go-posix-time

This is a small library whose purpose is to format a Go time.Time struct into a POSIX.1 TZ string.

Since the POSIX timezone string contains information about transitions between DST and Standard time zones, it was not possible to implement such a format before Go 1.19 when the ZoneBounds struct became available.

The library was created because the standard time format function of Go cannot produce this format.

For specifications of the format, please refer to UNIX Standard, Base Specifications, Issue 7 2018 available on-line at the Open Group Library

If you encounter any bugs, please open issues here.

Usage

import "github.com/isaric/go-posix-time/pkg/p_time"

loc, _ := time.LoadLocation("Europe/Madrid")
p_time.FormatTimeZone(time.Now().In(loc)) // "CET-1CEST,M3.5.0,M10.5.0/3"
p_time.FormatTimeZone(time.Now().In(sydney)) // "AEST-10AEDT,M10.1.0,M4.1.0/3"
p_time.FormatTimeZone(time.Now().In(kolkata)) // "IST-5:30"

Behaviour

• Transition rules are written in the wall clock in force just before the transition, as POSIX requires, so zones that fall back at midnight (EET-2EEST,M3.5.0/0,M10.5.0/0) come out right.
• A transition time of 02:00 is omitted, matching the strings in the IANA tzdata footers; any other time is written as /h[:mm[:ss]].
• Offsets keep minutes and seconds when present (<+0545>-5:45), and abbreviations that are not purely alphabetic are quoted in angle brackets.
• Zones that have abolished daylight saving produce a plain std offset.
• Rules are derived from the transitions of the year that contains the given time, so a zone whose rules change from year to year is only right for that year.