Expired Ajax Link Referencing Invalid PageID and Valid RenderCount Will Result
In a ComponentNotFound Exception When The CallBack References A Component Built
During A Page's onRender() Method - like GridView Components
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Key: WICKET-4229
URL: https://issues.apache.org/jira/browse/WICKET-4229
Project: Wicket
Issue Type: Bug
Components: wicket
Affects Versions: 1.5.3
Environment: Wicket 1.5.3
Reporter: gotama
While Wicket 1.5.3 addresses a situation where an ajax callback references a
not yet existing component because the Session may have expired and the PageID
referenced in the ajax callback link is invalid and returns a null page - and
in turn, creates a new page via reflection - this will only work for accessing
components which are created in the constructor of that newly created page, not
the components created during the page's onRender() method, such as when
GridView components are built by the page, this will result in a
ComponentNotFound Exception.
(example Wicket Ajax CallBack)
?11-3.IBehaviorListener.0-MyPanelNum1-MyPanelWithinAPanel-rows-19-cols-20-MyGridViewItemPanel-myContainerPanelCreatedDuringOnRender
In the above Wicket rendered ajax link, the "11" refers to the PageID. The "3"
is the RenderCount. The "rows" number and the "cols" number refers to
components built by a GridView. GridView components are created during
onRender(), not during the constructor. As such, if the Page is instantiated
via reflection, the constructor is executed, not the onRender(), and therefore
stepping through the Wicket 1.5.3 source code shows that in the above
ComponentPath of
"MyPanelNum1-MyPanelWithinAPanel-rows-19-cols-20-MyGridViewItemPanel-myContainerPanelCreatedDuringOnRender",
this ComponentPath becomes invalid at "MyPanelNum1-MyPanelWithinAPanel-rows"
(it has no child componets including "19") - this shows that while in fact the
Wicket 1.5.3 fix to patch the situation where the PageID of "11" is invalid,
and the isPageInstanceFresh() is true (the page was just created - as a new
page is created if the PageID is a page store cache hit miss) and a new
RenderPageRequestHandler is scheduled and the request recovers, the subsequent
situation where this fix created that page, yet did not render it and its
components, later becomes a cache hit and fails to find the components which
are suppose to be created during onRender() and in turn missing during
getComponent().
Further complicating this scenario is that if in fact the referenced
RenderCount ("3" in this example) in the ajax callback is in fact invalid, this
situation is not reproducible because a stale page exception is thrown instead.
However, in the edge case where the ajax callback is invalid due to the Session
invalidating (a valid PageID may then now be 1 perhaps, not 11) and the
RenderCount in the callback matches the stored page's RenderCount (just a
matter of time for the RenderCounts to match), this will result in the
ComponentNotFound exception - essentially a ticking RuntimeException to blow up
the page, while tough to reproduce, is in fact valid and will occur.
As a method of attempting to reproduce this issue, one can hi-jack the creation
of this Wicket CallBack URL and induce this situation as follows:
// int randomPageID = (int) (10 * Math.random());
int randomPageID = 5;
String myCallBackURL = myComponent.getCallbackUrl().toString();
myCallBackURL = "?" + randomPageID + "-0" +
myCallBackURL.substring(myCallBackURL.indexOf("."));
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