fix(bitcoin): do not create a change output below the dust limit

packages/extension/src/providers/bitcoin/libs/utils.ts

@@ -1,7 +1,7 @@
 import { BitcoinNetworkInfo, HaskoinUnspentType } from '../types';
 import { address as BTCAddress } from 'bitcoinjs-lib';
 import { GasPriceTypes } from '@/providers/common/types';
-import { fromBase } from '@enkryptcom/utils';
+import { fromBase, toBase } from '@enkryptcom/utils';
 import BigNumber from 'bignumber.js';
 import { BitcoinNetwork } from '../types/bitcoin-network';
 import { BTCTxInfo } from '../ui/types';
@@ -15,6 +15,16 @@ const isAddress = (address: string, network: BitcoinNetworkInfo): boolean => {
   }
 };
 
+/**
+ * The network's dust limit in base units.
+ *
+ * Nodes will not relay a transaction that carries an output below this, so a
+ * change output worth less than the limit cannot be added to a transaction. It
+ * has to be left behind as fee instead.
+ */
+const getDustThreshold = (network: BitcoinNetwork): number =>
+  Number(toBase(network.dust.toString(), network.decimals));
+
 const getTxInfo = (
   utxos: HaskoinUnspentType[],
   ordinalUTXO?: HaskoinUnspentType,
@@ -101,4 +111,4 @@ const getGasCostValues = async (
   };
   return gasCostValues;
 };
-export { isAddress, getGasCostValues, getTxInfo };
+export { isAddress, getGasCostValues, getTxInfo, getDustThreshold };

packages/extension/src/providers/bitcoin/tests/bitcoin.dust.test.ts

@@ -0,0 +1,28 @@
+// @vitest-environment node
+//
+// The bitcoin provider tests run in the node environment: bitcoinjs-lib checks
+// Buffer values against Uint8Array, and under jsdom the two come from different
+// realms.
+import { describe, it, expect } from 'vitest';
+import bitcoinNetworks from '../networks';
+import { getDustThreshold } from '../libs/utils';
+
+describe('Should report the dust limit in base units', () => {
+  it('should convert each network limit from whole coins', () => {
+    // 0.00000546 BTC
+    expect(getDustThreshold(bitcoinNetworks.bitcoin)).to.be.eq(546);
+    expect(getDustThreshold(bitcoinNetworks.bitcoinTest)).to.be.eq(546);
+    // 0.0001 LTC, an order of magnitude above the bitcoin limit
+    expect(getDustThreshold(bitcoinNetworks.litecoin)).to.be.eq(10000);
+    // 0.01 DOGE
+    expect(getDustThreshold(bitcoinNetworks.dogecoin)).to.be.eq(1000000);
+  });
+
+  it('should classify a change remainder against the limit', () => {
+    const litecoin = getDustThreshold(bitcoinNetworks.litecoin);
+    // the amount of change a small litecoin send is left with
+    expect(750 >= litecoin).to.be.eq(false);
+    expect(litecoin - 1 >= litecoin).to.be.eq(false);
+    expect(litecoin >= litecoin).to.be.eq(true);
+  });
+});

packages/extension/src/providers/bitcoin/ui/send-transaction/index.vue

@@ -186,7 +186,11 @@ import Browser from 'webextension-polyfill';
 import { ProviderName } from '@/types/provider';
 import PublicKeyRing from '@/libs/keyring/public-keyring';
 
-import { getGasCostValues, isAddress } from '../../libs/utils';
+import {
+  getDustThreshold,
+  getGasCostValues,
+  isAddress,
+} from '../../libs/utils';
 import BitcoinAPI from '@/providers/bitcoin/libs/api';
 import { calculateSizeBasedOnType } from '../libs/tx-size';
 import { HaskoinUnspentType } from '../../types';
@@ -517,7 +521,9 @@ const sendAction = async () => {
     });
   }
   const remainder = UTXOBalance.value.sub(toAmount).sub(currentFee);
-  if (remainder.gtn(0)) {
+  // Change worth less than the dust limit cannot be paid out: the node would
+  // reject the whole transaction as non standard. Leave it as fee instead.
+  if (remainder.gten(getDustThreshold(props.network as BitcoinNetwork))) {
     txInfo.outputs.push({
       address: props.network.displayAddress(addressFrom.value),
       value: remainder.toNumber(),

packages/extension/src/ui/action/views/swap/libs/swap-txs.ts

@@ -18,7 +18,10 @@ import { ApiPromise } from '@polkadot/api';
 import { TransactionType } from '../types';
 import { BitcoinNetwork } from '@/providers/bitcoin/types/bitcoin-network';
 import BitcoinAPI from '@/providers/bitcoin/libs/api';
-import { getTxInfo as getBTCTxInfo } from '@/providers/bitcoin/libs/utils';
+import {
+  getTxInfo as getBTCTxInfo,
+  getDustThreshold,
+} from '@/providers/bitcoin/libs/utils';
 import { toBN } from 'web3-utils';
 import { BTCTxInfo } from '@/providers/bitcoin/ui/types';
 
@@ -58,7 +61,9 @@ export const getBitcoinNativeTransaction = async (
     address: tx.to,
     value: toAmount.toNumber(),
   });
-  if (remainder > 0) {
+  // Change worth less than the dust limit cannot be paid out: the node would
+  // reject the whole transaction as non standard. Leave it as fee instead.
+  if (remainder >= getDustThreshold(network)) {
     txInfo.outputs.push({
       address: network.displayAddress(tx.from),
       value: remainder,