVers   map[string]uint32
-	db               database.DB
-	dbInfo           *databaseInfo
-	chainParams      *chaincfg.Params
-	timeSource       MedianTimeSource
-	notifications    NotificationCallback
-	sigCache         *txscript.SigCache
-	indexSubscriber  *indexers.IndexSubscriber
-	interrupt        <-chan struct{}
-	utxoCache        UtxoCacher
+	assumeValid              chainhash.Hash
+	allowOldForks            bool
+	expectedBlocksInTwoWeeks int64
+	deploymentVers           map[string]uint32
+	db                       database.DB
+	dbInfo                   *databaseInfo
+	chainParams              *chaincfg.Params
+	timeSource               MedianTimeSource
+	notifications            NotificationCallback
+	sigCache                 *txscript.SigCache
+	indexSubscriber          *indexers.IndexSubscriber
+	interrupt                <-chan struct{}
+	utxoCache                UtxoCacher
 
 	// subsidyCache is the cache that provides quick lookup of subsidy
 	// values.
@@ -204,16 +205,18 @@ type BlockChain struct {
 	disapprovedViewLock sync.Mutex
 	disapprovedView     *UtxoViewpoint
 
+	// rejectForksCheckpoint tracks the block to treat as a checkpoint for the
+	// purposes of rejecting old forks.  It will be nil when no suitable block
+	// is known or old forks are allowed for the current network.
+	//
+	// It is protected by the chain lock.
+	rejectForksCheckpoint *blockNode
+
 	// assumeValidNode tracks the assumed valid block.  It will be nil when a
 	// block header with the assumed valid block hash has not been discovered or
 	// when assume valid is disabled.  It is protected by the chain lock.
 	assumeValidNode *blockNode
 
-	// checkpointNode tracks the most recently known checkpoint.  It will be nil
-	// when no checkpoints are known or are disabled.  It is protected by the
-	// chain lock.
-	checkpointNode *blockNode
-
 	// The state is used as a fairly efficient way to cache information
 	// about the current best chain state that is returned to callers when
 	// requested.  It operates on the principle of MVCC such that any time a
@@ -2269,6 +2272,14 @@ type Config struct {
 	// This field is required.
 	ChainParams *chaincfg.Params
 
+	// AllowOldForks enables processing of blocks that are forks deep in the
+	// chain history.  This should realistically never need to be enabled in
+	// practice, however, it is provided for testing purposes as well as a
+	// recovery mechanism in the extremely unlikely case that a node were to
+	// somehow get stuck on a bad fork and be unable to reorg to the good one
+	// due to the old fork rejection semantics.
+	AllowOldForks bool
+
 	// AssumeValid is the hash of a block that has been externally verified to
 	// be valid.  It allows several validation checks to be skipped for blocks
 	// that are both an ancestor of the assumed valid block and an ancestor of
@@ -2277,12 +2288,6 @@ type Config struct {
 	// This field may not be set for networks that do not require it.
 	AssumeValid chainhash.Hash
 
-	// LatestCheckpoint specifies the most recent known checkpoint that is
-	// typically the default checkpoint in ChainParams.
-	//
-	// This field can be nil if the caller does not wish to specify a checkpoint.
-	LatestCheckpoint *chaincfg.Checkpoint
-
 	// TimeSource defines the median time source to use for things such as
 	// block processing and determining whether or not the chain is current.
 	//
@@ -2355,9 +2360,23 @@ func New(ctx context.Context, config *Config) (*BlockChain, error) {
 		subsidyCache = standalone.NewSubsidyCache(params)
 	}
 
+	// Calculate the expected number of blocks in 2 weeks and cache it in order
+	// to avoid repeated calculation.
+	const timeInTwoWeeks = time.Hour * 24 * 14
+	expectedBlksInTwoWeeks := int64(timeInTwoWeeks / params.TargetTimePerBlock)
+
+	// Fork rejection semantics are disabled when explicitly requested or the
+	// hard-coded assume valid hash is not set for the current network.
+	//
+	// Note that this is very intentionally using the hard-coded value specified
+	// in the chain params as opposed to the one that a user might have
+	// overridden in the passed config since fork rejection affects consensus.
+	allowOldForks := config.AllowOldForks || params.AssumeValid == *zeroHash
+
 	b := BlockChain{
 		assumeValid:                   config.AssumeValid,
-		latestCheckpoint:              config.LatestCheckpoint,
+		allowOldForks:                 allowOldForks,
+		expectedBlocksInTwoWeeks:      expectedBlksInTwoWeeks,
 		deploymentVers:                deploymentVers,
 		db:                            config.DB,
 		chainParams:                   params,

blockchain/chainio.go

@@ -1587,15 +1587,8 @@ func (b *BlockChain) initChainState(ctx context.Context,
 			return err
 		}
 
-		// Find the most recent checkpoint.
-		if b.latestCheckpoint != nil {
-			node := b.index.lookupNode(b.latestCheckpoint.Hash)
-			if node != nil {
-				log.Debugf("Most recent checkpoint is %s (height %d)",
-					node.hash, node.height)
-				b.checkpointNode = node
-			}
-		}
+		// Attempt to discover and set the old fork rejection checkpoint node.
+		b.maybeSetForkRejectionCheckpoint()
 
 		// Find the assumed valid node.
 		if b.assumeValid != *zeroHash {

blockchain/error.go

@@ -98,12 +98,8 @@ const (
 	// not match the expected value.
 	ErrBadCommitmentRoot = ErrorKind("ErrBadCommitmentRoot")
 
-	// ErrBadCheckpoint indicates a block that is expected to be at a
-	// checkpoint height does not match the expected one.
-	ErrBadCheckpoint = ErrorKind("ErrBadCheckpoint")
-
 	// ErrForkTooOld indicates a block is attempting to fork the block chain
-	// before the most recent checkpoint.
+	// before the fork rejection checkpoint.
 	ErrForkTooOld = ErrorKind("ErrForkTooOld")
 
 	// ErrNoTransactions indicates the block does not have a least one

blockchain/error_test.go

@@ -32,7 +32,6 @@ func TestErrorKindStringer(t *testing.T) {
 		{ErrHighHash, "ErrHighHash"},
 		{ErrBadMerkleRoot, "ErrBadMerkleRoot"},
 		{ErrBadCommitmentRoot, "ErrBadCommitmentRoot"},
-		{ErrBadCheckpoint, "ErrBadCheckpoint"},
 		{ErrForkTooOld, "ErrForkTooOld"},
 		{ErrNoTransactions, "ErrNoTransactions"},
 		{ErrNoTxInputs, "ErrNoTxInputs"},

blockchain/fullblocktests/params.go

@@ -133,9 +133,6 @@ var regNetParams = &chaincfg.Params{
 	StakeRewardProportionV2:  8,
 	BlockTaxProportion:       1,
 
-	// Checkpoints ordered from oldest to newest.
-	Checkpoints: nil,
-
 	// Consensus rule change deployments.
 	//
 	// The miner confirmation window is defined as: