held by Gevorg Topikyan
held by Shahen Hovhannisyan
Definitions of server, port, protocol.
Every request has method, status, headers, cookies and body.
Methods
Headers - metadata
Body - info that we're sending to backend (POST, PUT)
Cookies - information that backend sends to keep in browser to use it in the future as part of header for validation. On the browser side there's an api that sends cookie automaticaly to backend so you don't need to do it manually from frontend. It's safer than using localstorage but in mobile it's a headache (as everything else in mobile).
node index.js --inspect - allows us to debug node in browser
Request (from HTTP2) and Response are streams and if you're using express there's a way to get response as chunk.
/posts/:postId/comments/:commentIdreq.query.
/posts?last-20-10-2019&index=10Before response came to handler there're a lot of function that can affect on it. These functions are middlewares.
There's a way to create middleware - app.use and it has 3rd argument - next. If we call it without args, then it goes to another middlewares. In case if we pass object - it causes the error which we can handle by app.on('error', cb).
We can send headers by calling res.header('X_COMP_MAN', 'MAC').
Example
app.use([route], (req, res, next) => {
console.log('THIS IS MIDDLEWARE');
next();
});/usersapp.get('/users', (req, res) => {
res.json(users);
})/users/:id/users
We also need middleware for parsing body.app.use(express.json())Then request:
app.post('/users', (req, res) => {
const newUser = req.body;
users.push(newUser);
res.json(newUser);
res.end();
})/users/:idnpm i cookie-parser
const cookieParser = require('cookie-parser');
app.use(cookieParser());
app.get('/users', (req, res) => {
console.log(res.cookies);
})Cookies has key, value, ExpirationDate, secure, HTTPOnly, domain, path, etc
How to set cookies? Let's do it on user creation.
const users = [];
app.post('/users', (req, res) => {
const newUser = req.body;
users.push(newUser);
res.cookie('uid', newUser.id, {httpOnly: true, secure: false, expires: new Date('10-10-2099')});
res.json(newUser);
res.end();
});
app.get('/users', (req, res) => {
res.cookie('uid', 1, {httpOnly: true, secure: false, expires: new Date('10-10-2099')}).end();
});
// better to do this process in middleware
app.get('/me', (req, res) => {
const {uid} = req.cookies;
const user = users.find(u => u.id === +uid)
if (!user) {
res.status(404).end()
return
}
res.json(user);
});If you want to delete cookie, you need to change it's expires key to past date.
res.cookie('uid', 0, {
expires: new Date('10-10-1990')
});User signup --> Backend generates uuid --> Stores in object {[key: string]: {email, id, username} } (key is a uuid) --> sends uuid to frontend -->
User request with uuid --> Backend checks if there's a object with this uuid
Note,
held by Gevorg Topikyan
Main source: Express.js docs
Recommended Literature:
Mentioned Topics:
Express handlers are middlewares which use chain of responsibility pattern.
function (req, res, next)next - passes flow to another middleware. It can be called with 'route' argument to pass to another route instead of middleware.app.use(err, req, res, next)Note, we need to specify all args for express to help it understand that it's an error handling middleware.
body-parser - to parse response bodymorgan - for loggingconst router = express.Router();
app.use('/', router);
We can use this feature of express to create a lot of mini independent reusable applications and connect them to route (e.g. user handler to user, posts handler to post).
Task,
dotenv to insert variables to process.env.winston as logger. It has some advantages over morgan. For example, morgan can log only requests, winston on the other side can work with everything. Also, winston has tons of integrations (e.g. with mongodb)errorhandler - package for handling errorsheld by Shahen Hovhannisyan
Protocol - set of communication rules for two entities communication (e.g. client / server).
Every protocol has a multiple layers.
net package which allows to create tcp serverserver.js
const net = require('net');
const server = net.createServer();
server.on('listening', () => {
console.log('tcp server listening');
});
server.on('connection', socket => {
console.log(socket.localAddress);
// data is a Buffer
server.on('data', (data) => {
console.log(data.toString());
socket.write('ping');
});
// destroys socket
socket.destroy();
});
server.listen(1234);client.js
const socket = net.Socket()
socket.connect({
host: '127.0.0.1',
port: 1234
})
socket.on('data', (data) => {
console.log(data);
socket.write('pong');
});telnet cli commandIt may not send your request/response or in wrong order.
server.js
const dgram = require('dgram');
const socket = dgram.createSocket()
socket.on('message', (msg, info) => {
console.log(msg.toString())
})
socket.on('listening', () => {
console.log('listening');
});
socket.on('connect', () => {
console.log('connected')
});
socket.bind(3000)echo 'hi' | nc -w1 -u 127.0.0.1 3000
client.js
const socket = new dgram.createSocket('udp4');
socket.bind(1234, () => {
socket.send('hello DGRAM', 3000, '0.0.0.0), (err, bytes) => {
conosle.log(err, bytes);
}):
});websocket packagedocs as example)const ws = new WebSocket('ws://localhost:3000')
http://localhost:3000/socket.io/socket.io.js