contrib/mw-to-git/git-remote-mediawiki

#! /usr/bin/perl

# Copyright (C) 2011
#     Jérémie Nikaes <jeremie.nikaes@ensimag.imag.fr>
#     Arnaud Lacurie <arnaud.lacurie@ensimag.imag.fr>
#     Claire Fousse <claire.fousse@ensimag.imag.fr>
#     David Amouyal <david.amouyal@ensimag.imag.fr>
#     Matthieu Moy <matthieu.moy@grenoble-inp.fr>
# License: GPL v2 or later

# Gateway between Git and MediaWiki.
#   https://github.com/Bibzball/Git-Mediawiki/wiki
#
# Known limitations:
#
# - Only wiki pages are managed, no support for [[File:...]]
#   attachments.
#
# - Poor performance in the best case: it takes forever to check
#   whether we're up-to-date (on fetch or push) or to fetch a few
#   revisions from a large wiki, because we use exclusively a
#   page-based synchronization. We could switch to a wiki-wide
#   synchronization when the synchronization involves few revisions
#   but the wiki is large.
#
# - Git renames could be turned into MediaWiki renames (see TODO
#   below)
#
# - login/password support requires the user to write the password
#   cleartext in a file (see TODO below).
#
# - No way to import "one page, and all pages included in it"
#
# - Multiple remote MediaWikis have not been very well tested.

use strict;
use MediaWiki::API;
use DateTime::Format::ISO8601;
use encoding 'utf8';

# use encoding 'utf8' doesn't change STDERROR
# but we're going to output UTF-8 filenames to STDERR
binmode STDERR, ":utf8";

use URI::Escape;
use warnings;

# Mediawiki filenames can contain forward slashes. This variable decides by which pattern they should be replaced
use constant SLASH_REPLACEMENT => "%2F";

# It's not always possible to delete pages (may require some
# priviledges). Deleted pages are replaced with this content.
use constant DELETED_CONTENT => "[[Category:Deleted]]\n";

# It's not possible to create empty pages. New empty files in Git are
# sent with this content instead.
use constant EMPTY_CONTENT => "<!-- empty page -->\n";

# used to reflect file creation or deletion in diff.
use constant NULL_SHA1 => "0000000000000000000000000000000000000000";

my $remotename = $ARGV[0];
my $url = $ARGV[1];

# Accept both space-separated and multiple keys in config file.
# Spaces should be written as _ anyway because we'll use chomp.
my @tracked_pages = split(/[ \n]/, run_git("config --get-all remote.". $remotename .".pages"));
chomp(@tracked_pages);

# Just like @tracked_pages, but for MediaWiki categories.
my @tracked_categories = split(/[ \n]/, run_git("config --get-all remote.". $remotename .".categories"));
chomp(@tracked_categories);

my $wiki_login = run_git("config --get remote.". $remotename .".mwLogin");
# TODO: ideally, this should be able to read from keyboard, but we're
# inside a remote helper, so our stdin is connect to git, not to a
# terminal.
my $wiki_passwd = run_git("config --get remote.". $remotename .".mwPassword");
my $wiki_domain = run_git("config --get remote.". $remotename .".mwDomain");
chomp($wiki_login);
chomp($wiki_passwd);
chomp($wiki_domain);

# Import only last revisions (both for clone and fetch)
my $shallow_import = run_git("config --get --bool remote.". $remotename .".shallow");
chomp($shallow_import);
$shallow_import = ($shallow_import eq "true");

# Dumb push: don't update notes and mediawiki ref to reflect the last push.
#
# Configurable with mediawiki.dumbPush, or per-remote with
# remote.<remotename>.dumbPush.
#
# This means the user will have to re-import the just-pushed
# revisions. On the other hand, this means that the Git revisions
# corresponding to MediaWiki revisions are all imported from the wiki,
# regardless of whether they were initially created in Git or from the
# web interface, hence all users will get the same history (i.e. if
# the push from Git to MediaWiki loses some information, everybody
# will get the history with information lost). If the import is
# deterministic, this means everybody gets the same sha1 for each
# MediaWiki revision.
my $dumb_push = run_git("config --get --bool remote.$remotename.dumbPush");
unless ($dumb_push) {
	$dumb_push = run_git("config --get --bool mediawiki.dumbPush");
}
chomp($dumb_push);
$dumb_push = ($dumb_push eq "true");

my $wiki_name = $url;
$wiki_name =~ s/[^\/]*:\/\///;
# If URL is like http://user:password@example.com/, we clearly don't
# want the password in $wiki_name. While we're there, also remove user
# and '@' sign, to avoid author like MWUser@HTTPUser@host.com
$wiki_name =~ s/^.*@//;

# Commands parser
my $entry;
my @cmd;
while (<STDIN>) {
	chomp;
	@cmd = split(/ /);
	if (defined($cmd[0])) {
		# Line not blank
		if ($cmd[0] eq "capabilities") {
			die("Too many arguments for capabilities") unless (!defined($cmd[1]));
			mw_capabilities();
		} elsif ($cmd[0] eq "list") {
			die("Too many arguments for list") unless (!defined($cmd[2]));
			mw_list($cmd[1]);
		} elsif ($cmd[0] eq "import") {
			die("Invalid arguments for import") unless ($cmd[1] ne "" && !defined($cmd[2]));
			mw_import($cmd[1]);
		} elsif ($cmd[0] eq "option") {
			die("Too many arguments for option") unless ($cmd[1] ne "" && $cmd[2] ne "" && !defined($cmd[3]));
			mw_option($cmd[1],$cmd[2]);
		} elsif ($cmd[0] eq "push") {
			mw_push($cmd[1]);
		} else {
			print STDERR "Unknown command. Aborting...\n";
			last;
		}
	} else {
		# blank line: we should terminate
		last;
	}

	BEGIN { $| = 1 } # flush STDOUT, to make sure the previous
			 # command is fully processed.
}

########################## Functions ##############################

# MediaWiki API instance, created lazily.
my $mediawiki;

sub mw_connect_maybe {
	if ($mediawiki) {
	    return;
	}
	$mediawiki = MediaWiki::API->new;
	$mediawiki->{config}->{api_url} = "$url/api.php";
	if ($wiki_login) {
		if (!$mediawiki->login({
			lgname => $wiki_login,
			lgpassword => $wiki_passwd,
			lgdomain => $wiki_domain,
		})) {
			print STDERR "Failed to log in mediawiki user \"$wiki_login\" on $url\n";
			print STDERR "(error " .
			    $mediawiki->{error}->{code} . ': ' .
			    $mediawiki->{error}->{details} . ")\n";
			exit 1;
		} else {
			print STDERR "Logged in with user \"$wiki_login\".\n";
		}
	}
}

sub get_mw_first_pages {
	my $some_pages = shift;
	my @some_pages = @{$some_pages};

	my $pages = shift;

	# pattern 'page1|page2|...' required by the API
	my $titles = join('|', @some_pages);

	my $mw_pages = $mediawiki->api({
		action => 'query',
		titles => $titles,
	});
	if (!defined($mw_pages)) {
		print STDERR "fatal: could not query the list of wiki pages.\n";
		print STDERR "fatal: '$url' does not appear to be a mediawiki\n";
		print STDERR "fatal: make sure '$url/api.php' is a valid page.\n";
		exit 1;
	}
	while (my ($id, $page) = each(%{$mw_pages->{query}->{pages}})) {
		if ($id < 0) {
			print STDERR "Warning: page $page->{title} not found on wiki\n";
		} else {
			$pages->{$page->{title}} = $page;
		}
	}
}

sub get_mw_pages {
	mw_connect_maybe();

	my %pages; # hash on page titles to avoid duplicates
	my $user_defined;
	if (@tracked_pages) {
		$user_defined = 1;
		# The user provided a list of pages titles, but we
		# still need to query the API to get the page IDs.

		my @some_pages = @tracked_pages;
		while (@some_pages) {
			my $last = 50;
			if ($#some_pages < $last) {
				$last = $#some_pages;
			}
			my @slice = @some_pages[0..$last];
			get_mw_first_pages(\@slice, \%pages);
			@some_pages = @some_pages[51..$#some_pages];
		}
	}
	if (@tracked_categories) {
		$user_defined = 1;
		foreach my $category (@tracked_categories) {
			if (index($category, ':') < 0) {
				# Mediawiki requires the Category
				# prefix, but let's not force the user
				# to specify it.
				$category = "Category:" . $category;
			}
			my $mw_pages = $mediawiki->list( {
				action => 'query',
				list => 'categorymembers',
				cmtitle => $category,
				cmlimit => 'max' } )
			    || die $mediawiki->{error}->{code} . ': ' . $mediawiki->{error}->{details};
			foreach my $page (@{$mw_pages}) {
				$pages{$page->{title}} = $page;
			}
		}
	}
	if (!$user_defined) {
		# No user-provided list, get the list of pages from
		# the API.
		my $mw_pages = $mediawiki->list({
			action => 'query',
			list => 'allpages',
			aplimit => 500,
		});
		if (!defined($mw_pages)) {
			print STDERR "fatal: could not get the list of wiki pages.\n";
			print STDERR "fatal: '$url' does not appear to be a mediawiki\n";
			print STDERR "fatal: make sure '$url/api.php' is a valid page.\n";
			exit 1;
		}
		foreach my $page (@{$mw_pages}) {
			$pages{$page->{title}} = $page;
		}
	}
	return values(%pages);
}

sub run_git {
	open(my $git, "-|:encoding(UTF-8)", "git " . $_[0]);
	my $res = do { local $/; <$git> };
	close($git);

	return $res;
}


sub get_last_local_revision {
	# Get note regarding last mediawiki revision
	my $note = run_git("notes --ref=$remotename/mediawiki show refs/mediawiki/$remotename/master 2>/dev/null");
	my @note_info = split(/ /, $note);

	my $lastrevision_number;
	if (!(defined($note_info[0]) && $note_info[0] eq "mediawiki_revision:")) {
		print STDERR "No previous mediawiki revision found";
		$lastrevision_number = 0;
	} else {
		# Notes are formatted : mediawiki_revision: #number
		$lastrevision_number = $note_info[1];
		chomp($lastrevision_number);
		print STDERR "Last local mediawiki revision found is $lastrevision_number";
	}
	return $lastrevision_number;
}

# Remember the timestamp corresponding to a revision id.
my %basetimestamps;

sub get_last_remote_revision {
	mw_connect_maybe();

	my @pages = get_mw_pages();

	my $max_rev_num = 0;

	foreach my $page (@pages) {
		my $id = $page->{pageid};

		my $query = {
			action => 'query',
			prop => 'revisions',
			rvprop => 'ids|timestamp',
			pageids => $id,
		};

		my $result = $mediawiki->api($query);

		my $lastrev = pop(@{$result->{query}->{pages}->{$id}->{revisions}});

		$basetimestamps{$lastrev->{revid}} = $lastrev->{timestamp};

		$max_rev_num = ($lastrev->{revid} > $max_rev_num ? $lastrev->{revid} : $max_rev_num);
	}

	print STDERR "Last remote revision found is $max_rev_num.\n";
	return $max_rev_num;
}

# Clean content before sending it to MediaWiki
sub mediawiki_clean {
	my $string = shift;
	my $page_created = shift;
	# Mediawiki does not allow blank space at the end of a page and ends with a single \n.
	# This function right trims a string and adds a \n at the end to follow this rule
	$string =~ s/\s+$//;
	if ($string eq "" && $page_created) {
		# Creating empty pages is forbidden.
		$string = EMPTY_CONTENT;
	}
	return $string."\n";
}

# Filter applied on MediaWiki data before adding them to Git
sub mediawiki_smudge {
	my $string = shift;
	if ($string eq EMPTY_CONTENT) {
		$string = "";
	}
	# This \n is important. This is due to mediawiki's way to handle end of files.
	return $string."\n";
}

sub mediawiki_clean_filename {
	my $filename = shift;
	$filename =~ s/@{[SLASH_REPLACEMENT]}/\//g;
	# [, ], |, {, and } are forbidden by MediaWiki, even URL-encoded.
	# Do a variant of URL-encoding, i.e. looks like URL-encoding,
	# but with _ added to prevent MediaWiki from thinking this is
	# an actual special character.
	$filename =~ s/[\[\]\{\}\|]/sprintf("_%%_%x", ord($&))/ge;
	# If we use the uri escape before
	# we should unescape here, before anything

	return $filename;
}

sub mediawiki_smudge_filename {
	my $filename = shift;
	$filename =~ s/\//@{[SLASH_REPLACEMENT]}/g;
	$filename =~ s/ /_/g;
	# Decode forbidden characters encoded in mediawiki_clean_filename
	$filename =~ s/_%_([0-9a-fA-F][0-9a-fA-F])/sprintf("%c", hex($1))/ge;
	return $filename;
}

sub literal_data {
	my ($content) = @_;
	print STDOUT "data ", bytes::length($content), "\n", $content;
}

sub mw_capabilities {
	# Revisions are imported to the private namespace
	# refs/mediawiki/$remotename/ by the helper and fetched into
	# refs/remotes/$remotename later by fetch.
	print STDOUT "refspec refs/heads/*:refs/mediawiki/$remotename/*\n";
	print STDOUT "import\n";
	print STDOUT "list\n";
	print STDOUT "push\n";
	print STDOUT "\n";
}

sub mw_list {
	# MediaWiki do not have branches, we consider one branch arbitrarily
	# called master, and HEAD pointing to it.
	print STDOUT "? refs/heads/master\n";
	print STDOUT "\@refs/heads/master HEAD\n";
	print STDOUT "\n";
}

sub mw_option {
	print STDERR "remote-helper command 'option $_[0]' not yet implemented\n";
	print STDOUT "unsupported\n";
}

sub fetch_mw_revisions_for_page {
	my $page = shift;
	my $id = shift;
	my $fetch_from = shift;
	my @page_revs = ();
	my $query = {
		action => 'query',
		prop => 'revisions',
		rvprop => 'ids',
		rvdir => 'newer',
		rvstartid => $fetch_from,
		rvlimit => 500,
		pageids => $id,
	};

	my $revnum = 0;
	# Get 500 revisions at a time due to the mediawiki api limit
	while (1) {
		my $result = $mediawiki->api($query);

		# Parse each of those 500 revisions
		foreach my $revision (@{$result->{query}->{pages}->{$id}->{revisions}}) {
			my $page_rev_ids;
			$page_rev_ids->{pageid} = $page->{pageid};
			$page_rev_ids->{revid} = $revision->{revid};
			push(@page_revs, $page_rev_ids);
			$revnum++;
		}
		last unless $result->{'query-continue'};
		$query->{rvstartid} = $result->{'query-continue'}->{revisions}->{rvstartid};
	}
	if ($shallow_import && @page_revs) {
		print STDERR "  Found 1 revision (shallow import).\n";
		@page_revs = sort {$b->{revid} <=> $a->{revid}} (@page_revs);
		return $page_revs[0];
	}
	print STDERR "  Found ", $revnum, " revision(s).\n";
	return @page_revs;
}

sub fetch_mw_revisions {
	my $pages = shift; my @pages = @{$pages};
	my $fetch_from = shift;

	my @revisions = ();
	my $n = 1;
	foreach my $page (@pages) {
		my $id = $page->{pageid};

		print STDERR "page $n/", scalar(@pages), ": ". $page->{title} ."\n";
		$n++;
		my @page_revs = fetch_mw_revisions_for_page($page, $id, $fetch_from);
		@revisions = (@page_revs, @revisions);
	}

	return ($n, @revisions);
}

sub import_file_revision {
	my $commit = shift;
	my %commit = %{$commit};
	my $full_import = shift;
	my $n = shift;

	my $title = $commit{title};
	my $comment = $commit{comment};
	my $content = $commit{content};
	my $author = $commit{author};
	my $date = $commit{date};

	print STDOUT "commit refs/mediawiki/$remotename/master\n";
	print STDOUT "mark :$n\n";
	print STDOUT "committer $author <$author\@$wiki_name> ", $date->epoch, " +0000\n";
	literal_data($comment);

	# If it's not a clone, we need to know where to start from
	if (!$full_import && $n == 1) {
		print STDOUT "from refs/mediawiki/$remotename/master^0\n";
	}
	if ($content ne DELETED_CONTENT) {
		print STDOUT "M 644 inline $title.mw\n";
		literal_data($content);
		print STDOUT "\n\n";
	} else {
		print STDOUT "D $title.mw\n";
	}

	# mediawiki revision number in the git note
	if ($full_import && $n == 1) {
		print STDOUT "reset refs/notes/$remotename/mediawiki\n";
	}
	print STDOUT "commit refs/notes/$remotename/mediawiki\n";
	print STDOUT "committer $author <$author\@$wiki_name> ", $date->epoch, " +0000\n";
	literal_data("Note added by git-mediawiki during import");
	if (!$full_import && $n == 1) {
		print STDOUT "from refs/notes/$remotename/mediawiki^0\n";
	}
	print STDOUT "N inline :$n\n";
	literal_data("mediawiki_revision: " . $commit{mw_revision});
	print STDOUT "\n\n";
}

# parse a sequence of
# <cmd> <arg1>
# <cmd> <arg2>
# \n
# (like batch sequence of import and sequence of push statements)
sub get_more_refs {
	my $cmd = shift;
	my @refs;
	while (1) {
		my $line = <STDIN>;
		if ($line =~ m/^$cmd (.*)$/) {
			push(@refs, $1);
		} elsif ($line eq "\n") {
			return @refs;
		} else {
			die("Invalid command in a '$cmd' batch: ". $_);
		}
	}
}

sub mw_import {
	# multiple import commands can follow each other.
	my @refs = (shift, get_more_refs("import"));
	foreach my $ref (@refs) {
		mw_import_ref($ref);
	}
	print STDOUT "done\n";
}

sub mw_import_ref {
	my $ref = shift;
	# The remote helper will call "import HEAD" and
	# "import refs/heads/master".
	# Since HEAD is a symbolic ref to master (by convention,
	# followed by the output of the command "list" that we gave),
	# we don't need to do anything in this case.
	if ($ref eq "HEAD") {
		return;
	}

	mw_connect_maybe();

	my @pages = get_mw_pages();

	print STDERR "Searching revisions...\n";
	my $last_local = get_last_local_revision();
	my $fetch_from = $last_local + 1;
	if ($fetch_from == 1) {
		print STDERR ", fetching from beginning.\n";
	} else {
		print STDERR ", fetching from here.\n";
	}
	my ($n, @revisions) = fetch_mw_revisions(\@pages, $fetch_from);

	# Creation of the fast-import stream
	print STDERR "Fetching & writing export data...\n";

	$n = 0;
	my $last_timestamp = 0; # Placeholer in case $rev->timestamp is undefined

	foreach my $pagerevid (sort {$a->{revid} <=> $b->{revid}} @revisions) {
		# fetch the content of the pages
		my $query = {
			action => 'query',
			prop => 'revisions',
			rvprop => 'content|timestamp|comment|user|ids',
			revids => $pagerevid->{revid},
		};

		my $result = $mediawiki->api($query);

		my $rev = pop(@{$result->{query}->{pages}->{$pagerevid->{pageid}}->{revisions}});

		$n++;

		my %commit;
		$commit{author} = $rev->{user} || 'Anonymous';
		$commit{comment} = $rev->{comment} || '*Empty MediaWiki Message*';
		$commit{title} = mediawiki_smudge_filename(
			$result->{query}->{pages}->{$pagerevid->{pageid}}->{title}
		    );
		$commit{mw_revision} = $pagerevid->{revid};
		$commit{content} = mediawiki_smudge($rev->{'*'});

		if (!defined($rev->{timestamp})) {
			$last_timestamp++;
		} else {
			$last_timestamp = $rev->{timestamp};
		}
		$commit{date} = DateTime::Format::ISO8601->parse_datetime($last_timestamp);

		print STDERR "$n/", scalar(@revisions), ": Revision #$pagerevid->{revid} of $commit{title}\n";

		import_file_revision(\%commit, ($fetch_from == 1), $n);
	}

	if ($fetch_from == 1 && $n == 0) {
		print STDERR "You appear to have cloned an empty MediaWiki.\n";
		# Something has to be done remote-helper side. If nothing is done, an error is
		# thrown saying that HEAD is refering to unknown object 0000000000000000000
		# and the clone fails.
	}
}

sub error_non_fast_forward {
	my $advice = run_git("config --bool advice.pushNonFastForward");
	chomp($advice);
	if ($advice ne "false") {
		# Native git-push would show this after the summary.
		# We can't ask it to display it cleanly, so print it
		# ourselves before.
		print STDERR "To prevent you from losing history, non-fast-forward updates were rejected\n";
		print STDERR "Merge the remote changes (e.g. 'git pull') before pushing again. See the\n";
		print STDERR "'Note about fast-forwards' section of 'git push --help' for details.\n";
	}
	print STDOUT "error $_[0] \"non-fast-forward\"\n";
	return 0;
}

sub mw_push_file {
	my $diff_info = shift;
	# $diff_info contains a string in this format:
	# 100644 100644 <sha1_of_blob_before_commit> <sha1_of_blob_now> <status>
	my @diff_info_split = split(/[ \t]/, $diff_info);

	# Filename, including .mw extension
	my $complete_file_name = shift;
	# Commit message
	my $summary = shift;
	# MediaWiki revision number. Keep the previous one by default,
	# in case there's no edit to perform.
	my $newrevid = shift;

	my $new_sha1 = $diff_info_split[3];
	my $old_sha1 = $diff_info_split[2];
	my $page_created = ($old_sha1 eq NULL_SHA1);
	my $page_deleted = ($new_sha1 eq NULL_SHA1);
	$complete_file_name = mediawiki_clean_filename($complete_file_name);

	if (substr($complete_file_name,-3) eq ".mw") {
		my $title = substr($complete_file_name,0,-3);

		my $file_content;
		if ($page_deleted) {
			# Deleting a page usually requires
			# special priviledges. A common
			# convention is to replace the page
			# with this content instead:
			$file_content = DELETED_CONTENT;
		} else {
			$file_content = run_git("cat-file blob $new_sha1");
		}

		mw_connect_maybe();

		my $result = $mediawiki->edit( {
			action => 'edit',
			summary => $summary,
			title => $title,
			basetimestamp => $basetimestamps{$newrevid},
			text => mediawiki_clean($file_content, $page_created),
				  }, {
					  skip_encoding => 1 # Helps with names with accentuated characters
				  });
		if (!$result) {
			if ($mediawiki->{error}->{code} == 3) {
				# edit conflicts, considered as non-fast-forward
				print STDERR 'Warning: Error ' .
				    $mediawiki->{error}->{code} .
				    ' from mediwiki: ' . $mediawiki->{error}->{details} .
				    ".\n";
				return ($newrevid, "non-fast-forward");
			} else {
				# Other errors. Shouldn't happen => just die()
				die 'Fatal: Error ' .
				    $mediawiki->{error}->{code} .
				    ' from mediwiki: ' . $mediawiki->{error}->{details};
			}
		}
		$newrevid = $result->{edit}->{newrevid};
		print STDERR "Pushed file: $new_sha1 - $title\n";
	} else {
		print STDERR "$complete_file_name not a mediawiki file (Not pushable on this version of git-remote-mediawiki).\n"
	}
	return ($newrevid, "ok");
}

sub mw_push {
	# multiple push statements can follow each other
	my @refsspecs = (shift, get_more_refs("push"));
	my $pushed;
	for my $refspec (@refsspecs) {
		my ($force, $local, $remote) = $refspec =~ /^(\+)?([^:]*):([^:]*)$/
		    or die("Invalid refspec for push. Expected <src>:<dst> or +<src>:<dst>");
		if ($force) {
			print STDERR "Warning: forced push not allowed on a MediaWiki.\n";
		}
		if ($local eq "") {
			print STDERR "Cannot delete remote branch on a MediaWiki\n";
			print STDOUT "error $remote cannot delete\n";
			next;
		}
		if ($remote ne "refs/heads/master") {
			print STDERR "Only push to the branch 'master' is supported on a MediaWiki\n";
			print STDOUT "error $remote only master allowed\n";
			next;
		}
		if (mw_push_revision($local, $remote)) {
			$pushed = 1;
		}
	}

	# Notify Git that the push is done
	print STDOUT "\n";

	if ($pushed && $dumb_push) {
		print STDERR "Just pushed some revisions to MediaWiki.\n";
		print STDERR "The pushed revisions now have to be re-imported, and your current branch\n";
		print STDERR "needs to be updated with these re-imported commits. You can do this with\n";
		print STDERR "\n";
		print STDERR "  git pull --rebase\n";
		print STDERR "\n";
	}
}

sub mw_push_revision {
	my $local = shift;
	my $remote = shift; # actually, this has to be "refs/heads/master" at this point.
	my $last_local_revid = get_last_local_revision();
	print STDERR ".\n"; # Finish sentence started by get_last_local_revision()
	my $last_remote_revid = get_last_remote_revision();
	my $mw_revision = $last_remote_revid;

	# Get sha1 of commit pointed by local HEAD
	my $HEAD_sha1 = run_git("rev-parse $local 2>/dev/null"); chomp($HEAD_sha1);
	# Get sha1 of commit pointed by remotes/$remotename/master
	my $remoteorigin_sha1 = run_git("rev-parse refs/remotes/$remotename/master 2>/dev/null");
	chomp($remoteorigin_sha1);

	if ($last_local_revid > 0 &&
	    $last_local_revid < $last_remote_revid) {
		return error_non_fast_forward($remote);
	}

	if ($HEAD_sha1 eq $remoteorigin_sha1) {
		# nothing to push
		return 0;
	}

	# Get every commit in between HEAD and refs/remotes/origin/master,
	# including HEAD and refs/remotes/origin/master
	my @commit_pairs = ();
	if ($last_local_revid > 0) {
		my $parsed_sha1 = $remoteorigin_sha1;
		# Find a path from last MediaWiki commit to pushed commit
		while ($parsed_sha1 ne $HEAD_sha1) {
			my @commit_info =  grep(/^$parsed_sha1/, split(/\n/, run_git("rev-list --children $local")));
			if (!@commit_info) {
				return error_non_fast_forward($remote);
			}
			my @commit_info_split = split(/ |\n/, $commit_info[0]);
			# $commit_info_split[1] is the sha1 of the commit to export
			# $commit_info_split[0] is the sha1 of its direct child
			push(@commit_pairs, \@commit_info_split);
			$parsed_sha1 = $commit_info_split[1];
		}
	} else {
		# No remote mediawiki revision. Export the whole
		# history (linearized with --first-parent)
		print STDERR "Warning: no common ancestor, pushing complete history\n";
		my $history = run_git("rev-list --first-parent --children $local");
		my @history = split('\n', $history);
		@history = @history[1..$#history];
		foreach my $line (reverse @history) {
			my @commit_info_split = split(/ |\n/, $line);
			push(@commit_pairs, \@commit_info_split);
		}
	}

	foreach my $commit_info_split (@commit_pairs) {
		my $sha1_child = @{$commit_info_split}[0];
		my $sha1_commit = @{$commit_info_split}[1];
		my $diff_infos = run_git("diff-tree -r --raw -z $sha1_child $sha1_commit");
		# TODO: we could detect rename, and encode them with a #redirect on the wiki.
		# TODO: for now, it's just a delete+add
		my @diff_info_list = split(/\0/, $diff_infos);
		# Keep the first line of the commit message as mediawiki comment for the revision
		my $commit_msg = (split(/\n/, run_git("show --pretty=format:\"%s\" $sha1_commit")))[0];
		chomp($commit_msg);
		# Push every blob
		while (@diff_info_list) {
			my $status;
			# git diff-tree -z gives an output like
			# <metadata>\0<filename1>\0
			# <metadata>\0<filename2>\0
			# and we've split on \0.
			my $info = shift(@diff_info_list);
			my $file = shift(@diff_info_list);
			($mw_revision, $status) = mw_push_file($info, $file, $commit_msg, $mw_revision);
			if ($status eq "non-fast-forward") {
				# we may already have sent part of the
				# commit to MediaWiki, but it's too
				# late to cancel it. Stop the push in
				# the middle, but still give an
				# accurate error message.
				return error_non_fast_forward($remote);
			}
			if ($status ne "ok") {
				die("Unknown error from mw_push_file()");
			}
		}
		unless ($dumb_push) {
			run_git("notes --ref=$remotename/mediawiki add -m \"mediawiki_revision: $mw_revision\" $sha1_commit");
			run_git("update-ref -m \"Git-MediaWiki push\" refs/mediawiki/$remotename/master $sha1_commit $sha1_child");
		}
	}

	print STDOUT "ok $remote\n";
	return 1;
}