What is HTTP?

HTTP stands for (HyperText Transfer Protocol). WWW is a communication between web clients and servers. Communication between client computers and web servers is done by sending HTTP requests and receiving HTTP Responses. Servers are most often computers in the cloud. The World Wide Web is about communication between web clients and web servers. Clients are often browsers (Chrome, Edge, Safari), but they can be any type of program or device.

HTTP Request and Response

1. A client a browser sends an HTTP request to the web.
2. A web server receives the request.
3. The server runs an application to process the request.
4. The server returns an HTTP response (output) to the browser.
5. The client (the browser) receives the response.

Request Method

The request method indicates the method to be performed on the resource identified by the given Request-URI.

Method	Description
GET	GET is used to retrieve information from the given server using a given URI.
HEAD	HEAD is the Same as GET, but it transfers the status in line, and the header section only.
POST	POST is used for the request to send data to the server. Such as associate/ customer information, document upload, and much more. using HTML forms.
PUT	PUT is used for Replaces all the current representations of the data resource with the uploaded content.
DELETE	DELETE is used for Removes all the current representations of the data resource given by URI.
CONNECT	CONNECT is used for establishes a tunnel to the server identified by a given URI.
OPTIONS	OPTIONS is used for describing the communication options for the data resource.
TRACE	TRACE is used for a message loop backtest along with the path to the data resource.

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Tripod: https://amzn.to/33nZ5Qx

Camera: https://amzn.to/35C3KB4

Laptop: https://amzn.to/3bZcMJS

LED Tubelight: https://amzn.to/2ZwAF6C

Web Hosting: (1) https://www.siteground.com/index.htm?afcode=c434ad624e8607aa53ca1d322ef7ecdb

(2) https://www.hostg.xyz/aff_c?offer_id=6&aff_id=49097

(3) https://bluehost.sjv.io/joqOZ

Request-URI

Request-URI is a Uniform Resource Identifier and identifies the resource upon which to apply the request.

Request-URI = "*" | absoluteURI | abs_path | authority

S.N.	Method and Description
1	The asterisk * is used when an HTTP request does not apply to a particular resource, but to the server itself, and is only allowed when the method used does not necessarily apply to a resource. Such as: OPTIONS * HTTP/1.1
2	The absoluteURI is used when an HTTP request is being made to a proxy. The proxy is requested to forward the request or service from a valid cache and return the response. Such as: GET http://www.w3.org/pub/WWW/TitleofProject.html HTTP/1.1
3	The most common form of Request-URI is used to identify a resource on an origin server or gateway. Such as: a client wishing to retrieve a resource directly from the origin server would create a TCP connection to port 80 of the host "www.w3.org" and send the following lines: GET /pub/WWW/TitleofProject.html HTTP/1.1 Host: www.w3.org Note:- Absolute path cannot be empty; if none is present in the original URI, it MUST be given as "/" (the server root).

Examples of Request Message

HTTP request to fetch wctutorial.htm page from the web server running on wctutorial.com

GET /wctutorial.htm HTTP/1.1 User-Agent: Mozilla/4.0 (compatible; MSIE5.01; Windows NT) Host: www.wctutorial.com Accept-Language: en-us Accept-Encoding: gzip, deflate Connection: Keep-Alive

The connection is a general-header, and the rest of the headers are request headers.

POST /cgi-bin/process.cgi HTTP/1.1 User-Agent: Mozilla/4.0 (compatible; MSIE5.01; Windows NT) Host: www.wctutorial.com Content-Type: application/x-www-form-urlencoded Content-Length: <b>length</b> Accept-Language: en-us Accept-Encoding: gzip, deflate Connection: Keep-Alive licenseID=string&content=string&/paramsXML=string

Given URL  /cgi-bin/process.cgi will be used to process the passed data and accordingly, a response will be returned. content-type tells the server that the passed data is a simple web form data and length will be the actual length of the data put in the message body.

POST /cgi-bin/process.cgi HTTP/1.1 User-Agent: Mozilla/4.0 (compatible; MSIE5.01; Windows NT) Host: www.wctutorial.com Content-Type: text/xml; charset=utf-8 Content-Length: length Accept-Language: en-us Accept-Encoding: gzip, deflate Connection: Keep-Alive <?xml version="1.0" encoding="utf-8"?> <string xmlns="http://clearforest.com/">string</string>

Examples of Response Message

HTTP response for a request to fetch the hello.htm page from the web server running on tutorialspoint.com

HTTP/1.1 200 OK Date: Mon, 28 aug 2020 11:40:55 GMT Server: Apache/2.2.17 (Win64) Last-Modified: Wed, 22 sep 2020 20:17:57 GMT Content-Length: 88 Content-Type: text/html Connection: Closed

<html> <body> <h1>wctutorial.com, Coding Tutorial</h1> </body> </html>

When shows an HTTP response message displaying error condition when the web server could not find the requested page:

HTTP/1.1 404 Not Found Date: Mon, 28 sep 2020 10:36:20 GMT Server: Apache/2.2.14 (Win64) Content-Length: 230 Connection: Closed Content-Type: text/html; charset=iso-8859-1

<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"> <html> <head> <title>404 Not Found</title> </head> <body> <h1>URL Not Found</h1> <p>You requested URL /t.html was not found on the server.</p> </body> </html>

HTTP response message showing error condition when the webserver encountered a wrong HTTP version in the given HTTP request:

HTTP/1.1 400 Bad Request Date: Mon, 27 sep 2020 10:36:20 GMT Server: Apache/2.2.14 (Win64) Content-Length: 230 Content-Type: text/html; charset=iso-8859-1 Connection: Closed

<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"> <html> <head> <title>400 Bad URL Request</title> </head> <body> <h1>Bad URL Request</h1> <p>Your browser sent a request to the server could not load.</p> <p>The request line contained invalid characters following the protocol string.</p> </body> </html>

The HTTP Request Circle

1. The browser requests an HTML page. The server returns an HTML file.
2. The browser requests a style sheet. The server returns a CSS file.
3. The browser requests a JPG image. The server returns a JPG file.
4. The browser requests JavaScript code. The server returns a JS file
5. The browser requests data. The server returns data (in XML or JSON).

XHR - XML Http Request

• XHR is used for a JavaScript object that is used to data transfer between a web browser and a web server.
• XHR is used for request and receive data for the purpose of modifying a web page.

XHR Object is a Website Developers Dream because:

• Update a web page without reloading the page
• Send data to a server - in the background
• Receive data from a server - after the page has loaded
• Request data from a server - after the page has loaded