[xwiki-devs] [proposal] Extending the PluginInterface with beginParsing and endParsing

Hi devs, There's a blocker issue preventing the finalization of the SkinExtensions implementation (http://dev.xwiki.org/xwiki/bin/view/Design/SkinExtensions). To explain a bit what the problem is: - skin extensions are javascript or css pseudo-files, which are included ("linked to") in generated XHTML pages - a skin extension is "requested" by some code using, for example, $xwiki.jsx.use("XWiki.RightsManagement"); while generating the content, the jsx plugin builds a list of used extensions - after the whole page is parsed, the generated content must also include the links to the needed extensions The problem is that these links must be placed in the head part of the HTML, which is generated before the body, where the extensions are actually pulled in. This means that sometime after the parsing is done, and before sending the response to the client, some code must insert those links in the response. My dilemma was where... One solution was to use the new notification mechanism to send some parsing events that would allow listeners to change the content when the parsing was done. Vincent opposed, so I dropped the idea. Another solution would have been to write a Filter that would intercept the response and insert the links, but the problem is that the filter is isolated, without access to the context, the xwiki object, or the jsx/ssx plugins. The component manager _could_ be a solution, but for the moment it still needs the context, which is not available. Another solution is to just modify Utils.parseTemplate, but this is not elegant. It is more like a patchy workaround that would increase the messiness of the code even more, so I'm against it. Another solution could have been the existing plugin.endRendering, but it is called many times during a request, and only when rendering with Radeox, not when parsing, so it would not be called for the whole template (so the html header would be left out). The best solution I could come so far is to add two methods to the PluginInterface, beginParsing and endParsing, called before and after parsing the resulting template. This is generic enough, as it can be used by other plugins, there's no code targeting exactly the jsx and ssx plugins, it is extensible enough to allow other type of extensions to be added (link extensions?), and except the StrutsActions which cannot be added dynamically (at least not yet) it allows the SkinExtensions implementation to be completely pluggable. So, beginParsing will be called in com.xpn.xwiki.web.Utils.parseTemplate before parsing the template that generates the response, and it allows plugins to initialize some per-request variables. endParsing will be called in the same method, right after generating the response, and will allow plugins to change the resulting response or cleanup resources. The signature of these methods would be: public void beginParsing(XWikiContext context) public String endParsing(String content, XWikiContext context) endParsing could also be used by the FileUploadPlugin to cleanup the resources (see http://fisheye2.cenqua.com/browse/xwiki/xwiki-platform/core/trunk/xwiki-cor… ). Now, the thing that I don't like is that this changes a public interface, used by many plugins. It is good that most plugins extend DefaultPlugin, as there is only one place where these methods must be implemented, so the impact on existing plugins should be minimal. I also don't like that the plugin interface contains so many methods, but that is an acknowledged problem and it will be solved when everything would be a component. Until then, these two methods seem to me like they should already be there, given the other rendering-related methods. Any other (better) solutions I didn't see? Objections to this change? Thanks, -- Sergiu Dumitriu http://purl.org/net/sergiu/