Merge pull request #484 from isocolsky/fix/utxo-selection

Add threshold for change creation when selecting UTXOs

lib/common/defaults.js

@@ -63,4 +63,7 @@ Defaults.UTXO_SELECTION_MAX_FEE_VS_TX_AMOUNT_FACTOR = 0.05;
 // when fees are significant (proportional to how much we would pay for using that big input only).
 Defaults.UTXO_SELECTION_MAX_FEE_VS_SINGLE_UTXO_FEE_FACTOR = 5;
 
+// Do not generate change for less than the specified amount
+Defaults.UTXO_SELECTION_MIN_CHANGE_AMOUNT = 5000;
+
 module.exports = Defaults;

lib/server.js

@@ -1480,8 +1480,9 @@ WalletService.prototype._selectTxInputs = function(txp, utxosToExclude, cb) {
         var changeAmount = Math.round(total - txpAmount - fee);
         log.debug('Tx change: ', Utils.formatAmountInBtc(changeAmount));
 
-        if (changeAmount > 0 && changeAmount <= Bitcore.Transaction.DUST_AMOUNT) {
-          log.debug('Change below dust amount (' + Utils.formatAmountInBtc(Bitcore.Transaction.DUST_AMOUNT) + ')');
+        var smallChangeThreshold = Math.max(Defaults.UTXO_SELECTION_MIN_CHANGE_AMOUNT, Bitcore.Transaction.DUST_AMOUNT);
+        if (changeAmount > 0 && changeAmount <= smallChangeThreshold) {
+          log.debug('Change below threshold (' + Utils.formatAmountInBtc(smallChangeThreshold) + '). Incrementing fee to remove change.');
           // Remove dust change by incrementing fee
           fee += changeAmount;
         }

test/integration/server.js

@@ -2326,18 +2326,18 @@ describe('Wallet service', function() {
 
       it('should be possible to use a smaller fee', function(done) {
         helpers.stubUtxos(server, wallet, 1, function() {
-          var txOpts = helpers.createSimpleProposalOpts('18PzpUFkFZE8zKWUPvfykkTxmB9oMR8qP7', 0.99995, TestData.copayers[0].privKey_1H_0, {
+          var txOpts = helpers.createSimpleProposalOpts('18PzpUFkFZE8zKWUPvfykkTxmB9oMR8qP7', 0.9999, TestData.copayers[0].privKey_1H_0, {
             feePerKb: 80000
           });
           server.createTxLegacy(txOpts, function(err, tx) {
             should.exist(err);
             err.code.should.equal('INSUFFICIENT_FUNDS_FOR_FEE');
-            var txOpts = helpers.createSimpleProposalOpts('18PzpUFkFZE8zKWUPvfykkTxmB9oMR8qP7', 0.99995, TestData.copayers[0].privKey_1H_0, {
+            var txOpts = helpers.createSimpleProposalOpts('18PzpUFkFZE8zKWUPvfykkTxmB9oMR8qP7', 0.9999, TestData.copayers[0].privKey_1H_0, {
               feePerKb: 5000
             });
             server.createTxLegacy(txOpts, function(err, tx) {
               should.not.exist(err);
-              var estimatedFee = 5000 * 400 / 1000; // fully signed tx should have about 400 bytes
+              var estimatedFee = 5000 * 410 / 1000; // fully signed tx should have about 410 bytes
               tx.fee.should.be.within(0.9 * estimatedFee, 1.1 * estimatedFee);
 
               // Sign it to make sure Bitcore doesn't complain about the fees
@@ -3597,17 +3597,18 @@ describe('Wallet service', function() {
           });
         });
       });
-      it('should correct fee if resulting change would be below dust', function(done) {
+      it('should correct fee if resulting change would be below threshold', function(done) {
         helpers.stubUtxos(server, wallet, ['200bit', '500sat'], function() {
           var txOpts = {
             outputs: [{
               toAddress: '18PzpUFkFZE8zKWUPvfykkTxmB9oMR8qP7',
-              amount: 200e2,
+              amount: 150e2,
             }],
-            feePerKb: 400,
+            feePerKb: 100e2,
           };
           server.createTx(txOpts, function(err, txp) {
             should.not.exist(err);
+            txp.inputs.length.should.equal(1);
             (_.sum(txp.inputs, 'satoshis') - txp.outputs[0].amount - txp.fee).should.equal(0);
             var changeOutput = txp.getBitcoreTx().getChangeOutput();
             should.not.exist(changeOutput);