Fix TransactionBuilder failing to debug P2PKH-only transactions (#318)

Co-authored-by: Rosco Kalis <roscokalis@gmail.com>

Author: mainnet-pat

packages/cashscript/src/TransactionBuilder.ts

@@ -18,6 +18,7 @@ import {
   isUnlockableUtxo,
   isStandardUnlockableUtxo,
   StandardUnlockableUtxo,
+  isP2PKHUnlocker,
 } from './interfaces.js';
 import { NetworkProvider } from './network/index.js';
 import {
@@ -157,6 +158,11 @@ export class TransactionBuilder {
   }
 
   debug(): DebugResults {
+    // do not debug a pure P2PKH-spend transaction
+    if (this.inputs.every((input) => isP2PKHUnlocker(input.unlocker))) {
+      return {};
+    }
+
     if (this.inputs.some((input) => !isStandardUnlockableUtxo(input))) {
       throw new Error('Cannot debug a transaction with custom unlocker');
     }

packages/cashscript/test/TransactionBuilder.test.ts

@@ -9,6 +9,8 @@ import {
   carolAddress,
   carolPriv,
   bobTokenAddress,
+  aliceAddress,
+  alicePriv,
 } from './fixture/vars.js';
 import { Network } from '../src/interfaces.js';
 import { utxoComparator, calculateDust, randomUtxo, randomToken, isNonTokenUtxo, isFungibleTokenUtxo } from '../src/utils.js';
@@ -293,4 +295,55 @@ describe('Transaction Builder', () => {
       expect(JSON.parse(stringify(wcTransactionObj))).toEqual(expectedResult);
     });
   });
+
+  it('should not fail when validly spending from only P2PKH inputs', async () => {
+    const aliceUtxos = (await provider.getUtxos(aliceAddress)).filter(isNonTokenUtxo);
+    const sigTemplate = new SignatureTemplate(alicePriv);
+
+    expect(aliceUtxos.length).toBeGreaterThan(2);
+
+    const change = aliceUtxos[0].satoshis + aliceUtxos[1].satoshis - 1000n;
+
+    const transaction = new TransactionBuilder({ provider })
+      .addInput(aliceUtxos[0], sigTemplate.unlockP2PKH())
+      .addInput(aliceUtxos[1], sigTemplate.unlockP2PKH())
+      .addOutput({ to: aliceAddress, amount: change });
+
+    await expect(transaction.send()).resolves.not.toThrow();
+  });
+
+  // TODO: Currently, P2PKH inputs are not evaluated at all
+  it.skip('should fail when invalidly spending from only P2PKH inputs', async () => {
+    const aliceUtxos = (await provider.getUtxos(aliceAddress)).filter(isNonTokenUtxo);
+    const incorrectSigTemplate = new SignatureTemplate(bobPriv);
+
+    expect(aliceUtxos.length).toBeGreaterThan(2);
+
+    const change = aliceUtxos[0].satoshis + aliceUtxos[1].satoshis - 1000n;
+
+    const transaction = new TransactionBuilder({ provider })
+      .addInput(aliceUtxos[0], incorrectSigTemplate.unlockP2PKH())
+      .addInput(aliceUtxos[1], incorrectSigTemplate.unlockP2PKH())
+      .addOutput({ to: aliceAddress, amount: change });
+
+    await expect(transaction.send()).rejects.toThrow();
+  });
+
+  // TODO: Currently, P2PKH inputs are not evaluated at all
+  it.skip('should fail when invalidly spending from P2PKH and correctly from contract inputs', async () => {
+    const aliceUtxos = (await provider.getUtxos(aliceAddress)).filter(isNonTokenUtxo);
+    const p2pkhUtxos = (await p2pkhInstance.getUtxos()).filter(isNonTokenUtxo).sort(utxoComparator).reverse();
+    const incorrectSigTemplate = new SignatureTemplate(bobPriv);
+
+    expect(aliceUtxos.length).toBeGreaterThan(2);
+
+    const change = aliceUtxos[0].satoshis + aliceUtxos[1].satoshis - 1000n;
+
+    const transaction = new TransactionBuilder({ provider })
+      .addInput(aliceUtxos[0], incorrectSigTemplate.unlockP2PKH())
+      .addInput(p2pkhUtxos[0], p2pkhInstance.unlock.spend(carolPub, new SignatureTemplate(carolPriv)))
+      .addOutput({ to: aliceAddress, amount: change });
+
+    await expect(transaction.send()).rejects.toThrow();
+  });
 });

packages/cashscript/test/debugging-old-artifacts.test.ts

@@ -0,0 +1,57 @@
+import { Contract, MockNetworkProvider, randomUtxo, SignatureTemplate, TransactionBuilder } from '../src/index.js';
+import { alicePkh, alicePriv, alicePub, bobPriv } from './fixture/vars.js';
+
+const artifact = {
+  contractName: 'P2PKH',
+  constructorInputs: [
+    { name: 'pkh', type: 'bytes20' },
+  ],
+  abi: [
+    {
+      name: 'spend',
+      inputs: [
+        { name: 'pk', type: 'pubkey' },
+        { name: 's', type: 'sig' },
+      ],
+    },
+  ],
+  bytecode: 'OP_OVER OP_HASH160 OP_EQUALVERIFY OP_CHECKSIG',
+  source: 'pragma cashscript ^0.7.0;\n\ncontract P2PKH(bytes20 pkh) {\n    // Require pk to match stored pkh and signature to match\n    function spend(pubkey pk, sig s) {\n        require(hash160(pk) == pkh);\n        require(checkSig(s, pk));\n    }\n}\n',
+  compiler: {
+    name: 'cashc',
+    version: '0.7.0',
+  },
+  updatedAt: '2025-08-05T09:04:50.388Z',
+};
+
+describe('Debugging tests - old artifacts', () => {
+  it('should succeed when passing the correct parameters', () => {
+    const provider = new MockNetworkProvider();
+    const contractTestLogs = new Contract(artifact, [alicePkh], { provider });
+    const contractUtxo = randomUtxo();
+    provider.addUtxo(contractTestLogs.address, contractUtxo);
+
+    const transaction = new TransactionBuilder({ provider })
+      .addInput(contractUtxo, contractTestLogs.unlock.spend(alicePub, new SignatureTemplate(alicePriv)))
+      .addOutput({ to: contractTestLogs.address, amount: 10000n });
+
+    console.warn(transaction.bitauthUri());
+
+    expect(() => transaction.debug()).not.toThrow();
+  });
+
+  it('should fail when passing the wrong parameters', () => {
+    const provider = new MockNetworkProvider();
+    const contractTestLogs = new Contract(artifact, [alicePkh], { provider });
+    const contractUtxo = randomUtxo();
+    provider.addUtxo(contractTestLogs.address, contractUtxo);
+
+    const transaction = new TransactionBuilder({ provider })
+      .addInput(contractUtxo, contractTestLogs.unlock.spend(alicePub, new SignatureTemplate(bobPriv)))
+      .addOutput({ to: contractTestLogs.address, amount: 10000n });
+
+    console.warn(transaction.bitauthUri());
+
+    expect(() => transaction.debug()).toThrow();
+  });
+});