If REST applications are supposed to be stateless, how do you manage sessions?
I'm in need of some clarification. I've been reading about REST, and building RESTful applications. According to wikipedia, REST itself is defined to be Representational State Transfer. I therefore don't understand all this stateless gobbledeygook that everyone keeps spewing.
From wikipedia:
At any particular time, a client can either be in transition between application states or "at rest". A client in a rest state is able to interact with its user, but creates no load and consumes no per-client storage on the set of servers or on the network.
Are they just saying don't use session/application level data store???
I get that one goal of REST is to make URI access consistent and available, for instance, instead of hiding paging requests inside posts, making the page number of a request a part of the GET URI. Makes sense to me. But it seems like it is just going overboard saying that no per client data (session data) should ever be stored server side.
What if I had a queue of messages, and my user wanted to read the messages, but as he read them, wanted to block certain senders messages coming through for the duration of his session? Wouldn't it make sense to store this in a place on the server side, and have the server only send messages (or message ID's) that were not blocked by the user?
Do I really have to send the entire list of message senders to block each time I request the new message list? The message list pertinent to me wouldn't/shouldn't even be a publicly available resource in the first place..
Again, just trying to understand this. Someone please clarify.
Update:
I have found a stack overflow question that has an answer that doesn't quite get me all the way there: How to manage state in REST which says that the client state that is important should all be transferred on every request.... Ugg.. seems like a lot of overhead... Is this right??
The fundamental explanation is:
No client session state on the server.
By stateless it means that the server does not store any state about the client session on the server side.
The client session is stored on the client. The server is stateless means that every server can service any client at any time, there is no session affinity or sticky sessions. The relevant session information is stored on the client and passed to the server as needed.
That does not preclude other services that the web server talks to from maintaining state about business objects such as shopping carts, just not about the client's current application/session state.
The client's application state should never be stored on the server, but passed around from the client to every place that needs it.
That is where the ST in REST comes from, State Transfer. You transfer the state around instead of having the server store it. This is the only way to scale to millions of concurrent users. If for no other reason than because millions of sessions is millions of sessions.
The load of session management is amortized across all the clients, the clients store their session state and the servers can service many orders of magnitude or more clients in a stateless fashion.
Even for a service that you think will only need in the 10's of thousands of concurrent users, you still should make your service stateless. Tens of thousands is still tens of thousands and there will be time and space cost associated with it.
Stateless is how the HTTP protocol and the web in general was designed to operate and is an overall simpler implementation and you have a single code path instead of a bunch of server side logic to maintain a bunch of session state.
There are some very basic implementation principles:
These are principles not implementations, how you meet these principles may vary.
In summary, the five key principles are:
There is nothing about authentication or authorization in the REST dissertation.
Because there is nothing different from authenticating a request that is RESTful from one that is not. Authentication is irrelevant to the RESTful discussion.
Explaining how to create a stateless application for your particular requirements, is too-broad for StackOverflow.
Implementing Authentication and Authorization as it pertains to REST is even more so too-broad and various approaches to implementations are explained in great detail on the internet in general.
Comments asking for help/info on this will/should just be flagged as No Longer Needed .
Statelessness means that every HTTP request happens in complete isolation. When the client makes an HTTP request, it includes all information necessary for the server to fulfill that request. The server never relies on information from previous requests. If that information was important, the client would have sent it again in this request. Statelessness also brings new features. It's easier to distribute a stateless application across load-balanced servers. A stateless application is also easy to cache.
There are actually two kinds of state. Application State that lives on the client and Resource State that lives on the server.
A web service only needs to care about your application state when you're actually making a request. The rest of the time, it doesn't even know you exist. This means that whenever a client makes a request, it must include all the application states the server will need to process it.
Resource state is the same for every client, and its proper place is on the server. When you upload a picture to a server, you create a new resource: the new picture has its own URI and can be the target of future requests. You can fetch, modify, and delete this resource through HTTP.
Hope this helps differentiate what statelessness and various states mean.
Are they just saying don't use session/application level data store???
No. They aren't saying that in a trivial way.
They're saying do not define a "session". Don't login. Don't logout. Provide credentials with the request. Each request stands alone.
You still have data stores. You still have authentication and authorization. You just don't waste time establishing sessions and maintaining session state.
The point is that each request (a) stands completely alone and (b) can be trivially farmed out to a giant parallel server farm without any actual work. Apache or Squid can pass RESTful requests around blindly and successfully.
What if I had a queue of messages, and my user wanted to read the messages, but as he read them, wanted to block certain senders messages coming through for the duration of his session?
If the user wants a filter, then simply provide the filter on each request.
Wouldn't it make sense to ... have the server only send messages (or message ID's) that were not blocked by the user?
Yes. Provide the filter in the RESTful URI request.
Do I really have to send the entire list of message senders to block each time I request the new message list?
Yes. How big can this "list of message senders to block" be? A short list of PK's?
A GET request can be very large. If necessary, you can try a POST request even though it sounds like a kind of query.
链接地址: http://www.djcxy.com/p/1080.html