What does it mean for the web and the HTTP protocol to be stateless?

Question

What does it mean for the web and the HTTP protocol to be stateless? Why are they stateless?

Astro

Answer 1

Stateless meaning:

It does not keep track of configuration settings, transaction information or any other data for the next session. When a program "does not maintain state" (is stateless) or when the infrastructure of a system prevents a program from maintaining state, it cannot take information about the last session into the next, such as settings the user chose or conditions that arose during processing.

HTTP:

The HTTP protocol, which is the communications vehicle for Web transactions, is stateless. After a Web page is delivered to the user, the connection is closed. Counter measures, such as the use of cookies, have been developed to maintain the state of a user moving from page to page on a Web site.

OR it can be simple web definition:

A protocol is stateless if there is no relation between subsequent request-response pairs. The server can handle each request uniquely and does not have to keep a session state for the client.

Fein

Answer 2

When you write a rich client application, you can store state arbitrarily at your convenience. In the web, the client is not obligated to pass any information that you can use to retain permanent information, so your web server is potentially in a permanent state of amnesia. Every time your client asks for another page, you can only use clues or hints that it's the same person talking to you.

To simulate state, you have to use cookies (or certain authentication mechanisms), combined with server-side mechanisms for associating those cookies with actual per-user data. You also can't reliably trust the cookie, so you have to make tradeoffs to determine how reliable that association is. Also, a side effect is that you never really know when an user is "done" with your session, so you can't rely on return trips to do things like close out database connections. Essentially, you have to make all important decisions about an interaction on each request, then assume the user is never coming back.

Vortex

Answer 3

One way to understand HTTP and problems around sharing state between client and server is by "tampering" data from the communication between web browser and web site.

This firefox plugin is just great for doing this.

You can see that by sending a request from your browser, your client only says something about some basic set of parameters of your request.
That is not enough for the server to know what happened in the past (= state) on the client side.

Some way to pass the browser some information on your state is by using cookies, that is just some information in variables that gets attached to your request as you can also see with the tamperdata plugin.

Fdic

Answer 4

Stateful and stateless are adjectives that describe whether a computer or computer program is designed to note and remember one or more preceding events in a given sequence of interactions with a user, another computer or program, a device, or other outside element. Stateful means the computer or program keeps track of the state of interaction, usually by setting values in a storage field designated for that purpose. Stateless means there is no record of previous interactions and each interaction request has to be handled based entirely on information that comes with it. Stateful and stateless are derived from the usage of state as a set of conditions at a moment in time. (Computers are inherently stateful in operation, so these terms are used in the context of a particular set of interactions, not of how computers work in general.)

The Internet's basic protocol, the Internet Protocol (IP), is an example of a stateless interaction. Each packet travels entirely on its own without reference to any other packet. When you request a Web page from a Web site, the request travels in one or more packets, each independent of the other as far as the Internet Protocol program itself is concerned. (The upper layer Transmission Control Protocol - TCP - does relate packets to each other, but uses the information within the packet rather than some external information to do this.) The term connectionless is also used to describe communication in which a connection is made and terminated for each message that is sent. IP is connectionless as well as stateless.

The Web's Hypertext Transfer Protocol (HTTP), an application layer above TCP/IP, is also stateless. Each request from a user for a Web page or URL results in the requested pages being served, but without the Web (HTTP) server remembering the request later. In other words, there is no recorded continuity. Each communication is discrete and unrelated to those that precede or follow. In order to have stateful communication, a site developer must furnish a special program that the server can call that can record and retrieve state information. Web browsers such as Netscape Explorer and Microsoft Internet Explorer provide an area in their subdirectories where state information can be stored and accessed. The area and the information that Web browsers and server applications put in this area is called a cookie.

In formal protocol specifications, a finite state machine is an abstract description of how a stateful system works that describes the action that follows each possible state.

The Internet (including the World Wide Web) can be thought of as a stateless system or machine. Most computers, human beings, and elephants are stateful.

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