// 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 }