HTTP - Overview

The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information systems. This is the foundation for data communication for the World Wide Web (i.e. internet) since 1990. HTTP is a generic and stateless protocol which can be used for other purposes as well using extensions of its request methods, error codes, and headers.

HTTP - Parameters

This chapter is going to list down few of the important HTTP Protocol Parameters and their syntax the way they are used in the communication. For example, format for date, format of URL, etc. This will help you in constructing your request and response messages while writing HTTP client or server programs.

HTTP - Messages

HTTP is based on the client-server architecture model and a stateless request/response protocol that operates by exchanging messages across a reliable TCP/IP connection.
An HTTP "client" is a program (Web browser or any other client) that establishes a connection to a server for the purpose of sending one or more HTTP request messages.

HTTP - Requests

An HTTP client sends an HTTP request to a server in the form of a request message which includes following format:

A Request-line
Zero or more header (General|Request|Entity) fields followed by CRLF

HTTP - Responses

After receiving and interpreting a request message, a server responds with an HTTP response message:

A Status-line
Zero or more header (General|Response|Entity) fields followed by CRLF
An empty line (i.e., a line with nothing preceding the CRLF) 
indicating the end of the header fields

HTTP - Methods

The set of common methods for HTTP/1.1 is defined below and this set can be expanded based on requirements. These method names are case sensitive and they must be used in uppercase.

HTTP - Status Codes

The Status-Code element in a server response, is a 3-digit integer where the first digit of the Status-Code defines the class of response and the last two digits do not have any categorization role. There are 5 values for the first digit:

HTTP - Header Fields

HTTP header fields provide required information about the request or response, or about the object sent in the message body. There are four types of HTTP message headers:

• General-header: These header fields have general applicability for both request and response messages.
  

HTTP - Caching

HTTP is typically used for distributed information systems, where performance can be improved by the use of response caches. The HTTP/1.1 protocol includes a number of elements intended to make caching work.
The goal of caching in HTTP/1.1 is to eliminate the need to send requests in many cases, and to eliminate the need to send full responses in many other cases.

HTTP - URL Encoding

HTTP URLs can only be sent over the Internet using the ASCII character-set, which often contain characters outside the ASCII set. So these unsafe characters must be replaced with a % followed by two hexadecimal digits.

HTTP - Security

HTTP is used for communications over the internet, so application developers, information providers, and users should be aware of the security limitations in HTTP/1.1. This discussion does not include definitive solutions to the problems mentioned here but it does make some suggestions for reducing security risks.

HTTP - Message Examples

Example 1

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

Client request

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

HTTP - Quick Guide

The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information systems. This is the foundation for data communication for the World Wide Web (ie. internet) since 1990. HTTP is a generic and stateless protocol which can be used for other purposes as well using extension of its request methods, error codes and headers.

HTTP - Useful Resources

The following resources contain additional information on HTTP. Please use them to get more in-depth knowledge on this topic.