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