Run Session Serialization debug tool after Vaadin processes the request

[mcollovati]

Currently, the serialization debug tool runs as a RequestHandler, installed by a VaadinServiceInitListener and for this reason, it is executed before any other internal handler. More specifically, it runs before the UIDL handler, so the outcomes of the tool are referred to the previous request, not the current.

The tool should instead run after Vaadin completes to process the request.

Some ideas for the implementation:

• Make the tool run in a servlet Filter in combination with a request handler that triggers the execution (e.g. request attribute)
• Try to replace the UIDL handler with an extension that runs the tool after the UIDL request is processed

[mcollovati]

I did some attempts to run the debug tool after UI changes are applied and also notify the user in the browser (#46), but I did not yet found a good way

Suppose we have a component on the UI that shows a floating indicator only if there are failures

• RequestHandler It is executed before UI changes are applied (before UIDLRequestHandler), so information provided are related to the the previous request (current behaviour)
• Extending and replacing UIDLRequestHandler Requires a custom VaadinService to replace the handler May require changes in Flow to have an hook to to something after changes are collected but before the response is written
• Extending UIDLRequestHandler and put it on top of the list May break application logics? As above, may require changes in Flow
• UI.beforeClientResponse Serializes also NodeChanges, it may produce errors related to elements that has been removed
• Servlet Filter serializing at the end request Should produce correct advices, but cannot notify the browser because the response is already committed Solution may be wrapping the response, caching UIDL response, run the debug tool, manually add changes to UIDL, but it seems a bit tricky

[mcollovati]

An acceptable trade-off for the moment could be a solution with a RequestHandler that store as a request attribute a Runnable that performs the test and notifies the user if PUSH is enabled. Then a servlet Filter running at the end of the request that executes the runnable