Hi Sergiu, On Mar 15, 2008, at 8:11 AM, Sergiu Dumitriu wrote:
> Hi, > > How do you feel about the next usage scenarios for the observation > component? > > > A. Simple observing of changes [snip] > B. Simple observing of actions [snip] > C. Precondition/Postcondition enforcing > The previous two use cases allow a simple ping that something has > already happened. (Actually, the listeners can also change the passed > document, as the actual object is sent.) But I'd like to be able to > write a listener that can say "this is not allowed, please stop this > action", or "these changes are not OK, don't save this document". > So, a > precondition can be that "/save/" cannot be performed between 6PM and > 7AM, which would be a needed feature in some companies, or that "/ > view/" > cannot be performed on the "SectionA" space from the IP addresses like > 192.168.2.*, which belongs to the SectionB users (these are action > events). And a postcondition can be that the XWiki.XWikiPreferences > can > only be updated by changing XWikiGlobalRights objects, other types of > changes can only be performed by a superadmin only, or that adding > some > content that looks like spam is not allowed (these are document > events). > > So, on top of the previous use cases, I'd like to add a "phase" to the > events, which indicates if the event is sent before or after the > change > (or we can just add new events), and a new type of exception thrown by > the listeners, which is not ignored. Right now, if a listener throws > an > exception, it is ignored. This exception, when received by the code > that > sends the notification, should stop the normal processing and display > "action not allowed" + ex.getMessage to the user. My first reaction is that I'm not really fan of this approach. The way I had planned to implement this in the V2.0 architecture is by either: 1) replacing existing component with a different implementation. This is when the current behavior need to be modified/replaced by another one. 2) depending on the component, introduce new component. For example the Action Manager in the new action component allows defining new Actions that can be inserted before or after existing actions (or even replace existing actions but that's 1)). To summarize, I would agree with your idea except that with components there's another way of doing it and I don't think we should have too many ways. If you think about how you'd implement your idea you'll end up creating a state machine component to which actions are hooked to. This is what the Action Manager component is meant to do, although for the moment I have resisted introducing a FSM since I wanted to see the exact need first and with 1) and 2) I thought we could already do quite a lot (not sure what we cannot do to be honest). > D. Rendering hooks > While working on the SkinExtensions and trying to write a better #toc > macro, I was faced with the problem that there's no way a plugin can > change the rendered content at the end. Yes, it can alter it line by > line, and in theory there is an endRenderingHook sent with the > content, > but that is actually buggy, as an empty string is sent instead of the > content, and the result is discarded. Still, even if fixed, this is > sent > only for *rendered* content, not *parsed* content. My initial idea was > to change the PluginInterface by adding two new methods that will be > called before and after the content was generated, but that is a bad > idea, since the PluginInterface is already too big and has too many > types of methods. And since the new rendering component is not yet > available, I thought that we can also use events for this. > > So, instead of writing new methods in the PluginInterface, we can add > other type of events, which gets sent in the parsing/rendering > process. > That way, we don't need to have a plugin that implements all these > methods, and adding a new feature will require just sending a new type > of event, instead of changing an interface (which is dangerous). > > The source would be an object holding the string, which can be > modified > by the listeners. Other information could be the content document, if > there is one, the rendering/parsing context, anything else? Again my first reaction is that I'm no fan... :) The reason is that I have this implemented in the new rendering component. First any piece of code can get the parsed content of a text having any kind of syntax (Element Blocks or DOM). Second, it's possible to write any Macro that will manipulate this DOM and make any modification to it. This is how the Toc Macro is going to be rewritten actually. However you're right in that right now all I have planned for are Macros and these are triggered by the macro syntax in the text to parse/rendering. So it's a good idea to add a small FSM in the rendering component since we already need an order in the macro execution but also to add the ability to register macros to be executed regardless of whether they appear in the parsed text or not. > E. Other generic events > Like FlushCacheEvent, StartupEvent, ShutdownEvent, VirtualInitEvent, > VirtualShutdownEvent (sent when a wiki is deleted by the > WikiManagerEvent), Application[Added/Enabled/Disabled/Removed]Event > (sent by the ApplicationManager), Space[Added/Removed]Event (sent by > the > SpaceManagerPlugin), etc. +1 to those. Thanks -Vincent _______________________________________________ devs mailing list [email protected] http://lists.xwiki.org/mailman/listinfo/devs
