Feature Proposal: viewRedirectHandler() in plug-ins

Motivation

You may need to redirect view access to a certain web or topic. Or you may want to redirect under certain circumstances

Description and Documentation

Plug-ins will be able to have viewRedirectHandler($session, $web, $topic). And $session->{plugins}->dispatch('viewRedirectHandler', $session, $web, $topic) will be put in the beginning of TWiki::UI::View::view().

viewRedirectHandler() returns 1 if it did $session->redirect(...). It returns 0 otherwise. The plug-in dispatcher calls viewRedirectHandler() of enabled plug-ins until one plug-in returns 1.

Examples

Let's assume the following situation.

• You migrate from one TWiki build (core + plug-ins + configurations) to another
• There are many subtle but noticeable incompatibilities between the old and new TWiki build
• The TWiki site has many webs

Given those you may take the following migration strategy.

• During the transition from the old build to the new, you run the old and new builds in parallel at different URLs: oldtwiki.example.com and newtwiki.example.com
• The webs on oldtwiki.ms.com are migrated from the old build to the new one by one
• The two builds share data files (data/* and pub/*) in such a manner that the old build can see the new build data read-only and vice versa. This is for cross web linking (Web.Topic) and cross web inclusion keep working between migrated and not-yet-migrated webs
• Let's say NotMigratedWeb.PageA has a link to MigratedWeb.PageB
  • For this link to work properly,
    http://oldtwiki.example.com/cgi-bin/view/MigratedWeb/PageB needs to be redirected to
    http://newtwiki.example.com/cgi-bin/view/MigratedWeb/PageB
• Let's say MigratedWeb.PageC has a link to NotMigratedWeb.PageD
  • For this link to work properly,
    http://newtwiki.example.com/cgi-bin/NotMigratedWeb/PageD needs to be redirected to
    http://oldtwiki.example.com/cgi-bin/NotMigratedWeb/PageD
• Because of the incompatibilities between the two builds, migrated webs need to be displayed on the new build while not-yet-migrated webs needs to be displayed on the old build.
• Links and inclusion need to work during and after transition from the old build to the new, which means links and inclusion needs to work in all permutation of a source topic, a destination topic, residing in the old build, residing in the new build

The redirection mentioned above can be cleanly implemented using a plug-in having a viewRedirectHandler(). After the transition is completed, the redirection mechanism can be cleanly removed by removing the plug-in.

Impact

Implementation

-- Contributors: Hideyo Imazu - 2013-02-01

Discussion

It's regarded as accepted after 7 days of the feedback period. I'm still open to feedback but move forward.

-- Hideyo Imazu - 2013-02-11

I do not understand the need, but I am sure there is a good one. Yes, accepted by 7 day rule.

-- Peter Thoeny - 2013-02-11

Added an example. Hope it helps.

-- Hideyo Imazu - 2013-02-12