blockchain.go

package blockchain

import (
	"bytes"
	"crypto/ecdsa"
	"encoding/hex"
	"errors"
	"fmt"
	"log"
	"os"

	"github.com/boltdb/bolt"
)

const dbFile = "/blockchain_%s.db"
const blocksBucket = "blocks"
const genesisCoinbaseData = "The Times 03/Jan/2009 Chancellor on brink of second bailout for banks"

// Blockchain keeps a sequence of Blocks
type Blockchain struct {
	Tip []byte
  Db *bolt.DB
}

// MineBlock saves provided data as a block in the blockchain
func (bc *Blockchain) MineBlock(transactions []*Transaction) *Block {
  var lastHash []byte
	var lastHeight int

	for _, tx := range transactions {
		if bc.VerifyTransaction(tx) != true {
			log.Panic("ERROR: Invalid transaction")
		}
	}

  err := bc.Db.View(func(tx *bolt.Tx) error {
    b := tx.Bucket([]byte(blocksBucket))
    lastHash = b.Get([]byte("l"))

		blockData := b.Get(lastHash)
		block := DeserializeBlock(blockData)

		lastHeight = block.Height
    return nil
  })

  if err != nil {
    log.Panic(err)
  }

  newBlock := NewBlock(transactions, lastHash, lastHeight+1)

  err = bc.Db.Update(func(tx *bolt.Tx) error {
    b := tx.Bucket([]byte(blocksBucket))
    err := b.Put(newBlock.Hash, newBlock.Serialize())
    if err != nil {
      log.Panic(err)
    }

    err = b.Put([]byte("l"), newBlock.Hash)
    if err != nil {
      log.Panic(err)
    }

    bc.Tip = newBlock.Hash
    return nil
  })

	if err != nil {
		log.Panic(err)
	}
	return newBlock
}

// VerifyTransaction verifies transaction input signatures
func (bc *Blockchain) VerifyTransaction(tx *Transaction) bool {
	prevTXs := make(map[string]Transaction)

	for _, vin := range tx.Vin {
		prevTX, err := bc.FindTransaction(vin.Txid)
		if err != nil {
			log.Panic(err)
		}
		prevTXs[hex.EncodeToString(prevTX.ID)] = prevTX
	}

	return tx.Verify(prevTXs)
}

// SignTransaction signs inputs of a Transaction
func (bc *Blockchain) SignTransaction(tx *Transaction, privKey ecdsa.PrivateKey) {
	prevTXs := make(map[string]Transaction)

	for _, vin := range tx.Vin {
		prevTX, err := bc.FindTransaction(vin.Txid)
		if err != nil {
			log.Panic(err)
		}
		prevTXs[hex.EncodeToString(prevTX.ID)] = prevTX
	}

	tx.Sign(privKey, prevTXs)
}

// FindTransaction finds a transaction by its ID
func (bc *Blockchain) FindTransaction(ID []byte) (Transaction, error) {
	bci := bc.Iterator()

	for {
		block := bci.Next()

		for _, tx := range block.Transactions {
			if bytes.Compare(tx.ID, ID) == 0 {
				return *tx, nil
			}
		}

		if len(block.PrevBlockHash) == 0 {
			break
		}
	}

	return Transaction{}, errors.New("Transaction is not found")
}

//  FindUTXO finds all unspent transaction outputs and returns transactions with spent outputs removed
func (bc *Blockchain) FindUTXO() map[string]TXOutputs {
	UTXO := make(map[string]TXOutputs)
	spentTXOs := make(map[string][]int)
	bci := bc.Iterator()

	for {
		block := bci.Next()

		for _, tx := range block.Transactions {
			txID := hex.EncodeToString(tx.ID)

			Outputs:
				for outIdx, out := range tx.Vout {
					// Was the output spent?
					if spentTXOs[txID] != nil {
						for _, spentOutIdx := range spentTXOs[txID] {
							if spentOutIdx == outIdx {
								continue Outputs
							}
						}
					}

					outs := UTXO[txID]
					outs.Outputs = append(outs.Outputs, out)
					UTXO[txID] = outs
				}

				if tx.IsCoinbase() == false {
					for _, in := range tx.Vin {
						inTxID := hex.EncodeToString(in.Txid)
						spentTXOs[inTxID] = append(spentTXOs[inTxID], in.Vout)
					}
				}
		}
		if len(block.PrevBlockHash) == 0 {
			break
		}
	}

	return UTXO
}

// NewBlockchain creates a new Blockchain with genesis Block
func NewBlockchain(nodeID string) *Blockchain {
	dataDir := os.Getenv("DATA_DIR")
	dbFile := dataDir + fmt.Sprintf(dbFile, nodeID)
	if dbExists(dbFile) == false {
		fmt.Println("No existing blockchain found. Create one first.")
		os.Exit(1)
	}

  var tip []byte
	db, err := bolt.Open(dbFile, 0600, nil)
	if err != nil {
		log.Panic(err)
	}

	err = db.Update(func(tx *bolt.Tx) error {
		b := tx.Bucket([]byte(blocksBucket))
		tip = b.Get([]byte("l"))
		return nil
	})

	if err != nil {
		log.Panic(err)
	}

	bc := Blockchain{tip, db}
	return &bc
}

// AddBlock saves the block into the blockchain
func (bc *Blockchain) AddBlock(block *Block) {
	err := bc.Db.Update(func(tx *bolt.Tx) error {
		b := tx.Bucket([]byte(blocksBucket))
		blockInDb := b.Get(block.Hash)

		if blockInDb != nil {
			return nil
		}

		blockData := block.Serialize()
		err := b.Put(block.Hash, blockData)
		if err != nil {
			log.Panic(err)
		}

		lastHash := b.Get([]byte("l"))
		lastBlockData := b.Get(lastHash)
		lastBlock := DeserializeBlock(lastBlockData)

		if block.Height > lastBlock.Height {
			err = b.Put([]byte("l"), block.Hash)
			if err != nil {
				log.Panic(err)
			}
			bc.Tip = block.Hash
		}

		return nil
	})
	if err != nil {
		log.Panic(err)
	}
}

// CreateBlockchain creates a new blockchain DB
func CreateBlockchain(address, nodeID string) *Blockchain {
	dataDir := os.Getenv("DATA_DIR")
	dbFile := dataDir + fmt.Sprintf(dbFile, nodeID)
	if dbExists(dbFile) {
		fmt.Println("Blockchain already exists.")
		os.Exit(1)
	}

	var tip []byte
	cbtx := NewCoinbaseTX(address, genesisCoinbaseData)
	genesis := NewGenesisBlock(cbtx)

	db, err := bolt.Open(dbFile, 0600, nil)
	if err != nil {
		log.Panic(err)
	}

	err = db.Update(func(tx *bolt.Tx) error {
		b, err := tx.CreateBucket([]byte(blocksBucket))
		if err != nil {
			log.Panic(err)
		}

		err = b.Put(genesis.Hash, genesis.Serialize())
		if err != nil {
			log.Panic(err)
		}

		err = b.Put([]byte("l"), genesis.Hash)
		if err != nil {
			log.Panic(err)
		}
		tip = genesis.Hash

		return nil
	})

	if err != nil {
		log.Panic(err)
	}

	bc := Blockchain{tip, db}

	return &bc
}

// Iterator ...
func (bc *Blockchain) Iterator() *BlockchainIterator {
	bci := &BlockchainIterator{bc.Tip, bc.Db}

	return bci
}

// GetBestHeight returns the height of the latest block
func (bc *Blockchain) GetBestHeight() int {
	var lastBlock Block

	err := bc.Db.View(func(tx *bolt.Tx) error {
		b := tx.Bucket([]byte(blocksBucket))
		lastHash := b.Get([]byte("l"))
		blockData := b.Get(lastHash)
		lastBlock = *DeserializeBlock(blockData)

		return nil
	})
	if err != nil {
		log.Panic(err)
	}

	return lastBlock.Height
}

// GetBlock finds a block by its hash and returns it
func (bc *Blockchain) GetBlock(blockHash []byte) (Block, error) {
	var block Block

	err := bc.Db.View(func(tx *bolt.Tx) error {
		b := tx.Bucket([]byte(blocksBucket))

		blockData := b.Get(blockHash)

		if blockData == nil {
			return errors.New("Block is not found.")
		}

		block = *DeserializeBlock(blockData)

		return nil
	})
	if err != nil {
		return block, err
	}

	return block, nil
}

// GetBlockHashes returns a list of hashes of all the blocks in the chain
func (bc *Blockchain) GetBlockHashes() [][]byte {
	var blocks [][]byte
	bci := bc.Iterator()

	for {
		block := bci.Next()

		blocks = append(blocks, block.Hash)

		if len(block.PrevBlockHash) == 0 {
			break
		}
	}

	return blocks
}

func dbExists(dbFile string) bool {
	if _, err := os.Stat(dbFile); os.IsNotExist(err) {
		return false
	}

	return true
}