path: root/IkiWiki/Rcs/git.pm

#!/usr/bin/perl
# Git backend for IkiWiki.
# Copyright 2006  Recai Oktaş <roktas@debian.org>
#
# Licensed under the same terms as IkiWiki.

use warnings;
use strict;
use IkiWiki;

package IkiWiki;

my $origin_branch    = 'origin';            # Git ref for main repository
my $master_branch    = 'master';            # Working branch
my $sha1_pattern     = qr/[0-9a-fA-F]{40}/; # pattern to validate Git sha1sums
my $dummy_commit_msg = 'dummy commit';      # will be used in all dummy commits
                            # and skipped in recent changes list
my $web_commit_msg   = qr/^web commit by (\w+):?(.*)/; # pattern for web commits

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.
        open STDERR, ">&STDOUT"
            or error("Cannot dup STDOUT: $!");
        # Git commands want to be in wc.
        chdir $config{srcdir}
            or error("Cannot chdir to $config{srcdir}: $!");
        exec @cmdline or error("Cannot exec '@cmdline': $!");
    }
    # In parent.

    my @lines;
    while (<$OUT>) {
        chomp;
        push @lines, $_;
    }

    close $OUT;

    ($error_handler || sub { })->("'@cmdline' failed: $!") if $?;

    return wantarray ? @lines : ($? == 0);
}
# Convenient wrappers.
sub run_or_die ($@) { _safe_git(\&IkiWiki::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, $target)
               or debug("rename '$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', $master_branch)) {
                run_or_cry('git-checkout','-f',$master_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', $master_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;
} #}}}

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) = @_;

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

    my %ci;

    # Header line.
    HEADER: while (my $line = shift @{ $dt_ref }) {
        return if $line !~ m/^diff-tree (\S+)/;

        my $sha1 = $1;
        $ci{'sha1'} = $sha1;
        last HEADER;
    }

    # Identification lines for the commit.
    IDENT: 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 ($name =~ m/^([^<]+) <([^@]+)/) {
                my ($fullname, $username) = ($1, $2);
                $ci{"${who}_fullname"}    = $fullname;
                $ci{"${who}_username"}    = $username;
            } else {
                $ci{"${who}_fullname"} =
                    $ci{"${who}_username"} = $name;
            }
        } elsif ($line =~ m/^$/) {
            # Trailing empty line signals next section.
            last IDENT;
        }
    }

    error("No 'tree' or 'parents' seen in diff-tree output")
        if !defined $ci{'tree'} || !defined $ci{'parents'};

    $ci{'parent'} = @{ $ci{'parents'} }[0];

    # Commit message.
    COMMENT: while (my $line = shift @{ $dt_ref }) {
        if ($line =~ m/^$/) {
            # Trailing empty line signals next section.
            last COMMENT;
        };
        $line =~ s/^    //;
        push @{ $ci{'comment'} }, $line;
    }

    # Modified files.
    FILE: while (my $line = shift @{ $dt_ref }) {
        if ($line =~ m{^
            :([0-7]{6})[ ]       # from mode
            ([0-7]{6})[ ]        # to mode
            ([0-9a-fA-F]{40})[ ] # from sha1
            ([0-9a-fA-F]{40})[ ] # to sha1
            (.)                  # status
            ([0-9]{0,3})\t       # similarity
            (.*)                 # file
        $}xo) {
            my ($sha1_from, $sha1_to, $file) =
               ($3,         $4,       $7   );

            if ($file =~ m/^"(.*)"$/) {
                ($file=$1) =~ s/\\([0-7]{1,3})/chr(oct($1))/eg;
            }
            if (length $file) {
                push @{ $ci{'details'} }, {
                    'file'      => $file,
                    'sha1_from' => $sha1_from,
                    'sha1_to'   => $sha1_to,
                };
            }
            next FILE;
        };
        last FILE;
    }

    error("No detail in diff-tree output") if !defined $ci{'details'};

    return \%ci;
} #}}}

sub git_commit_info (;$$) { #{{{
    # Return an array of commit info hashes of num commits (default: 1)
    # starting from the given sha1sum (default: HEAD).

    my ($sha1, $num) = @_;

    $num ||= 1;

    my @raw_lines =
        run_or_die(qq{git-rev-list --max-count=$num $sha1 |
        git-diff-tree --stdin --pretty=raw -c -M -r});

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

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

sub git_sha1 (;$) { #{{{
    # Return head sha1sum (of given file).

    my $file = shift || q{--};

    my ($sha1) = run_or_die('git-rev-list', '--max-count=1', 'HEAD', $file);
    ($sha1) = $sha1 =~ m/($sha1_pattern)/; # sha1sum is untainted now
    debug("Empty sha1sum for '$file'.") if !length $sha1;
    return $sha1;
} #}}}

sub rcs_update () { #{{{
    # Update working directory.

    run_or_cry('git-pull', $origin_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) = @_;

    my $sha1 = git_sha1($file);
    return defined $sha1 ? $sha1 : q{};
} #}}}

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 ($file, $message, $rcstoken) = @_;

    # XXX: Wiki directory is in the unlocked state when starting this
    # action.  But it takes time for a Git process to finish its job
    # (especially if a merge required), so we must re-lock to prevent
    # race conditions.  Only when the time of the real commit action
    # (i.e. git-push(1)) comes, we'll unlock the directory.
    lockwiki();

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

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

    # git-commit(1) returns non-zero if file has not been really changed.
    # so we should ignore its exit status (hence run_or_non).
    if (run_or_non('git-commit', '-m', $message, '-i', $file)) {
        unlockwiki();
        run_or_cry('git-push', $origin_branch);
    }

    return undef; # success
} #}}}

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

    my ($file) = @_;

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

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

    my ($num) = @_;

    eval q{use CGI 'escapeHTML'};
    eval q{use Date::Parse};
    eval q{use Time::Duration};

    my ($sha1, $type, $when, $diffurl, $user, @pages, @message, @rets);
    INFO: foreach my $ci (git_commit_info('HEAD', $num)) {
        my $title = @{ $ci->{'comment'} }[0];

        # Skip redundant commits.
        next INFO if ($title eq $dummy_commit_msg);

        $sha1 = $ci->{'sha1'};
        $type = "web";
        $when = concise(ago(time - $ci->{'author_epoch'}));

        foreach my $bit (@{ $ci->{'details'} }) {
            my $diffurl = $config{'diffurl'};
            my $file    = $bit->{'file'};

            $diffurl =~ s/\[\[file\]\]/$file/go;
            $diffurl =~ s/\[\[sha1_parent\]\]/$ci->{'parent'}/go;
            $diffurl =~ s/\[\[sha1_from\]\]/$bit->{'sha1_from'}/go;
            $diffurl =~ s/\[\[sha1_to\]\]/$bit->{'sha1_to'}/go;

            push @pages, {
                link => htmllink("", pagename($file), 1),
                diffurl => $diffurl,
            },
        }

        push @message, { line => escapeHTML($title) };

        if (defined $message[0] &&
            $message[0]->{line} =~ m/$web_commit_msg/) {
            $user = "$1";
            $message[0]->{line} = $2;
        } else {
            $type ="git";
            $user = $ci->{'author_username'};
        }

        push @rets, {
            rev        => $sha1,
            user       => htmllink("", $user, 1),
            committype => $type,
            when       => $when,
            message    => [@message],
            pages      => [@pages],
        } if @pages;

        $sha1 = $type = $when = $diffurl = $user = undef;
        @pages = @message = ();
    }

    return @rets;
} #}}}

sub rcs_notify () { #{{{
    # Send notification mail to subscribed users.
    #
    # In usual Git usage, hooks/update script is presumed to send
    # notification mails (see git-receive-pack(1)).  But we prefer
    # hooks/post-update to support IkiWiki commits coming from a
    # cloned repository (through command line) because post-update
    # is called _after_ each ref in repository is updated (update
    # hook is called _before_ the repository is updated).  Since
    # post-update hook does not accept command line arguments, we
    # don't have an $ENV variable in this function.
    #
    # Here, we rely on a simple fact: we can extract all parts of the
    # notification content by parsing the "HEAD" commit (which also
    # triggers a refresh of IkiWiki pages) and we can obtain the diff
    # by comparing HEAD and HEAD^ (the previous commit).

    my $sha1 = 'HEAD'; # the commit which triggers this action

    my $ci = git_commit_info($sha1);
    if (!defined $ci) {
        warn "Cannot parse info for '$sha1' commit";
        return;
    }

    my @changed_pages = map { $_->{'file'} } @{ $ci->{'details'} };

    my ($user, $message);
    if (@{ $ci->{'comment'} }[0] =~ m/$web_commit_msg/) {
        $user    = "$1";
        $message = $2;
    } else {
        $user    = $ci->{'author_username'};
        $message = join "\n", @{ $ci->{'comment'} };
    }

    require IkiWiki::UserInfo;
    my @email_recipients = commit_notify_list($user, @changed_pages);
    return if !@email_recipients;

    # TODO: if a commit spans multiple pages, this will send
    # subscribers a diff that might contain pages they did not
    # sign up for. Should separate the diff per page and
    # reassemble into one mail with just the pages subscribed to.
    my $diff = join "\n", run_or_die('git-diff', "${sha1}^", $sha1);

    my $subject = "$config{wikiname} update of ";
    if (@changed_pages > 2) {
        $subject .= "$changed_pages[0] $changed_pages[1] etc";
    } else {
        $subject .= join " ", @changed_pages;
    }
    $subject .= " by $user";

    my $template = HTML::Template->new(
        filename => "$config{templatedir}/notifymail.tmpl"
    );
    $template->param(
        wikiname => $config{wikiname},
        diff     => $diff,
        user     => $user,
        message  => $message,
    );

    eval q{use Mail::Sendmail};
    foreach my $email (@email_recipients) {
        sendmail(
            To      => $email,
            From    => "$config{wikiname} <$config{adminemail}>",
            Subject => $subject,
            Message => $template->output,
        ) or error("Failed to send update notification mail: $!");
    }
} #}}}

sub rcs_getctime ($) { #{{{
    # Get the ctime of file.

    my ($file) = @_;

    my $sha1  = git_sha1($file);
    my $ci    = git_commit_info($sha1);
    my $ctime = $ci->{'author_epoch'};
    debug("ctime for '$file': ". localtime($ctime) . "\n");

    return $ctime;
} #}}}

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