HTTP - Hypertext Transfer Protocol

Tap to Read ➤ Buzzle Staff May 13, 2019

Hypertext Transfer Protocol is an application protocol which is the basis of communication for accessing the Internet over the World Wide Web.

A protocol is a set of rules and procedures that computers must follow in order to receive and transmit messages. Most common protocols in use today are HTTP, SMTP, FTP, IMAP, POP3, etc.

Background

World Wide Web Consortium (W3C) and the Internet Engineering Task Force (IETF) coordinated HTTP's development. Its initial purpose was to provide a way to retrieve and publish HTML documents. It comes under application layer (Layer 5) of the TCP/IP model.

Its clients, known as user agents, make requests to its protocol and the concerned server handles these requests. Typical clients are web browsers, search engine spiders, web enabled applications, etc.

Definition

HTTP is a protocol which contains a set of rules and procedures used to communicate over the World Wide Web.

Clients & Servers Communication

HTTP clients, such as web browsers, connect to its server that generally runs on port 80. This server in turn, interprets the request, processes it, and responds to the client, if needed. Typical contents of a request message are: Request line Headers Empty line Optional message body

Client Request Methods

HEAD - This method asks information from the server just as the GET method would do. The basic difference is that HEAD method doesn't contain a response body. GET - This method requests a resource from the web server. GET method is one of the most commonly used methods on the web today.

POST - The POST method submits data to the web server for processing, experienced while submitting web forms. PUT - Uploads a specified resource to the server. DELETE - Deletes the specified resource from the web server. TRACE - This method echoes the received request so the client can see what intermediate servers are adding or changing in the request.

OPTIONS - This method helps determine the server functionality like determining which method the web server supports. CONNECT - This method converts the request connection to a transparent TCP/IP tunnel. This helps in facilitating Secure Socket Layer (SSL) communication through the unencrypted HTTP proxy.

Response Status Codes

Response is originated at the web server; it means it is a reply, result or an answer to the client request. Here is a list of web server response codes - 1xx - Informational 100 - Continue 101 - Switching protocols 102 - Processing (WebDAV)

2xx - Success 200 - Ok 201 - Created 202 - Accepted 203 - Non-Authoritative Information 204 - No Content 205 - Reset Content 206 - Partial Content 207 - Multi-Status (WebDAV )

3xx - Redirection 300 - Multiple Choices 301 - Moved Permanently 302 - Not found 303 - See Other 304 - Not Modified 305 - Use Proxy 306 - Switch Proxy 307 - Temporary Redirect

4xx - Client-side Error 400 - Bad Request 401 - Unauthorized 402 - Payment Required 403 - Forbidden 404 - Not Found 405 - Method Not Allowed 406 - Not Acceptable 407 - Proxy Authentication Required 408 - Request Timeout 409 - Conflict 410 - Gone 411 - Length Required 412 - Precondition Failed

413 - Request Entity Too Large 414 - Request-URI Too Long 415 - Unsupported Media Type 416 - Requested Range not satisfiable 417 - Expectation Failed 422 - Unprocessable Entity (WebDAV) 423 - Locked (WebDAV) 424 - Failed Dependency (WebDAV) 425 - Unordered Collection 426 - Upgrade Required 449 - Retry With

5xx - Server-side Error 500 - Internal Server Error 501 - Not Implemented 502 - Bad Gateway 503 - Service Unavailable 504 - Gateway Timeout 505 - HTTP Version Not Supported 506 - Variant Also Negotiates 507 - Insufficient Storage (WebDAV) 509 - Bandwidth Limit Exceeded 510 - Not Extended

Simple HTTP Communication Scenario

1. The client makes a connection and sends a request method to the web server.

2. The server processes the client's request, while the client waits for the server's response.

3. The web server responds with the status code and data (if available) and closes the connection.