#!/usr/bin/perl

use strict ;
use warnings ;

use CGI ;
use CGI::Carp qw( fatalsToBrowser ) ;
use Fcntl qw( :DEFAULT :flock ) ;

my $cgi = new CGI ;
print $cgi->header ;

my $dir   = "/www/test" ;
my $count = "/www/test/counter.dat" ;
my $file  = $cgi->param( 'file' ) ;

if ( $file =~ /.(jpe?g|gif)$/i )
{
    accept_file( $file, $dir, next_file_number( $count ), $1 ) ;
}
else
{
    print <<"END_OF_MSG" ;
<h1>$file</h1>
Sorry, but you have either not selected a file to upload or you are
trying to upload an invalid picture file.  Only the following file
extensions are supported: /.jpeg/.gif/.jpg.  Please press the 'back'
button below to return to the Upload form.
END_OF_MSG
}

sub accept_file
{
    my ( $file, $path, $file_num, $ext ) = @_ ;
    open FH, ">$path/$file_num.$ext"
      or die "Can't open $path/$file_num.$ext: $!" ;
    binmode FH ;
    while ( <$file> )
    {
        print FH $_;
    }
    close FH ;
}

sub next_file_number
{
    my $counter_file = shift ;
    sysopen FH, $counter_file, O_RDWR|O_CREAT 
                            or die "Can't open $counter_file: $!" ;
    flock( FH, LOCK_EX )    or die "Can't write-lock $counter_file: $!" ;
    # Now we have acquired the lock, it's safe for I/O
    my $num = <FH> || 0 ;
    seek FH, 0, 0           or die "Can't rewind $counter_file: $!" ;
    truncate FH, 0          or die "Can't truncate $counter_file: $!" ;
    print FH ++$num, "\n"   or die "Can't write $counter_file: $!" ;
    close FH                or die "Can't close $counter_file: $!" ;
    return $num ;
}