determine signers in a 2-of-3 Dogecoin multisig transaction

/// determine signers in a 2-of-3 Dogecoin multisig transaction
/// uses sochain
/// requirements:
/// node.js and npm
/// npm install bitcoinjs-lib ecpair tiny-secp256k1

const https = require('https');

const { script, Transaction } = require('bitcoinjs-lib');
const { ECPairFactory } = require('ecpair');
const tinysecp = require('tiny-secp256k1');

const ECPair = ECPairFactory(tinysecp);

//////////////////////////////////////////
///// functions to fetch tx from chain.so
/////////////////////////////////////////

const HTTPS_OPTIONS = {
  hostname: 'chain.so',
  port: 443,
  method: 'GET'
};

function options(path) {
  const out = {};
  Object.keys(HTTPS_OPTIONS).forEach(k => {
    out[k] = HTTPS_OPTIONS[k];
  });
  out["path"] = path;
  return out;
};

function fetch(path) {
  return new Promise(function (r,f) {
      opts = options(path);
      const req = https.request(opts, res => {
        const chunks = [];
        if (res.statusCode != 200) {
          return f(new Error("Server returned status " + res.statusCode));
        }
        res.on('data', d => chunks.push(d));
        res.on('end', () => r(Buffer.concat(chunks)));
      });
      req.on('error', e => f(e));
      req.end();
  });
}

async function fetchJSON(path) {
  let data = await fetch(path);
  return JSON.parse(data.toString('utf8'));
}

async function getTx(txid) {
  return await fetchJSON('/api/v2/get_tx/DOGE/' + txid);
}

//////////////////////////////////////////
///// script parsing functions
/////////////////////////////////////////

function getSignaturePosition(tx, index, key) {
  const iptScript = script.decompile(tx.ins[index].script)
  const hash = tx.hashForSignature(index, iptScript[3], 0x01);
  return [1,2].reduce((a,b) => {
    const sig = script.signature.decode(iptScript[b]);
    return key.verify(hash, sig.signature) ? b : a;
  }, 0);
}

function extractAllECKeys(tx) {
  const sigScripts = tx.ins.map(ipt => script.decompile(ipt.script));

  const uniqueRS = {};
  sigScripts.forEach(s => {
    if (s[0] != 0) return;
    uniqueRS[s[s.length - 1].toString('hex')] = true;
  });

  const uniqueRSKeys = {};
  Object.keys(uniqueRS).forEach(rs => {
    let chunks = script.decompile(Buffer.from(rs, 'hex'));
    chunks.slice(1,4).forEach(key => uniqueRSKeys[key.toString('hex')] = true);
  });

  return Object.keys(uniqueRSKeys).map(k => ECPair.fromPublicKey(Buffer.from(k, 'hex')));

}

//////////////////////////////////////////
///// main loop to analyze a tx
/////////////////////////////////////////

async function main() {
  const txid = process.argv[2];

  let txdata = await getTx(txid);
  const tx = Transaction.fromHex(txdata.data.tx_hex);
  const keys = extractAllECKeys(tx);

  console.log("tx:        " + txid);
  console.log("inputs:    " + tx.ins.length);
  console.log("keys:      " + keys.length);
  keys.forEach((k, i) => {
    console.log("Key " + (i + 1) + ":     " + k.publicKey.toString('hex'));
  });
  console.log("============================");

  tx.ins.forEach((ipt, idx) => {
    keys.forEach((key, n) => {
      sigPos = getSignaturePosition(tx, idx, key);
      if (sigPos)
        console.log("Key " + (n + 1) + " signed input " + idx + ", sig " + sigPos);
    });
  });

}

main().catch(console.log);