sessions, continuation keys, restful urls and component state
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Hi,
I've noticed a problem with cookies enabled and Pier. The problem arises when you browse to a URL without the continuation key, which causes a new instance of the application to be created ie PRPierFrame new. You can see the issue with the following single page WACounter Pier app:
| rootPage | rootPage := (PRPage named: 'rootPage') contents: '+counter+'; yourself.
rootPage localEnvironment: ((PRComponent named: 'contents') componentClass: PRContentsWidget; yourself). rootPage addChild: ((PRComponent named: 'counter') componentClass: WACounter; yourself).
PRKernel reset. (PRPierFrame registerAsApplication: 'pier' kernel: (PRKernel named: 'testKernel' root: rootPage)) preferenceAt: #useCookies put: true.
Browse to localhost:xxxx/pier you should see the familiar counter component. Increment the counter a few times. Now open a new tab, browse to localhost:xxxx/pier and decrement the counter a couple of times. Return to the first tab and try incrementing again. The counter will increment from the value of the second counter.
I tested the same code snippet in Pier 1 on Seaside 2.8 and the component increments from the value on the page ie it behaves as you'd expect a Seaside component to behave. The problem appears to arise in:
WASession>>#handleFiltered: aRequestContext | key continuation | key := aRequestContext request fields at: self actionField ifAbsent: [ ^ self start ]. continuation := continuations at: key ifAbsent: [ ^ self unknownRequest ]. continuation value if there is no continuation key, #start is called on the session, which creates a new root component. I have a fix, though it's in such a core part of Seaside, I'm hesitant to suggest it. If I change WARenderLoopMain>>#start from:
start | root | root := self createRoot. self session properties at: #presenter put: root. self prepareRoot: root. ((self application preferenceAt: #renderPhaseContinuationClass) new) captureAndInvoke to: start | root | root := self session presenter. root ifNil: [ root := self createRoot. self session properties at: #presenter put: root. self prepareRoot: root ]. ((self application preferenceAt: #renderPhaseContinuationClass) new) captureAndInvoke ...the root component is recovered from the session (if present) and no longer created.
Is this a valid fix? Thanks Nick _______________________________________________ Magritte, Pier and Related Tools ... https://www.iam.unibe.ch/mailman/listinfo/smallwiki |
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>From Julian:
I'm sure if this is relevant anymore but it's what I was writing
before we talked. Feel free to forward to the list if you think it's relevant/helpful/interesting/whatever. Julian --------------- I'm not sure it's a good fix in the general case. If you don't have a continuation key, you shouldn't (by definition) have any existing (backtracked) state. Relying on the root presenter currently in the Session is problematic since that value is backtracked for each request; you'll simply get whichever root happened to be used by whatever request was last handled by that session. If you don't happen to be ever changing the root, then it may well be what you want, but it's not right in the general case. Incidentally, this also touches on the flaw I was discussing the other week with our snapshots: because we have no continuation key, we really ought to nil out any backtracked data before processing the request (at least that way we have a consistent state while handling the request). We don't run into the problem with the root presenter because #start reinitializes it, but for other backtracked state, you'd just get random stuff in there based on the last-handled request. A more appropriate general fix (at least in this case) could be to take the last-used continuation and apply its state before handling a request with no _k. However, we don't always know the last-used (depending on the caching mechanism in place) and I'm not convinced that is actually always what people want. I still feel pretty confident that the "right" semantics of an Application/Session request with no _k is to start a new main/render-loop. On 18 May 2011 15:33, Nick Ager <[hidden email]> wrote: Hi, _______________________________________________ Magritte, Pier and Related Tools ... https://www.iam.unibe.ch/mailman/listinfo/smallwiki |
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