To find the timezone swaks will get the localtime() and gmtime() of the unix time (seconds since 1970-01-01 00:00:00 UTC), then use timelocal() to convert both of them back to unix time. The problem is timelocal() does a daylight savings aware version of the conversion, so if you are in a +1000/+1100 timezone then for a period of 11 hours after daylight savings starts the gmtime() function will return a time that's not in daylight savings time according to local time (as used by localtime() and timelocal()), so this will mess up the time zone calculations and make swaks put a bogus Date: header.
I've attached a program testdate.pl to demonstrate this. Run it with a parameter that is just after the start or end of daylight savings in your time zone to demonstrate (not that the "RIGHT" version of the code in my test program agrees with the date command). I will send a patch for swaks shortly. etbe@liv:/tmp$ date -d "1970-01-01 1601778959 sec utc" -R Sun, 04 Oct 2020 13:35:59 +1100 etbe@liv:/tmp$ /tmp/testdate.pl 1601778959 WRONG: Sun, 04 Oct 2020 13:35:59 +1000 RIGHT: Sun, 04 Oct 2020 13:35:59 +1100 I've also run the date -R command, my Perl code, and the swaks code on every 3000 seconds for over a year. My code gives the same result as date -R, here's the diff between my code/date -R and swaks for Australian Eastern Standard Time: $ diff date.txt swaksdate.txt 1,12c1,12 < Sun, 04 Oct 2020 04:06:22 +1100 < Sun, 04 Oct 2020 04:56:22 +1100 < Sun, 04 Oct 2020 05:46:22 +1100 < Sun, 04 Oct 2020 06:36:22 +1100 < Sun, 04 Oct 2020 07:26:22 +1100 < Sun, 04 Oct 2020 08:16:22 +1100 < Sun, 04 Oct 2020 09:06:22 +1100 < Sun, 04 Oct 2020 09:56:22 +1100 < Sun, 04 Oct 2020 10:46:22 +1100 < Sun, 04 Oct 2020 11:36:22 +1100 < Sun, 04 Oct 2020 12:26:22 +1100 < Sun, 04 Oct 2020 13:16:22 +1100 --- > Sun, 04 Oct 2020 04:06:22 +1000 > Sun, 04 Oct 2020 04:56:22 +1000 > Sun, 04 Oct 2020 05:46:22 +1000 > Sun, 04 Oct 2020 06:36:22 +1000 > Sun, 04 Oct 2020 07:26:22 +1000 > Sun, 04 Oct 2020 08:16:22 +1000 > Sun, 04 Oct 2020 09:06:22 +1000 > Sun, 04 Oct 2020 09:56:22 +1000 > Sun, 04 Oct 2020 10:46:22 +1000 > Sun, 04 Oct 2020 11:36:22 +1000 > Sun, 04 Oct 2020 12:26:22 +1000 > Sun, 04 Oct 2020 13:16:22 +1000 5243,5254c5243,5254 < Sun, 04 Apr 2021 03:26:22 +1000 < Sun, 04 Apr 2021 04:16:22 +1000 < Sun, 04 Apr 2021 05:06:22 +1000 < Sun, 04 Apr 2021 05:56:22 +1000 < Sun, 04 Apr 2021 06:46:22 +1000 < Sun, 04 Apr 2021 07:36:22 +1000 < Sun, 04 Apr 2021 08:26:22 +1000 < Sun, 04 Apr 2021 09:16:22 +1000 < Sun, 04 Apr 2021 10:06:22 +1000 < Sun, 04 Apr 2021 10:56:22 +1000 < Sun, 04 Apr 2021 11:46:22 +1000 < Sun, 04 Apr 2021 12:36:22 +1000 --- > Sun, 04 Apr 2021 03:26:22 +1100 > Sun, 04 Apr 2021 04:16:22 +1100 > Sun, 04 Apr 2021 05:06:22 +1100 > Sun, 04 Apr 2021 05:56:22 +1100 > Sun, 04 Apr 2021 06:46:22 +1100 > Sun, 04 Apr 2021 07:36:22 +1100 > Sun, 04 Apr 2021 08:26:22 +1100 > Sun, 04 Apr 2021 09:16:22 +1100 > Sun, 04 Apr 2021 10:06:22 +1100 > Sun, 04 Apr 2021 10:56:22 +1100 > Sun, 04 Apr 2021 11:46:22 +1100 > Sun, 04 Apr 2021 12:36:22 +1100 10483,10496c10483,10496 < Sun, 03 Oct 2021 03:06:22 +1100 < Sun, 03 Oct 2021 03:56:22 +1100 < Sun, 03 Oct 2021 04:46:22 +1100 < Sun, 03 Oct 2021 05:36:22 +1100 < Sun, 03 Oct 2021 06:26:22 +1100 < Sun, 03 Oct 2021 07:16:22 +1100 < Sun, 03 Oct 2021 08:06:22 +1100 < Sun, 03 Oct 2021 08:56:22 +1100 < Sun, 03 Oct 2021 09:46:22 +1100 < Sun, 03 Oct 2021 10:36:22 +1100 < Sun, 03 Oct 2021 11:26:22 +1100 < Sun, 03 Oct 2021 12:16:22 +1100 < Sun, 03 Oct 2021 13:06:22 +1100 < Sun, 03 Oct 2021 13:56:22 +1100 --- > Sun, 03 Oct 2021 03:06:22 +1000 > Sun, 03 Oct 2021 03:56:22 +1000 > Sun, 03 Oct 2021 04:46:22 +1000 > Sun, 03 Oct 2021 05:36:22 +1000 > Sun, 03 Oct 2021 06:26:22 +1000 > Sun, 03 Oct 2021 07:16:22 +1000 > Sun, 03 Oct 2021 08:06:22 +1000 > Sun, 03 Oct 2021 08:56:22 +1000 > Sun, 03 Oct 2021 09:46:22 +1000 > Sun, 03 Oct 2021 10:36:22 +1000 > Sun, 03 Oct 2021 11:26:22 +1000 > Sun, 03 Oct 2021 12:16:22 +1000 > Sun, 03 Oct 2021 13:06:22 +1000 > Sun, 03 Oct 2021 13:56:22 +1000 -- My Main Blog http://etbe.coker.com.au/ My Documents Blog http://doc.coker.com.au/
testdate.pl
Description: Perl program
