Merge branch 'master' of ssh://git.ikiwiki.info

[git.ikiwiki.info.git] / doc / todo / git-annex_support.mdwn

A dear [[wishlist]] which would resolve [[this question|forum/ikiwiki_and_big_files]]: ikiwiki should support git-annex repositories.

I am not sure how this would work, but from my POV, it should do a `git annex get` when new commits are pushed to its bare repo. This would assume, of course, that there's another repo somewhere that ikiwiki has access to, which works for HTTP-style remotes, but could be more problematic for SSH remotes that require a key.

Another solution would be to make ikiwiki a remote itself and allow users to push big files to it. The only problem I see with this is those files would end up in the bare repository and not necessarily show up in the web rendering. Ideally, a big file pushed would be hardlinked between the two repos, but it seems [git-annex doesn't support that yet](http://git-annex.branchable.com/todo/wishlist:_use_hardlinks_for_local_clones). --[[anarcat]]

> One technical problem with this is that ikiwiki doesn't allow symlinks
> for [[security]], but git-annex relies on symlinks (unless you're in
> direct mode, but I'm not sure that's really desirable here).
> I'd like to make symlinks possible without compromising security,
> but it'll be necessary to be quite careful. --[[smcv]]

First implementation
====================

So as the [[discussion]] shows, it seems it's perfectly possible to actually do this! There's this [gallery site](http://stockholm.kalleswork.net) which uses the [[plugins/contrib/album]] plugin and git-annex to manage its files.

The crucial steps are:

 1. setup a git annex remote in `$srcdir`

 2. configure direct mode because ikiwiki ignores symlinks for [[security]] reasons:

        cd $srcdir
        git annex init
        git annex direct

 3. configure files to be considered by git-annex (those will be not committed into git directly):

        git config annex.largefiles 'largerthan=100kb and not (include=*.mdwn or include=*.txt)'

 4. make the bare repository (the remote of `$srcdir`) ignored by git-annex:

        cd $srcdir
        git config remote.origin.annex-ignore true
        git config remote.origin.annex-sync false

    (!) This needs to be done on *ANY* clone of the repository, which is annoying, but it's important because we don't want to see git-annex stuff in the bare repo. (why?)

 5. deploy the following crappy plugin to make commits work again and make sure the right files are added in git-annex:

[[!format perl """
#!/usr/bin/perl
package IkiWiki::Plugin::gitannex;

use warnings;
use strict;
use IkiWiki 3.00;

sub import {
        hook(type => "getsetup", id => "gitannex", call => \&getsetup);
        hook(type => "savestate", id => "gitannex", call => \&rcs_commit);
        # we need to handle all rcs commands maybe?
}

sub getsetup () {
        return
                plugin => {
                        safe => 1, # rcs plugin
                        rebuild => undef,
                        section => "misc",
                },
}

# XXX: we want to copy or reuse safe_git

sub rcs_commit (@) {
    chdir $config{srcdir};
    `git annex add --auto`;
    `git annex sync`;
}

sub rcs_commit_staged (@) {
    rcs_commit($@);
}

1
"""]]
This assumes you know what `srcdir`, `repository` and so on mean, if you forgot (like me), see this reference: [[rcs/git/]].


What doesn't work
-----------------

 * the above plugin is kind of flaky and ugly.
 * it's not an RCS plugin, but probably should be, replacing the git plugin, because really: git doesn't work at all anymore at this point

What remains to be clarified
----------------------------

 * how do files get pushed to the `$srcdir`? Only through the web interface?
 * why do we ignore the bare repository?

See the [[discussion]] for a followup on that. --[[anarcat]]

Alternative implementation
==========================

An alternative implementation, which remains to be detailed but is mentionned in [[forum/ikiwiki_and_big_files]], is to use the [[underlay]] feature combined with the `hardlink` option to deploy the git-annex'd files. Then git-annex is separate from the base ikiwiki git repo. See also [[tips/Ikiwiki_with_git-annex__44___the_album_and_the_underlay_plugins]] for an example.

Also note that ikiwiki-hosting has a [patch waiting](https://ikiwiki-hosting.branchable.com/todo/git-annex_support) to allow pushes to work with git-annex. This could potentially be expanded to sync content to the final checkout properly, avoiding some of the problems above (esp. wrt to non-annex bare repos).

Combined with the [[underlay]] feature, this could work very nicely indeed... --[[anarcat]]

Here's an attempt:

<pre>
cd /home/user
git clone source.git source.annex
cd source.annex
git annex direct
cd ../source.git
git annex group . transfer
git remote add annex ../source.annex
git annex sync annex
</pre>

Make sure the `hardlink` setting is enabled, and add the annex as an underlay, in `ikiwiki.setup`:

<pre>
hardlink: 1
add_underlays:
- /home/w-anarcat/source.annex
</pre>

Then moving files to the underlay is as simple as running this command in the bare repo:

<pre>
#!/bin/sh

echo "moving big files to annex repository..."
git annex move --to annex
</pre>

I have added this as a hook in `$HOME/source.git/hooks/post-receive` (don't forget to `chmod +x`).

The problem with the above is that the underlay wouldn't work: for some reason it wouldn't copy those files in place properly. Maybe it's freaking out because it's a full copy of the repo... My solution was to make the source repository itself a direct repo, and then add it as a remote to the bare repo. --[[anarcat]]

Back from the top
=================

Obviously, the final approach of making the `source` repository direct mode will fail because ikiwiki will try to commit files there from the web interface which will fail (at best) and (at worst) add big files into git-annex (or vice-versa, not sure what's worse actually).

Also, I don't know how others here made the underlay work, but it didn't work for me. I think it's because in the "source" repository, there are (dead) symlinks for the annexed files. This overrides the underlay, because of [[security]] - although I am unclear as to why this is discarded so early. So in order to make the original idea above work properly (ie. having a separate git-annex repo in direct mode) work, we must coerce ikiwiki into tolerating symlinks in the srcdir a little more:

<pre>
diff --git a/IkiWiki.pm b/IkiWiki.pm
index 1043ef4..949273c 100644
--- a/IkiWiki.pm
+++ b/IkiWiki.pm
@@ -916,11 +916,10 @@ sub srcfile_stat {
        my $file=shift;
        my $nothrow=shift;

-       return "$config{srcdir}/$file", stat(_) if -e "$config{srcdir}/$file";
-       foreach my $dir (@{$config{underlaydirs}}, $config{underlaydir}) {
-               return "$dir/$file", stat(_) if -e "$dir/$file";
+       foreach my $dir ($config{srcdir}, @{$config{underlaydirs}}, $config{underlaydir}) {
+               return "$dir/$file", stat(_) if (-e "$dir/$file" && ! -l "$dir/$file");
        }
-       error("internal error: $file cannot be found in $config{srcdir} or underlay") unless $nothrow;
+       error("internal error: $file cannot be found in $config{srcdir} or underlays @{$config{underlaydirs}} $config{underlaydir}") unless $nothrow;
        return;
 }

diff --git a/IkiWiki/Render.pm b/IkiWiki/Render.pm
index 9d6f636..e0b4cf8 100644
--- a/IkiWiki/Render.pm
+++ b/IkiWiki/Render.pm
@@ -337,7 +337,7 @@ sub find_src_files (;$$$) {

                if ($underlay) {
                        # avoid underlaydir override attacks; see security.mdwn
-                       if (! -l "$abssrcdir/$f" && ! -e _) {
+                       if (1 || ! -l "$abssrcdir/$f" && ! -e _) {
                                if (! $pages{$page}) {
                                        push @files, $f;
                                        push @IkiWiki::underlayfiles, $f;
</pre>

<del>Now obviously this patch is incomplete: I am not sure we actually avoid the attack, ie. i am not sure the check in `srcdir()` is sufficient to remove completely the check in `find_src_files()`.</del>

After reviewing the code further, it seems that `find_src_files` in three places in ikiwiki:

<pre>
../IkiWiki/Render.pm:421:       find_src_files(1, \@files, \%pages);
../IkiWiki/Render.pm:846:               ($files, $pages)=find_src_files();
../po/po2wiki:18:my ($files, $pages)=IkiWiki::find_src_files();
</pre>

The first occurence is in `IkiWiki::Render::process_changed_files`, where it is used mostly for populating `@IkiWiki::underlayfiles`, the only side effect of 
`find_src_files`. The second occurence is in `IkiWiki::Render::refresh`. There things are a little more complicated (to say the least) and a lot of stuff happens. To put it in broad terms, first it does a `IkiWiki::Render::scan` and then a `IkiWiki::Render::render`. The last two call `srcfile()` appropriately (where i put an extra symlink check), except for  `will_render()` in `scan`, which I can't figure out right now and that seems to have a lot of global side effects. It still looks fairly safe at first glance. The `rcs_get_current_rev`, `refresh`, `scan` and `rendered` hooks are also called in there, but I assume those to be safe, since they are called with sanitized values already.

The patch does work: the files get picked up from the underlay and properly hardlinked into the target `public_html` directory! So with the above patch, then the following hook in `source.git/hooks/post-receive`:

<pre>
#!/bin/sh

OLD_GIT_DIR="$GIT_DIR"
unset GIT_DIR
echo "moving big files to annex repository..."
git annex copy --to annex
git annex sync annex
</pre>

(I am not sure anymore why GIT_DIR is necessary, but I remember it destroyed all files in my repo because git-annex synced against the `setup` branch in the parent directory. fun times.)

Then the `annex` repo is just a direct clone of the source.git:

<pre>
cd /home/user
git clone --shared source.git annex
cd annex
git annex direct
cd ../source.git
git remote add annex ../annex
</pre>

And we need the following config:

<pre>
hardlink: 1
add_underlays:
- /home/w-anarcat/annex
add_plugins:
- underlay
</pre>

... and the `ikiwiki-hosting` patch mentionned earlier to allow git-annex-shell to run at all. Also, the `--shared` option will [make git-annex use hardlinks itself between the two repos](https://git-annex.branchable.com/todo/wishlist:_use_hardlinks_for_local_clones/), so the files will be available for download as well. --[[anarcat]]

> <del>...aaaand this doesn't work anymore. :( i could have sworn this was working minutes ago, but for some reason the annexed files get skipped again now. :(</del> Sorry for the noise, the annex repo wasn't in direct mode - the above works! --[[anarcat]]