HTTP (Hypertext Transfer Protocol)

HTTP (Hypertext Transfer Protocol) is the foundational protocol used for transmitting data over the web. It defines the rules for formatting and transferring web page data between clients (typically web browsers) and servers. Most important characteristics of HTTP:

1. Stateless Protocol. HTTP is stateless, meaning each request from a client to server is treated as independent; servers do not retain session information between requests.
2. Client-Server Model. In this model, clients send requests to servers to retrieve web resources, and servers respond with the requested information.
3. Request/Response. Communication via HTTP involves a series of request messages from clients and corresponding response messages from servers. Requests and responses include headers for passing additional information and, optionally, body content.
4. Methods. HTTP includes several methods such as GET (to retrieve resources), POST (to submit data to a server), and PUT (to update or replace resources).
5. Status Codes. Servers reply with status codes in responses to indicate the outcome of the requested operations, such as '200 OK' for successful requests, '404 Not Found' for invalid URLs, and '500 Internal Server Error' for server issues.

Versions

Over the years, HTTP has evolved through several versions, each enhancing the protocol to improve performance, security, and functionality:

HTTP/0.9

Introduced in 1991, this was the first version of HTTP, extremely simple and limited to handling only GET requests for fetching HTML pages without HTTP headers.

HTTP/1.0 (RFC 1945)

Formalized in 1996, this version introduced the concept of HTTP headers, enabling the transmission of metadata about the request or the response. HTTP/1.0 supports various methods like GET, POST, and HEAD, and status codes to indicate different responses from the server.

HTTP/1.1 (RFC 2616, later updated by RFCs 7230-7235)

Released in 1997 and updated in 1999, HTTP/1.1 is a major revision that introduced persistent connections, chunked transfers, and additional cache control mechanisms. It significantly improved the efficiency of the protocol by allowing multiple requests and responses over a single connection.

HTTP/2 (RFC 7540)

Standardized in 2015, HTTP/2 introduced a new binary framing layer that allows for multiplexing multiple requests over a single connection without blocking (a significant performance improvement over HTTP/1.x). It supports stream prioritization and server push capabilities, where servers can proactively send resources to the client.

HTTP/3

Currently in the process of being standardized, HTTP/3 builds upon HTTP/2 and introduces QUIC as a transport layer protocol instead of TCP. QUIC supports multiplexed streams over a single connection, similar to HTTP/2, but reduces connection and transport latency through improved congestion control and by largely eliminating the TCP and TLS handshake delays.

In overall, HTTP is crucial for the operation of the World Wide Web, enabling the fetching of web resources and the navigation between web pages through hyperlinks. It serves as the backbone for data communication on the internet, underpinning many other protocols and technologies in network communication.