Re: simple message board gone very wrong?

I looked at MSA's board and there were a handful of things I didn't like about it. I'm no perl saint, but here's what I came up with as a quick & dirty:

#!/usr/bin/perl -w
use CGI;
use strict;
my ($CGID, $i, $date);
my $P = CGI::new();
$P->import_names('NM');
if ($0=~m#^(.*)\\#){ $CGID = "$1";
} elsif ($0=~m#^(.*)/# ){ $CGID = "$1";
} else  {`pwd` =~ /(.*)/;
$CGID = "$1";
} my $gb = "$CGID/../www/html/fan/fan_main.html";
open (FH, "$gb") || die "Can't Open $gb: $!\n";
my @LINES=<FH>;
close(FH);
my $SIZE=@LINES;
my $minutes = (localtime)[1];
($minutes = "0".$minutes) if ($minutes < 10);
$date = ('Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday',  
    'Friday', 'Saturday')[(localtime)[6]] . ', ' . ('January', 
    'February', 'March', 'April', 'May', 'June', 'July', 'August', 
    'September', 'October', 'November', 
    'December')[(localtime)[4]] . " " . (localtime)[3] . ", " . 
    ((localtime)[5] + 1900) . " at " . (localtime)[2] . ":" . 
    (localtime)[1];
open (FH,">$gb") || die "Can't Open $gb: $!\n";
for ($i=0;$i<=$SIZE;$i++) { $_=$LINES[$i];
if (/<!--begin-->/) { print FH "<!--begin-->\n";
$NM::message =~ s/(\S{20})/$1 /g;
$NM::message =~ s/</&lt;/g;
$NM::message =~ s/>/&gt;/g;
$NM::message =~ s/\cM\n/<br>\n/g;
print FH "<b>$NM::message</b><!-- $ENV{'REMOTE_HOST'} --><br>\n";
if ( $NM::email ){ 
    print FH " \&lt;<a href = 'mailto:$NM::email'>$NM::name</a>\&gt;";
} else { print FH " \&lt;$NM::name\&gt;";
} print FH "<br>\n - $date<p><hr>\n\n";
} else { print FH $_;
}} close (FH);
open(FH, $gb) or die "Can't open $gb: $!";
local($/) = undef;
my $template = <FH>;
close(FH);
print "Content-type: text/html\n\n$template";
exit (0);
[download]

I'd like to add flock to that, but I haven't quite gotten it working for some reason... Any suggestions welcome.

Comment on Re: simple message board gone very wrong? Download Code

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Re: Re: simple message board gone very wrong? by AgentM (Curate) on Dec 12, 2000 at 03:35 UTC
Nice ++, but you should know that even WITH flock(), you're not absolutely safe. In any interpreted language, ALL function calls not matter how harmless-looking, are interruptable. And "interruptable" means potential race condition when your functions access the same variable (in this case, a file). While with the simple flock() call, your chances are better that you will not end in a race condition (and basically, for messages less than _POSIX_PIPE_BUF in <limits.h> there is almost zero chance of it). But the possibility still exists, so in the interests of full security and functionality, the filesystem should not be depended on as a backbone to a multiuser interfaces. Sadly, that's not an option here and it looks like the %dbhash via Perl's DBM APIs are the best bet (hint, hint, jptxs). AgentM Systems nor Nasca Enterprises nor Bone::Easy nor Macperl is responsible for the comments made by AgentM. Remember, you can build any logical system with NOR.	[reply]
Re: Re: simple message board gone very wrong? by turnstep (Parson) on Dec 12, 2000 at 07:49 UTC
At the top: `use Fcntl qw(:flock);` [download] Immediately after the 'read open': `flock(FH, LOCK_SH);` [download] Change the 'write open' to: `open(FH, "<+ $gb") or die "Could not open $gb: $!\n"; flock(FH, LOCK_EX); seek(FH,0,0); truncate(FH,0) or die "Could not truncate $gb: $!\n";` [download] Once you use flock, make sure that every process that accesess the files also uses flock. Also, the "local $/" should be in it's own block, otherwise anything else you add to the bottom of this script will be in "ultraslurp mode"	[reply] [d/l] [select]

AgentM Systems nor Nasca Enterprises nor Bone::Easy nor Macperl is responsible for the comments made by AgentM. Remember, you can build any logical system with NOR.