---
title: '03 NodeJS HTTP Server'
disqus: hackmd
---
03 NodeJS HTTP Server
===
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## Table of Contents
[TOC]
HTTP
---
- most popular app layer protocol used for communicating between client and server
- provides standardised way for comps to communicate with ea other
- specifies how client's request data will be constructed and set to server
- and how server responds to these reqs
- to comm with server, client must indicate HTTP action like
- GET
- POST
- PUT
- DELETE
- TRACE
- OPTIONS
- CONNECT
- in http protocol, req msg typically carries info like action and target URL in req msg
- when server receives req, server will
- retrieve data from its data storage
- package data in appropriate format
- send data back to client
- data is typically in html/css/js or JSON format for resful web services
### HTTP Request Format
### HTTP Response Format
- 3 parts
- status line
- Eg. 200
- headers
- Eg. data format encoding of returned msg data
- actual body of msg
- Eg. html code for index.html
- OR JSON format
### Common HTTP Response Codes
Javascript Object Notation (JSON)
---
### Features
- lightweight
- language independent
- easy to read and write
- text based, human readable data exchange format
- uses key pairs describing the obj
```javascript=
var student1={
"name":"John",
"age":"18",
"course":"DIT"
};
// directly use json obj by calling name of var and prop
console.log(student1.name);
console.log(student1.age);
console.log(student1.course);
// convert js obj to json, use stringify
var jsonStudent=JSON.stringify(jsStudent);
```
1st Node Server App
---
- js modules built into nodejs
- http module
- provides high performing foundation for http stack
- path module
- provides resolving of full paths, check of file paths etc.
- file module
- provides file reading, checking purposes
### HTTP Modules
- http module supports `createServer` function which takes in callback as a param
- callback has 2 params, request and response
- req is req msg that comes from client to process and extract info from
- resp is resp msg we construct with header values and body of http resp msg
### Path Module
- enables us to exmine whether file exists/more details abt file eg. file extension
- has func for us to convert relative path to absolute
### Creating HTTP Server
- create `public/` folder which will contain all static files to be served to client
- `npm init`
- create `server.js` at root
```javascript=
const http = require('http');
const fs = require('fs');
const path = require('path');
const hostname = 'localhost';
const port = 3000;
const server = http.createServer((req, res) => {
console.log('Request for page ' + req.url + ' using ' + req.method + ‘method’);
if (req.method == 'GET') {
var fileUrl=req.url;
if (req.url == '/') //default file is index.html
fileUrl = '/index.html';
var filePath = path.resolve('./public'+fileUrl);
fs.exists(filePath, (exists) => {
if (!exists) {
fileUrl='/error.html';
filePath = path.resolve('./public'+fileUrl);
}else{
res.statusCode = 200;
res.setHeader('Content-Type', 'text/html');
}
fs.createReadStream(filePath).pipe(res);
});
}
else {
fileUrl='/error.html';
filePath = path.resolve('./public'+fileUrl);
fs.createReadStream(filePath).pipe(res);
}
});
server.listen(port, hostname, () => {
console.log(`Server started and accessible via http://${hostname}:${port}/`);
});
```
```bash
# to run server
node server.js
# or use nodemon
```
#### Creating Static html Files
```htmlembedded=
<!-- index.html -->
<html>
<body>
Welcome to Node JS!!
</body>
</html>
<!-- error.html -->
<html>
<body>
File does not exist or web server does not support post method!
</body>
</html>
```
###### tags: `BED` `DISM` `School` `Notes`
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