What causes "EISDIR, read" in expressjs/express?

Point sendFile at an actual file — typically append the filename: `res.sendFile(path.join(buildDir, 'index.html'))`.

expressjs/express · error · Error

EISDIR

EISDIR

Error message

EISDIR, read

What it means

In the same `sendfile` helper, the `send` stream emits a `directory` event when the resolved path is a directory rather than a regular file. Express's `ondirectory` handler (lib/response.js:939-946) converts that into `new Error('EISDIR, read')` with `code: 'EISDIR'`, mimicking the Node.js fs error you would get from reading a directory. It means `res.sendFile()`/`res.download()` was pointed at a directory, which cannot be streamed as a file.

Source

Thrown at lib/response.js:943

  var done = false;
  var streaming;

  // request aborted
  function onaborted() {
    if (done) return;
    done = true;

    var err = new Error('Request aborted');
    err.code = 'ECONNABORTED';
    callback(err);
  }

  // directory
  function ondirectory() {
    if (done) return;
    done = true;

    var err = new Error('EISDIR, read');
    err.code = 'EISDIR';
    callback(err);
  }

  // errors
  function onerror(err) {
    if (done) return;
    done = true;
    callback(err);
  }

  // ended
  function onend() {
    if (done) return;
    done = true;
    callback();
  }

View on GitHub ↗ (pinned to a3714473fe)

Solutions

Point sendFile at an actual file — typically append the filename: `res.sendFile(path.join(buildDir, 'index.html'))`.
If serving user-derived paths, validate with `fs.stat` (or catch `err.code === 'EISDIR'` in the sendFile callback) and respond 404 for directories.
If you want directory-index behavior (serve index.html for a folder), use `express.static(dir)` instead of hand-rolled sendFile routes.
Check the deployed filesystem layout — confirm the target is a file, not a folder created by the build or extraction step.

Example fix

// before
app.get('*', function (req, res) {
  res.sendFile(path.join(__dirname, 'build')); // 'build' is a directory -> EISDIR
});

// after
app.get('*', function (req, res) {
  res.sendFile(path.join(__dirname, 'build', 'index.html'));
});

Defensive patterns

Strategy: validation

Validate before calling

const fs = require('fs');
const path = require('path');

const resolved = path.resolve(root, requestedName);
const stats = fs.statSync(resolved, { throwIfNoEntry: false });
if (!stats || !stats.isFile()) {
  return res.status(404).end(); // directory or missing — don't call sendFile
}
res.sendFile(resolved);

Type guard

function isEisdir(err) {
  return err != null && typeof err === 'object' && err.code === 'EISDIR';
}

Try / catch

res.sendFile(filePath, function (err) {
  if (err) {
    if (err.code === 'EISDIR' || err.code === 'ENOENT') {
      return res.status(404).end(); // path is a directory or missing
    }
    next(err);
  }
});

Prevention

stat the resolved path and require stats.isFile() before calling res.sendFile — directories should map to a 404 (or an explicit index file), never reach sendFile
Never build sendFile paths directly from user input; resolve against a fixed root and reject paths that escape it or end with a separator
Map EISDIR to a 404 in the sendFile callback rather than leaking a 500 with filesystem details to the client
If directory URLs should serve an index page, append index.html explicitly (or use express.static with its index option) instead of passing the directory to sendFile
Add tests that request a known directory path (e.g. '/uploads/') to lock in the 404 behavior

When it happens

Trigger: `res.sendFile(path)` or `res.download(path)` where `path` resolves to a directory: passing the folder itself instead of a file inside it, building the path from user input or a route param that is empty/`.`/ends in a slash, or joining `root` with a relative segment that lands on a directory. Note Express does not follow directory-index behavior here — unlike `express.static`, sendFile never serves `index.html` for a directory.

Common situations: SPA fallbacks written as `res.sendFile(path.join(__dirname, 'build'))` (missing `'index.html'`); file-serving routes like `/files/:name` hit with an empty or dot name; deployment layouts where the expected file was replaced by a directory of the same name; refactors that changed a build output from a single bundle file to a folder.

Related errors

AI-assisted analysis of expressjs/express@a3714473fe (2026-07-31). Data as JSON: /data/errors/68ac2f914a80b151.json. Report an issue: GitHub ↗.