Why is it said that "HTTP is a stateless protocol"?
HTTP has HTTP Cookies. Cookies allow the server to track the user state, the number of connections, last connection, etc.
HTTP has persistent connections (Keep-Alive) where several requests can be sent from the same TCP Connection.
Even though multiple requests can be sent over the same HTTP connection, the server does not attach any special meaning to their arriving over the same socket. That is solely a performance thing, intended to minimize the time/bandwidth that'd otherwise be spent reestablishing a connection for each request.
As far as HTTP is concerned, they are all still separate requests and must contain enough information on their own to fulfill the request. That is the essence of "statelessness". Requests will not be associated with each other absent some shared info the server knows about, which in most cases is a session ID in a cookie.
From Wikipedia:
HTTP is a stateless protocol. A stateless protocol does not require the server to retain information or status about each user for the duration of multiple requests.
But some web applications may have to track the user's progress from page to page, for example when a web server is required to customize the content of a web page for a user. Solutions for these cases include:
- the use of HTTP cookies.
- server side sessions,
- hidden variables (when the current page contains a form), and
- URL-rewriting using URI-encoded parameters, e.g., /index.php?session_id=some_unique_session_code.
What makes the protocol stateless is that the server is not required to track state over multiple requests, not that it cannot do so if it wants to. This simplifies the contract between client and server, and in many cases (for instance serving up static data over a CDN) minimizes the amount of data that needs to be transferred. If servers were required to maintain the state of clients' visits the structure of issuing and responding to requests would be more complex. As it is, the simplicity of the model is one of its greatest features.
Because a stateless protocol does not require the server to retain session information or status about each communications partner for the duration of multiple requests.
HTTP is a stateless protocol, which means that the connection between the browser and the server is lost once the transaction ends.
HTTP is called as a stateless protocol because each request is executed independently, without any knowledge of the requests that were executed before it, which means once the transaction ends the connection between the browser and the server is also lost.
What makes the protocol stateless is that in its original design, HTTP is a relatively simple file transfer protocol:
- make a request for a file named by a URL,
- get the file in response,
- disconnect.
There was no relationship maintained between one connection and another, even from the same client. This simplifies the contract between client and server, and in many cases minimizes the amount of data that needs to be transferred.