What is HTTP? HTTP is the language web clients (a browser) and web servers use to communicate with each other. When computers communicate with each other they use a protocol, an agreed language or medium of communication. HTTP, Hypertext Transfer Protocol is the foundation protocol of the world-wide web (WWW) and is used specifically for applications which involve hypertext.
HTTP is not a protocol for transferring hypertext; rather it is a protocol for transmitting information with the efficiency necessary for making hypertext jumps. The information transferred using HTTP can be plain text, hypertext, audio, images, basically any Internet accessible information.
The purpose of HTTP is to efficiently transfer data requests & responses over the Internet. Current protocol version is HTTP1.1.
Why HTTP? HTTP is a transaction-oriented protocol. All HTTP transactions follow the same general format. A client sends a request to a web server and the server answers the request with a response.
Flexibility
HTTP makes use of TCP (Transfer Control Protocol) to establish a reliable connection between the web client and the server. However it is a 'stateless' protocol, which means that a new connection between the client and a server is established for each transaction, the transaction occurs and then the connection is terminated. Each specific HTTP client server transaction is executed independently, creating a new TCP connection for each HTTP transaction.
It is this stateless nature of HTTP which makes it particularly suited to the web. If you think about how a user browses the web, typically they will jump from website to website. Their browser makes a rapid sequence of requests from a number of distributed servers. The flexible stateless nature of HTTP facilitates this kind of communication.
As a web designer, understanding this stateless nature of HTTP is important when considering website design and websites which need to maintain user sessions, for example shopping carts, or profiled sessions where a user has 'logged in'.
Versatility
Another important feature of HTTP is its versatility. It can handle a range of file formats. When a client issues a request to a server it may include a prioritised list of formats it can handle. The server then responds with the appropriate format. This arrangement prevents the transmission of unnecessary information, making more effeicient use of the connection.
How does HTTP work?
HTTP is the language web clients and servers use to communicate with each other. Clients (web browsers) send requests to web servers for web elements such as web pages and images. Communications between clients and servers can be described as transactions. The client requests something from the server, and the server completes the transaction by responding to the client in some way.
The HTTP Transaction
HTTP transactions are always initiated by a client. For example, a user who inputs a URL makes a request to view a particular webpage. Remember in web site design, a web page may be composed of a number of different resource elements, a HTML file, image files, or audio files. The browser will request each of the resources required to view the completed web page in turn. Each time the client requests on of these resources and the server respond to this request a HTTP transaction occurs.
The Two Sides of the Story
The request message is sent by the browser to the server where the web page is hosted. In order to communicate this request to the server a TCP connection is first established. Once this is in place the HTTP request is transmitted, and is processed by the server. The server then sends a response message to the client and the transaction is complete. The web designer can use a knowledge of HTTP, to implement some controls on the requests made by clients. They can also use this knowledge to reply with meaningful server responses when the server has a problem with the client's request.
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