How to properly parse timezone codes

Question

In the example bellow the result is always "[date] 05:00:00 +0000 UTC" regardless the timezone you choose for the parseAndPrint function. What is wrong with this code? The time should change depending on the timezone you choose. (Go Playground servers are apparently configured in UTC timezone).

http://play.golang.org/p/wP207BWYEd

package main

import (
    "fmt"
    "time"
)

func main() {
    now := time.Now()
    parseAndPrint(now, "BRT")
    parseAndPrint(now, "EDT")
    parseAndPrint(now, "UTC")
}

func parseAndPrint(now time.Time, timezone string) {
    test, err := time.Parse("15:04:05 MST", fmt.Sprintf("05:00:00 %s", timezone))
    if err != nil {
        fmt.Println(err)
        return
    }

    test = time.Date(
        now.Year(),
        now.Month(),
        now.Day(),
        test.Hour(),
        test.Minute(),
        test.Second(),
        test.Nanosecond(),
        test.Location(),
    )

    fmt.Println(test.UTC())
}

Answer 1

When you Parse a time, you are parsing it in your current location, which is OK as long as that's what you're expecting, and the timezone abbreviation is known from within your location.

If you can forgo timezones, it's far easier to normalize all the times you're dealing with into UTC.

The next easiest is handling everything with explicit offsets, like -05:00.

If you want to deal with times originating in other timezones, you need to use time.Location. You can load Locations from the local timezone db with time.LoadLocation, and parse times there with time.ParseInLocation.