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takuti/TxHadler.java Secret

Created Apr 21, 2021
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import java.util.ArrayList;
import java.util.HashSet;
public class TxHandler {
/**
* Creates a public ledger whose current UTXOPool (collection of unspent transaction outputs) is
* {@code utxoPool}. This should make a copy of utxoPool by using the UTXOPool(UTXOPool uPool)
* constructor.
*/
private UTXOPool utxoPool;
public TxHandler(UTXOPool utxoPool) {
this.utxoPool = new UTXOPool(utxoPool);
}
/**
* @return true if:
* (1) all outputs claimed by {@code tx} are in the current UTXO pool,
* (2) the signatures on each input of {@code tx} are valid,
* (3) no UTXO is claimed multiple times by {@code tx},
* (4) all of {@code tx}s output values are non-negative, and
* (5) the sum of {@code tx}s input values is greater than or equal to the sum of its output
* values; and false otherwise.
*/
public boolean isValidTx(Transaction tx) {
HashSet<UTXO> claimedUTXO = new HashSet<>();
double inTotal = 0.d;
for (int i = 0; i < tx.numInputs(); i++) {
Transaction.Input in = tx.getInput(i);
UTXO ut = new UTXO(in.prevTxHash, in.outputIndex);
// (1)
if (!utxoPool.contains(ut)) return false;
// (2)
Transaction.Output out = utxoPool.getTxOutput(ut);
if (!Crypto.verifySignature(out.address, tx.getRawDataToSign(i), in.signature)) return false;
// (3)
if (claimedUTXO.contains(ut)) return false;
claimedUTXO.add(ut);
// for (5)
inTotal += out.value;
}
for (Transaction.Output out : tx.getOutputs()) {
// (4)
if (out.value < 0.d) return false;
// (5)
inTotal -= out.value;
if (inTotal < 0.d) return false; // when total output value exceeds total input
}
return true;
}
/**
* Handles each epoch by receiving an unordered array of proposed transactions, checking each
* transaction for correctness, returning a mutually valid array of accepted transactions, and
* updating the current UTXO pool as appropriate.
*/
public Transaction[] handleTxs(Transaction[] possibleTxs) {
ArrayList<Transaction> acceptedTxs = new ArrayList<>();
for (Transaction tx : possibleTxs) {
if (!isValidTx(tx)) continue;
acceptedTxs.add(tx);
// remove spent from prev tx
for (Transaction.Input in : tx.getInputs()) {
UTXO ut = new UTXO(in.prevTxHash, in.outputIndex);
utxoPool.removeUTXO(ut);
}
// add coins created by this tx
for (int i = 0; i < tx.numOutputs(); i++) {
UTXO ut = new UTXO(tx.getHash(), i);
utxoPool.addUTXO(ut, tx.getOutput(i));
}
}
return acceptedTxs.toArray(new Transaction[acceptedTxs.size()]);
}
public UTXOPool getUTXOPool() {
return utxoPool;
}
}
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