path: root/IkiWiki/Plugin/git.pm

#!/usr/bin/perl
package IkiWiki::Plugin::git;

use warnings;
use strict;
use IkiWiki;
use Encode;
use open qw{:utf8 :std};

my $sha1_pattern     = qr/[0-9a-fA-F]{40}/; # pattern to validate Git sha1sums
my $dummy_commit_msg = 'dummy commit';      # message to skip in recent changes
my $git_dir=undef;

sub import {
    hook(type => "checkconfig", id => "git", call => \&checkconfig);
    hook(type => "getsetup", id => "git", call => \&getsetup);
    hook(type => "genwrapper", id => "git", call => \&genwrapper);
    hook(type => "rcs", id => "rcs_update", call => \&rcs_update);
    hook(type => "rcs", id => "rcs_prepedit", call => \&rcs_prepedit);
    hook(type => "rcs", id => "rcs_commit", call => \&rcs_commit);
    hook(type => "rcs", id => "rcs_commit_staged", call => \&rcs_commit_staged);
    hook(type => "rcs", id => "rcs_add", call => \&rcs_add);
    hook(type => "rcs", id => "rcs_remove", call => \&rcs_remove);
    hook(type => "rcs", id => "rcs_rename", call => \&rcs_rename);
    hook(type => "rcs", id => "rcs_recentchanges", call => \&rcs_recentchanges);
    hook(type => "rcs", id => "rcs_diff", call => \&rcs_diff);
    hook(type => "rcs", id => "rcs_getctime", call => \&rcs_getctime);
    hook(type => "rcs", id => "rcs_getmtime", call => \&rcs_getmtime);
    hook(type => "rcs", id => "rcs_receive", call => \&rcs_receive);
    hook(type => "rcs", id => "rcs_preprevert", call => \&rcs_preprevert);
    hook(type => "rcs", id => "rcs_revert", call => \&rcs_revert);
}

sub checkconfig () {
    if (! defined $config{gitorigin_branch}) {
        $config{gitorigin_branch}="origin";
    }
    if (! defined $config{gitmaster_branch}) {
        $config{gitmaster_branch}="master";
    }
    if (defined $config{git_wrapper} &&
        length $config{git_wrapper}) {
        push @{$config{wrappers}}, {
            wrapper => $config{git_wrapper},
            wrappermode => (defined $config{git_wrappermode} ? $config{git_wrappermode} : "06755"),
            wrapper_background_command => $config{git_wrapper_background_command},
        };
    }

    if (defined $config{git_test_receive_wrapper} &&
        length $config{git_test_receive_wrapper} &&
        defined $config{untrusted_committers} &&
        @{$config{untrusted_committers}}) {
        push @{$config{wrappers}}, {
            test_receive => 1,
            wrapper => $config{git_test_receive_wrapper},
            wrappermode => (defined $config{git_wrappermode} ? $config{git_wrappermode} : "06755"),
        };
    }

    # Avoid notes, parser does not handle and they only slow things down.
    $ENV{GIT_NOTES_REF}="";
    
    # Run receive test only if being called by the wrapper, and not
    # when generating same.
    if ($config{test_receive} && ! exists $config{wrapper}) {
        require IkiWiki::Receive;
        IkiWiki::Receive::test();
    }
}

sub getsetup () {
    return
        plugin => {
            safe => 0, # rcs plugin
            rebuild => undef,
            section => "rcs",
        },
        git_wrapper => {
            type => "string",
            example => "/git/wiki.git/hooks/post-update",
            description => "git hook to generate",
            safe => 0, # file
            rebuild => 0,
        },
        git_wrapper_background_command => {
            type => "string",
            example => "git push github",
            description => "shell command for git_wrapper to run, in the background",
            safe => 0, # command
            rebuild => 0,
        },
        git_wrappermode => {
            type => "string",
            example => '06755',
            description => "mode for git_wrapper (can safely be made suid)",
            safe => 0,
            rebuild => 0,
        },
        git_test_receive_wrapper => {
            type => "string",
            example => "/git/wiki.git/hooks/pre-receive",
            description => "git pre-receive hook to generate",
            safe => 0, # file
            rebuild => 0,
        },
        untrusted_committers => {
            type => "string",
            example => [],
            description => "unix users whose commits should be checked by the pre-receive hook",
            safe => 0,
            rebuild => 0,
        },
        historyurl => {
            type => "string",
            example => "http://git.example.com/gitweb.cgi?p=wiki.git;a=history;f=[[file]];hb=HEAD",
            description => "gitweb url to show file history ([[file]] substituted)",
            safe => 1,
            rebuild => 1,
        },
        diffurl => {
            type => "string",
            example => "http://git.example.com/gitweb.cgi?p=wiki.git;a=blobdiff;f=[[file]];h=[[sha1_to]];hp=[[sha1_from]];hb=[[sha1_commit]];hpb=[[sha1_parent]]",
            description => "gitweb url to show a diff ([[file]], [[sha1_to]], [[sha1_from]], [[sha1_commit]], and [[sha1_parent]] substituted)",
            safe => 1,
            rebuild => 1,
        },
        gitorigin_branch => {
            type => "string",
            example => "origin",
            description => "where to pull and push changes (set to empty string to disable)",
            safe => 0, # paranoia
            rebuild => 0,
        },
        gitmaster_branch => {
            type => "string",
            example => "master",
            description => "branch that the wiki is stored in",
            safe => 0, # paranoia
            rebuild => 0,
        },
}

sub genwrapper {
    if ($config{test_receive}) {
        require IkiWiki::Receive;
        return IkiWiki::Receive::genwrapper();
    }
    else {
        return "";
    }
}

sub safe_git (&@) {
    # Start a child process safely without resorting /bin/sh.
    # Return command output or success state (in scalar context).

    my ($error_handler, @cmdline) = @_;

    my $pid = open my $OUT, "-|";

    error("Cannot fork: $!") if !defined $pid;

    if (!$pid) {
        # In child.
        # Git commands want to be in wc.
        if (! defined $git_dir) {
            chdir $config{srcdir}
                or error("cannot chdir to $config{srcdir}: $!");
        }
        else {
            chdir $git_dir
                or error("cannot chdir to $git_dir: $!");
        }
        exec @cmdline or error("Cannot exec '@cmdline': $!");
    }
    # In parent.

    # git output is probably utf-8 encoded, but may contain
    # other encodings or invalidly encoded stuff. So do not rely
    # on the normal utf-8 IO layer, decode it by hand.
    binmode($OUT);

    my @lines;
    while (<$OUT>) {
        $_=decode_utf8($_, 0);

        chomp;

        push @lines, $_;
    }

    close $OUT;

    $error_handler->("'@cmdline' failed: $!") if $? && $error_handler;

    return wantarray ? @lines : ($? == 0);
}
# Convenient wrappers.
sub run_or_die ($@) { safe_git(\&error, @_) }
sub run_or_cry ($@) { safe_git(sub { warn @_ },  @_) }
sub run_or_non ($@) { safe_git(undef,            @_) }


sub merge_past ($$$) {
    # Unlike with Subversion, Git cannot make a 'svn merge -rN:M file'.
    # Git merge commands work with the committed changes, except in the
    # implicit case of '-m' of git checkout(1).  So we should invent a
    # kludge here.  In principle, we need to create a throw-away branch
    # in preparing for the merge itself.  Since branches are cheap (and
    # branching is fast), this shouldn't cost high.
    #
    # The main problem is the presence of _uncommitted_ local changes.  One
    # possible approach to get rid of this situation could be that we first
    # make a temporary commit in the master branch and later restore the
    # initial state (this is possible since Git has the ability to undo a
    # commit, i.e. 'git reset --soft HEAD^').  The method can be summarized
    # as follows:
    #
    #   - create a diff of HEAD:current-sha1
    #   - dummy commit
    #   - create a dummy branch and switch to it
    #   - rewind to past (reset --hard to the current-sha1)
    #   - apply the diff and commit
    #   - switch to master and do the merge with the dummy branch
    #   - make a soft reset (undo the last commit of master)
    #
    # The above method has some drawbacks: (1) it needs a redundant commit
    # just to get rid of local changes, (2) somewhat slow because of the
    # required system forks.  Until someone points a more straight method
    # (which I would be grateful) I have implemented an alternative method.
    # In this approach, we hide all the modified files from Git by renaming
    # them (using the 'rename' builtin) and later restore those files in
    # the throw-away branch (that is, we put the files themselves instead
    # of applying a patch).

    my ($sha1, $file, $message) = @_;

    my @undo;      # undo stack for cleanup in case of an error
    my $conflict;  # file content with conflict markers

    eval {
        # Hide local changes from Git by renaming the modified file.
        # Relative paths must be converted to absolute for renaming.
        my ($target, $hidden) = (
            "$config{srcdir}/${file}", "$config{srcdir}/${file}.${sha1}"
        );
        rename($target, $hidden)
            or error("rename '$target' to '$hidden' failed: $!");
        # Ensure to restore the renamed file on error.
        push @undo, sub {
            return if ! -e "$hidden"; # already renamed
            rename($hidden, $target)
                or warn "rename '$hidden' to '$target' failed: $!";
        };

        my $branch = "throw_away_${sha1}"; # supposed to be unique

        # Create a throw-away branch and rewind backward.
        push @undo, sub { run_or_cry('git', 'branch', '-D', $branch) };
        run_or_die('git', 'branch', $branch, $sha1);

        # Switch to throw-away branch for the merge operation.
        push @undo, sub {
            if (!run_or_cry('git', 'checkout', $config{gitmaster_branch})) {
                run_or_cry('git', 'checkout','-f',$config{gitmaster_branch});
            }
        };
        run_or_die('git', 'checkout', $branch);

        # Put the modified file in _this_ branch.
        rename($hidden, $target)
            or error("rename '$hidden' to '$target' failed: $!");

        # _Silently_ commit all modifications in the current branch.
        run_or_non('git', 'commit', '-m', $message, '-a');
        # ... and re-switch to master.
        run_or_die('git', 'checkout', $config{gitmaster_branch});

        # Attempt to merge without complaining.
        if (!run_or_non('git', 'pull', '--no-commit', '.', $branch)) {
            $conflict = readfile($target);
            run_or_die('git', 'reset', '--hard');
        }
    };
    my $failure = $@;

    # Process undo stack (in reverse order).  By policy cleanup
    # actions should normally print a warning on failure.
    while (my $handle = pop @undo) {
        $handle->();
    }

    error("Git merge failed!\n$failure\n") if $failure;

    return $conflict;
}

{
my $prefix;
sub decode_git_file ($) {
    my $file=shift;

    # git does not output utf-8 filenames, but instead
    # double-quotes them with the utf-8 characters
    # escaped as \nnn\nnn.
    if ($file =~ m/^"(.*)"$/) {
        ($file=$1) =~ s/\\([0-7]{1,3})/chr(oct($1))/eg;
    }

    # strip prefix if in a subdir
    if (! defined $prefix) {
        ($prefix) = run_or_die('git', 'rev-parse', '--show-prefix');
        if (! defined $prefix) {
            $prefix="";
        }
    }
    $file =~ s/^\Q$prefix\E//;

    return decode("utf8", $file);
}
}

sub parse_diff_tree ($) {
    # Parse the raw diff tree chunk and return the info hash.
    # See git-diff-tree(1) for the syntax.
    my $dt_ref = shift;

    # End of stream?
    return if !defined @{ $dt_ref } ||
          !defined @{ $dt_ref }[0] || !length @{ $dt_ref }[0];

    my %ci;
    # Header line.
    while (my $line = shift @{ $dt_ref }) {
        return if $line !~ m/^(.+) ($sha1_pattern)/;

        my $sha1 = $2;
        $ci{'sha1'} = $sha1;
        last;
    }

    # Identification lines for the commit.
    while (my $line = shift @{ $dt_ref }) {
        # Regexps are semi-stolen from gitweb.cgi.
        if ($line =~ m/^tree ([0-9a-fA-F]{40})$/) {
            $ci{'tree'} = $1;
        }
        elsif ($line =~ m/^parent ([0-9a-fA-F]{40})$/) {
            # XXX: collecting in reverse order
            push @{ $ci{'parents'} }, $1;
        }
        elsif ($line =~ m/^(author|committer) (.*) ([0-9]+) (.*)$/) {
            my ($who, $name, $epoch, $tz) =
               ($1,   $2,    $3,     $4 );

            $ci{  $who          } = $name;
            $ci{ "${who}_epoch" } = $epoch;
            $ci{ "${who}_tz"    } = $tz;

            if ($name =~ m/^([^<]+)\s+<([^@>]+)/) {
                $ci{"${who}_name"} = $1;
                $ci{"${who}_username"} = $2;
            }
            elsif ($name =~ m/^([^<]+)\s+<>$/) {
                $ci{"${who}_username"} = $1;
            }
            else {
                $ci{"${who}_username"} = $name;
            }
        }
        elsif ($line =~ m/^$/) {
            # Trailing empty line signals next section.
            last;
        }
    }

    debug("No 'tree' seen in diff-tree output") if !defined $ci{'tree'};
    
    if (defined $ci{'parents'}) {
        $ci{'parent'} = @{ $ci{'parents'} }[0];
    }
    else {
        $ci{'parent'} = 0 x 40;
    }

    # Commit message (optional).
    while ($dt_ref->[0] =~ /^    /) {
        my $line = shift @{ $dt_ref };
        $line =~ s/^    //;
        push @{ $ci{'comment'} }, $line;
    }
    shift @{ $dt_ref } if $dt_ref->[0] =~ /^$/;

    # Modified files.
    while (my $line = shift @{ $dt_ref }) {
        if ($line =~ m{^
            (:+)       # number of parents
            ([^\t]+)\t # modes, sha1, status
            (.*)       # file names
        $}xo) {
            my $num_parents = length $1;
            my @tmp = split(" ", $2);
            my ($file, $file_to) = split("\t", $3);
            my @mode_from = splice(@tmp, 0, $num_parents);
            my $mode_to = shift(@tmp);
            my @sha1_from = splice(@tmp, 0, $num_parents);
            my $sha1_to = shift(@tmp);
            my $status = shift(@tmp);

            if (length $file) {
                push @{ $ci{'details'} }, {
                    'file'      => decode_git_file($file),
                    'sha1_from' => $sha1_from[0],
                    'sha1_to'   => $sha1_to,
                    'mode_from' => $mode_from[0],
                    'mode_to'   => $mode_to,
                    'status'    => $status,
                };
            }
            next;
        };
        last;
    }

    return \%ci;
}

sub git_commit_info ($;$) {
    # Return an array of commit info hashes of num commits
    # starting from the given sha1sum.
    my ($sha1, $num) = @_;

    my @opts;
    push @opts, "--max-count=$num" if defined $num;

    my @raw_lines = run_or_die('git', 'log', @opts,
        '--pretty=raw', '--raw', '--abbrev=40', '--always', '-c',
        '-r', $sha1, '--', '.');

    my @ci;
    while (my $parsed = parse_diff_tree(\@raw_lines)) {
        push @ci, $parsed;
    }

    warn "Cannot parse commit info for '$sha1' commit" if !@ci;

    return wantarray ? @ci : $ci[0];
}

sub git_sha1 (;$) {
    # Return head sha1sum (of given file).
    my $file = shift || q{--};

    # Ignore error since a non-existing file might be given.
    my ($sha1) = run_or_non('git', 'rev-list', '--max-count=1', 'HEAD',
        '--', $file);
    if ($sha1) {
        ($sha1) = $sha1 =~ m/($sha1_pattern)/; # sha1 is untainted now
    }
    else {
        debug("Empty sha1sum for '$file'.");
    }
    return defined $sha1 ? $sha1 : q{};
}

sub rcs_update () {
    # Update working directory.

    if (length $config{gitorigin_branch}) {
        run_or_cry('git', 'pull', '--prune', $config{gitorigin_branch});
    }
}

sub rcs_prepedit ($) {
    # Return the commit sha1sum of the file when editing begins.
    # This will be later used in rcs_commit if a merge is required.
    my ($file) = @_;

    return git_sha1($file);
}

sub rcs_commit (@) {
    # Try to commit the page; returns undef on _success_ and
    # a version of the page with the rcs's conflict markers on
    # failure.
    my %params=@_;

    # Check to see if the page has been changed by someone else since
    # rcs_prepedit was called.
    my $cur    = git_sha1($params{file});
    my ($prev) = $params{token} =~ /^($sha1_pattern)$/; # untaint

    if (defined $cur && defined $prev && $cur ne $prev) {
        my $conflict = merge_past($prev, $params{file}, $dummy_commit_msg);
        return $conflict if defined $conflict;
    }

    return rcs_commit_helper(@_);
}

sub rcs_commit_staged (@) {
    # Commits all staged changes. Changes can be staged using rcs_add,
    # rcs_remove, and rcs_rename.
    return rcs_commit_helper(@_);
}

sub rcs_commit_helper (@) {
    my %params=@_;
    
    my %env=%ENV;

    if (defined $params{session}) {
        # Set the commit author and email based on web session info.
        my $u;
        if (defined $params{session}->param("name")) {
            $u=$params{session}->param("name");
        }
        elsif (defined $params{session}->remote_addr()) {
            $u=$params{session}->remote_addr();
        }
        if (defined $u) {
            $u=encode_utf8($u);
            $ENV{GIT_AUTHOR_NAME}=$u;
        }
        if (defined $params{session}->param("nickname")) {
            $u=encode_utf8($params{session}->param("nickname"));
            $u=~s/\s+/_/g;
            $u=~s/[^-_0-9[:alnum:]]+//g;
        }
        if (defined $u) {
            $ENV{GIT_AUTHOR_EMAIL}="$u\@web";
        }
    }

    $params{message} = IkiWiki::possibly_foolish_untaint($params{message});
    my @opts;
    if ($params{message} !~ /\S/) {
        # Force git to allow empty commit messages.
        # (If this version of git supports it.)
        my ($version)=`git --version` =~ /git version (.*)/;
        if ($version ge "1.5.4") {
            push @opts, '--cleanup=verbatim';
        }
        else {
            $params{message}.=".";
        }
    }
    if (exists $params{file}) {
        push @opts, '--', $params{file};
    }
    # git commit returns non-zero if nothing really changed.
    # So we should ignore its exit status (hence run_or_non).
    if (run_or_non('git', 'commit', '-m', $params{message}, '-q', @opts)) {
        if (length $config{gitorigin_branch}) {
            run_or_cry('git', 'push', $config{gitorigin_branch});
        }
    }
    
    %ENV=%env;
    return undef; # success
}

sub rcs_add ($) {
    # Add file to archive.

    my ($file) = @_;

    run_or_cry('git', 'add', $file);
}

sub rcs_remove ($) {
    # Remove file from archive.

    my ($file) = @_;

    run_or_cry('git', 'rm', '-f', $file);
}

sub rcs_rename ($$) {
    my ($src, $dest) = @_;

    run_or_cry('git', 'mv', '-f', $src, $dest);
}

sub rcs_recentchanges ($) {
    # List of recent changes.

    my ($num) = @_;

    eval q{use Date::Parse};
    error($@) if $@;

    my @rets;
    foreach my $ci (git_commit_info('HEAD', $num || 1)) {
        # Skip redundant commits.
        next if ($ci->{'comment'} && @{$ci->{'comment'}}[0] eq $dummy_commit_msg);

        my ($sha1, $when) = (
            $ci->{'sha1'},
            $ci->{'author_epoch'}
        );

        my @pages;
        foreach my $detail (@{ $ci->{'details'} }) {
            my $file = $detail->{'file'};

            my $diffurl = defined $config{'diffurl'} ? $config{'diffurl'} : "";
            $diffurl =~ s/\[\[file\]\]/$file/go;
            $diffurl =~ s/\[\[sha1_parent\]\]/$ci->{'parent'}/go;
            $diffurl =~ s/\[\[sha1_from\]\]/$detail->{'sha1_from'}/go;
            $diffurl =~ s/\[\[sha1_to\]\]/$detail->{'sha1_to'}/go;
            $diffurl =~ s/\[\[sha1_commit\]\]/$sha1/go;

            push @pages, {
                page => pagename($file),
                diffurl => $diffurl,
            };
        }

        my @messages;
        my $pastblank=0;
        foreach my $line (@{$ci->{'comment'}}) {
            $pastblank=1 if $line eq '';
            next if $pastblank && $line=~m/^ *(signed[ \-]off[ \-]by[ :]|acked[ \-]by[ :]|cc[ :])/i;
            push @messages, { line => $line };
        }

        my $user=$ci->{'author_username'};
        my $web_commit = ($ci->{'author'} =~ /\@web>/);
        my $nickname;

        # Set nickname only if a non-url author_username is available,
        # and author_name is an url.
        if ($user !~ /:\/\// && defined $ci->{'author_name'} &&
            $ci->{'author_name'} =~ /:\/\//) {
            $nickname=$user;
            $user=$ci->{'author_name'};
        }

        # compatability code for old web commit messages
        if (! $web_commit &&
              defined $messages[0] &&
              $messages[0]->{line} =~ m/$config{web_commit_regexp}/) {
            $user = defined $2 ? "$2" : "$3";
            $messages[0]->{line} = $4;
            $web_commit=1;
        }

        push @rets, {
            rev        => $sha1,
            user       => $user,
            nickname   => $nickname,
            committype => $web_commit ? "web" : "git",
            when       => $when,
            message    => [@messages],
            pages      => [@pages],
        } if @pages;

        last if @rets >= $num;
    }

    return @rets;
}

sub rcs_diff ($) {
    my $rev=shift;
    my ($sha1) = $rev =~ /^($sha1_pattern)$/; # untaint
    my @lines;
    foreach my $line (run_or_non("git", "show", $sha1)) {
        if (@lines || $line=~/^diff --git/) {
            push @lines, $line."\n";
        }
    }
    if (wantarray) {
        return @lines;
    }
    else {
        return join("", @lines);
    }
}

{
my %time_cache;

sub findtimes ($$) {
    my $file=shift;
    my $id=shift; # 0 = mtime ; 1 = ctime

    if (! keys %time_cache) {
        my $date;
        foreach my $line (run_or_die('git', 'log',
                '--pretty=format:%at',
                '--name-only', '--relative')) {
            if (! defined $date && $line =~ /^(\d+)$/) {
                $date=$line;
            }
            elsif (! length $line) {
                $date=undef;
            }
            else {
                my $f=decode_git_file($line);

                if (! $time_cache{$f}) {
                    $time_cache{$f}[0]=$date; # mtime
                }
                $time_cache{$f}[1]=$date; # ctime
            }
        }
    }

    return exists $time_cache{$file} ? $time_cache{$file}[$id] : 0;
}

}

sub rcs_getctime ($) {
    my $file=shift;

    return findtimes($file, 1);
}

sub rcs_getmtime ($) {
    my $file=shift;

    return findtimes($file, 0);
}

{
my $ret;
sub git_find_root {
    # The wiki may not be the only thing in the git repo.
    # Determine if it is in a subdirectory by examining the srcdir,
    # and its parents, looking for the .git directory.

    return @$ret if defined $ret;
    
    my $subdir="";
    my $dir=$config{srcdir};
    while (! -d "$dir/.git") {
        $subdir=IkiWiki::basename($dir)."/".$subdir;
        $dir=IkiWiki::dirname($dir);
        if (! length $dir) {
            error("cannot determine root of git repo");
        }
    }

    $ret=[$subdir, $dir];
    return @$ret;
}

}

sub git_parse_changes {
    my @changes = @_;

    my ($subdir, $rootdir) = git_find_root();
    my @rets;
    foreach my $ci (@changes) {
        foreach my $detail (@{ $ci->{'details'} }) {
            my $file = $detail->{'file'};

            # check that all changed files are in the subdir
            if (length $subdir &&
                ! ($file =~ s/^\Q$subdir\E//)) {
                error sprintf(gettext("you are not allowed to change %s"), $file);
            }

            my ($action, $mode, $path);
            if ($detail->{'status'} =~ /^[M]+\d*$/) {
                $action="change";
                $mode=$detail->{'mode_to'};
            }
            elsif ($detail->{'status'} =~ /^[AM]+\d*$/) {
                $action="add";
                $mode=$detail->{'mode_to'};
            }
            elsif ($detail->{'status'} =~ /^[DAM]+\d*/) {
                $action="remove";
                $mode=$detail->{'mode_from'};
            }
            else {
                error "unknown status ".$detail->{'status'};
            }

            # test that the file mode is ok
            if ($mode !~ /^100[64][64][64]$/) {
                error sprintf(gettext("you cannot act on a file with mode %s"), $mode);
            }
            if ($action eq "change") {
                if ($detail->{'mode_from'} ne $detail->{'mode_to'}) {
                    error gettext("you are not allowed to change file modes");
                }
            }

            # extract attachment to temp file
            if (($action eq 'add' || $action eq 'change') &&
                ! pagetype($file)) {
                eval q{use File::Temp};
                die $@ if $@;
                my $fh;
                ($fh, $path)=File::Temp::tempfile(undef, UNLINK => 1);
                my $cmd = "cd $git_dir && ".
                          "git show $detail->{sha1_to} > '$path'";
                if (system($cmd) != 0) {
                    error("failed writing temp file '$path'.");
                }
            }

            push @rets, {
                file => $file,
                action => $action,
                path => $path,
            };
        }
    }

    return @rets;
}

sub rcs_receive () {
    my @rets;
    while (<>) {
        chomp;
        my ($oldrev, $newrev, $refname) = split(' ', $_, 3);

        # only allow changes to gitmaster_branch
        if ($refname !~ /^refs\/heads\/\Q$config{gitmaster_branch}\E$/) {
            error sprintf(gettext("you are not allowed to change %s"), $refname);
        }

        # Avoid chdir when running git here, because the changes
        # are in the master git repo, not the srcdir repo.
        # (Also, if a subdir is involved, we don't want to chdir to
        # it and only see changes in it.)
        # The pre-receive hook already puts us in the right place.
        $git_dir=".";
        push @rets, git_parse_changes(git_commit_info($oldrev."..".$newrev));
        $git_dir=undef;
    }

    return reverse @rets;
}

sub rcs_preprevert ($) {
    my $rev=shift;
    my ($sha1) = $rev =~ /^($sha1_pattern)$/; # untaint

    # Examine changes from root of git repo, not from any subdir,
    # in order to see all changes.
    my ($subdir, $rootdir) = git_find_root();
    $git_dir=$rootdir;
    my @commits=git_commit_info($sha1, 1);
    $git_dir=undef;

    if (! @commits) {
        error "unknown commit"; # just in case
    }

    # git revert will fail on merge commits. Add a nice message.
    if (exists $commits[0]->{parents} &&
        @{$commits[0]->{parents}} > 1) {
        error gettext("you are not allowed to revert a merge");
    }

    return git_parse_changes(@commits);
}

sub rcs_revert ($) {
    # Try to revert the given rev; returns undef on _success_.
    my $rev = shift;
    my ($sha1) = $rev =~ /^($sha1_pattern)$/; # untaint

    if (run_or_non('git', 'revert', '--no-commit', $sha1)) {
        return undef;
    }
    else {
        run_or_die('git', 'reset', '--hard');
        return sprintf(gettext("Failed to revert commit %s"), $sha1);
    }
}

1