Re: [Chicken-users] Timezone bugs in the posix module

[Jim Ursetto]

Posix is pretty much useless for handling timezones correctly; behavior varies 
greatly based on the OS, and I am fairly sure the direction of the wind plays a 
part as well.
Jim 

> On Sep 29, 2013, at 12:28, Andy Bennett <address@hidden> wrote:
> 
> Hi,
> 
> There seem to be some inconsistencies in the timezone handling in the
> posix module.
> 
> 
> http://api.call-cc.org/doc/library/current-seconds
> -----
> (current-seconds) procedure
> 
>    Returns the number of seconds since midnight, Jan. 1, 1970.
> -----
> 
> This seems to be true and it appears to be in Zulu time.
> 
> On a machine in BST:
> 
> -----
> $ date; csi -p '(use posix) (current-seconds)'
> Sun Sep 29 18:06:50 BST 2013
> #<unspecified>
> 1380474410.0
> -----
> 
> On a machine in CDT:
> 
> -----
> $ date; csi -p '(use posix) (current-seconds)'
> Sun Sep 29 12:06:50 CDT 2013
> #<unspecified>
> 1380474410.0
> -----
> 
> ...we get the same value. All is well.
> 
> 
> 
> However,
> 
> http://api.call-cc.org/doc/posix/seconds-%3Estring
> -----
> (seconds->string [SECONDS]) procedure
> 
>    Converts the local time represented in SECONDS into a string of the
> form "Tue May 21 13:46:22 1991". SECONDS defaults to the value of
> (current-seconds).
> -----
> 
> ..seems to be misleading as [SECONDS] is in Zulu time (as shown above).
> It is seconds->string itself which does the conversion to local time for
> the resulting string:
> 
> -----
> $ date; csi -p '(use posix) (seconds->string 0)'
> Sun Sep 29 12:08:15 CDT 2013
> #<unspecified>
> Wed Dec 31 18:00:00 1969
> -----
> 
> 
> However, there's also a bug as I get the following on a machine in BST:
> 
> -----
> $ date; csi -p '(use posix) (seconds->string 0)'
> Sun Sep 29 18:09:02 BST 2013
> #<unspecified>
> Thu Jan  1 01:00:00 1970
> -----
> 
> 
> ...and if I force that machine into BST:
> 
> -----
> $ export TZ=BST; date; csi -p '(use posix) (seconds->string 0)'
> Sun Sep 29 17:21:34 BST 2013
> #<unspecified>
> Thu Jan  1 00:00:00 1970
> -----
> 
> 
> ...and UTC:
> -----
> $ export TZ=UTC; date; csi -p '(use posix) (seconds->string 0)'
> Sun Sep 29 17:09:46 UTC 2013
> #<unspecified>
> Thu Jan  1 00:00:00 1970
> -----
> 
> 
> ...and Europe/London:
> 
> -----
> $ export TZ=Europe/London; date; csi -p '(use posix) (seconds->string 0)'
> Sun Sep 29 18:21:50 BST 2013
> #<unspecified>
> Thu Jan  1 01:00:00 1970
> -----
> 
> 
> ...and a definitely bogus timezone:
> 
> -----
> $ export TZ=rubbish; date; csi -p '(use posix) (seconds->string 0)'
> Sun Sep 29 17:25:47 rubbish 2013
> #<unspecified>
> Thu Jan  1 00:00:00 1970
> -----
> 
> ...so seconds->string sometimes ignores the timezone and doesn't throw
> an error.
> 
> -----
> $ wdate
> Sun Sep 29 12:15:19 CDT 2013 (America/Chicago)
> Sun Sep 29 17:15:19 UTC 2013 (UTC)
> Sun Sep 29 18:15:19 BST 2013 (Europe/London)
> Sun Sep 29 19:15:19 CEST 2013 (Europe/Rome)
> Mon Sep 30 06:15:19 NZDT 2013 (NZ)
> -----
> 
> 
> 
> 
> On the machine in BST:
> 
> -----
> $ export TZ=CDT; date; csi -p '(use posix) (seconds->string 0)'
> Sun Sep 29 17:10:58 CDT 2013
> #<unspecified>
> Thu Jan  1 00:00:00 1970
> -----
> 
> -----
> $ export TZ=America/Chicago; date; csi -p '(use posix) (seconds->string 0)'
> Sun Sep 29 12:11:43 CDT 2013
> #<unspecified>
> Wed Dec 31 18:00:00 1969
> -----
> 
> ...so it seems that the posix unit does not support the same names for
> timezones as the underlying operating system / date command (Linux in
> this case).
> 
> 
> -----
> $ export TZ=Europe/Rome; date; csi -p '(use posix) (seconds->string 0)'
> Sun Sep 29 19:12:52 CEST 2013
> #<unspecified>
> Thu Jan  1 01:00:00 1970
> 
> $ export TZ=CEST; date; csi -p '(use posix) (seconds->string 0)'
> Sun Sep 29 17:13:10 CEST 2013
> #<unspecified>
> Thu Jan  1 00:00:00 1970
> 
> $ export TZ=NZ; date; csi -p '(use posix) (seconds->string 0)'
> Mon Sep 30 06:14:00 NZDT 2013
> #<unspecified>
> Thu Jan  1 12:00:00 1970
> 
> $ export TZ=NZDT; date; csi -p '(use posix) (seconds->string 0)'
> Sun Sep 29 17:14:15 NZDT 2013
> #<unspecified>
> Thu Jan  1 00:00:00 1970
> -----
> 
> 
> 
> 
> 
> 
> Regards,
> @ndy
> 
> -- 
> address@hidden
> http://www.ashurst.eu.org/
> 0x7EBA75FF
> 
> 
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