feat(abstract-utxo): add descriptorWallet explainPsbt

Not integrated yet

TICKET: BTC-1450

Author: OttoAllmendinger

modules/abstract-utxo/src/abstractUtxoCoin.ts

@@ -146,6 +146,7 @@ export function isWalletOutput(output: Output): output is FixedScriptWalletOutpu
 
 export interface TransactionExplanation extends BaseTransactionExplanation<string, string> {
   locktime: number;
+  /** NOTE: this actually only captures external outputs */
   outputs: Output[];
   changeOutputs: Output[];
 

modules/abstract-utxo/src/transaction/descriptor/explainPsbt.ts

@@ -0,0 +1,56 @@
+import * as utxolib from '@bitgo/utxo-lib';
+import { ITransactionRecipient } from '@bitgo/sdk-core';
+
+import * as coreDescriptors from '../../core/descriptor';
+import { ParsedOutput } from '../../core/descriptor/psbt/parse';
+import { toExtendedAddressFormat } from '../recipient';
+import { TransactionExplanation } from '../../abstractUtxoCoin';
+
+function toRecipient(output: ParsedOutput, network: utxolib.Network): ITransactionRecipient {
+  return {
+    address: toExtendedAddressFormat(output.script, network),
+    amount: output.value.toString(),
+  };
+}
+
+function sumValues(arr: { value: bigint }[]): bigint {
+  return arr.reduce((sum, e) => sum + e.value, BigInt(0));
+}
+
+function getInputSignaturesForInputIndex(psbt: utxolib.bitgo.UtxoPsbt, inputIndex: number): number {
+  const { partialSig } = psbt.data.inputs[inputIndex];
+  if (!partialSig) {
+    return 0;
+  }
+  return partialSig.reduce((agg, p) => {
+    const valid = psbt.validateSignaturesOfInputCommon(inputIndex, p.pubkey);
+    return agg + (valid ? 1 : 0);
+  }, 0);
+}
+
+function getInputSignatures(psbt: utxolib.bitgo.UtxoPsbt): number[] {
+  return psbt.data.inputs.map((_, i) => getInputSignaturesForInputIndex(psbt, i));
+}
+
+export function explainPsbt(
+  psbt: utxolib.bitgo.UtxoPsbt,
+  descriptors: coreDescriptors.DescriptorMap
+): TransactionExplanation {
+  const parsedTransaction = coreDescriptors.parse(psbt, descriptors, psbt.network);
+  const { inputs, outputs } = parsedTransaction;
+  const externalOutputs = outputs.filter((o) => o.scriptId === undefined);
+  const changeOutputs = outputs.filter((o) => o.scriptId !== undefined);
+  const fee = sumValues(inputs) - sumValues(outputs);
+  const inputSignatures = getInputSignatures(psbt);
+  return {
+    inputSignatures,
+    signatures: inputSignatures.reduce((a, b) => Math.min(a, b), Infinity),
+    locktime: psbt.locktime,
+    id: psbt.getUnsignedTx().getId(),
+    outputs: externalOutputs.map((o) => toRecipient(o, psbt.network)),
+    outputAmount: sumValues(externalOutputs).toString(),
+    changeOutputs: changeOutputs.map((o) => toRecipient(o, psbt.network)),
+    changeAmount: sumValues(changeOutputs).toString(),
+    fee: fee.toString(),
+  };
+}

modules/abstract-utxo/src/transaction/descriptor/index.ts

@@ -0,0 +1,2 @@
+export { DescriptorMap } from '../../core/descriptor';
+export { explainPsbt } from './explainPsbt';

modules/abstract-utxo/test/transaction/descriptor/explainPsbt.ts

@@ -0,0 +1,30 @@
+import assert from 'assert';
+
+import { explainPsbt } from '../../../src/transaction/descriptor';
+import { mockPsbtDefaultWithDescriptorTemplate } from '../../core/descriptor/psbt/mock.utils';
+import { getDescriptorMap } from '../../core/descriptor/descriptor.utils';
+import { getFixture } from '../../core/fixtures.utils';
+import { getKeyTriple } from '../../core/key.utils';
+import { TransactionExplanation } from '../../../src';
+
+async function assertEqualFixture(name: string, v: unknown) {
+  assert.deepStrictEqual(v, await getFixture(__dirname + '/fixtures/' + name, v));
+}
+
+function assertSignatureCount(expl: TransactionExplanation, signatures: number, inputSignatures: number[]) {
+  assert.deepStrictEqual(expl.signatures, signatures);
+  assert.deepStrictEqual(expl.inputSignatures, inputSignatures);
+}
+
+describe('explainPsbt', function () {
+  it('has expected values', async function () {
+    const psbt = mockPsbtDefaultWithDescriptorTemplate('Wsh2Of3');
+    const keys = getKeyTriple('a');
+    const descriptorMap = getDescriptorMap('Wsh2Of3', keys);
+    await assertEqualFixture('explainPsbt.a.json', explainPsbt(psbt, descriptorMap));
+    psbt.signAllInputsHD(keys[0]);
+    assertSignatureCount(explainPsbt(psbt, descriptorMap), 1, [1, 1]);
+    psbt.signAllInputsHD(keys[1]);
+    assertSignatureCount(explainPsbt(psbt, descriptorMap), 2, [2, 2]);
+  });
+});

modules/abstract-utxo/test/transaction/descriptor/fixtures/explainPsbt.a.json

@@ -0,0 +1,24 @@
+{
+  "inputSignatures": [
+    0,
+    0
+  ],
+  "signatures": 0,
+  "locktime": 0,
+  "id": "b9b272a1f0407ea461aca2da115b3399311f424949653c37d5c0023102add158",
+  "outputs": [
+    {
+      "address": "bc1qvn279lx29cg843u77p3c37npay7w4uc4xw5d92xxa92z8gd3lkuq4w8477",
+      "amount": "400000"
+    }
+  ],
+  "outputAmount": "400000",
+  "changeOutputs": [
+    {
+      "address": "bc1q2yau645jl7k577lmanqn9a0ulcgcqm0wrrmx09dppd3kcwguvyzqk86umj",
+      "amount": "400000"
+    }
+  ],
+  "changeAmount": "400000",
+  "fee": "1200000"
+}