How to make transaction id unique?

[guihao-liang]

I'm reading part 4, and I think if txid is not unique for this tutorial. Txid should be unique for blockchain. Otherwise, you can't lookup each transaction by txid.

The logic to generate txid. It generates the same id for newly mined coin:

blockchain_go/transaction.go

Lines 64 to 72 in e17722e

	func NewCoinbaseTX(to, data string) *Transaction {
	if data == "" {
	data = fmt.Sprintf("Reward to '%s'", to)
	}
	txin := TXInput{[]byte{}, -1, data}
	txout := TXOutput{subsidy, to}
	tx := Transaction{nil, []TXInput{txin}, []TXOutput{txout}}
	tx.SetID()

the FindUnspentTransactions would go wrong:

blockchain_go/blockchain.go

Lines 78 to 82 in e17722e

	if spentTXOs[txID] != nil {
	for _, spentOut := range spentTXOs[txID] {
	if spentOut == outIdx {
	continue Outputs
	}

for example, could you mine 2 new coins with duplicated txid by calling NewCoinbaseTX("same_miner", "")

Then one coin could be used and the other is not. The above FindUnspentTransactions logic can't distinguish those 2 coins.

Even if you add rand in part 6, it still has a chance of colliding.

blockchain_go/transaction.go

Lines 174 to 188 in 0538111

	func NewCoinbaseTX(to, data string) *Transaction {
	if data == "" {
	randData := make([]byte, 20)
	_, err := rand.Read(randData)
	if err != nil {
	log.Panic(err)
	}
	data = fmt.Sprintf("%x", randData)
	}
	txin := TXInput{[]byte{}, -1, nil, []byte(data)}
	txout := NewTXOutput(subsidy, to)
	tx := Transaction{nil, []TXInput{txin}, []TXOutput{*txout}}
	tx.ID = tx.Hash()

Any suggestion to make sure that the txid is unique?

[Anmilover]

您好，邮件已查收。Anmi、