wallet rbf: add new in/out if necessary

lib/primitives/mtx.js

@@ -1227,11 +1227,25 @@ class MTX extends TX {
  async fund(coins, options) {
  assert(options, 'Options are required.');
  assert(options.changeAddress, 'Change address is required.');
- assert(this.inputs.length === 0, 'TX is already funded.');
+ if (!options.bumpFee)
+ assert(this.inputs.length === 0, 'TX is already funded.');
 
  // Select necessary coins.
  const select = await this.selectCoins(coins, options);
 
+ // Bump Fee mode:
+ // We want the coin selector to ignore the values of
+ // all existing inputs and outputs, but still consider their size.
+ // Inside the coin selector this is done by making a copy of the TX
+ // and then setting the total output value to 0
+ // (input value is already ignored).
+ // The coin selector will add coins to cover the fee on the entire TX
+ // including paying for any inputs it adds.
+ // Now that coin selection is done, we add back in the fee paid by
+ // the original existing inputs and outputs so we can create change.
+ if (options.bumpFee)
+ select.fee += this.getFee();
+
  // Add coins to transaction.
  for (const coin of select.chosen)
  this.addCoin(coin);

lib/wallet/coinselector.js

@@ -71,6 +71,7 @@ class CoinSelector {
  this.changeAddress = null;
  this.inputs = new BufferMap();
  this.useSelectEstimate = false;
+ this.bumpFee = false;
 
  // Needed for size estimation.
  this.getAccount = null;
@@ -158,6 +159,11 @@ class CoinSelector {
  this.useSelectEstimate = options.useSelectEstimate;
  }
 
+ if (options.bumpFee != null) {
+ assert(typeof options.bumpFee === 'boolean');
+ this.bumpFee = options.bumpFee;
+ }
+
  if (options.changeAddress) {
  const addr = options.changeAddress;
  if (typeof addr === 'string') {
@@ -209,7 +215,7 @@ class CoinSelector {
 
  async init(coins) {
  this.coins = coins.slice();
- this.outputValue = this.tx.getOutputValue();
+ this.outputValue = this.bumpFee ? 0 : this.tx.getOutputValue();
  this.chosen = [];
  this.change = 0;
  this.fee = CoinSelector.MIN_FEE;

lib/wallet/wallet.js

@@ -1143,7 +1143,8 @@ class Wallet extends EventEmitter {
  rate: rate,
  maxFee: options.maxFee,
  useSelectEstimate: options.useSelectEstimate,
- getAccount: this.getAccountByAddress.bind(this)
+ getAccount: this.getAccountByAddress.bind(this),
+ bumpFee: options.bumpFee
  });
 
  assert(mtx.getFee() <= CoinSelector.MAX_FEE, 'TX exceeds MAX_FEE.');
@@ -1376,27 +1377,35 @@ class Wallet extends EventEmitter {
  }
  }
 
- if (!change)
- throw new Error('Transaction has no change output.');
-
- // Start by reducing absolute fee to 0
- change.value += oldFee;
- if (mtx.getFee() !== 0)
- throw new Error('Arithmetic error for change.');
-
- // Pay for replacement fees: BIP 125 rule #3
- change.value -= oldFee;
-
- // Pay for our own current fee: BIP 125 rule #4
- change.value -= currentFee;
-
- if (change.value < 0)
- throw new Error('Change output insufficient for fee.');
-
- // If change output is below dust, give it all to fee
- if (change.isDust()) {
- mtx.outputs.splice(mtx.changeIndex, 1);
- mtx.changeIndex = -1;
+ if (change) {
+ // Start by reducing absolute fee to 0
+ change.value += oldFee;
+ if (mtx.getFee() !== 0)
+ throw new Error('Arithmetic error for change.');
+
+ // Pay for replacement fees: BIP 125 rule #3
+ change.value -= oldFee;
+
+ // Pay for our own current fee: BIP 125 rule #4
+ change.value -= currentFee;
+
+ // We need to add more inputs.
+ // This will obviously also fail the dust test next
+ // and conveniently remove the change output for us.
+ if (change.value < 0)
+ throw new Error('Change value insufficient to bump fee.');
+
+ // If change output is below dust,
+ // give it all to fee (remove change output)
+ if (change.isDust()) {
+ mtx.outputs.splice(mtx.changeIndex, 1);
+ mtx.changeIndex = -1;
+ }
+ } else {
+ // We need to add another input + change to increase the fee
+ // Since the original inputs and outputs already paid for
+ // their own fee (rule #3) all we have to do is pay for this new TX fee.
+ await this.fund(mtx, {rate, bumpFee: true});
  }
 
  if (!sign)
@@ -1420,7 +1429,7 @@ class Wallet extends EventEmitter {
  await this.wdb.send(ntx);
  }
 
- return ntx;
+ return mtx;
  }
 
  /**

test/wallet-rbf-test.js

@@ -186,4 +186,35 @@ describe('Wallet RBF', function () {
  });
  await node.rpc.generateToAddress([1, aliceReceive]);
  });
+
+ it('should bump a tx with no change by adding new in/out pair', async () => {
+ const coins = await alice.getCoins();
+ let coin;
+ for (coin of coins) {
+ if (!coin.coinbase)
+ break;
+ }
+ const mtx = new MTX();
+ mtx.addCoin(coin);
+ mtx.addOutput(bobReceive, coin.value - 200);
+ mtx.inputs[0].sequence = 0xfffffffd;
+ await alice.sign(mtx);
+ const tx = mtx.toTX();
+ assert.strictEqual(tx.inputs.length, 1);
+ assert.strictEqual(tx.outputs.length, 1);
+ await alice.wdb.addTX(tx);
+ await alice.wdb.send(tx);
+ await forEvent(node.mempool, 'tx');
+
+ const rtx = await alice.bumpTXFee(tx.hash(), 2000 /* satoshis per kvB */, true, null);
+ assert.strictEqual(rtx.inputs.length, 2);
+ assert.strictEqual(rtx.outputs.length, 2);
+ assert(rtx.getRate() > 1999 && rtx.getRate() < 3000);
+
+ await forEvent(node.mempool, 'tx');
+ assert(!node.mempool.hasEntry(tx.hash()));
+ assert(node.mempool.hasEntry(rtx.hash()));
+
+ await node.rpc.generateToAddress([1, aliceReceive]);
+ });
 });