X-Git-Url: http://git.vanrenterghem.biz/git.ikiwiki.info.git/blobdiff_plain/89347d858619a764a2009c47909c6deb4c8d8ca6..c87c7edf288ca69e96721ed6ff46f12b7f478540:/doc/about_rcs_backends.mdwn diff --git a/doc/about_rcs_backends.mdwn b/doc/about_rcs_backends.mdwn index 764fece97..d1454bdda 100644 --- a/doc/about_rcs_backends.mdwn +++ b/doc/about_rcs_backends.mdwn @@ -1,16 +1,18 @@ -## A few bits about the RCS backends +A few bits about the RCS backends -### Terminology +[[toc ]] + +## Terminology ``web-edit'' means that a page is edited by using the web (CGI) interface as opposed to using a editor and the RCS interface. -### [[Subversion]] +## [[Subversion]] -Subversion was that first RCS to be supported by ikiwiki. +Subversion was the first RCS to be supported by ikiwiki. -#### How does it work internally? +### How does it work internally? Master repository M. @@ -22,15 +24,19 @@ HTML is generated from W. rcs_update() will update from M to W. CGI operates on W. rcs_commit() will commit from W to M. +For all the gory details of how ikiwiki handles this behind the scenes, +see [[commit-internals]]. + You browse and web-edit the wiki on W. -### [darcs](http://darcs.net/) (not yet included) +## [darcs](http://darcs.net/) (not yet included) Support for using darcs as a backend is being worked on by [Thomas -Schwinge](mailto:tschwinge@gnu.org). +Schwinge](mailto:tschwinge@gnu.org), although development is on hold curretly. +There is a patch in the [[patchqueue]]. -#### How will it work internally? +### How will it work internally? ``Master'' repository R1. @@ -45,29 +51,115 @@ There is a working copy of R1: R2. CGI operates on R2. rcs_commit() will push from R2 to R1. You browse the wiki on R1 and web-edit it on R2. This means for example -that R2 needs to be updated from R1 if you are going the web-edit a page, +that R2 needs to be updated from R1 if you are going to web-edit a page, as the user otherwise might be irritated otherwise... How do changes get from R1 to R2? Currently only internally in -rcs_commit(). Is rcs_prepedit() suitable? +rcs\_commit(). Is rcs\_prepedit() suitable? It follows that the HTML rendering and the CGI handling can be completely separated parts in ikiwiki. What repository should [[RecentChanges]] and [[History]] work on? R1? -##### Rationale for doing it differently than in the Subversion case +#### Rationale for doing it differently than in the Subversion case darcs is a distributed RCS, which means that every checkout of a repository is equal to the repository it was checked-out from. There is no forced hierarchy. -R1 is the nevertheless called the master repository. It's used for +R1 is nevertheless called the master repository. It's used for collecting all the changes and publishing them: on the one hand via the rendered HTML and on the other via the standard darcs RCS interface. -R2, the repository where CGI operates on, is just a checkout of R1 and +R2, the repository the CGI operates on, is just a checkout of R1 and doesn't really differ from the other checkouts that people will branch off from R1. (To be continued.) + +#### Another possible approach + +Here's what I (tuomov) think, would be a “cleaner” approach: + + 1. Upon starting to edit, Ikiwiki gets a copy of the page, and `darcs changes --context`. + This context _and_ the present version of the page are stored in as the “version” of the + page in a hidden control of the HTML. + Thus the HTML includes all that is needed to generate a patch wrt. to the state of the + repository at the time the edit was started. This is of course all that darcs needs. + 2. Once the user is done with editing, _Ikiwiki generates a patch bundle_ for darcs. + This should be easy with existing `Text::Diff` or somesuch modules, as the Web edits + only concern single files. The reason why the old version of the page is stored in + the HTML (possibly compressed) is that the diff can be generated. + 3. Now this patch bundle is applied with `darcs apply`, or sent by email for moderation… + there are many possibilities. + +This approach avoids some of the problems of concurrent edits that the previous one may have, +although there may be conflicts, which may or may not propagate to the displayed web page. +(Unfortunately there is not an option to `darcs apply` to generate some sort of ‘confliction resolution +bundle’.) Also, only one repository is needed, as it is never directly modified +by Ikiwiki. + +This approach might be applicable to other distributed VCSs as well, although they're not as oriented +towards transmitting changes with standalone patch bundles (often by email) as darcs is. + +## [[Git]] + +Regarding the Git support, Recai says: + +I have been testing it for the past few days and it seems satisfactory. I +haven't observed any race condition regarding the concurrent blog commits +and it handles merge conflicts gracefully as far as I can see. + +As you may notice from the patch size, GIT support is not so trivial to +implement (for me, at least). Being a fairly fresh code base it has some +bugs. It also has some drawbacks (especially wrt merge which was the hard +part). GIT doesn't have a similar functionality like 'svn merge -rOLD:NEW +FILE' (please see the relevant comment in mergepast for more details), so I +had to invent an ugly hack just for the purpose. + +By design, Git backend uses a "master-clone" repository pair approach in contrast +to the single repository approach (here, _clone_ may be considered as the working +copy of a fictious web user). Even though a single repository implementation is +possible, it somewhat increases the code complexity of backend (I couldn't figure +out a uniform method which doesn't depend on the prefered repository model, yet). +By exploiting the fact that the master repo and _web user_'s repo (`srcdir`) are all +on the same local machine, I suggest to create the latter with the "`git clone -l -s`" +command to save disk space. + +Note that, as a rule of thumb, you should always put the rcs wrapper (`post-update`) +into the master repository (`.git/hooks/`) as can be noticed in the Git wrappers of +the sample [[ikiwiki.setup]]. + +## [[Mercurial]] + +The Mercurial backend is still in a early phase, so it may not be mature +enough, but it should be simple to understand and use. + +As Mercurial is a distributed RCS, it lacks the distinction between +repository and working copy (every wc is a repo). + +This means that the Mercurial backend uses directly the repository as +working copy (the master M and the working copy W described in the svn +example are the same thing). + +You only need to specify 'srcdir' (the repository M) and 'destdir' (where +the HTML will be generated). + +Master repository M. + +RCS commit from the outside are installed into M. + +M is directly used as working copy (M is also W). + +HTML is generated from the working copy in M. rcs_update() will update +to the last committed revision in M (the same as 'hg update'). +If you use an 'update' hook you can generate automatically the HTML +in the destination directory each time 'hg update' is called. + +CGI operates on M. rcs_commit() will commit directly in M. + +If you have any question or suggestion about the Mercurial backend +please refer to [Emanuele](http://nerd.ocracy.org/em/) + +## [[tla]]