X-Git-Url: http://git.vanrenterghem.biz/git.ikiwiki.info.git/blobdiff_plain/36305652eade849e19801dca856ba74e21d6a9b1..e71622d233660b5ba305d68e586d7d14ff2124e6:/doc/todo/git-annex_support.mdwn?ds=sidebyside

diff --git a/doc/todo/git-annex_support.mdwn b/doc/todo/git-annex_support.mdwn
index 30d79843d..f1a4e787c 100644
--- a/doc/todo/git-annex_support.mdwn
+++ b/doc/todo/git-annex_support.mdwn
@@ -3,3 +3,242 @@ A dear [[wishlist]] which would resolve [[this question|forum/ikiwiki_and_big_fi
 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]]
+
+This [[!taglink patch]] still applies - anything else I should be doing here to try to get this fixed? A summary maybe? --[[anarcat]]
+
+> Sorry, I don't have the mental bandwidth at the moment to work through the
+> implications of this change. I know you want this feature, I know it's an
+> attractive solution to several use cases, and git annex support is in the
+> queue, but at right now I'm still trying to deal with mitigating
+> CVE-2016-3714, and the last thing I want to do is merge new security
+> risks. --[[smcv]]
+
+> > No problem at all, glad that you still have that in the queue, and I hope
+> > my work was somewhat useful in pushing this forward! Thanks for taking
+> > care of the Imagetragick situation... :/ --[[anarcat]]