[Xymon] Bug in holidays calculation

[Tom Schmidt (tschmidt)]

I have noticed a bug in the holidays feature of Xymon.  I am using Xymon 
4.3.24 and have seen it on previous releases as well.  The issue is that 
the US Holiday of Thanksgiving is not showing the correct date during 
leap years.  Thanksgiving is the fourth Thursday in November, so is 
using this entry in holidays.cfg:

Thanksgiving:type=thu month=11 offset=4

This works correctly during non-leap years, but it is a day off during 
leap years like 2016.  I added these simple entries to holidays.cfg to 
better show the issue:

November Week 1 Thu:type=thu month=11 offset=1
November Week 2 Thu:type=thu month=11 offset=2
November Week 3 Thu:type=thu month=11 offset=3

When I look at the holidays that it calculates, I get this in the info 
column:

Holidays 2015/2016 (USA)
November Week 1 Thu	Nov 05
November Week 2 Thu	Nov 12
November Week 3 Thu	Nov 19
Thanksgiving		Nov 26
Christmas Day		Dec 25
New Year's Day		Jan 01
Easter Sunday		Mar 27
Memorial Day		May 30
Independence Day	Jul 04
Labor Day		Sep 05
November Week 1 Thu	Nov 03
November Week 2 Thu	Nov 09
November Week 3 Thu	Nov 16
Thanksgiving		Nov 23

Note that the November 2015 dates are correct, but the November 2016 
dates for Week 2 and later are a day early.  Thus it thinks Thanksgiving 
2016 is on November 23 instead of the correct November 24 date.

I looked at the source code some, but I could not follow the logic of 
how it is calculating this date incorrectly.  It is a minor bug only 
affecting those that use the holidays feature for alerts or look at the 
holidays table in the info tab.  Can someone figure out why it is not 
calculating the date offsets correctly?  It only seems to be doing this 
during leap years.

Thanks...Tom
-- 
Micron Technology, Inc., Confidential and Proprietary

Tom L. Schmidt
Central Engineering System Administrator Lead
Micron Technology, Inc.  http://www.micron.com/
8000 S. Federal Way  P.O. Box 6  Mail Stop 01-351  Boise, Idaho USA 
83707-0006
mailto:tschmidt at micron.com