// checkProofOfWork ensures the block header bits which indicate the target
// difficulty is in min/max range and that the block hash is less than the
// target difficulty as claimed.
//
// The flags modify the behavior of this function as follows:
// - BFNoPoWCheck: The check to ensure the block hash is less than the target
// difficulty is not performed.
func checkProofOfWork(header *wire.BlockHeader, powLimit *big.Int, flags BehaviorFlags) error {
// The target difficulty must be larger than zero.
target := CompactToBig(header.Bits)
if target.Sign() <= 0 {
str := fmt.Sprintf("block target difficulty of %064x is too low",
target)
return ruleError(ErrUnexpectedDifficulty, str)
}
// The target difficulty must be less than the maximum allowed.
if target.Cmp(powLimit) > 0 {
str := fmt.Sprintf("block target difficulty of %064x is "+
"higher than max of %064x", target, powLimit)
return ruleError(ErrUnexpectedDifficulty, str)
}
// The block hash must be less than the claimed target unless the flag
// to avoid proof of work checks is set.
if flags&BFNoPoWCheck != BFNoPoWCheck {
// The block hash must be less than the claimed target.
hash := header.BlockHash()
hashNum := HashToBig(&hash)
if hashNum.Cmp(target) > 0 {
str := fmt.Sprintf("block hash of %064x is higher than "+
"expected max of %064x", hashNum, target)
return ruleError(ErrHighHash, str)
}
}
return nil
}
// checkBlockHeaderContext peforms several validation checks on the block header
// which depend on its position within the block chain.
//
// The flags modify the behavior of this function as follows:
// - BFFastAdd: All checks except those involving comparing the header against
// the checkpoints are not performed.
//
// This function MUST be called with the chain state lock held (for writes).
func (b *BlockChain) checkBlockHeaderContext(header *wire.BlockHeader, prevNode *blockNode, flags BehaviorFlags) error {
// The genesis block is valid by definition.
if prevNode == nil {
return nil
}
fastAdd := flags&BFFastAdd == BFFastAdd
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,
header.Timestamp)
if err != nil {
return err
}
blockDifficulty := header.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 !header.Timestamp.After(medianTime) {
str := "block timestamp of %v is not after expected %v"
str = fmt.Sprintf(str, header.Timestamp, medianTime)
return ruleError(ErrTimeTooOld, str)
}
}
// The height of this block is one more than the referenced previous
// block.
blockHeight := prevNode.height + 1
// Ensure chain matches up to predetermined checkpoints.
blockHash := header.BlockHash()
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)
}
// Reject outdated block versions once a majority of the network
// has upgraded. These were originally voted on by BIP0034,
// BIP0065, and BIP0066.
params := b.chainParams
if header.Version < 2 && blockHeight >= params.BIP0034Height ||
header.Version < 3 && blockHeight >= params.BIP0066Height ||
header.Version < 4 && blockHeight >= params.BIP0065Height {
str := "new blocks with version %d are no longer valid"
str = fmt.Sprintf(str, header.Version)
return ruleError(ErrBlockVersionTooOld, str)
}
return nil
}