// Create a payment transaction with valueToMe going back to us
private synchronized Wallet.SendRequest makeUnsignedChannelContract(Coin valueToMe) {
Transaction tx = new Transaction(wallet.getParams());
if (!totalValue.subtract(valueToMe).equals(Coin.ZERO)) {
clientOutput.setValue(totalValue.subtract(valueToMe));
tx.addOutput(clientOutput);
}
tx.addInput(multisigContract.getOutput(0));
return Wallet.SendRequest.forTx(tx);
}
/**
* Updates the outputs on the payment contract transaction and re-signs it. The state must be
* READY in order to call this method. The signature that is returned should be sent to the server
* so it has the ability to broadcast the best seen payment when the channel closes or times out.
*
* <p>The returned signature is over the payment transaction, which we never have a valid copy of
* and thus there is no accessor for it on this object.
*
* <p>To spend the whole channel increment by {@link PaymentChannelClientState#getTotalValue()} -
* {@link PaymentChannelClientState#getValueRefunded()}
*
* @param size How many satoshis to increment the payment by (note: not the new total).
* @throws ValueOutOfRangeException If size is negative or the channel does not have sufficient
* money in it to complete this payment.
*/
public synchronized IncrementedPayment incrementPaymentBy(Coin size)
throws ValueOutOfRangeException {
checkState(state == State.READY);
checkNotExpired();
checkNotNull(size); // Validity of size will be checked by makeUnsignedChannelContract.
if (size.signum() < 0) throw new ValueOutOfRangeException("Tried to decrement payment");
Coin newValueToMe = valueToMe.subtract(size);
if (newValueToMe.compareTo(Transaction.MIN_NONDUST_OUTPUT) < 0 && newValueToMe.signum() > 0) {
log.info(
"New value being sent back as change was smaller than minimum nondust output, sending all");
size = valueToMe;
newValueToMe = Coin.ZERO;
}
if (newValueToMe.signum() < 0)
throw new ValueOutOfRangeException(
"Channel has too little money to pay " + size + " satoshis");
Transaction tx = makeUnsignedChannelContract(newValueToMe);
log.info("Signing new payment tx {}", tx);
Transaction.SigHash mode;
// If we spent all the money we put into this channel, we (by definition) don't care what the
// outputs are, so
// we sign with SIGHASH_NONE to let the server do what it wants.
if (newValueToMe.equals(Coin.ZERO)) mode = Transaction.SigHash.NONE;
else mode = Transaction.SigHash.SINGLE;
TransactionSignature sig = tx.calculateSignature(0, myKey, multisigScript, mode, true);
valueToMe = newValueToMe;
updateChannelInWallet();
IncrementedPayment payment = new IncrementedPayment();
payment.signature = sig;
payment.amount = size;
return payment;
}
/**
* Creates the initial multisig contract and incomplete refund transaction which can be requested
* at the appropriate time using {@link PaymentChannelClientState#getIncompleteRefundTransaction}
* and {@link PaymentChannelClientState#getMultisigContract()}. The way the contract is crafted
* can be adjusted by overriding {@link
* PaymentChannelClientState#editContractSendRequest(com.google.bitcoin.core.Wallet.SendRequest)}.
* By default unconfirmed coins are allowed to be used, as for micropayments the risk should be
* relatively low.
*
* @throws ValueOutOfRangeException if the value being used is too small to be accepted by the
* network
* @throws InsufficientMoneyException if the wallet doesn't contain enough balance to initiate
*/
public synchronized void initiate() throws ValueOutOfRangeException, InsufficientMoneyException {
final NetworkParameters params = wallet.getParams();
Transaction template = new Transaction(params);
// We always place the client key before the server key because, if either side wants some
// privacy, they can
// use a fresh key for the the multisig contract and nowhere else
List<ECKey> keys = Lists.newArrayList(myKey, serverMultisigKey);
// There is also probably a change output, but we don't bother shuffling them as it's obvious
// from the
// format which one is the change. If we start obfuscating the change output better in future
// this may
// be worth revisiting.
TransactionOutput multisigOutput =
template.addOutput(totalValue, ScriptBuilder.createMultiSigOutputScript(2, keys));
if (multisigOutput.getMinNonDustValue().compareTo(totalValue) > 0)
throw new ValueOutOfRangeException("totalValue too small to use");
Wallet.SendRequest req = Wallet.SendRequest.forTx(template);
req.coinSelector = AllowUnconfirmedCoinSelector.get();
editContractSendRequest(req);
req.shuffleOutputs = false; // TODO: Fix things so shuffling is usable.
wallet.completeTx(req);
Coin multisigFee = req.tx.getFee();
multisigContract = req.tx;
// Build a refund transaction that protects us in the case of a bad server that's just trying to
// cause havoc
// by locking up peoples money (perhaps as a precursor to a ransom attempt). We time lock it so
// the server
// has an assurance that we cannot take back our money by claiming a refund before the channel
// closes - this
// relies on the fact that since Bitcoin 0.8 time locked transactions are non-final. This will
// need to change
// in future as it breaks the intended design of timelocking/tx replacement, but for now it
// simplifies this
// specific protocol somewhat.
refundTx = new Transaction(params);
refundTx
.addInput(multisigOutput)
.setSequenceNumber(0); // Allow replacement when it's eventually reactivated.
refundTx.setLockTime(expiryTime);
if (totalValue.compareTo(Coin.CENT) < 0) {
// Must pay min fee.
final Coin valueAfterFee = totalValue.subtract(Transaction.REFERENCE_DEFAULT_MIN_TX_FEE);
if (Transaction.MIN_NONDUST_OUTPUT.compareTo(valueAfterFee) > 0)
throw new ValueOutOfRangeException("totalValue too small to use");
refundTx.addOutput(valueAfterFee, myKey.toAddress(params));
refundFees = multisigFee.add(Transaction.REFERENCE_DEFAULT_MIN_TX_FEE);
} else {
refundTx.addOutput(totalValue, myKey.toAddress(params));
refundFees = multisigFee;
}
refundTx.getConfidence().setSource(TransactionConfidence.Source.SELF);
log.info(
"initiated channel with multi-sig contract {}, refund {}",
multisigContract.getHashAsString(),
refundTx.getHashAsString());
state = State.INITIATED;
// Client should now call getIncompleteRefundTransaction() and send it to the server.
}
/**
* Closes this channel and broadcasts the highest value payment transaction on the network.
*
* <p>This will set the state to {@link State#CLOSED} if the transaction is successfully broadcast
* on the network. If we fail to broadcast for some reason, the state is set to {@link
* State#ERROR}.
*
* <p>If the current state is before {@link State#READY} (ie we have not finished initializing the
* channel), we simply set the state to {@link State#CLOSED} and let the client handle getting its
* refund transaction confirmed.
*
* @return a future which completes when the provided multisig contract successfully broadcasts,
* or throws if the broadcast fails for some reason. Note that if the network simply rejects
* the transaction, this future will never complete, a timeout should be used.
* @throws InsufficientMoneyException If the payment tx would have cost more in fees to spend than
* it is worth.
*/
public synchronized ListenableFuture<Transaction> close() throws InsufficientMoneyException {
if (storedServerChannel != null) {
StoredServerChannel temp = storedServerChannel;
storedServerChannel = null;
StoredPaymentChannelServerStates channels =
(StoredPaymentChannelServerStates)
wallet.getExtensions().get(StoredPaymentChannelServerStates.EXTENSION_ID);
channels.closeChannel(
temp); // May call this method again for us (if it wasn't the original caller)
if (state.compareTo(State.CLOSING) >= 0) return closedFuture;
}
if (state.ordinal() < State.READY.ordinal()) {
log.error("Attempt to settle channel in state " + state);
state = State.CLOSED;
closedFuture.set(null);
return closedFuture;
}
if (state != State.READY) {
// TODO: What is this codepath for?
log.warn("Failed attempt to settle a channel in state " + state);
return closedFuture;
}
Transaction tx = null;
try {
Wallet.SendRequest req = makeUnsignedChannelContract(bestValueToMe);
tx = req.tx;
// Provide a throwaway signature so that completeTx won't complain out about unsigned inputs
// it doesn't
// know how to sign. Note that this signature does actually have to be valid, so we can't use
// a dummy
// signature to save time, because otherwise completeTx will try to re-sign it to make it
// valid and then
// die. We could probably add features to the SendRequest API to make this a bit more
// efficient.
signMultisigInput(tx, Transaction.SigHash.NONE, true);
// Let wallet handle adding additional inputs/fee as necessary.
req.shuffleOutputs = false;
req.missingSigsMode = Wallet.MissingSigsMode.USE_DUMMY_SIG;
wallet.completeTx(req); // TODO: Fix things so shuffling is usable.
feePaidForPayment = req.tx.getFee();
log.info("Calculated fee is {}", feePaidForPayment);
if (feePaidForPayment.compareTo(bestValueToMe) > 0) {
final String msg =
String.format(
Locale.US,
"Had to pay more in fees (%s) than the channel was worth (%s)",
feePaidForPayment,
bestValueToMe);
throw new InsufficientMoneyException(feePaidForPayment.subtract(bestValueToMe), msg);
}
// Now really sign the multisig input.
signMultisigInput(tx, Transaction.SigHash.ALL, false);
// Some checks that shouldn't be necessary but it can't hurt to check.
tx.verify(); // Sanity check syntax.
for (TransactionInput input : tx.getInputs())
input.verify(); // Run scripts and ensure it is valid.
} catch (InsufficientMoneyException e) {
throw e; // Don't fall through.
} catch (Exception e) {
log.error(
"Could not verify self-built tx\nMULTISIG {}\nCLOSE {}",
multisigContract,
tx != null ? tx : "");
throw new RuntimeException(e); // Should never happen.
}
state = State.CLOSING;
log.info("Closing channel, broadcasting tx {}", tx);
// The act of broadcasting the transaction will add it to the wallet.
ListenableFuture<Transaction> future = broadcaster.broadcastTransaction(tx).future();
Futures.addCallback(
future,
new FutureCallback<Transaction>() {
@Override
public void onSuccess(Transaction transaction) {
log.info("TX {} propagated, channel successfully closed.", transaction.getHash());
state = State.CLOSED;
closedFuture.set(transaction);
}
@Override
public void onFailure(Throwable throwable) {
log.error("Failed to settle channel, could not broadcast", throwable);
state = State.ERROR;
closedFuture.setException(throwable);
}
});
return closedFuture;
}
/**
* Called when the client provides us with a new signature and wishes to increment total payment
* by size. Verifies the provided signature and only updates values if everything checks out. If
* the new refundSize is not the lowest we have seen, it is simply ignored.
*
* @param refundSize How many satoshis of the original contract are refunded to the client (the
* rest are ours)
* @param signatureBytes The new signature spending the multi-sig contract to a new payment
* transaction
* @throws VerificationException If the signature does not verify or size is out of range (incl
* being rejected by the network as dust).
* @return true if there is more value left on the channel, false if it is now fully used up.
*/
public synchronized boolean incrementPayment(Coin refundSize, byte[] signatureBytes)
throws VerificationException, ValueOutOfRangeException, InsufficientMoneyException {
checkState(state == State.READY);
checkNotNull(refundSize);
checkNotNull(signatureBytes);
TransactionSignature signature = TransactionSignature.decodeFromBitcoin(signatureBytes, true);
// We allow snapping to zero for the payment amount because it's treated specially later, but
// not less than
// the dust level because that would prevent the transaction from being relayed/mined.
final boolean fullyUsedUp = refundSize.equals(Coin.ZERO);
if (refundSize.compareTo(clientOutput.getMinNonDustValue()) < 0 && !fullyUsedUp)
throw new ValueOutOfRangeException(
"Attempt to refund negative value or value too small to be accepted by the network");
Coin newValueToMe = totalValue.subtract(refundSize);
if (newValueToMe.signum() < 0)
throw new ValueOutOfRangeException("Attempt to refund more than the contract allows.");
if (newValueToMe.compareTo(bestValueToMe) < 0)
throw new ValueOutOfRangeException("Attempt to roll back payment on the channel.");
// Get the wallet's copy of the multisigContract (ie with confidence information), if this is
// null, the wallet
// was not connected to the peergroup when the contract was broadcast (which may cause issues
// down the road, and
// disables our double-spend check next)
Transaction walletContract = wallet.getTransaction(multisigContract.getHash());
checkNotNull(
walletContract,
"Wallet did not contain multisig contract {} after state was marked READY",
multisigContract.getHash());
// Note that we check for DEAD state here, but this test is essentially useless in production
// because we will
// miss most double-spends due to bloom filtering right now anyway. This will eventually fixed
// by network-wide
// double-spend notifications, so we just wait instead of attempting to add all dependant
// outpoints to our bloom
// filters (and probably missing lots of edge-cases).
if (walletContract.getConfidence().getConfidenceType()
== TransactionConfidence.ConfidenceType.DEAD) {
close();
throw new VerificationException("Multisig contract was double-spent");
}
Transaction.SigHash mode;
// If the client doesn't want anything back, they shouldn't sign any outputs at all.
if (fullyUsedUp) mode = Transaction.SigHash.NONE;
else mode = Transaction.SigHash.SINGLE;
if (signature.sigHashMode() != mode || !signature.anyoneCanPay())
throw new VerificationException(
"New payment signature was not signed with the right SIGHASH flags.");
Wallet.SendRequest req = makeUnsignedChannelContract(newValueToMe);
// Now check the signature is correct.
// Note that the client must sign with SIGHASH_{SINGLE/NONE} | SIGHASH_ANYONECANPAY to allow us
// to add additional
// inputs (in case we need to add significant fee, or something...) and any outputs we want to
// pay to.
Sha256Hash sighash = req.tx.hashForSignature(0, multisigScript, mode, true);
if (!clientKey.verify(sighash, signature))
throw new VerificationException("Signature does not verify on tx\n" + req.tx);
bestValueToMe = newValueToMe;
bestValueSignature = signatureBytes;
updateChannelInWallet();
return !fullyUsedUp;
}