Middleware

Middleware functions run on every request before the route handler. They can modify the request or response, set headers, perform logging, or attach utilities to the request object.

Middleware interface

type MiddlewareHandler = (
  req: Request,
  res: Response,
  next: NextFunction,
) => void;

Middleware can also be async:

type MiddlewareHandler = (
  req: Request,
  res: Response,
  next: NextFunction,
) => Promise<void>;

Creating middleware

Create a file that exports a standard Express middleware function:

// src/middleware/my-middleware/my-middleware.ts
import type { Request } from '../../types';
import { NextFunction, Response } from 'express';

export function myMiddleware(req: Request, res: Response, next: NextFunction) {
  // Modify request, set headers, or run side effects
  next();
}

For async middleware (e.g. fetching data from the database), use an async function:

import type { Request } from '../../types';
import { NextFunction, Response } from 'express';
import models from '../../models';

export async function myMiddleware(
  req: Request,
  res: Response,
  next: NextFunction,
): Promise<void> {
  const Setting = models.get('Setting');
  const setting = await Setting.fetchById('my-setting', {}, req.trx);
  req.mySetting = setting;
  next();
}

Registration

In a profile’s init() function, import and register the middleware:

import middleware from '../../middleware';
import { myMiddleware } from '../../middleware/my-middleware/my-middleware';

// In init():
middleware.register(myMiddleware);

All registered middleware is mounted globally via middleware.use(app) in src/app.ts, which calls app.use(handler) for each handler.

Per-route middleware

For middleware that should only apply to specific routes (e.g. rate limiters), use the middleware field on the route definition instead of the global registry.