// 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;
  }