X-Git-Url: https://sipb.mit.edu/gitweb.cgi/ikiwiki.git/blobdiff_plain/4a1b921f6d1c91e62cecc9827ce3a15e1a2fff3e..6a8c921ee1bbfd4c980ffaf2c43e5b45e452f4de:/doc/about_rcs_backends.mdwn diff --git a/doc/about_rcs_backends.mdwn b/doc/about_rcs_backends.mdwn index 476525e3c..7af4a952e 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 the first RCS to be supported by ikiwiki. -#### How does it work internally? +### How does it work internally? Master repository M. @@ -27,13 +29,16 @@ see [[commit-internals]]. You browse and web-edit the wiki on W. +W "belongs" to ikiwiki and should not be edited directly. + -### [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 [[todo/darcs]]. -#### How will it work internally? +### How will it work internally? ``Master'' repository R1. @@ -59,7 +64,7 @@ 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 @@ -75,10 +80,46 @@ 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]] (not yet included) +> The mercurial plugin seems to just use one repo and edit it directly - is +> there some reason that's okay there but not for darcs? I agree with tuomov +> that having just the one repo would be preferable; the point of a dvcs is +> that there's no difference between one repo and another. I've got a +> darcs.pm based on mercurial.pm, that's almost usable... --bma -A patch with full [Git](http://git.or.cz) support is at . Regarding the patch, Recai says: +>> IMHO it comes down to whatever works well for a given RCS. Seems like +>> the darcs approach _could_ be done with most any distributed system, but +>> it might be overkill for some (or all?) While there is the incomplete darcs +>> plugin in [[todo/darcs]], if you submit one that's complete, I will +>> probably accept it into ikiwiki.. --[[Joey]] + +## [[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 @@ -91,34 +132,92 @@ 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. -Some other notes: +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]] -- There are two separate helper packages in git.pm. To keep things self - confined, I haven't split it up. +## rcs -- I've used a (mini) Debug.pm during the tests and made it a separate file - for the convenience of others. It relies on the "constant folding" - feature of Perl, so there shouldn't be a runtime penalty (at least this - is what the 'perl -MO=Deparse shows', haven't made a real benchmark). +There is a patch that needs a bit of work linked to from [[todo/rcs]]. -- rcs_notify() has not been implemented yet (I have noticed it after I - finished the main work). +## [Monotone](http://monotone.ca/) -- GIT backend uses the gitweb for repository browsing (the counterpart of - ViewCVS). +In normal use, monotone has a local database as well as a workspace/working copy. +In ikiwiki terms, the local database takes the role of the master repository, and +the srcdir is the workspace. As all monotone workspaces point to a default +database, there is no need to tell ikiwiki explicitly about the "master" database. It +will know. -- There might be some subs in GIT name space which you may prefer to move to - the main code. +The patch currently supports normal committing and getting the history of the page. +To understand the parallel commit approach, you need to understand monotone's +approach to conflicts: -- Due to the reasons explained in the code, I've written an rcs_invoke() - wrapper. May be there should be a better approach to reach the same - goal. +Monotone allows multiple micro-branches in the database. There is a command, +`mtn merge`, that takes the heads of all these branches and merges them back together +(turning the tree of branches into a dag). Conflicts in monotone (at time of writing) +need to be resolved interactively during this merge process. +It is important to note that having multiple heads is not an error condition in a +monotone database. This condition will occur in normal use. In this case +'update' will choose a head if it can, or complain and tell the user to merge. -- There are some parts which I may change in future, like using a global - rcs_fatal_error and the ugly error reporting code in _rcs_commit. +For the ikiwiki plugin, the monotone ikiwiki plugin borrows some ideas from the svn ikiwiki plugin. +On prepedit() we record the revision that this change is based on (I'll refer to this as the prepedit revision). When the web user +saves the page, we check if that is still the current revision. If it is, then we commit. +If it isn't then we check to see if there were any changes by anyone else to the file +we're editing while we've been editing (a diff bewteen the prepedit revision and the current rev). +If there were no changes to the file we're editing then we commit as normal. -- Documentation is missing. +It is only if there have been parallel changes to the file we're trying to commit that +things get hairy. In this case the current approach is to +commit the web changes as a branch from the prepedit revision. This +will leave the repository with multiple heads. At this point, all data is saved. +The system then tries to merge the heads with a merger that will fail if it cannot +resolve the conflict. If the merge succeeds then everything is ok. -It works for me, but of course in the end, the final decision is yours (due -to mostly GIT quirks, the implementation is not clean as SVN). Feel free -to fix/delete/add whatever you want. Hope it doesn't have any serious bug. \ No newline at end of file +If that merge failed then there are conflicts. In this case, the current patch calls +merge again with a merger that inserts conflict markers. It commits this new +revision with conflict markers to the repository. It then returns the text to the +user for cleanup. This is less neat than it could be, in that a conflict marked +revision gets committed to the repository.