HTTP (Hyper Text Transfer Protocol) is the most successful and popular application protocol of TCP/IP, the suite of protocols that powers the Internet. It is the driving force behind the World Wide Web, allowing web browsers like Chrome, Firefox, and Edge to communicate with remote servers that host web pages.

The development of HTTP can be traced back to 1989 when Tim Berners-Lee worked at CERN, the European Center of Nuclear Research. The initial goal of HTTP was to facilitate the exchange and interlinking of research papers among scientists. At that time, the internet’s main applications consisted of FTP, email, and Usenet. However, with the release of Mosaic, the first graphical web browser in 1993, the Web quickly gained traction and became the “killer app” of the Internet.

While the Web and its ecosystem have evolved significantly over time, the basics of HTTP remain the same. In addition to powering web pages, HTTP is now used for accessing REST APIs, which allow for programmatically accessing services over the Internet.

The HTTP protocol underwent a minor revision in 1997 with HTTP/1.1, and its successor, HTTP/2, was standardized in 2015 and has been implemented by major web servers globally. However, HTTP is considered insecure when not served over an encrypted connection. To address this, there has been a growing push towards using HTTPS, which is HTTP served over TLS.

HTML documents are at the core of HTTP. Web browsers use HTTP to transfer hypertext files, typically written in HTML, over the network. These files are then rendered graphically by the browser with interactive links. Hyperlinks within documents allow users to navigate to other documents by specifying the protocol, server address, and document path.

HTTP requests are composed of the URL, the HTTP method (also known as the verb), and a set of HTTP headers. The URL specifies the resource being requested, while the HTTP method defines the action to be performed on that resource. Common HTTP methods include GET, POST, HEAD, PUT, DELETE, OPTIONS, and TRACE.

GET is the most frequently used method and is used when typing a URL in the browser address bar or clicking a link. It retrieves the requested resource as a response. HEAD is similar to GET but only returns the headers without the response body. POST is used to send data to the server, often utilized in forms and interacting with REST APIs. PUT creates a resource at a specific URL, while DELETE is used to request resource deletion. OPTIONS retrieves the list of allowed HTTP methods for a specific URL, and TRACE returns the received request back to the client for debugging purposes.

HTTP communication between clients and servers is stateless, meaning servers do not retain information about the client’s past requests. Each request is treated independently. This statelessness allows web servers to handle concurrent requests efficiently. Additionally, HTTP communication is lightweight, resulting in minimal overhead compared to other protocols.

To illustrate the HTTP communication process, a message is composed of an initial line containing the HTTP method, resource relative path, and protocol version. HTTP request headers follow this line, providing specific information to the server. The telnet command-line tool can be used to manually send HTTP requests to a server and receive responses.

In addition to HTML files, HTTP servers can serve other types of resources such as CSS, JS, SVG, PNG, and JPG files. The client interprets these resources based on their file types, making it possible for web pages to display properly.

In conclusion, HTTP is a crucial protocol that powers the Web and allows for seamless communication between clients and servers. Its simplicity, efficiency, and flexibility have contributed to its widespread adoption.