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Re: Unzipping files using Archive::Zip

by Dr. Mu (Hermit)
on Aug 11, 2001 at 12:03 UTC ( #104125=note: print w/replies, xml ) Need Help??

in reply to Unzipping files using Archive::Zip

The docs are a tad confusing, and it took me awhile to figure them out, too. Here are snippets of a script that works for me. It unzips a zipfile of a known/expected name that contains one data file of a known/expected name.

Disclaimer: Omitted is a lot of security stuff that is necessary when accepting files via CGI and which is beyond the scope of this subject. Also, since this was written for a private website, there are assumptions made here that might not be appropriate for general use. Finally, be sure to use strict, and turn tainting on.

use CGI; use CGI::Carp qw(fatalsToBrowser); use Fcntl qw(:DEFAULT :flock); use Archive::Zip; my $DataPath = '/MyDataDirectory'; # ... my $query = new CGI; my $InpFile = $query->param('filData'); # 'filData' is the name of the form's file selection # control. my $FileName = reverse($InpFile); $FileName =~ s/\\.*//; # Assuming a Windows client (\), strip client's path info # from file name. $FileName = reverse($FileName); # There's GOTTA be a better way ... $FileName eq '' or die 'Wrong file.'; undef $/; my $ZipContents = <$FileName>; $/ = "\n"; OpenLockTruncate (*ZIPFILE, "$DataPath/temp/"); my $OldDefaultHandle = select(ZIPFILE); $| = 1; # Force flush without closing/unlocking file. select($OldDefaultHandle); print ZIPFILE $ZipContents; OpenLockTruncate (*INPFILE, "$DataPath/temp/unzipped.dat"); close INPFILE; my $zip = Archive::Zip->new("$DataPath/temp/"); my $file = ($zip->memberNames)[0]; $file eq 'unzipped.dat' or die "Can't find correct data file in zip."; $file = $zip->memberNamed($file) or die "Can't access data file in zip."; $file->extractToFileNamed("$DataPath/temp/unzipped.dat") == AZ_OK or die "Unable to extract data file."; # ... sub OpenLockTruncate { local *FH = $_[0]; sysopen (FH, $_[1], O_RDWR|O_CREAT, 0600) or die "Can't open $_[1]: $!"; flock (FH, LOCK_EX) or die "Can't lock $_[1]: $!"; seek (FH, 0, 0) or die "Can't rewind $_[1]: $!"; truncate (FH, 0) or die "Can't truncate $_[1]: $!"; return 1; }
As I reread this, I see there's possibly an issue with INPFILE getting unlocked when it's closed, leaving unzipped.dat vulnerable before it's extracted. I say "possibly" because ZIPFILE is still locked. If it's used consistently throughout the application as a semaphore file for unzipped.dat, there's no problem. But I suspect this may be a bug in my app that needs fixing. Once again, there's no shorter path to one's own understanding of something than to explain it to others!

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