path: root/doc/todo/darcs.mdwn

Here's Thomas Schwinge unfinished darcs support for ikiwiki.

(Finishing this has been suggested as a [[soc]] project.)

> I haven't been working on this for months and also won't in the near
> future.  Feel free to use what I have done so
> far and bring it into an usable state!  Also, feel free to contact me
>  if there are questions.

-- [Thomas Schwinge](mailto:tschwinge@gnu.org)

[[!toggle text="show"]]
[[!toggleable text="""
	# Support for the darcs rcs, <URL:http://darcs.net/>.
	# Copyright (C) 2006  Thomas Schwinge <tschwinge@gnu.org>
	#
	# This program is free software; you can redistribute it and/or modify it
	# under the terms of the GNU General Public License as published by the
	# Free Software Foundation; either version 2 of the License, or (at your
	# option) any later version.
	#
	# This program is distributed in the hope that it will be useful, but
	# WITHOUT ANY WARRANTY; without even the implied warranty of
	# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
	# General Public License for more details.
	#
	# You should have received a copy of the GNU General Public License along
	# with this program; if not, write to the Free Software Foundation, Inc.,
	# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
	
	
	# We're guaranteed to be the only instance of ikiwiki running at a given
	# time.  It is essential that only ikiwiki is working on a particular
	# repository.  That means one instance of ikiwiki and it also means that
	# you must not `darcs push' into this repository, as this might create
	# race conditions, as I understand it.
	
	
	use warnings;
	use strict;
	use IkiWiki;
	
	package IkiWiki;
	
	
	# Which darcs executable to use.
	my $darcs = ($ENV{DARCS} or 'darcs');
	
	
	# Internal functions.
	
	sub darcs_info ($$$) {
	    my $field = shift;
	    my $repodir = shift;
	    my $file = shift; # Relative to the repodir.
	
	    my $child = open(DARCS_CHANGES, "-|");
	    if (! $child) {
		exec($darcs, 'changes', '--repo=' . $repodir, '--xml-output', $file) or
		    error('failed to run `darcs changes\'');
	    }
	
	    # Brute force for now.  :-/
	    while (<DARCS_CHANGES>) {
		last if /^<\/created_as>$/;
	    }
	    ($_) = <DARCS_CHANGES> =~ /$field=\'([^\']+)/;
	    $field eq 'hash' and s/\.gz//; # Strip away the `.gz' from `hash'es.
	
	    close(DARCS_CHANGES) or error('`darcs changes\' exited ' . $?);
	
	    return $_;
	}
	
	
	# Exported functions.
	
	sub rcs_update () {
	    # Not needed.
	}
	
	sub rcs_prepedit ($) {
	    # Prepares to edit a file under revision control.  Returns a token that
	    # must be passed to rcs_commit() when the file is to be commited.  For us,
	    # this token the hash value of the latest patch that modifies the file,
	    # i.e. something like its current revision.  If the file is not yet added
	    # to the repository, we return TODO: the empty string.
	
	    my $file = shift; # Relative to the repodir.
	
	    my $hash = darcs_info('hash', $config{srcdir}, $file);
	    return defined $hash ? $hash : "";
	}
	
	sub rcs_commit ($$$) {
	    # Commit the page.  Returns `undef' on success and a version of the page
	    # with conflict markers on failure.
	
	    my $file = shift; # Relative to the repodir.
	    my $message = shift;
	    my $rcstoken = shift;
	
	    # Compute if the ``revision'' of $file changed.
	    my $changed = darcs_info('hash', $config{srcdir}, $file) ne $rcstoken;
	
	    # Yes, the following is a bit convoluted.
	    if ($changed) {
		# TODO.  Invent a better, non-conflicting name.
		rename("$config{srcdir}/$file", "$config{srcdir}/$file.save") or
		    error("failed to rename $file to $file.save: $!");
	
		# Roll the repository back to $rcstoken.
	
		# TODO.  Can we be sure that no changes are lost?  I think that
		# we can, if we make sure that the `darcs push' below will always
		# succeed.
	
		# We need to revert everything as `darcs obliterate' might choke
		# otherwise.
	        # TODO: `yes | ...' needed?  Doesn't seem so.
		system($darcs, "revert", "--repodir=" . $config{srcdir}, "--all") and
		    error("`darcs revert' failed");
		# Remove all patches starting at $rcstoken.
		# TODO.  Something like `yes | darcs obliterate ...' seems to be needed.
		system($darcs, "obliterate", "--quiet", "--repodir" . $config{srcdir},
		       "--match", "hash " . $rcstoken) and
			   error("`darcs obliterate' failed");
		# Restore the $rcstoken one.
		system($darcs, "pull", "--quiet", "--repodir=" . $config{srcdir},
		       "--match", "hash " . $rcstoken, "--all") and
			   error("`darcs pull' failed");
	
		# We're back at $rcstoken.  Re-install the modified file.
		rename("$config{srcdir}/$file.save", "$config{srcdir}/$file") or
		    error("failed to rename $file.save to $file: $!");
	    }
	
	    # Record the changes.
	    # TODO: What if $message is empty?
	    writefile("$file.log", $config{srcdir}, $message);
	    system($darcs, 'record', '--repodir=' . $config{srcdir}, '--all',
		   '--logfile=' . "$config{srcdir}/$file.log",
		   '--author=' . 'web commit <web-hurd@gnu.org>', $file) and
		       error('`darcs record\' failed');
	
	    # Update the repository by pulling from the default repository, which is
	    # master repository.
	    system($darcs, "pull", "--quiet", "--repodir=" . $config{srcdir},
		   "--all") and error("`darcs pull' failed\n");
	
	    # If this updating yields any conflicts, we'll record them now to resolve
	    # them.  If nothing is recorded, there are no conflicts.
	    $rcstoken = darcs_info('hash', $config{srcdir}, $file);
	    # TODO: Use only the first line here, i.e. only the patch name?
	    writefile("$file.log", $config{srcdir}, 'resolve conflicts: ' . $message);
	    system($darcs, 'record', '--repodir=' . $config{srcdir}, '--all',
		   '--logfile=' . "$config{srcdir}/$file.log",
		   '--author=' . 'web commit <web-hurd@gnu.org>', $file) and
		       error('`darcs record\' failed');
	    my $conflicts = darcs_info('hash', $config{srcdir}, $file) ne $rcstoken;
	    unlink("$config{srcdir}/$file.log") or
		error("failed to remove `$file.log'");
	
	    # Push the changes to the main repository.
	    system($darcs, 'push', '--quiet', '--repodir=' . $config{srcdir}, '--all')
		and error('`darcs push\' failed');
	    # TODO: darcs send?
	
	    if ($conflicts) {
		my $document = readfile("$config{srcdir}/$file");
		# Try to leave everything in a consistent state.
	        # TODO: `yes | ...' needed?  Doesn't seem so.
		system($darcs, "revert", "--repodir=" . $config{srcdir}, "--all") and
		    warn("`darcs revert' failed.\n");
		return $document;
	    } else {
		return undef;
	    }
	}
	
	sub rcs_add ($) {
	    my $file = shift; # Relative to the repodir.
	
	    # Intermediate directories will be added automagically.
	    system($darcs, 'add', '--quiet', '--repodir=' . $config{srcdir},
		   '--boring', $file) and error('`darcs add\' failed');
	}
	
	sub rcs_recentchanges ($) {
	    warn('rcs_recentchanges() is not implemented');
	    return 'rcs_recentchanges() is not implemented';
	}
	
	sub rcs_notify () {
	    warn('rcs_notify() is not implemented');
	}
	
	sub rcs_getctime () {
	    warn('rcs_getctime() is not implemented');
	}
	
	1
"""]]

This is my ([bma](bma@bmalee.eu)) darcs.pm - it's messy (my Perl isn't up to much) but seems to work. It uses just one repo, like the mercurial plugin (unlike the above version, which AIUI uses two).

`rcs_commit()` uses backticks instead of `system()`, to prevent darcs' output being sent to the browser and mucking with the HTTP headers (`darcs record` has no --quiet option). And `rcs_recentchanges()` uses regexes rather than parsing darcs' XML output.

[[!toggle text="show" id="bma"]]
[[!toggleable id="bma" text="""

	#!/usr/bin/perl
	
	use warnings;
	use strict;
	use IkiWiki;
	use Date::Parse;
	use open qw{:utf8 :std};
	
	package IkiWiki;
	
	sub rcs_update () { #{{{
		# Do nothing - there's nowhere to update *from*.
	} #}}}
	
	sub rcs_prepedit ($) { #{{{
	} #}}}
	
	sub rcs_commit ($$$;$$) { #{{{
		my ($file, $message, $rcstoken, $user, $ipaddr) = @_;
	
		# $user should probably be a name and an email address, by darcs
		# convention.
		if (defined $user) {
			$user = possibly_foolish_untaint($user);
		}
		elsif (defined $ipaddr) {
			$user = "Anonymous from $ipaddr";
		}
		else {
			$user = "Anonymous";
		}
	
		$message = possibly_foolish_untaint($message);
		
		# BUG: this outputs one line of text, and there's not a -q or --quiet
		# option. Redirecting output to /dev/null works, but I still get the
		# HTTP status and location headers displayed in the browser - is that
		# darcs' fault or ikiwiki's?
		# Doing it in backticks *works*, but I'm sure it could be done better.
		my @cmdline = ("darcs", "record", "--repodir", "$config{srcdir}",
		               "-a", "-m", "$message", "--author", "$user", $file);
		`darcs record --repodir "$config{srcdir}" -a -m "$message" --author "$user" $file`; # Return value? Output? Who needs 'em?
		#if (system(@cmdline) != 0) {
		#	warn "'@cmdline' failed: $!";
		#}
	
		return undef; # success
		
	sub rcs_add ($) { # {{{
		my ($file) = @_;
	
		my @cmdline = ("darcs", "add", "--repodir", "$config{srcdir}", "-a", "-q", "$file");
		if (system(@cmdline) != 0) {
			warn "'@cmdline' failed: $!";
		}
	} #}}}
	
	sub rcs_recentchanges ($) { #{{{
		# TODO: This is horrible code. It doesn't work perfectly, and uses regexes
		# rather than parsing Darcs' XML output.
		my $num=shift;
		my @ret;
		
		return unless -d "$config{srcdir}/_darcs";
	
		my $changelog = `darcs changes --xml --summary --repodir "$config{srcdir}"`;
		$changelog = join("", split(/\s*\n\s*/, $changelog));
		my @changes = split(/<\/patch>.*?<patch/m, $changelog);
	
	
		foreach my $change (@changes) {
			$change =~ m/hash='(.*?)'/;
			my $rev = $1;
			$change =~ m/author='(.*?)'/;
			my $user = $1."\n";
			my $committype = "web";
			if($user =~ m/&lt;/) {
				# Author fields generated by darcs include an email address: look for the "<".
				$committype = "darcs";
				use HTML::Entities;
				$user = decode_entities $user;
			}
			$change =~ m/local_date='(.*?)'/;
			my $when = $1;
			$when=time - str2time($when, 'UTC');
			$change =~ m/<name>(.*?)<\/name>/g;
			my @message = {line => $1};
			foreach my $match ($change =~ m/<comment>(.*?)<\/comment>/gm) {
				push @message, {line => $1};
			}

			my @pages;
			foreach my $match ($change =~ m/<.*?_(file|directory)>(.*?)(<(added|removed)_lines.*\/>)*<\/.*?_(file|directory)>/g) {
				# My perl-fu is weak. I'm probably going about this all wrong, anyway.
				push @pages, {page => pagename($match)} if ( -f $config{srcdir}."/".$match || -d $config{srcdir}."/".$match) and not $match =~ m/^$/;
			}
			push @ret, { rev => $rev,
					user => $user,
					committype => $committype,
					when => $when,
					message => [@message],
					pages => [@pages],
				}
		}
		return @ret;
	} #}}}
	
	sub rcs_notify () { #{{{
		# TODO
	} #}}}
	
	sub rcs_getctime ($) { #{{{
		error gettext("getctime not implemented");
	} #}}}
	
	1



"""]]

---

Well, here's my version too. It only does getctime -- using a real XML parser, instead of regexp ugliness -- and maybe recentchanges, but that may be bitrotted, or maybe I never finished it, as I only need the getctime. As for actual commits, I have previously voiced my opinion, that this should be done by the plugin generating a patch bundle, and forwarding it to darcs in some way (`darcs apply` or even email to another host, possibly moderated), instead of the hacky direct modification of a working copy. It could also be faster to getctime in a batch. Just reading in all the changes the first time they're needed, might not be a big improvement in many cases, but if we got a batch request from ikiwiki, we could keep reaing the changes until all the files in this batch request have been met.  --[[tuomov]]

[[!toggle text="show" id="tuomov"]]
[[!toggleable id="tuomov" text="""
<pre>
#!/usr/bin/perl
# Stubs for no revision control.

use warnings;
use strict;
use IkiWiki;

package IkiWiki;

sub rcs_update () {
}

sub rcs_prepedit ($) {
	return ""
}

sub rcs_commit ($$$) {
	return undef # success
}

sub rcs_add ($) {
}

sub rcs_recentchanges ($) {
	my $num=shift;
	my @ret;
	
	eval q{use Date::Parse};
	eval q{use XML::Simple};
	
	my $repodir=$config{srcdir};
	
	if (-d "$config{srcdir}/_darcs") {
		my $child = open(LOG, "-|");
		if (! $child) {
			exec("darcs", "changes", "--xml", 
			     "--repodir", "$repodir",
			     "--last", "$num")
			|| error("darcs changes failed to run");
		}
		my $data=<LOG>;
		close LOG;
		
		my $log = XMLin($data, ForceArray => 1);
		
		foreach my $patch ($log->{patch}) {
			my $date=$patch->{local_date};
			my $hash=$patch->{hash};
			my $when=concise(ago(time - str2time($date)));
			my @pages;
			
			my $child = open(SUMMARY, "-|");
			if (! $child) {
				exec("darcs", "annotate", "-s", "--xml", 
				     "--match", "hash: $hash",
				     "--repodir", "$repodir")
				|| error("darcs annotate failed to run");
			}
			my $data=<SUMMARY>;
			close SUMMARY;
		
			my $summary = XMLin("<lame>$data</lame>", ForceArray => 1);

			# TODO: find @pages
			
			push @ret, {
				#rev => $rev,
				user => $patch->{author},
				#committype => $committype,
				when => $when, 
				#message => [@message],
				pages => [@pages],
			}; # if @pages;
			return @ret if @ret >= $num;
		}
	}
	
	return @ret;
}

sub rcs_notify () {
}

sub rcs_getctime ($) {
	my $file=shift;
	
	eval q{use Date::Parse};
	eval q{use XML::Simple};
	local $/=undef;
	
	# Sigh... doing things the hard way again
	my $repodir=$config{srcdir};
	
	my $filer=substr($file, length($repodir));
	$filer =~ s:^[/]+::;
	
	my $child = open(LOG, "-|");
	if (! $child) {
		exec("darcs", "changes", "--xml", "--reverse",
		     "--repodir", "$repodir", "$filer")
		|| error("darcs changes $filer failed to run");
	}
	
	my $data=<LOG>;
	close LOG;
	
	my $log = XMLin($data, ForceArray => 1);
	
	my $datestr=$log->{patch}[0]->{local_date};
	
	if (! defined $datestr) {
		warn "failed to get ctime for $filer";
		return 0;
	}
	
	my $date=str2time($datestr);
	
	debug("found ctime ".localtime($date)." for $file");
	
	return $date;
}

1
</pre>
"""]]

---

I merged the two versions above and made some fixes; it is recording my web edits in darcs and showing a recent changes page.
It is in a [darcs repository](http://joyful.com/darcsweb/darcsweb.cgi?r=ikiwiki-darcs), please send patches. --[[Simon_Michael]]

> I'd like to see at least the following fixed before I commit this: --[[Joey]]
> * Running `darcs record $filename` in backticks is not good (security)
>   The thing to do is to open stdout to /dev/null before execing darcs.
> * Get `rcs_recentchanges_xml` working, parsing xml with regexps does
>   not seem like a maintenance win.
> * `rcs_notify` should be removed, it's no longer used.
> * Some form of conflict handling. Using darcs to attempt to merge
>   the changes is I gusss optional (although every other rcs backend,
>   including svn manages to do this), but it needs to at *least* detect
>   conflicts and return a page with conflict markers for the user to fix
>   the conflict.

I have addressed the recentchanges bit, you can find my hacked up darcs.pm at <http://web.mornfall.net/stuff/web-root/IkiWiki/Rcs/darcs.pm>.

It's got couple of FIXMEs, and a very site-specific filter for recentchanges. Not sure how to do that better though. I will eventually add web commits, probably of my own (and mention it here).

---

And here's yet another one, including an updated `ikiwiki-makerepo`. :)

<http://khjk.org/~pesco/ikiwiki-darcs/> (now a darcs repo)

> Note that there's a 'darcs' branch in git that I'm keeping a copy of your
> code in. Just in case. :-)

I've taken all the good stuff from the above and added the missing hooks. The code hasn't seen a lot of testing, so some bugs are likely yet to surface. Also, I'm not experienced with perl and don't know where I should have used the function `possibly_foolish_untaint`.

Regarding the repository layout: There are two darcs repositories. One is the `srcdir`, the other we'll call `master`.

 *  HTML is generated from `srcdir`.
 *  CGI edits happen in `srcdir`.
 *  The backend pulls updates from `master` into `srcdir`, i.e. darcs commits should happen to `master`.
 *  `master` calls ikiwiki (through a wrapper) in its apply posthook, i.e. `master/_darcs/prefs/defaults` should look like this:

        apply posthook ikiwrap
        apply run-posthook

    (I'm not sure, should/could it be `ikiwrap --refresh` above?)
 *  The backend pushes CGI edits from `srcdir` back into `master` (triggering the apply hook).
 *  The working copies in `srcdir` and `master` should *not* be touched by the user, only by the CGI or darcs, respectively.

> Review of this one:
> 
> * Should use tab indentation.
> * `rcs_getctime` should not need to use a ctime cache (such a cache should 
>   also not be named `.ikiwiki.ctimes`). `rcs_getctime` is run exactly
>   once per page, ever, and the data is cached in ikiwiki's index.
> * I doubt that ENV{DARCS} will be available, since the wrapper clobbers> the entire
>   environment. I'd say remove that.
> * I don't understand what `darcs_info` is doing, but it seems to be
>   parsing xml with a regexp?
> * Looks like `rcs_commit` needs a few improvements, as marked TODO
> * `rcs_remove` just calls "rm"? Does darcs record notice the file was removed
>    and automatically commit the removal? (And why `system("rm")` and not
>    `unlink`?)
> * Is the the darcs info in [[details]] still up-to-date re this version?
> --[[Joey]]

> Update:
>
> I think I've addressed all of the above except for the XML parsing in `darcs_info`.
> The function determines the md5 hash of the last patch the given file appears in.
> That's indeed being done with regexps but my Perl isn't good enough for a quick recode
> right now.
>
> As for the darcs info in [[rcs/details]], it does not accurately describe the way
> this version works. It's similar, but the details differ slightly.
> You could copy my description above to replace it.
>
> There is still some ironing to do, for instance the current version doesn't allow for
> modifying attachments by re-uploading them via CGI ("darcs add failed"). Am I assuming
> correctly that "adding" a file that's already in the repo should just be a no-op?
> --pesco

>> It should result in the new file contents being committed by
>> `rcs_commit_staged`. For some revision control systems, which
>> automatically commit modifications, it would be a no-op. --[[Joey]]

>>> Done. --pesco

[[!tag patch]]