Error while using time.Parse when timezone and offset are together

Question

I have the following code :

package main

import (
    "fmt"
    "time"
    "log"
)

func main() {
    date, err := time.Parse("Monday, 2 January 2006 15:04:05 PM MST-07:00" ,"Thursday, 17 August 2020 13:20:00 PM GMT+08:00")
    if err != nil {
      log.Fatal(err.Error())
    }
    fmt.Println(date)
}

And it fails with the following error :

2009/11/10 23:00:00 parsing time "Thursday, 17 August 2020 13:20:00 PM GMT+08:00" as "Monday, 2 January 2006 15:04:05 PM MST-07:00": cannot parse ":00" as "-07:00"

But it succeeds if I separate MST-07:00 with a space as : "MST -07:00" in both layout sample and actual string.

What am I doing wrong?

Answer 1

GMT times undergo special handling by time.Parse . The signed offset for GMT in the value must be in the range -23 through +23 excluding zero, and may not include a colon. The layout should just specify MST without an offset.

For example:

package main

import (
    "fmt"
    "log"
    "time"
)

func main() {
    for _, ts := range []string{
        "Thursday, 17 August 2020 13:20:00 PM GMT",
        "Thursday, 17 August 2020 13:20:00 PM GMT+2",
        "Thursday, 17 August 2020 13:20:00 PM GMT-2",
    } {
        date, err := time.Parse("Monday, 2 January 2006 15:04:05 PM MST", ts)
        if err != nil {
            log.Fatal(err.Error())
        }
        fmt.Println(date)
    }
}

yields the output:

crow@mac:tp$ ./example
2020-08-17 13:20:00 +0000 GMT
2020-08-17 15:20:00 +0200 GMT+2
2020-08-17 11:20:00 -0200 GMT-2

An issue was raised for this a while back, and the outcome was (with reference to an example time string containing GMT+10:00 ):

The special handling of GMT, which is needed for other things, makes it very difficult to know whether the +10:00 should be considered part of the time zone or left alone to match the layout.

and so the issue was closed without proposed changes.