fs.existsSync api, return true also no matches found

[BrookZhao]

Version

14.17.3

Platform

Darwin brooks-mac-mini-g.local 21.3.0 Darwin Kernel Version 21.3.0: Wed Jan 5 21:37:58 PST 2022; root:xnu-8019.80.24~20/RELEASE_X86_64 x86_64

Subsystem

fs

What steps will reproduce the bug?

No response

How often does it reproduce? Is there a required condition?

No response

What is the expected behavior?

let filepath = self.appdataPath + '\\' + self.hotUpgradeInfo.filename
  // 检查文件是否存在
  log.info(`hotUpgradeInfo watch filepath: ${filepath}`)
  if (fs.existsSync(filepath)) {
    fs.openSync(filepath)
    const { execFile } = window.require('child_process')
    execFile('node', ['--version'], function () {
      let hash = crypto.createHash('md5')
      let hex = ''
      const upgradeReader = fs.createReadStream(filepath)
      upgradeReader.on('data', hash.update.bind(hash))
      upgradeReader.on('end', function () {
        hex = hash.digest('hex')
        log.info('hotUpgrade watch md5:' + self.hotUpgradeInfo.md5 + ', ' + hex)
        // 校验MD5
        if (self.hotUpgradeInfo.md5 === hex) {
          self.upgradePrepare()
        } else {
          self.downloadUpgradeFile(true)
        }
      })
    })
  }

What do you see instead?

[2022-07-15 17:09:07.952] [info]  hotUpgradeInfo watch filepath: /Users/zhaoshanwei/Library/Application Support/tjjVault\Cloudaemon ESZ_Private_V1.1.544(debug).pkg
[2022-07-15 17:11:01.923] [info]  start refresh_token. refreshErrCount =  0
[2022-07-15 17:13:45.001] [info]  start refresh_token. refreshErrCount =  0
[2022-07-15 17:13:45.623] [info]  hotUpgrade watch md5:23049e70467690883028d53935873dcf, 23049e70467690883028d53935873dcf

Additional information

No response

[bnoordhuis]

That the file exists doesn't mean you can open it.

Your code also contains a TOCTOU bug. Just open the file and handle the error when it's missing, don't check for its existence and only then try to open it.

[aduh95]

Another issue with your code is that you open the file but don't use the file descriptor afterwards. I think you'd get better results with the following code:

let filepath = self.appdataPath + '\\' + self.hotUpgradeInfo.filename;
log.info(`hotUpgradeInfo watch filepath: ${filepath}`);
let fd;
try {
  fd = fs.openSync(filepath);
} catch (err) {
  if (err?.code !== "ENOENT") throw err;
  // Here you can handle the case when file doesn't exist.
}
if (fd != null) {
  const { execFile } = window.require('child_process');
  const { pipeline } = window.require('stream');
  execFile('node', ['--version'], function () {
    let hash = crypto.createHash('md5');
    pipeline(fs.createReadStream(filepath, { fd, autoClose: true }), hash, function () {
      let hex = hash.digest('hex');
      log.info('hotUpgrade watch md5:' + self.hotUpgradeInfo.md5 + ', ' + hex);
      if (self.hotUpgradeInfo.md5 === hex) {
        self.upgradePrepare();
      } else {
        self.downloadUpgradeFile(true);
      }
    });
  });
}