Converting datetime string to valid localtime value (seconds)

vladb has asked for the wisdom of the Perl Monks concerning the following question:

While working on a small log monitoring utility, I encountered a few issues trying to convert datetime string appearing in a log entry to a valid localtime value such that localtime($logtime_in_seconds) would represent the exact time the log entry was made.

I've played with a number of Date:: modules to no avail. One particular module that I thought would help is Date::Manip. Here's the code snippet that demonstrates the problem (or shell I call it a 'bug'?):

use strict;
use Date::Manip;

my $line = qq{1.2.3.4 - - [15/May/2003:01:05:02 -0600] "GET /foobar"};

my( @mon ) = ( "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug",
+ "Sep" , "Oct", "Nov", "Dec" );
my $i = 0;
my %mon = map { $_ => ++$i } @mon;

if ($aline =~ m/
        ([\d\.]+)   # IP        
        .*?\[([^\s]+?)\s  # date        
         ([-+]\d+)  # zone
         \]\s
         (.*)       # text
         /x) 
 {

    my ($ip, $date, $zone, $text) = ($1, $2, $3, $4);    
    print "($ip, $date, $zone, $text)\n";
    my ($d, $mon, $timestr) = split("/", $date);
    $d =~ s/^0//g; 
    my ($y, $h, $mn, $s) = split(":", $timestr);

    # calculate zone offset (in seconds)
    my $zf = ($zone =~ m/^-/) ? -1 : 1; # zone factor
    my @z = split("",$zone); shift @z; 
    my $zsec = $z[0]*216000+$z[1]*3600+$z[2]*60+$z[3];

    print "Log date values: $mon{$mon}, $d, $y, $h, $mn, $s\n";
    print "*** ERROR ***>> Date_SecsSince1970($mon{$mon}, $d, $y, $h, 
+$mn, $s) = " . 
        localtime(Date_SecsSince1970($mon{$mon}, $d, $y, $h, $mn, $s))
+ . " <<***\n";

    my $time = Date_SecsSince1970($mon{$mon}, $d, $y, $h, $mn, $s) + $
+zf*$zsec;
    print "parsed time: ".localtime($time)."; original: $date $zone\n"
+;
}
[download]

This produces the following output:

(1.2.3.4, 15/May/2003:01:05:02, -0600, "GET /foobar")
Log date values: 5, 15, 2003, 01, 05, 02
*** ERROR ***>> Date_SecsSince1970(5, 15, 2003, 01, 05, 02) = Wed May 
+14 18:05:02 2003 <<***
parsed time: Wed May 14 12:05:02 2003; original: 15/May/2003:01:05:02 
+-0600
[download]

Note the *** ERROR *** line. While the log date value is 15 (of May), the Date_SecsSince1970() method converts it to 14th (or, to be precise, it returns an invalid second count value by, apparently, missing a day). You may disregard the hour value as this may be related to time zone offset calculations (the $zsec variable).

Having played with this module for awhile, I now feel it may not be the right tool in this case. Has any of you come across similar issues? What would be the best module / approach to use?

_____________________
"We've all heard that a million monkeys banging on a million typewriters will eventually reproduce
the entire works of Shakespeare. Now, thanks to the Internet, we know this is not true."

Robert Wilensky, University of California

Back to Seekers of Perl Wisdom