FIX: TX with extra small change output throws dust error

HDWallet.test.js

@@ -1,6 +1,7 @@
 /* global it, jasmine */
 import { SegwitP2SHWallet, SegwitBech32Wallet, HDSegwitP2SHWallet, HDLegacyBreadwalletWallet, HDLegacyP2PKHWallet } from './class';
 let assert = require('assert');
+let bitcoin = require('bitcoinjs-lib');
 
 it('can convert witness to address', () => {
   let address = SegwitP2SHWallet.witnessToAddress('035c618df829af694cb99e664ce1b34f80ad2c3b49bcd0d9c0b1836c66b2d25fd8');
@@ -88,7 +89,6 @@ it('HD (BIP49) can create TX', async () => {
     '010000000001029d98d81fe2b596fd79e845fa9f38d7e0b6fb73303c40fac604d04df1fa137aee00000000171600142f18e8406c9d210f30c901b24e5feeae78784eb7ffffffff67fb86f310df24e508d40fce9511c7fde4dd4ee91305fd08a074279a70e2cd22000000001716001468dde644410cc789d91a7f36b823f38369755a1cffffffff02780500000000000017a914a3a65daca3064280ae072b9d6773c027b30abace87dc0500000000000017a914850f4dbc255654de2c12c6f6d79cf9cb756cad038702483045022100dc8390a9fd34c31259fa47f9fc182f20d991110ecfd5b58af1cf542fe8de257a022004c2d110da7b8c4127675beccc63b46fd65c706951f090fd381fa3b21d3c5c08012102edd141c5a27a726dda66be10a38b0fd3ccbb40e7c380034aaa43a1656d5f4dd60247304402207c0aef8313d55e72474247daad955979f62e56d1cbac5f2d14b8b022c6ce112602205d9aa3804f04624b12ab8a5ab0214b529c531c2f71c27c6f18aba6502a6ea0a80121030db3c49461a5e539e97bab62ab2b8f88151d1c2376493cf73ef1d02ef60637fd00000000',
   );
 
-  let bitcoin = require('bitcoinjs-lib');
   txhex = hd.createTx(hd.utxo, 0.000005, 0.000001, '3GcKN7q7gZuZ8eHygAhHrvPa5zZbG5Q1rK');
   var tx = bitcoin.Transaction.fromHex(txhex);
   assert.equal(tx.ins.length, 1);
@@ -118,6 +118,15 @@ it('HD (BIP49) can create TX', async () => {
   chunksIn = bitcoin.script.decompile(tx.outs[0].script);
   toAddress = bitcoin.address.fromOutputScript(chunksIn);
   assert.equal('3GcKN7q7gZuZ8eHygAhHrvPa5zZbG5Q1rK', toAddress);
+
+  // checking that change amount is at least 3x of fee, otherwise screw the change, just add it to fee.
+  // theres 0.00003 on UTXOs, lets transfer (0.00003 - 100sat), soo fee is equal to change (100 sat)
+  // which throws @dust error if broadcasted
+  txhex = hd.createTx(hd.utxo, 0.000028, 0.000001, '3GcKN7q7gZuZ8eHygAhHrvPa5zZbG5Q1rK');
+  tx = bitcoin.Transaction.fromHex(txhex);
+  assert.equal(tx.ins.length, 2);
+  assert.equal(tx.outs.length, 1); // only 1 output, which means change is neglected
+  assert.equal(tx.outs[0].value, 2800);
 });
 
 it('Segwit HD (BIP49) can fetch UTXO', async function() {

models/signer.js

@@ -32,7 +32,7 @@ exports.createHDSegwitTransaction = function(utxos, toAddress, amount, fixedFee,
     ourOutputs[outputNum].amount = unspent.amount;
     unspentAmountSatoshi += unspent.amount;
     if (unspentAmountSatoshi >= amountToOutputSatoshi + feeInSatoshis) {
-      // found enough inputs su satisfy payee and pay fees
+      // found enough inputs to satisfy payee and pay fees
       break;
     }
     outputNum++;
@@ -47,7 +47,11 @@ exports.createHDSegwitTransaction = function(utxos, toAddress, amount, fixedFee,
   txb.addOutput(toAddress, amountToOutputSatoshi);
   if (amountToOutputSatoshi + feeInSatoshis < unspentAmountSatoshi) {
     // sending less than we have, so the rest should go back
-    txb.addOutput(changeAddress, unspentAmountSatoshi - amountToOutputSatoshi - feeInSatoshis);
+    if (unspentAmountSatoshi - amountToOutputSatoshi - feeInSatoshis > 3 * feeInSatoshis) {
+      // to prevent @dust error change transferred amount should be at least 3xfee.
+      // if not - we just dont send change and it wil add to fee
+      txb.addOutput(changeAddress, unspentAmountSatoshi - amountToOutputSatoshi - feeInSatoshis);
+    }
   }
 
   // now, signing every input with a corresponding key
@@ -86,7 +90,12 @@ exports.createSegwitTransaction = function(utxos, toAddress, amount, fixedFee, W
   txb.addOutput(toAddress, amountToOutput);
   if (amountToOutput + feeInSatoshis < unspentAmount) {
     // sending less than we have, so the rest should go back
-    txb.addOutput(changeAddress, unspentAmount - amountToOutput - feeInSatoshis);
+
+    if (unspentAmount - amountToOutput - feeInSatoshis > 3 * feeInSatoshis) {
+      // to prevent @dust error change transferred amount should be at least 3xfee.
+      // if not - we just dont send change and it wil add to fee
+      txb.addOutput(changeAddress, unspentAmount - amountToOutput - feeInSatoshis);
+    }
   }
 
   for (let c = 0; c < utxos.length; c++) {

tests/unit/signer.js

@@ -67,6 +67,21 @@ describe('unit - signer', function () {
       assert.equal(tx, '0100000000010160d3d8d96a31d6bae5e2927bb4fe7be81702bb1787b3f9770a8084040359051601000000171600141e16a923b1a9e8d0c2a044030608a6aa13f97e9affffffff0230e60200000000001976a914f7c6c1f9f6142107ed293c8fbf85fbc49eb5f1b988ac400d03000000000017a914e0d81f03546ab8f29392b488ec62ab355ee7c573870247304402202c962e14ae6abd45dc9613d2f088ad487e805670548e244deb25d762b310a60002204f12c7f9b8da3567b39906ff6c46b27ce087e7ae91bbe34fb1cdee1b994b9d3001210314389c888e9669ae05739819fc7c43d7a50fdeabd2a8951f9607c8cad394fd4b00000000')
       done()
     })
+
+
+
+    it('should return valid tx hex for segwit transactions if change is too small so it causes @dust error', function (done) {
+      // checking that change amount is at least 3x of fee, otherwise screw the change, just add it to fee
+      let signer = require('../../models/signer')
+      let utxos = [ { 'txid': '160559030484800a77f9b38717bb0217e87bfeb47b92e2e5bad6316ad9d8d360', 'vout': 1, 'address': '3NBtBset4qPD8DZeLw4QbFi6SNjNL8hg7x', 'account': '3NBtBset4qPD8DZeLw4QbFi6SNjNL8hg7x', 'scriptPubKey': 'a914e0d81f03546ab8f29392b488ec62ab355ee7c57387', 'amount': 0.00400000, 'confirmations': 271, 'spendable': false, 'solvable': false, 'safe': true } ]
+      let txhex = signer.createSegwitTransaction(utxos, '1Pb81K1xJnMjUfFgKUbva6gr1HCHXxHVnr', 0.003998, 0.000001, 'L4iRvejJG9gRhKVc3rZm5haoyd4EuCi77G91DnXRrvNDqiXktkXh')
+      let bitcoin = require('bitcoinjs-lib')
+      let tx = bitcoin.Transaction.fromHex(txhex);
+      assert.equal(tx.ins.length, 1);
+      assert.equal(tx.outs.length, 1); // only 1 output, which means change is neglected
+      assert.equal(tx.outs[0].value, 399700);
+      done()
+    })
   })
 
   describe('WIF2address()', function () {