// findCandidates searches the chain backwards for checkpoint candidates and
// returns a slice of found candidates, if any. It also stops searching for
// candidates at the last checkpoint that is already hard coded into btcchain
// since there is no point in finding candidates before already existing
// checkpoints.
func findCandidates(chain *blockchain.BlockChain, latestHash *chainhash.Hash) ([]*chaincfg.Checkpoint, error) {
// Start with the latest block of the main chain.
block, err := chain.BlockByHash(latestHash)
if err != nil {
return nil, err
}
// Get the latest known checkpoint.
latestCheckpoint := chain.LatestCheckpoint()
if latestCheckpoint == nil {
// Set the latest checkpoint to the genesis block if there isn't
// already one.
latestCheckpoint = &chaincfg.Checkpoint{
Hash: activeNetParams.GenesisHash,
Height: 0,
}
}
// The latest known block must be at least the last known checkpoint
// plus required checkpoint confirmations.
checkpointConfirmations := int32(blockchain.CheckpointConfirmations)
requiredHeight := latestCheckpoint.Height + checkpointConfirmations
if block.Height() < requiredHeight {
return nil, fmt.Errorf("the block database is only at height "+
"%d which is less than the latest checkpoint height "+
"of %d plus required confirmations of %d",
block.Height(), latestCheckpoint.Height,
checkpointConfirmations)
}
// For the first checkpoint, the required height is any block after the
// genesis block, so long as the chain has at least the required number
// of confirmations (which is enforced above).
if len(activeNetParams.Checkpoints) == 0 {
requiredHeight = 1
}
// Indeterminate progress setup.
numBlocksToTest := block.Height() - requiredHeight
progressInterval := (numBlocksToTest / 100) + 1 // min 1
fmt.Print("Searching for candidates")
defer fmt.Println()
// Loop backwards through the chain to find checkpoint candidates.
candidates := make([]*chaincfg.Checkpoint, 0, cfg.NumCandidates)
numTested := int32(0)
for len(candidates) < cfg.NumCandidates && block.Height() > requiredHeight {
// Display progress.
if numTested%progressInterval == 0 {
fmt.Print(".")
}
// Determine if this block is a checkpoint candidate.
isCandidate, err := chain.IsCheckpointCandidate(block)
if err != nil {
return nil, err
}
// All checks passed, so this node seems like a reasonable
// checkpoint candidate.
if isCandidate {
checkpoint := chaincfg.Checkpoint{
Height: block.Height(),
Hash: block.Hash(),
}
candidates = append(candidates, &checkpoint)
}
prevHash := &block.MsgBlock().Header.PrevBlock
block, err = chain.BlockByHash(prevHash)
if err != nil {
return nil, err
}
numTested++
}
return candidates, nil
}
