Middleware

Middleware functions are functions that have access to the request object (req), the response object (res), and the next middleware function in the application’s request-response cycle.

Global Middleware

Global middleware runs for every request to the application.

app.use((req, res, next) => {
  console.log(`[${new Date().toISOString()}] ${req.method} ${req.url}`);
  next();
});

Path-Specific Middleware

You can mount middleware at a specific path. The middleware function is executed when the base of the requested path matches path.

app.use('/admin', (req, res, next) => {
  // Only runs for requests starting with /admin
  const token = req.headers.authorization;
  if (token) {
    next();
  } else {
    res.status(401).send('Unauthorized');
  }
});

Route-Level Middleware

Middleware can be applied to specific routes by passing them as arguments before the final route handler.

const auth = (req, res, next) => {
    // Auth logic
    next();
};

app.get('/protected', auth, (req, res) => {
    res.json({ message: "This is protected data" });
});

Async Middleware

Newgate supports async/await in middleware functions.

app.use(async (req, res, next) => {
  try {
    const user = await db.getUser(req.headers.userid);
    req.user = user;
    next();
  } catch (err) {
    next(err);
  }
});

Error Handling Middleware

Error-handling middleware functions are defined in the same way as other middleware functions, except they have four arguments instead of three: (err, req, res, next).

app.useError((err, req, res, next) => {
  console.error(err.stack);
  res.status(500).send('Something broke!');
});

Notice the use of app.useError to register error handlers. This ensures they are treated correctly by the framework's error propagation mechanism.