blockdiff_merge

#! /usr/bin/perl

use 5.008;
use strict;
use warnings;
use Errno;

sub readall {
    my ($fh, $buf, $len) = @_;
    my $off = 0;
    while ($off != $len) {
	my $r = sysread($fh, $$buf, $len - $off, $off);
	if ($r == 0) {
	    return $off;
	} elsif ($r == -1) {
	    if ($! != Errno::EAGAIN) {
		return $off || -1;
	    }
	} else {
	    $off += $r;
	}
    }
    return $off;
}

my $DEBUG = $ENV{DEBUG} || undef;

my $fn = shift @ARGV
    or die "Usage: $0 <file>\n";

open my $fh, (-e $fn ? '+<' : '>'), $fn
    or die "failed to open file:$fn:$!";

my $blocksize = do {
    readall(\*STDIN, \my $bsbin, 4) == 4
        or die "invalid input";
    unpack'V', $bsbin;
};
warn "block size: $blocksize" if $DEBUG;

while (readall(\*STDIN, \my $offbin, 8) == 8) {
    my $rlen = readall(\*STDIN, \my $block, $blocksize);
    die "unexpected eof while reading input:$!"
        if $rlen <= 0;
    my $offset = do {
        my @o = unpack 'V2', $offbin;
        $o[0] + $o[1] * 2**32;
    };
    warn "writing at:$offset, size:$rlen" if $DEBUG;
    sysseek $fh, $offset, 0
        or die "seek failed to offset $offset:$!";
    syswrite($fh, $block, $rlen) == $rlen
        or die "write failed:$!";
}

close $fh
    or die "failed to close file:$fn:$!";

exit 0;

__END__

=head1 NAME

blockdiff_merge - merge tool for block-based diff

=head1 SYNOPSIS

    restore full backup
    % blockdiff_merge file < backup.1

    apply inrcemental backups
    % blockdiff_merge file < backup.2
    % blockdiff_merge file < backup.3
    ...

=head1 DESCRIPTION

Blockdiff_merge is a restoration tool for block-based diffs.

=head1 SEE ALSO

L<App::Blockdiff> - for general information

=head1 AUTHOR

Copyright (C) 2009 Cybozu Labs, Inc., written by Kazuho Oku

=head1 LICENSE

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

See http://www.perl.com/perl/misc/Artistic.html

=cut