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ForwardingService: make the forwarding a safe operation

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By using a CoinSelector that selects exactly the outputs that have been sent to us,
we make sure that

* we exactly send the value that has been sent to us, minus fee
* if the incoming transaction became invalid (e.g. due to a re-org),
  our outgoing transaction would become invalid, too

Strictly speaking, after this change we would not need to wait for confirmations any
more.
This commit is contained in:
Andreas Schildbach 2022-07-19 00:58:54 +02:00
parent afe8086aec
commit adb6bcc921
1 changed files with 25 additions and 1 deletions
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26
examples/src/main/java/org/bitcoinj/examples/ForwardingService.java
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@ -18,6 +18,7 @@ package org.bitcoinj.examples;
import org.bitcoinj.base.BitcoinNetwork;
import org.bitcoinj.base.ScriptType;
import org.bitcoinj.base.Sha256Hash;
import org.bitcoinj.core.Address;
import org.bitcoinj.base.Coin;
import org.bitcoinj.core.Context;
@ -26,16 +27,21 @@ import org.bitcoinj.core.NetworkParameters;
import org.bitcoinj.core.Transaction;
import org.bitcoinj.core.TransactionBroadcast;
import org.bitcoinj.core.TransactionConfidence;
import org.bitcoinj.core.TransactionOutput;
import org.bitcoinj.crypto.KeyCrypterException;
import org.bitcoinj.kits.WalletAppKit;
import org.bitcoinj.utils.BriefLogFormatter;
import org.bitcoinj.wallet.CoinSelection;
import org.bitcoinj.wallet.CoinSelector;
import org.bitcoinj.wallet.KeyChainGroupStructure;
import org.bitcoinj.wallet.SendRequest;
import org.bitcoinj.wallet.Wallet;
import org.bitcoinj.wallet.listeners.WalletCoinsReceivedEventListener;
import java.io.File;
import java.util.List;
import java.util.concurrent.CompletableFuture;
import java.util.stream.Collectors;
/**
* ForwardingService demonstrates basic usage of the library. It sits on the network and when it receives coins, simply
@ -169,8 +175,9 @@ public class ForwardingService implements AutoCloseable {
.thenCompose(confidence -> {
// Required confirmations received, now compose a call to broadcast the forwarding transaction
System.out.printf("Incoming tx has received %d confirmations.\n", confidence.getDepthInBlocks());
// Now send the coins onwards by sending the entire contents of our wallet
// Now send the coins onwards by sending exactly the outputs that have been sent to us
SendRequest sendRequest = SendRequest.emptyWallet(forwardingAddress);
sendRequest.coinSelector = new ForwardingCoinSelector(incomingTx);
System.out.printf("Creating outgoing transaction for %s...\n", forwardingAddress);
return sendTransaction(sendRequest);
})
@ -243,4 +250,21 @@ public class ForwardingService implements AutoCloseable {
static String getPrefix(BitcoinNetwork network) {
return String.format("forwarding-service-%s", network.toString());
}
static class ForwardingCoinSelector implements CoinSelector {
private final Sha256Hash forwardTxId;
public ForwardingCoinSelector(Transaction transactionToForward) {
this.forwardTxId = transactionToForward.getTxId();
}
@Override
public CoinSelection select(Coin target, List<TransactionOutput> candidates) {
var selected =
candidates.stream()
.filter(output -> output.getParentTransactionHash().equals(forwardTxId))
.collect(Collectors.toList());
return new CoinSelection(selected);
}
}
}