Http Programming in Node.txt

		   								Http Programming in Node
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Node was created to build non blocking web server and web applications.
Node provides single event loop thread which handles lot of concurrent http requests.
Node offers high level http wrapper apis to talk to os apis.
Node offers http as object.

HTTP Objects

1.Agent -  http.Agent
  For handling connections between and server

2.ClientRequest - http.clientRequest
  For creating http clients

3.Server - http.Server
  For creating web servers, we can create app and deploy on top of server.
  
4.ServerResponse - http.ServerResponse
  ServerResponse is outputstream of "http socket"

5.IncomingMessage -http.IncomingMessage
    The payload which is sent by client -  Message

6.OutgoingMessage -http.OutgoingMessage
    The data which is sent by server - Message

7.Global Methods of http
   1.createServer
    factory method to create http server instance.

HTTP events:
 
 There are three types of events

1.HTTP Request events
  Which are triggered whenever client request is received by server
  request.on('nameoftheevent',listner)

2.Http Response events
   Which are triggered whenever server response is sent by server
  response.on('nameoftheevent',listner)

3.Server Events
   Server events are triggered during server startup,connection,handshake,request
   server.on('nameoftheevent',listner)
common events:
 data
 error
 close
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Simple Web Server:
const http = require('node:http')

const PORT = 3000 
//create server
const server = http.createServer((req, res) => {
    //process client request and send response
    res.write('Hello')
    res.end()
})

//start the server
server.listen(PORT,()=>{
    console.log(`Http Server is listening at ${PORT}`)
})
**************************************************
Attaching Server Events

const http = require('node:http')

const PORT = 3000
//create server
const server = http.createServer((req, res) => {
    //process client request and send response
    res.write('Hello')
    res.end()
})

//start the server
server.listen(PORT, () => {
    console.log(`Http Server is listening at ${PORT}`)
})

//attach server event: request event
server.on('request', (req, res) => {
    console.log('Request Recived on', `[${new Date().toISOString()}]`, "URL is", req.url, "method ", req.method)
})
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								  Routing Pattern

const http = require('node:http')

const PORT = 3000

//create server
const server = http.createServer((req, res) => {
    //url  - '/'
    if (req.url === '/') {
        res.end('Home Page')
    } else if (req.url === '/about') {
        res.end('About Page')
    } else if (req.url === '/services') {
        res.end('Service Page')
    } else {
        res.end('404 Not Found Page')
    }
})
//start the server
server.listen(PORT, () => {
    console.log('Server running at http://localhost:3000')
})

//server listener
server.on('request', (req, res) => {
    console.log('Request Recived on', `[${new Date().toISOString()}]`, "URL is", req.url, "method ", req.method)

})


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										JSON response
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const http = require('node:http')

const PORT = 3000
//create server
const server = http.createServer((req, res) => {
    //process client request and send response
    const data = [{ id: 1, name: 'Subramanian'},{ id: 2, name: 'Murugan' }]
    res.write(data)
    res.end()
})

//start the server
server.listen(PORT, () => {
    console.log(`Http Server is listening at ${PORT}`)
})

//attach server event: request event
server.on('request', (req, res) => {
    console.log('Request Recived on', `[${new Date().toISOString()}]`, "URL is", req.url, "method ", req.method)

})

Http Server is listening at 3000
node:_http_outgoing:949
    throw new ERR_INVALID_ARG_TYPE(
    ^

TypeError [ERR_INVALID_ARG_TYPE]: The "chunk" argument must be of type string or an instance of Buffer or Uint8Array. Received an instance of Array
    at write_ (node:_http_outgoing:949:11)
    at ServerResponse.write (node:_http_outgoing:904:15)
    at Server.<anonymous> (G:\IBM\2025\July\Node\httpapp\src\index.js:8:9)
    at Server.emit (node:events:536:35)
    at parserOnIncoming (node:_http_server:1153:12)
    at HTTPParser.parserOnHeadersComplete (node:_http_common:117:17) {
  code: 'ERR_INVALID_ARG_TYPE'
}

Node.js v22.13.0

Here we are trying to send array object, we cant , then we have to convert into string (json)

const http = require('http')

const PORT = 3000

//create server and deploy app
const server = http.createServer((req, res) => {
    const users = [{
        id: 1,
        name: 'admin'
    }, {
        id: 2,
        name: 'guest'
    }]
    const usersJson = JSON.stringify(users)
    res.writeHead(200, {
        'Content-Type': 'application/json',
        'Connection': 'keep-alive',
        'Keep-Alive': 'timeout=10'
    });
    res.end(usersJson)
})
//increase server timeout
server.keepAliveTimeout = 10000 //10 secs
//start server
server.listen(PORT, () => {
    console.log(`Http Server is listening at ${PORT}`)
})
//server events
server.on('request', (req, res) => {
    console.log('Request Recived on', `[${new Date().toISOString()}]`, "URL is", req.url, "method ", req.method)
})
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								  Modularization 
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Controller  -  Web listener
Services  -    Hold Biz logic

Controller:
const http = require('node:http')
const todoService = require('./services/todo.service')

const PORT = 3000
const server = http.createServer((req, res) => {
    const jsonData = JSON.stringify(todoService.findAll())
    res.writeHead(200, {
        'Content-Type': 'application/json',
    });
    res.write(jsonData)
    res.end()
})

//start the server
server.listen(PORT, () => {
    console.log(`Http Server is listening at ${PORT}`)
})

//attach server event: request event
server.on('request', (req, res) => {
    console.log('Request Recived on', `[${new Date().toISOString()}]`, "URL is", req.url, "method ", req.method)

})

Service Layer:
const TODOS = require('../mock-data/todos')

class TodoService {

    findAll() {
        return TODOS
    }
}
module.exports = new TodoService()
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							Async apis and Modularization -  callbacks, promises
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Callbacks:
const TODOS = require('../mock-data/todos')

class TodoService {

    //async callback
    findAll(resolve, reject) {
        if (TODOS) {
            setTimeout(resolve, 1000, TODOS)
        } else {
            setTimeout(reject, 1000, { message: 'Records Not Found' })
        }
    }
}
module.exports = new TodoService()

const http = require('node:http')
const { findAll } = require('./services/todo.service')

const PORT = 3000
const server = http.createServer((req, res) => {
    findAll(todos => {
        res.writeHead(200, {
            'Content-Type': 'application/json',
        });
        const jsonData = JSON.stringify(todos)
        res.write(jsonData)
        res.end()
    }, err => {
        res.writeHead(500, {
            'Content-Type': 'application/json',
        });
        res.write({ err: err })
        res.end()
    })
})

//start the server
server.listen(PORT, () => {
    console.log(`Http Server is listening at ${PORT}`)
})

//attach server event: request event
server.on('request', (req, res) => {
    console.log('Request Recived on', `[${new Date().toISOString()}]`, "URL is", req.url, "method ", req.method)

})

Promise Based:
..........................
const TODOS = require('../mock-data/todos')
// const TODOS=null
class TodoService {

    //async callback
    findAll() {
        return new Promise((resolve, reject) => {
            if (TODOS) {
                setTimeout(resolve, 1000, TODOS)
            } else {
                setTimeout(reject, 1000, { message: 'Records Not Found' })
            }
        })
    }
}
module.exports = new TodoService()

Promise with Then and Catch:
const http = require('node:http')
const { findAll } = require('./services/todo.service')

const PORT = 3000
const server = http.createServer((req, res) => {

    findAll().then(todos => {
        res.writeHead(200, {
            'Content-Type': 'application/json',
        });
        const jsonData = JSON.stringify(todos)
        res.write(jsonData)
        res.end()
    }).catch(err => {
        res.writeHead(500, {
            'Content-Type': 'application/json',
        });
        res.write({ err: err })
        res.end()
    })

})

//start the server
server.listen(PORT, () => {
    console.log(`Http Server is listening at ${PORT}`)
})

//attach server event: request event
server.on('request', (req, res) => {
    console.log('Request Recived on', `[${new Date().toISOString()}]`, "URL is", req.url, "method ", req.method)

})

Promise with async and await:
const http = require('node:http')
const { findAll } = require('./services/todo.service');

const PORT = 3000
const server = http.createServer(async (req, res) => {

    try {
        res.writeHead(200, {
            'Content-Type': 'application/json',
        });
        const todos = await findAll()
        const jsonData = JSON.stringify(todos)
        res.write(jsonData)
        res.end()
    }
    catch (err) {
        res.writeHead(500, {
            'Content-Type': 'application/json',
        });
        res.write({ err: err })
        res.end()
    }


})

//start the server
server.listen(PORT, () => {
    console.log(`Http Server is listening at ${PORT}`)
})

//attach server event: request event
server.on('request', (req, res) => {
    console.log('Request Recived on', `[${new Date().toISOString()}]`, "URL is", req.url, "method ", req.method)

})
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											Payload
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const http = require('node:http')

const PORT = 3000
//create server
const server = http.createServer((req, res) => {
    //how to read input
    let data = ''
    req.on('data', (chunk) => {
        data += chunk
    })
    req.on('end', () => {
        console.log(data)
        res.end('Saved')
    })
})

//start the server
server.listen(PORT, () => {
    console.log(`Http Server is listening at ${PORT}`)
})

//attach server event: request event
server.on('request', (req, res) => {
    console.log('Request Recived on', `[${new Date().toISOString()}]`, "URL is", req.url, "method ", req.method)

})
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									CURD - HTTP module
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const http = require('node:http')

const PORT = 3000
//create server
const server = http.createServer((req, res) => {
    const { method, url } = req
    if (method === 'GET') {
        res.end('GET')
    } else if (method === 'POST') {
        res.end('POST')
    } else if (method === 'PUT') {
        res.end('PUT')
    } else if (method === 'DELETE') {
        console.log('delete is called')
        res.end('DELETE')
    } else {
        res.end('NOT Supported')
    }

})

//start the server
server.listen(PORT, () => {
    console.log(`Http Server is listening at ${PORT}`)
})

//attach server event: request event
server.on('request', (req, res) => {
    console.log('Request Recived on', `[${new Date().toISOString()}]`, "URL is", req.url, "method ", req.method)

})
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									HTTP, With FS Module
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const http = require('node:http')
const fs = require('node:fs')
const path = require('node:path')

const PORT = 3000

//create server
const server = http.createServer((req, res) => {
    const filePath = path.join(__dirname, '../index.html')
    fs.readFile(filePath, null, (err, data) => {
        if (err) {
            console.log(err)
            res.writeHead(500)
            return res.end('Error Loading File...')
        }
        res.writeHead(200, { 'Content-Type': 'text/html' })
        res.end(data)
    })
})
//start the server
server.listen(PORT, () => {
    console.log('Server running at http://localhost:3000')
})})

Streaming with files:
const http = require('node:http')
const fs = require('node:fs')
const path = require('node:path')

const PORT = 3000

//create server
const server = http.createServer((req, res) => {
    const filePath = path.join(__dirname, '../index.html')
    fs.access(filePath, fs.constants.F_OK, (err) => {
        if (err) {
            res.writeHead(404, { 'Content-Type': 'text/plain' })
            return res.end('The Requested file not found')
        }
        res.writeHead(200, { 'Content-Type': 'text/html' })
        //create stream
        const readStream = fs.createReadStream(filePath)
        //pipe
        readStream.pipe(res)

        readStream.on('error', (streamErr) => {
            console.log('Stream Error', streamErr)
            res.end('Streaming Error')
        })

    })

})
//start the server
server.listen(PORT, () => {
    console.log('Server running at http://localhost:3000')
})
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									   Building RestFull web services
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1.Resources
   Customer, Product, Item, Payment

2.API
   findAll,findBYId,update,Remove,filter

3.URL 
   Resources and apis must be identified by URL

4.APIs are mapped against HTTP verbs
  Read - GET
  Save  -POST
  update - PUT
  remove -  DELETE

Each Resource is identified by unique url

  /api/customer
  /api/products

Each Resource has collection of apis and which mapped against HTTP verbs

 findAll - GET

Having core node.js http module we cant build production ready webservices with minimum code, we need to write plenty of 										boiler plate code.

					Node.js team in the beginning started working on an abstraction called "framework"
			   							 "Express.js"