feat(abstract-utxo): support custom change wallets in explainPsbt(Wasm)

modules/abstract-utxo/src/keychains.ts

@@ -1,6 +1,7 @@
 import assert from 'assert';
 
 import * as t from 'io-ts';
+import { bitgo } from '@bitgo/utxo-lib';
 import { BIP32Interface, bip32 } from '@bitgo/secp256k1';
 import { IRequestTracer, IWallet, KeyIndices, promiseProps, Triple } from '@bitgo/sdk-core';
 
@@ -47,9 +48,15 @@ export function toKeychainTriple(keychains: UtxoNamedKeychains): Triple<UtxoKeyc
 }
 
 export function toBip32Triple(
-  keychains: UtxoNamedKeychains | Triple<{ pub: string }> | Triple<string>
+  keychains: bitgo.RootWalletKeys | UtxoNamedKeychains | Triple<{ pub: string }> | string[]
 ): Triple<BIP32Interface> {
+  if (keychains instanceof bitgo.RootWalletKeys) {
+    return keychains.triple;
+  }
   if (Array.isArray(keychains)) {
+    if (keychains.length !== 3) {
+      throw new Error('expected 3 keychains');
+    }
     return keychains.map((keychain: { pub: string } | string) => {
       const v = typeof keychain === 'string' ? keychain : keychain.pub;
       return bip32.fromBase58(v);
@@ -59,6 +66,34 @@ export function toBip32Triple(
   return toBip32Triple(toKeychainTriple(keychains));
 }
 
+function toXpub(keychain: { pub: string } | string | BIP32Interface): string {
+  if (typeof keychain === 'string') {
+    if (keychain.startsWith('xpub')) {
+      return keychain;
+    }
+    throw new Error('expected xpub');
+  }
+  if ('neutered' in keychain) {
+    return keychain.neutered().toBase58();
+  }
+  if ('pub' in keychain) {
+    return toXpub(keychain.pub);
+  }
+  throw new Error('expected keychain');
+}
+
+export function toXpubTriple(
+  keychains: UtxoNamedKeychains | Triple<{ pub: string }> | Triple<string> | Triple<BIP32Interface>
+): Triple<string> {
+  if (Array.isArray(keychains)) {
+    if (keychains.length !== 3) {
+      throw new Error('expected 3 keychains');
+    }
+    return keychains.map((k) => toXpub(k)) as Triple<string>;
+  }
+  return toXpubTriple(toKeychainTriple(keychains));
+}
+
 export async function fetchKeychains(
   coin: AbstractUtxoCoin,
   wallet: IWallet,

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

@@ -3,7 +3,7 @@ import { ITransactionRecipient } from '@bitgo/sdk-core';
 import * as coreDescriptors from '@bitgo/utxo-core/descriptor';
 
 import { toExtendedAddressFormat } from '../recipient';
-import type { TransactionExplanationUtxolibPsbt } from '../fixedScript/explainTransaction';
+import type { TransactionExplanationDescriptor } from '../fixedScript/explainTransaction';
 
 function toRecipient(output: coreDescriptors.ParsedOutput, network: utxolib.Network): ITransactionRecipient {
   return {
@@ -34,7 +34,7 @@ function getInputSignatures(psbt: utxolib.bitgo.UtxoPsbt): number[] {
 export function explainPsbt(
   psbt: utxolib.bitgo.UtxoPsbt,
   descriptors: coreDescriptors.DescriptorMap
-): TransactionExplanationUtxolibPsbt {
+): TransactionExplanationDescriptor {
   const parsedTransaction = coreDescriptors.parse(psbt, descriptors, psbt.network);
   const { inputs, outputs } = parsedTransaction;
   const externalOutputs = outputs.filter((o) => o.scriptId === undefined);

modules/abstract-utxo/src/transaction/fixedScript/explainPsbtWasm.ts

@@ -9,6 +9,35 @@ function scriptToAddress(script: Uint8Array): string {
   return `scriptPubKey:${Buffer.from(script).toString('hex')}`;
 }
 
+type ParsedWalletOutput = fixedScriptWallet.ParsedOutput & { scriptId: fixedScriptWallet.ScriptId };
+type ParsedExternalOutput = fixedScriptWallet.ParsedOutput & { scriptId: null };
+
+function isParsedWalletOutput(output: ParsedWalletOutput | ParsedExternalOutput): output is ParsedWalletOutput {
+  return output.scriptId !== null;
+}
+
+function isParsedExternalOutput(output: ParsedWalletOutput | ParsedExternalOutput): output is ParsedExternalOutput {
+  return output.scriptId === null;
+}
+
+function toChangeOutput(output: ParsedWalletOutput): FixedScriptWalletOutput {
+  return {
+    address: output.address ?? scriptToAddress(output.script),
+    amount: output.value.toString(),
+    chain: output.scriptId.chain,
+    index: output.scriptId.index,
+    external: false,
+  };
+}
+
+function toExternalOutput(output: ParsedExternalOutput): Output {
+  return {
+    address: output.address ?? scriptToAddress(output.script),
+    amount: output.value.toString(),
+    external: true,
+  };
+}
+
 export function explainPsbtWasm(
   psbt: fixedScriptWallet.BitGoPsbt,
   walletXpubs: Triple<string>,
@@ -17,44 +46,45 @@ export function explainPsbtWasm(
       checkSignature?: boolean;
       outputScripts: Buffer[];
     };
+    customChangeWalletXpubs?: Triple<string>;
   }
 ): TransactionExplanationWasm {
   const parsed = psbt.parseTransactionWithWalletKeys(walletXpubs, params.replayProtection);
 
   const changeOutputs: FixedScriptWalletOutput[] = [];
   const outputs: Output[] = [];
+  const parsedCustomChangeOutputs = params.customChangeWalletXpubs
+    ? psbt.parseOutputsWithWalletKeys(params.customChangeWalletXpubs)
+    : undefined;
 
-  parsed.outputs.forEach((output) => {
-    const address = output.address ?? scriptToAddress(output.script);
+  const customChangeOutputs: FixedScriptWalletOutput[] = [];
 
-    if (output.scriptId) {
+  parsed.outputs.forEach((output, i) => {
+    const parseCustomChangeOutput = parsedCustomChangeOutputs?.[i];
+    if (isParsedWalletOutput(output)) {
       // This is a change output
-      changeOutputs.push({
-        address,
-        amount: output.value.toString(),
-        chain: output.scriptId.chain,
-        index: output.scriptId.index,
-        external: false,
-      });
+      changeOutputs.push(toChangeOutput(output));
+    } else if (parseCustomChangeOutput && isParsedWalletOutput(parseCustomChangeOutput)) {
+      customChangeOutputs.push(toChangeOutput(parseCustomChangeOutput));
+    } else if (isParsedExternalOutput(output)) {
+      outputs.push(toExternalOutput(output));
     } else {
-      // This is an external output
-      outputs.push({
-        address,
-        amount: output.value.toString(),
-        external: true,
-      });
+      throw new Error('Invalid output');
     }
   });
 
-  const changeAmount = changeOutputs.reduce((sum, output) => sum + BigInt(output.amount), BigInt(0));
   const outputAmount = outputs.reduce((sum, output) => sum + BigInt(output.amount), BigInt(0));
+  const changeAmount = changeOutputs.reduce((sum, output) => sum + BigInt(output.amount), BigInt(0));
+  const customChangeAmount = customChangeOutputs.reduce((sum, output) => sum + BigInt(output.amount), BigInt(0));
 
   return {
     id: psbt.unsignedTxid(),
     outputAmount: outputAmount.toString(),
     changeAmount: changeAmount.toString(),
+    customChangeAmount: customChangeAmount.toString(),
     outputs,
     changeOutputs,
+    customChangeOutputs,
     fee: parsed.minerFee.toString(),
   };
 }