Re: [BackupPC-users] jLib bug with md5sum stuff

Robin Lee Powell wrote at about 21:48:17 -0800 on Monday, December 6, 2010:
 > On Mon, Dec 06, 2010 at 12:32:01PM -0800, Robin Lee Powell wrote:
 > > 
 > > substr outside of string at /usr/local/lib64/BackupPC/jLib.pm line 162.
 > > Use of uninitialized value in concatenation (.) or string at 
 > > /usr/local/lib64/BackupPC/jLib.pm line 162.
 > > 
 > > The line(s) in question:
 > > 
 > >             $datalast = substr($data[($i-1)%2], $rsize, _128KB-$rsize)
 > >                         . substr($data[$i%2], 0 ,$rsize);
 > > 
 > > in zFile2MD5
 > > 
 > > I have no idea how that could happen.  -_-  Will help debug any way
 > > requested.
 > 
 > Had to figure it out sooner rather than later.  :)
 > 
 > It happens when a file is > 128KiB but < 256KiB, so only one buffer
 > is full.  Fix:
 > 
 > --- /tmp/jLib.pm        2010-12-07 05:47:42.086646699 +0000
 > +++ /usr/local/lib64/BackupPC/jLib.pm   2010-12-07 05:46:55.108231972 +0000
 > @@ -159,8 +159,8 @@
 >                 while ( ($rsize = $fh->read(\$data[(++$i)%2], _128KB)) == 
 > _128KB
 >                         &&  ($totsize += $rsize) < _1MB) {}
 >                 $totsize +=$rsize if $rsize < _128KB; # Add back in partial 
 > read
 > -           $datalast = ( $data[($i-1)%2] ? substr($data[($i-1)%2], $rsize, 
 > _128KB-$rsize) : '' )
 > -                       . ( $data[$i%2] ? substr($data[$i%2], 0 ,$rsize) : 
 > '' );
 > +           $datalast = substr($data[($i-1)%2], $rsize, _128KB-$rsize)
 > +                       . substr($data[$i%2], 0 ,$rsize);
 >      }
 >      $filesize = $totsize if $totsize < _1MB; #Already know the size because 
 > read it all
 >      if ($filesize == 0) { # Try to find size from attrib file
 > 

OK I was confused for a second there since usually the convention is
to use '---' as the original code and '+++' as the new code...

Well actually, I had found and fixed that bug a *long* time ago (Dec
2009) or earlier but the new version was not updated on the Wiki.

Actually, my correction is IMO simpler and less kludgey. Here it is
and my apologies for not updating it earlier
Hmmmm if per convention the '---' is the original code, then I don't
remember writing the code that way (it looks rather klugey so if I did
my apologies). The '+++' code which by convention is the mod seems
wrong for exactly the reason you mention.

            $datalast = ($i > 1 ? 
                                         substr($data[($i-1)%2], $rsize, 
_128KB-$rsize) : '')
                        . substr($data[$i%2], 0 ,$rsize); #Last 128KB (up to 
1MB)

In fact, the "$i>1" is precisely there to make sure that it is done
correctly when only one buffer is full (it concatenates it with '').

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