stack/packages/bus/src/peercred.mjs

import { spawn as nodeSpawn } from 'node:child_process';
import { fileURLToPath } from 'node:url';
import { lstatSync } from 'node:fs';
import { BusError } from './broker.mjs';

const helper = fileURLToPath(new URL('./peercred.py', import.meta.url));
const refused = () => new BusError('peercred-required');
export function createPeerReader({ interpreter, spawn = nodeSpawn, timeout = 1000, stat = lstatSync } = {}) {
  try { const s = stat(helper); if (!s.isFile() || s.isSymbolicLink()) throw Error(); }
  catch { throw refused(); }
  const children = new Set();
  let closed = false;
  return {
    read(socket) {
      if (closed || children.size >= 16) return Promise.reject(refused());
      return new Promise((resolve, reject) => {
        let child, timer, output = '', settled = false, invalid = false;
        const finish = (error, value) => {
          if (settled) return;
          settled = true;
          clearTimeout(timer);
          error ? reject(refused()) : resolve(value);
        };
        try {
          // Keep this connection's Socket in this closure. Never borrow another pending fd.
          child = spawn(interpreter.path, ['-I', '-S', helper],
            { env: {}, stdio: ['ignore', 'pipe', 'pipe', socket] });
          children.add(child);
          timer = setTimeout(() => { child.kill('SIGKILL'); finish(true); }, timeout);
          child.stdout.on('data', data => {
            output += data.toString('utf8');
            if (Buffer.byteLength(output) > 256) { invalid = true; child.kill('SIGKILL'); finish(true); }
          });
          child.stderr.on('data', () => { invalid = true; });
          child.on('error', () => { children.delete(child); finish(true); });
          child.on('close', (code, signal) => {
            children.delete(child);
            if (settled) return;
            try {
              if (closed || invalid || code !== 0 || signal) throw Error();
              const p = JSON.parse(output);
              if (!p || Array.isArray(p) || Object.keys(p).sort().join(',') !== 'gid,pid,uid' ||
                !['pid', 'uid', 'gid'].every(k => Number.isSafeInteger(p[k])) || p.pid < 2 || p.uid < 0 || p.gid < 0) throw Error();
              finish(false, Object.freeze(p));
            } catch { finish(true); }
          });
        } catch { finish(true); }
      });
    },
    async close() {
      closed = true;
      await Promise.all([...children].map(child => new Promise(resolve => {
        child.once('close', resolve);
        child.kill('SIGKILL');
      })));
    },
  };
}