proofofwork.go

// proofofwork.go
package main

import (
	"bytes"
	"crypto/sha256"
	"fmt"
	"math"
	"math/big"
)

var maxNonce = math.MaxInt64

const targetBits = 15 // smaller targetBits, easier difficulty

type ProofOfWork struct {
	block  *Block
	target *big.Int
}

// return a new ProofOfWork instance
func NewProofOfWork(b *Block) *ProofOfWork {
	target := big.NewInt(1)
	target.Lsh(target, uint(256-targetBits)) // target == 0x10000000......

	pow := &ProofOfWork{b, target}

	return pow
}

func (pow *ProofOfWork) prepareData(nonce int) []byte {
	data := bytes.Join(
		[][]byte{
			pow.block.PrevBlockHash,
			pow.block.HashTransactions(),
			IntToHex(pow.block.Timestamp),
			IntToHex(int64(targetBits)),
			IntToHex(int64(nonce)),
		},
		[]byte{},
	)
	return data
}
func (pow *ProofOfWork) Run() (int, []byte) {
	var hashInt big.Int
	var hash [32]byte
	nonce := 0
	fmt.Printf("Mining a block")
	fmt.Printf("target: %d\n", pow.target)
	for nonce < maxNonce {
		data := pow.prepareData(nonce)

		hash = sha256.Sum256(data)
		fmt.Printf("\r%x", hash)  // \r will recover previous line. It presents the same line is changing.
		hashInt.SetBytes(hash[:]) // convert hash buffer into integer

		if hashInt.Cmp(pow.target) == -1 {
			break
		} else {
			nonce++
		}
	}
	fmt.Printf("\n\n")
	return nonce, hash[:]
}

func (pow *ProofOfWork) Validate() bool {
	var hashInt big.Int
	data := pow.prepareData(pow.block.Nonce)
	hash := sha256.Sum256(data)
	hashInt.SetBytes(hash[:])

	isValid := hashInt.Cmp(pow.target) == -1

	return isValid
}