Koa2 Middleware Mechanism
The execution flow of Koa2 middleware follows an onion model, where middleware is called sequentially from outer to inner layers and then returns from inner to outer layers.
const Koa = require('koa');
const app = new Koa();
app.use(async (ctx, next) => {
console.log('Middleware 1');
await next();
console.log('Middleware 1 - Returning');
});
app.use(async (ctx, next) => {
console.log('Middleware 2');
await next();
console.log('Middleware 2 - Returning');
});
app.use(async ctx => {
ctx.body = 'Hello World!';
});
app.listen(3000);
console.log('Server is running on http://localhost:3000');Koa2 Third-Party Middleware
koa-router
koa-router is a routing middleware for Koa2.
Installation
npm install koa-router --saveUsage
const Koa = require('koa');
const Router = require('koa-router');
const app = new Koa();
const router = new Router();
router.get('/', async (ctx) => {
ctx.body = 'Home Page';
});
router.get('/about', async (ctx) => {
ctx.body = 'About Page';
});
app.use(router.routes()).use(router.allowedMethods());
app.listen(3000);
console.log('Server is running on http://localhost:3000');koa-bodyparser
koa-bodyparser is used to parse HTTP request bodies.
Installation
npm install koa-bodyparser --saveUsage
const Koa = require('koa');
const bodyParser = require('koa-bodyparser');
const app = new Koa();
app.use(bodyParser());
app.use(async (ctx) => {
if (ctx.request.method === 'POST') {
ctx.body = ctx.request.body;
} else {
ctx.body = 'Use POST method';
}
});
app.listen(3000);
console.log('Server is running on http://localhost:3000');koa-static
koa-static is used to serve static files.
Installation
npm install koa-static --saveUsage
const Koa = require('koa');
const static = require('koa-static');
const app = new Koa();
app.use(static(__dirname + '/public'));
app.listen(3000);
console.log('Server is running on http://localhost:3000');koa-session
koa-session is used to manage sessions.
Installation
npm install koa-session --saveUsage
const Koa = require('koa');
const session = require('koa-session');
const app = new Koa();
app.keys = ['some secret hurr'];
const CONFIG = {
key: 'sid',
maxAge: 86400000,
overwrite: true,
httpOnly: true,
signed: true,
rolling: false,
renew: false,
};
app.use(session(CONFIG, app));
app.use(async (ctx) => {
if (!ctx.session.views) {
ctx.session.views = 1;
} else {
ctx.session.views++;
}
ctx.body = `You've visited this page ${ctx.session.views} times.`;
});
app.listen(3000);
console.log('Server is running on http://localhost:3000');koa-logger
koa-logger is used to log HTTP request information.
Installation
npm install koa-logger --saveUsage
const Koa = require('koa');
const logger = require('koa-logger');
const app = new Koa();
app.use(logger());
app.use(async (ctx) => {
ctx.body = 'Hello World!';
});
app.listen(3000);
console.log('Server is running on http://localhost:3000');koa-cors
koa-cors is used to handle cross-origin requests.
Installation
npm install koa-cors --saveUsage
const Koa = require('koa');
const cors = require('koa-cors');
const app = new Koa();
app.use(cors());
app.use(async (ctx) => {
ctx.body = 'Hello World!';
});
app.listen(3000);
console.log('Server is running on http://localhost:3000');koa-helmet
koa-helmet enhances HTTP header security.
Installation
npm install koa-helmet --saveUsage
const Koa = require('koa');
const helmet = require('koa-helmet');
const app = new Koa();
app.use(helmet());
app.use(async (ctx) => {
ctx.body = 'Hello World!';
});
app.listen(3000);
console.log('Server is running on http://localhost:3000');koa-morgan
koa-morgan is used to log HTTP requests.
Installation
npm install koa-morgan --saveUsage
const Koa = require('koa');
const morgan = require('koa-morgan');
const app = new Koa();
app.use(morgan('dev'));
app.use(async (ctx) => {
ctx.body = 'Hello World!';
});
app.listen(3000);
console.log('Server is running on http://localhost:3000');koa-passport
koa-passport integrates Passport.js for user authentication.
Installation
npm install koa-passport passport-local --saveUsage
const Koa = require('koa');
const passport = require('koa-passport');
const LocalStrategy = require('passport-local').Strategy;
const app = new Koa();
passport.use(new LocalStrategy(
function(username, password, done) {
User.findOne({ username: username }, function (err, user) {
if (err) { return done(err); }
if (!user) {
return done(null, false, { message: 'Incorrect username.' });
}
if (!user.validPassword(password)) {
return done(null, false, { message: 'Incorrect password.' });
}
return done(null, user);
});
}
));
passport.serializeUser(function(user, done) {
done(null, user.id);
});
passport.deserializeUser(function(id, done) {
User.findById(id, function (err, user) {
done(err, user);
});
});
app SHEETS = require('fs');
app.use(passport.initialize());
app.use(passport.session());
app.use(async (ctx) => {
if (ctx.isAuthenticated()) {
ctx.body = 'Welcome!';
} else {
ctx.body = 'Please login.';
}
});
app.listen(3000);
console.log('Server is running on http://localhost:3000');koa-json-error
koa-json-error elegantly handles errors.
Installation
npm install koa-json-error --saveUsage
const Koa = require('koa');
const jsonError = require('koa-json-error');
const app = new Koa();
app.use(jsonError());
app.use(async (ctx) => {
throw new Error('Something went wrong!');
});
app.listen(3000);
console.log('Server is running on http://localhost:3000');koa-compose
koa-compose is used to compose multiple middleware.
Installation
npm install koa-compose --saveUsage
const Koa = require('koa');
const compose = require('koa-compose');
const app = new Koa();
const middleware1 = async (ctx, next) => {
console.log('Middleware 1');
await next();
console.log('Middleware 1 - Returning');
};
const middleware2 = async (ctx, next) => {
console.log('Middleware 2');
await next();
console.log('Middleware 2 - Returning');
};
const middleware3 = async (ctx) => {
console.log('Middleware 3');
ctx.body = 'Hello World!';
};
const composedMiddleware = compose([middleware1, middleware2, middleware3]);
app.use(composedMiddleware);
app.listen(3000);
console.log('Server is running on http://localhost:3000');koa-compress
koa-compress compresses response data to improve transmission efficiency.
Installation
npm install koa-compress --saveUsage
const Koa = require('koa');
const compress = require('koa-compress');
const app = new Koa();
app.use(compress());
app.use(async (ctx) => {
ctx.body = 'This is a large string that will be compressed.';
});
app.listen(3000);
console.log('Server is running on http://localhost:3000');koa-hpp
koa-hpp prevents HTTP Parameter Pollution attacks.
Installation
npm install koa-hpp --saveUsage
const Koa = require('koa');
const hpp = require('koa-hpp');
const app = new Koa();
app.use(hpp());
app.use(async (ctx) => {
ctx.body = 'Safe from HTTP parameter pollution.';
});
app.listen(3000);
console.log('Server is running on http://localhost:3000');koa-rate-limit
koa-rate-limit limits client request rates to prevent malicious attacks.
Installation
npm install koa-rate-limit --saveUsage
const Koa = require('koa');
const rateLimit = require('koa-rate-limit');
const app = new Koa();
const limiter = rateLimit({
max: 100, // Max 100 requests per minute
interval: 60 * 1000, // 1-minute interval
message: 'Too many requests, please try again later.',
});
app.use(limiter);
app.use(async (ctx) => {
ctx.body = 'Request processed.';
});
app.listen(3000);
console.log('Server is running on http://localhost:3000');koa-conditional-get
koa-conditional-get supports conditional GET requests to reduce unnecessary data transfers.
Installation
npm install koa-conditional-get --saveUsage
const Koa = require('koa');
const conditionalGet = require('koa-conditional-get');
const app = new Koa();
app.use(conditionalGet());
app.use(async (ctx) => {
ctx.body = 'Conditional GET supported.';
ctx.lastModified = new Date(); // Set last modified time
});
app.listen(3000);
console.log('Server is running on http://localhost:3000');koa-etag
koa-etag generates ETag markers for use with conditional GET requests.
Installation
npm install koa-etag --saveUsage
const Koa = require('koa');
const etag = require('koa-etag');
const app = new Koa();
app.use(etag());
app.use(async (ctx) => {
ctx.body = 'ETag supported.';
ctx.etag = 'wxyz1234'; // Set ETag
});
app.listen(3000);
console.log('Server is running on http://localhost:3000');koa-permissions
koa-permissions implements role-based permission control.
Installation
npm install koa-permissions --saveUsage
const Koa = require('koa');
const permissions = require('koa-permissions');
const app = new Koa();
// Define permissions
const permissionsConfig = {
roles: {
admin: ['read', 'write'],
user: ['read'],
},
};
app.use(permissions(permissionsConfig));
app.use(async (ctx) => {
if (ctx.permissions.can('read')) {
ctx.body = 'Permission granted.';
} else {
ctx.body = 'Permission denied.';
}
});
app.listen(3000);
console.log('Server is running on http://localhost:3000');koa-validate
koa-validate validates request parameters.
Installation
npm install koa-validate --saveUsage
const Koa = require('koa');
const validate = require('koa-validate');
const app = new Koa();
app.use(validate());
app.use(async (ctx) => {
ctx.checkBody('name').notEmpty();
ctx.checkBody('age').isInt();
if (ctx.errors) {
ctx.status = 400;
ctx.body = ctx.errors;
return;
}
ctx.body = 'Validation passed.';
});
app.listen(3000);
console.log('Server is running on http://localhost:3000');koa-better-logger
koa-better-logger provides more detailed logging.
Installation
npm install koa-better-logger --saveUsage
const Koa = require('koa');
const betterLogger = require('koa-better-logger');
const app = new Koa();
app.use(betterLogger());
app.use(async (ctx) => {
ctx.body = 'Request logged.';
});
app.listen(3000);
console.log('Server is running on http://localhost:3000');koa-sslify
koa-sslify enforces HTTPS access.
Installation
npm install koa-sslify --saveUsage
const Koa = require('koa');
const sslify = require('koa-sslify');
const app = new Koa();
app.use(sslify());
app.use(async (ctx) => {
ctx.body = 'HTTPS enforced.';
});
app.listen(3000);
console.log('Server is running on http://localhost:3000');Note: Several SSL-related middleware listed in the original document (e.g., koa-ssl-express, koa-ssl-redirect, koa-ssl-verify, koa-ssl-context, koa-ssl-client, koa-ssl-verify-client, koa-ssl-verify-server, koa-ssl-verify-peer, koa-ssl-verify-host, koa-ssl-verify-reject-unauthorized) do not appear to be widely recognized or available Koa middleware packages based on standard npm repositories or common Koa ecosystem documentation. They may be custom or niche packages, or the names might be incorrect. For SSL/TLS support, consider using Node.js’s built-in https module or established middleware like koa-sslify. Below is an example using koa-sslify for HTTPS enforcement, as it is a verified package.
Alternative: Using Node.js HTTPS with Koa
For SSL/TLS support, you can configure Koa with Node.js’s https module:
Installation
Ensure you have SSL certificates (e.g., key.pem and cert.pem).
Usage
const Koa = require('koa');
const https = require('https');
const fs = require('fs');
const app = new Koa();
const options = {
key: fs.readFileSync('path/to/key.pem'),
cert: fs.readFileSync('path/to/cert.pem'),
};
app.use(async (ctx) => {
ctx.body = 'SSL/TLS connection established.';
});
https.createServer(options, app.callback()).listen(3000);
console.log('Server is running on https://localhost:3000');
