bitcoinjs-lib/ts_src/psbt.ts

import { Psbt as PsbtBase } from 'bip174';
import { Signer } from './ecpair';
import * as payments from './payments';
import { Transaction } from './transaction';

export class Psbt extends PsbtBase {
  constructor() {
    super();
  }

  signInput(inputIndex: number, keyPair: Signer): Psbt {
    // TODO: Implement BIP174 pre-sign checks:
    // https://github.com/bitcoin/bips/blob/master/bip-0174.mediawiki#signer
    //
    // if non_witness_utxo.exists:
    //     assert(sha256d(non_witness_utxo) == psbt.tx.innput[i].prevout.hash)
    //     if redeemScript.exists:
    //         assert(non_witness_utxo.vout[psbt.tx.input[i].prevout.n].scriptPubKey == P2SH(redeemScript))
    //         sign_non_witness(redeemScript)
    //     else:
    //         sign_non_witness(non_witness_utxo.vout[psbt.tx.input[i].prevout.n].scriptPubKey)
    // else if witness_utxo.exists:
    //     if redeemScript.exists:
    //         assert(witness_utxo.scriptPubKey == P2SH(redeemScript))
    //         script = redeemScript
    //     else:
    //         script = witness_utxo.scriptPubKey
    //     if IsP2WPKH(script):
    //         sign_witness(P2PKH(script[2:22]))
    //     else if IsP2WSH(script):
    //         assert(script == P2WSH(witnessScript))
    //         sign_witness(witnessScript)
    // else:
    //     assert False

    const input = this.inputs[inputIndex];
    if (input === undefined) throw new Error(`No input #${inputIndex}`);

    if (input.nonWitnessUtxo) {
      const unsignedTx = Transaction.fromBuffer(this.globalMap.unsignedTx!);
      const nonWitnessUtxoTx = Transaction.fromBuffer(input.nonWitnessUtxo);

      const prevoutHash = unsignedTx.ins[inputIndex].hash;
      const utxoHash = nonWitnessUtxoTx.getHash();

      // If a non-witness UTXO is provided, its hash must match the hash specified in the prevout
      if (Buffer.compare(prevoutHash, utxoHash) !== 0) {
        throw new Error(
          `Non-witness UTXO hash for input #${inputIndex} doesn't match the hash specified in the prevout`,
        );
      }

      if (input.redeemScript) {
        const prevoutIndex = unsignedTx.ins[inputIndex].index;
        const prevout = nonWitnessUtxoTx.outs[prevoutIndex];

        const redeemScriptOutput = payments.p2sh({
          redeem: { output: input.redeemScript },
        }).output as Buffer;

        // If a redeemScript is provided, the scriptPubKey must be for that redeemScript
        if (Buffer.compare(prevout.script, redeemScriptOutput) !== 0) {
          throw new Error(
            `Redeem script for input #${inputIndex} doesn't match the scriptPubKey in the prevout`,
          );
        }
      }
    }

    // TODO: Get hash to sign
    const hash = Buffer.alloc(32);

    const partialSig = {
      pubkey: keyPair.publicKey,
      signature: keyPair.sign(hash),
    };

    // Just hardcode this for now to satisfy the stricter sig type checks
    partialSig.signature = Buffer.from(
      '304302200424b58effaaa694e1559ea5c93bbfd4a89064224055cdf070b6' +
        '771469442d07021f5c8eb0fea6516d60b8acb33ad64ede60e8785bfb3aa9' +
        '4b99bdf86151db9a9a01',
      'hex',
    );

    return this.addPartialSigToInput(inputIndex, partialSig);
  }
}