// maybeAcceptBlock potentially accepts a block into the memory block chain.
// It performs several validation checks which depend on its position within
// the block chain before adding it. The block is expected to have already gone
// through ProcessBlock before calling this function with it.
//
// The flags modify the behavior of this function as follows:
// - BFFastAdd: The somewhat expensive BIP0034 validation is not performed.
// - BFDryRun: The memory chain index will not be pruned and no accept
// notification will be sent since the block is not being accepted.
func (b *BlockChain) maybeAcceptBlock(block *btcutil.Block, flags BehaviorFlags) error {
fastAdd := flags&BFFastAdd == BFFastAdd
dryRun := flags&BFDryRun == BFDryRun
// Get a block node for the block previous to this one. Will be nil
// if this is the genesis block.
prevNode, err := b.getPrevNodeFromBlock(block)
if err != nil {
log.Errorf("getPrevNodeFromBlock: %v", err)
return err
}
// The height of this block is one more than the referenced previous
// block.
blockHeight := int64(0)
if prevNode != nil {
blockHeight = prevNode.height + 1
}
block.SetHeight(blockHeight)
blockHeader := &block.MsgBlock().Header
if !fastAdd {
// Ensure the difficulty specified in the block header matches
// the calculated difficulty based on the previous block and
// difficulty retarget rules.
expectedDifficulty, err := b.calcNextRequiredDifficulty(prevNode,
block.MsgBlock().Header.Timestamp)
if err != nil {
return err
}
blockDifficulty := blockHeader.Bits
if blockDifficulty != expectedDifficulty {
str := "block difficulty of %d is not the expected value of %d"
str = fmt.Sprintf(str, blockDifficulty, expectedDifficulty)
return ruleError(ErrUnexpectedDifficulty, str)
}
// Ensure the timestamp for the block header is after the
// median time of the last several blocks (medianTimeBlocks).
medianTime, err := b.calcPastMedianTime(prevNode)
if err != nil {
log.Errorf("calcPastMedianTime: %v", err)
return err
}
if !blockHeader.Timestamp.After(medianTime) {
str := "block timestamp of %v is not after expected %v"
str = fmt.Sprintf(str, blockHeader.Timestamp,
medianTime)
return ruleError(ErrTimeTooOld, str)
}
// Ensure all transactions in the block are finalized.
for _, tx := range block.Transactions() {
if !IsFinalizedTransaction(tx, blockHeight,
blockHeader.Timestamp) {
str := fmt.Sprintf("block contains "+
"unfinalized transaction %v", tx.Sha())
return ruleError(ErrUnfinalizedTx, str)
}
}
}
// Ensure chain matches up to predetermined checkpoints.
// It's safe to ignore the error on Sha since it's already cached.
blockHash, _ := block.Sha()
if !b.verifyCheckpoint(blockHeight, blockHash) {
str := fmt.Sprintf("block at height %d does not match "+
"checkpoint hash", blockHeight)
return ruleError(ErrBadCheckpoint, str)
}
// Find the previous checkpoint and prevent blocks which fork the main
// chain before it. This prevents storage of new, otherwise valid,
// blocks which build off of old blocks that are likely at a much easier
// difficulty and therefore could be used to waste cache and disk space.
checkpointBlock, err := b.findPreviousCheckpoint()
if err != nil {
return err
}
if checkpointBlock != nil && blockHeight < checkpointBlock.Height() {
str := fmt.Sprintf("block at height %d forks the main chain "+
"before the previous checkpoint at height %d",
blockHeight, checkpointBlock.Height())
return ruleError(ErrForkTooOld, str)
}
if !fastAdd {
// Reject version 1 blocks once a majority of the network has
// upgraded. This is part of BIP0034.
if blockHeader.Version < 2 {
if b.isMajorityVersion(2, prevNode,
b.netParams.BlockV1RejectNumRequired,
b.netParams.BlockV1RejectNumToCheck) {
str := "new blocks with version %d are no " +
"longer valid"
str = fmt.Sprintf(str, blockHeader.Version)
return ruleError(ErrBlockVersionTooOld, str)
}
}
// Ensure coinbase starts with serialized block heights for
// blocks whose version is the serializedHeightVersion or
// newer once a majority of the network has upgraded. This is
// part of BIP0034.
if blockHeader.Version >= serializedHeightVersion {
if b.isMajorityVersion(serializedHeightVersion,
prevNode,
b.netParams.CoinbaseBlockHeightNumRequired,
b.netParams.CoinbaseBlockHeightNumToCheck) {
expectedHeight := int64(0)
if prevNode != nil {
expectedHeight = prevNode.height + 1
}
coinbaseTx := block.Transactions()[0]
err := checkSerializedHeight(coinbaseTx,
expectedHeight)
if err != nil {
return err
}
}
}
}
// Prune block nodes which are no longer needed before creating
// a new node.
if !dryRun {
err = b.pruneBlockNodes()
if err != nil {
return err
}
}
// Create a new block node for the block and add it to the in-memory
// block chain (could be either a side chain or the main chain).
newNode := newBlockNode(blockHeader, blockHash, blockHeight)
if prevNode != nil {
newNode.parent = prevNode
newNode.height = blockHeight
newNode.workSum.Add(prevNode.workSum, newNode.workSum)
}
// Connect the passed block to the chain while respecting proper chain
// selection according to the chain with the most proof of work. This
// also handles validation of the transaction scripts.
err = b.connectBestChain(newNode, block, flags)
if err != nil {
return err
}
// 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.
if !dryRun {
b.sendNotification(NTBlockAccepted, block)
}
return nil
}