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Date: Mon, 18 Aug 2003 23:59:14 +0200 (CEST)
To: Luke Ehresman <lehresma@css.tayloru.edu>
cc: internals@lists.php.net
In-Reply-To: <20030818215556.GB23568@john.css.tayloru.edu>
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References: <20030818215556.GB23568@john.css.tayloru.edu>
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Subject: Re: [PHP-DEV] Resolved gmmktime() bug (patch enclosed)
From: derick@php.net (Derick Rethans)

Hi,

can you please put all this information in the bugreport, so that we can 
track thie proceedings of this problem? I'll assign it to myself that so 
that I won't forget about it either :)

regards,
Derick

On Mon, 18 Aug 2003, Luke Ehresman wrote:

> Hi,
> 
> A co-worker and I have been working on some intensive timestamp/timezone
> manipulation code for the past week or so, and ran across what we believed
> to be a bug in the way PHP handled gmmktime().  Browsing through the code,
> sure enough I found the source of the problem.  I fixed it, and have
> attached a patch.
> 
> As I was searching around, I discovered that this has been an open bug
> since 4.0.6 (2 years!).  I believe that this patch should fix most of the
> issues related to the following problem:
>     http://bugs.php.net/bug.php?id=14391
> 
> 
> The Problem:
> ============
> The function gmmktime() is supposed to take a date in GMT as a paramter
> and return a timestamp in GMT.  No manipulation of the time should occur.
> The only circumstance in which manipulation of the time should happen is
> if the seventh parameter (is_dst) is set to 1.  This is the expected
> behavior.  However, in reality I noticed that when I didn't specify a
> seventh parameter, it was applying a daylight savings time offset when I
> tried to get the epoch.  See the example code.
> 
> <?php
> 
>     // Get a timestamp for the epoch (jan 1, 1970)
>     echo "<pre>";
>     echo gmmktime(0,0,0,1,1,1970,1)."\n";
>     echo gmmktime(0,0,0,1,1,1970,0)."\n";
>     echo gmmktime(0,0,0,1,1,1970)."\n";
> 
>     // Now get timestamp for June 1
>     echo "\n";
>     echo gmmktime(0,0,0,6,1,1970,1)."\n";
>     echo gmmktime(0,0,0,6,1,1970,0)."\n";
>     echo gmmktime(0,0,0,6,1,1970)."\n";
> 
> ?>
> 
> I expected the first set of outputs to look like this:
> 
>     -3600
>     0
>     0
> 
> Which it does, so this is fine.  However, The second block of outputs is
> in June which if I had been using simply mktime(), I would have expected a
> DST offset (note: DST = daylight savings time) to be applied by default
> (on the 3rd command).  However, since I'm using gmmktime() by default no
> DST offset should be applied.  The odd behavior manifests itself in the
> second block of output:
> 
>     13046400
>     13050000
>     13046400
> 
> This is pretty meaningless until you realize what is actually going on.
> The last output, which is generated by a gmmktime() that has no 7th
> parameter, is applying an offset for daylight savings time.
> 
> The Solution
> ============
> I had a moment of panic and was sincerely hoping that GMT did not actually
> use daylight savings time, so I did some research and found that while the
> timezone that contains Greenwich actually does use daylight savings time,
> the GMT standard time reference does not.  So right there I knew something
> was wrong on the PHP side.  I loaded up the source of PHP (like a good
> open source enthusiast), and sure enough, I discovered the source of the
> problem (no pun intended).
> 
> PHP is using the C function php_mktime() for both mktime() and gmmktime().
> There is a flag as a parameter called "gm" which is 1 or 0 depending on
> whether it was called from mktime() or gmmktime().  The problem is that
> there is no check before applying the server's daylight savings
> information to the timestamp.
> 
> As a fix for this, I changed the behavior so that by default if there is
> no 7th parameter for gmmktime, it will not apply any DST offset.  This
> differs from mktime which by default will appy the server's DST offset.
> 
> I have attached patches for both PHP php-5.0.0b1 and php-4.3.2.  I would
> imagine the same code would work on most recent versions of PHP as it
> doesn't seem that this function has had much recent development.  The
> patch can be applied by using the following:
> 
>     $ cd /usr/local/php-4.3.2
>     $ patch -p2 < ~/gmmktime-php_4.3.2.patch
> 
> Feel free to contact me if you have any questions.
> 
> Luke
> 

-- 
"Interpreting what the GPL actually means is a job best left to those
                    that read the future by examining animal entrails."
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 Derick Rethans                                 http://derickrethans.nl/ 
 International PHP Magazine                          http://php-mag.net/
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