Why is it said that “HTTP is a stateless protocol”

问题:

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.

回答1:

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.

回答2:

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.

回答3:

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.

回答4:

If protocol HTTP is given as State full protocol,browser window uses single connection to communicate with web server for multiple request given to web application.this gives chance to browser window to engage the connections between browser window and web servers for long time and to keep them in idle state for long time.This may create the situation of reaching to maximum connections of web server even though most of the connections in clients are idle.

回答5:

HTTP is a connectionless and this is a direct result that HTTP is a stateless protocol. The server and client are aware of each other only during a current request. Afterwards, both of them forget about each other. Due to this nature of the protocol, neither the client nor the browser can retain information between different request across the web pages.

回答6:

HTTP is stateless. TCP is stateful. There is no so-called 'HTTP connection', but only 'HTTP request' and 'HTTP response'. We don't need anything to be maintained to make another 'HTTP request'. A connection header that is "keep-alive" means the TCP will be reused by the subsequent HTTP requests and responses, instead of disconnecting and re-establishing TCP connection all the time.

回答7:

Statelessness says that the possible states of the server are also resources, and should be given their own URIs. The client should not have to coax the server into a certain state to make it receptive to a certain request.

回答8:

It isn't stateless. HTTP is (usually) built on top of TCP, which is stateful. It maintains connection information, at the very least. If it were built on UDP things would be different.

Saying that HTTP is stateless is like saying that computer programs are electron-less because the computers that host them are what use the electrons. That's nonsense. In the same way, you can't completely separate HTTP from TCP.