Fixes race in scripts/install-binary.mjs

[qwerdenkerXD]

Hello there, I found a race in the scripts/install-binary.mjs in WSL.

npm error code 1                                                                                                                                                                                                                   
npm error path /mnt/c/Users/.../node_modules/node-jq                                                                                                                     
npm error command failed                                                                                                                                                                                                           
npm error command sh -c npm run install-binary                                                                                                                                                                                     
npm error > node-jq@6.3.1 install-binary                                                                                                                                                                                           
npm error > node scripts/install-binary.mjs                                                                                                                                                                                        
npm error                                                                                                                                                                                                                          
npm error /mnt/c/Users/.../node_modules/node-jq/bin directory was created                                                                                                
npm error Downloading jq from https://github.com/jqlang/jq/releases/download/jq-1.7.1/jq-linux-amd64                                                                                                                               
Downloading jq: 100.00%q: 0.06%                                                                                                                                                                                                    
npm error Download complete                                                                                                                                                                                                        
npm error node:fs:2064                                                                                                                                                                                                             
npm error   binding.chmod(path, mode);                                                                                                                                                                                             
npm error           ^                                                                                                                                                                                                              
npm error                                                                                                                                                                                                                          
npm error Error: ENOENT: no such file or directory, chmod '/mnt/c/Users/.../node_modules/node-jq/bin/jq'                                                                 
npm error     at chmodSync (node:fs:2064:11)                                                                                                                                                                                       
npm error     at downloadJqBinary (file:///mnt/c/Users/Franz-Eric%20Sill/Documents/Git%20Repos/node_modules/node-jq/scripts/install-binary.mjs:123:5)                                                    
npm error     at process.processTicksAndRejections (node:internal/process/task_queues:105:5) {                                                                                                                                     
npm error   errno: -2,                                                                                                                                                                                                             
npm error   code: 'ENOENT',                                                                                                                                                                                                        
npm error   syscall: 'chmod',                                                                                                                                                                                                      
npm error   path: '/mnt/c/Users/.../node_modules/node-jq/bin/jq'                                                                                                         
npm error }                                                                                                                                                                                                                        
npm error                                                                                                                                                                                                                          
npm error Node.js v23.9.0                                                                                                                                                                                                          
npm error A complete log of this run can be found in: /home/franz/.npm/_logs/2026-07-13T06_22_28_283Z-debug-0.log

I have a script to reproduce this. It adds a timeout to the end function of the file stream writer. It takes the target path as first argument. With a mounted path like node race-repro.js /mnt/c/Users/<name>/Desktop it fails, but with a native path like node race-repro.js ~ it succeeds.

See code

// Reproduction of a real race condition in node-jq's install script
// (node_modules/node-jq/scripts/install-binary.mjs, downloadJqBinary()).
//
// That script does:
//   dataStream.on("end", () => {
//     fileStream.end();   // schedules an async flush+close, does NOT wait for it
//     resolve();          // resolves immediately, same tick
//   })
// then, back in the caller:
//   renameSync(...)
//   if (fileExist(distPath)) chmodSync(distPath, 0o755)
//
// fileStream.end() with no callback/await only *schedules* the flush+close;
// it does not block until the file is actually finished being written. Since
// resolve() fires synchronously right after, the awaited promise can resolve
// before the file is fully flushed and its descriptor closed.
//
// On a real POSIX filesystem this is usually invisible: rename()/chmod() only
// need the directory entry to exist (created the moment the file was opened),
// not for pending writes to be flushed, so this race rarely manifests.
//
// On WSL's /mnt/c mount (DrvFs, a 9P-protocol passthrough to the Windows
// filesystem), renaming/chmod'ing a file while its write handle is still open
// is NOT reliable the same way -- which is exactly the ENOENT error node-jq's
// install script throws there.
//
// Usage:
//   node node-jq-install-race-repro.js                  # runs against os.tmpdir()
//   node node-jq-install-race-repro.js /mnt/c/some/dir   # runs against a DrvFs path
//
// On a native Linux filesystem (e.g. /tmp) both the "buggy" and "fixed"
// variants below succeed. On a DrvFs path, the buggy variant reproduces the
// same ENOENT node-jq hits; the fixed variant (which waits for end()'s
// callback) succeeds every time.

const fs = require("fs");
const os = require("os");
const path = require("path");
const { Readable } = require("stream");

const TARGET_DIR = process.argv[2] || os.tmpdir();

// A Writable that behaves like fs.createWriteStream, but artificially delays
// the moment it actually finishes flushing -- simulating a slow/high-latency
// filesystem deterministically, regardless of what disk this actually runs on.
function slowWriteStream(dest, delayMs) {
  const real = fs.createWriteStream(dest);
  const originalEnd = real.end.bind(real);
  real.end = (...args) => {
    const cb = typeof args[args.length - 1] === "function" ? args.pop() : null;
    setTimeout(() => {
      originalEnd(...args, () => {
        if (cb) cb();
      });
    }, delayMs);
    return real;
  };
  return real;
}

async function buggyDownload(dest) {
  const fileStream = slowWriteStream(dest, 2000); // simulate a slow flush
  const dataStream = Readable.from([Buffer.from("x".repeat(1000))]);

  return new Promise((resolve, reject) => {
    dataStream.pipe(fileStream);
    dataStream.on("end", () => {
      fileStream.end(); // <-- the bug: no callback, no await (matches install-binary.mjs)
      resolve(); // resolves immediately, NOT when the file is actually flushed
    });
    dataStream.on("error", reject);
  });
}

async function fixedDownload(dest) {
  const fileStream = slowWriteStream(dest, 2000);
  const dataStream = Readable.from([Buffer.from("x".repeat(1000))]);

  return new Promise((resolve, reject) => {
    dataStream.pipe(fileStream);
    dataStream.on("end", () => {
      fileStream.end(() => resolve()); // <-- fixed: wait for the callback
    });
    dataStream.on("error", reject);
  });
}

async function demo(label, downloadFn) {
  const src = path.join(TARGET_DIR, `race-src-${Date.now()}`);
  const dest = path.join(TARGET_DIR, `race-dest-${Date.now()}`);
  await downloadFn(src);
  try {
    fs.renameSync(src, dest); // mirrors install-binary.mjs's renameSync(...)
    fs.chmodSync(dest, 0o755); // mirrors install-binary.mjs's chmodSync(distPath, 0o755)
    console.log(`[${label}] OK — chmod succeeded immediately after "download"`);
    fs.unlinkSync(dest);
  } catch (err) {
    console.log(`[${label}] FAILED — ${err.code}: ${err.message}`);
  }
}

(async () => {
  console.log(`Target directory: ${TARGET_DIR}`);
  await demo("buggy (no await on end())", buggyDownload);
  await demo("fixed (waits for end() callback)", fixedDownload);
})();

Fix: resolve in callback function, so:
Turn this:

    dataStream.on('end', () => {
      console.log('\nDownload complete')
      fileStream.end()
      resolve()
    })

    dataStream.on('error', (err) => {
      fileStream.end()
      reject(err)
    })

into this:

    dataStream.on('end', () => {
      console.log('\nDownload complete')
      fileStream.end(() => resolve())
    })

    dataStream.on('error', (err) => {
      fileStream.end(() => reject(err))
    })

This resolves cleanly.