Possible Daylight Saving Time issue

[jlanzarotta]

Hello,

Thanks for a great library, it is very helpful. I am looking to upgrade from v2.5.4 to v2.6.0; however, I ran into an issue with Daylight Savings Time and wanted to ask about what is going on...

To prove out the issue, I wrote a simple program that just uses the current time and prints it out in various formats.

Version 2.5.4

package main

import (
  "log"
  "time"
  "github.com/dromara/carbon/v2"
)

func main() {
    log.SetFlags(0)

    log.Printf("***** Using Go.Time\n")

    // Gets the current time
    t_now := time.Now()

    // Get the current timezone location
    location := t_now.Location()

    // Print the current timezone name
    log.Printf("Current Timezone[%s]\n", location.String())
    log.Printf("Current Time[%s]\n", t_now)

    log.Printf("***** Converting Go.Time -> Carbon\n")

    var c carbon.Carbon = carbon.NewCarbon(t_now)
    log.Printf("carbon timezone[%s].\n", c.Timezone())
    log.Printf("carbon IS08601 date/time[%s].\n", c.ToIso8601String())
    log.Printf("carbon RFC3339 date/time[%s].\n", c.ToRfc3339String())
    log.Printf("carbon IsDST[%v].\n", c.IsDST())

    log.Printf("***** Using Carbon\n")

    carbon.SetTimezone(carbon.UTC)
    carbon.SetWeekStartsAt(carbon.Sunday)
    carbon.SetLocale("en")

    var now carbon.Carbon = carbon.Now()
    log.Printf("  UTC String()            now=[%s]\n", now.String())
    log.Printf("  UTC ToString()          now=[%s]\n", now.ToString())
    log.Printf("  UTC ToDateTimeString    now=[%s]\n", now.ToDateTimeString())

    log.Printf("Local now=[%s]\n", now.SetTimezone(carbon.Local))
    log.Printf("Local String()            now=[%s]\n", now.String())
    log.Printf("Local ToString()          now=[%s]\n", now.ToString())
    log.Printf("Local ToDateTimeString()  now=[%s]\n", now.ToDateTimeString())

    log.Printf("  EST now=[%s]\n", now.SetTimezone(carbon.EST))
    log.Printf("  EST String()            now=[%s]\n", now.String())
    log.Printf("  EST ToString()          now=[%s]\n", now.ToString())
    log.Printf("  EST ToDateTimeString()  now=[%s]\n", now.ToDateTimeString())
}

Version 2.6.0

package main

import (
    "log"
    "time"

    "github.com/dromara/carbon/v2"
)

func main() {
    log.SetFlags(0)

    log.Printf("***** Using Go.Time\n")

    // Gets the current time
    t_now := time.Now()

    // Get the current timezone location
    location := t_now.Location()

    // Print the current timezone name
    log.Printf("Current Timezone[%s]\n", location.String())
    log.Printf("Current Time[%s]\n", t_now)

    log.Printf("***** Converting Go.Time -> Carbon\n")

    var c carbon.Carbon = *carbon.NewCarbon(t_now)
    log.Printf("carbon timezone[%s].\n", c.Timezone())
    log.Printf("carbon IS08601 date/time[%s].\n", c.ToIso8601String())
    log.Printf("carbon RFC3339 date/time[%s].\n", c.ToRfc3339String())
    log.Printf("carbon IsDST[%v].\n", c.IsDST())

    log.Printf("***** Using Carbon\n")

    carbon.SetLayout(carbon.ISO8601Layout)
    carbon.SetTimezone(carbon.UTC)
    carbon.SetWeekStartsAt(carbon.Sunday)
    carbon.SetLocale("en")

    var now carbon.Carbon = *carbon.Now()
    log.Printf("  UTC String()            now=[%s]\n", now.String())
    log.Printf("  UTC ToString()          now=[%s]\n", now.ToString())
    log.Printf("  UTC ToDateTimeString    now=[%s]\n", now.ToDateTimeString())

    log.Printf("Local now=[%s]\n", now.SetTimezone(carbon.Local))
    log.Printf("Local String()            now=[%s]\n", now.String())
    log.Printf("Local ToString()          now=[%s]\n", now.ToString())
    log.Printf("Local ToDateTimeString()  now=[%s]\n", now.ToDateTimeString())

    log.Printf("  EST now=[%s]\n", now.SetTimezone(carbon.EST))
    log.Printf("  EST String()            now=[%s]\n", now.String())
    log.Printf("  EST ToString()          now=[%s]\n", now.ToString())
    log.Printf("  EST ToDateTimeString()  now=[%s]\n", now.ToDateTimeString())
}

The output for each program is as follows...

Version 2.5.4

***** Using Go.Time
Current Timezone[Local]
Current Time[2025-03-26 12:20:46.4571965 -0400 EDT m=+0.000508701]
***** Converting Go.Time -> Carbon
carbon timezone[EDT].
carbon IS08601 date/time[2025-03-26T12:20:46-04:00].
carbon RFC3339 date/time[2025-03-26T12:20:46-04:00].
carbon IsDST[true].
***** Using Carbon
  UTC String()            now=[2025-03-26 12:20:46]
  UTC ToString()          now=[2025-03-26 12:20:46.4587764 -0400 EDT]
  UTC ToDateTimeString    now=[2025-03-26 12:20:46]
Local now=[2025-03-26 12:20:46]
Local String()            now=[2025-03-26 12:20:46]
Local ToString()          now=[2025-03-26 12:20:46.4587764 -0400 EDT]
Local ToDateTimeString()  now=[2025-03-26 12:20:46]
  EST now=[2025-03-26 11:20:46]
  EST String()            now=[2025-03-26 12:20:46]
  EST ToString()          now=[2025-03-26 12:20:46.4587764 -0400 EDT]
  EST ToDateTimeString()  now=[2025-03-26 12:20:46]

Vs

Version 2.6.0

***** Using Go.Time
Current Timezone[Local]
Current Time[2025-03-26 12:21:47.744579 -0400 EDT m=+0.000558001]
***** Converting Go.Time -> Carbon
carbon timezone[Local].
carbon IS08601 date/time[2025-03-26T12:21:47-04:00].
carbon RFC3339 date/time[2025-03-26T12:21:47-04:00].
carbon IsDST[true].
***** Using Carbon
  UTC String()            now=[2025-03-26T16:21:47+00:00]
  UTC ToString()          now=[2025-03-26 16:21:47.7451059 +0000 UTC]
  UTC ToDateTimeString    now=[2025-03-26 16:21:47]
Local now=[2025-03-26T16:21:47+00:00]
Local String()            now=[2025-03-26T16:21:47+00:00]
Local ToString()          now=[2025-03-26 16:21:47.7451059 +0000 UTC]
Local ToDateTimeString()  now=[2025-03-26 16:21:47]
  EST now=[2025-03-26T11:21:47-05:00]
  EST String()            now=[2025-03-26T11:21:47-05:00]
  EST ToString()          now=[2025-03-26 11:21:47.7451059 -0500 EST]
  EST ToDateTimeString()  now=[2025-03-26 11:21:47]

As you might have notices, the EST times are off by 1 hour between the two versions. Version 2.5.4 says -0400 EST, while version 2.6.0 says -0500 EST. Is there something I am not doing correctly, or is this an issue in the library? Again, thanks for the library, I greatly appreciate it.

[kuafuRace]

The reason for the difference is that the default timezone of v2.5.X is Local, but the default timezone of v2.6.X is UTC, and the default timezone of time.Now() is also Local. So in v2.6.X, you need to specify the timezone of time.Now().In(time.UTC).

[jlanzarotta]

Thanks for the reply.

There still seems to be something wrong in my logic... I have removed the dependency on time and I am just using carbon...

Taken this code example,

package main

import (
	"log"
	"github.com/dromara/carbon/v2"
)

func main() {
     log.SetFlags(0)

    carbon.SetLayout(carbon.ISO8601Layout)
    carbon.SetTimezone(carbon.UTC)
    carbon.SetWeekStartsAt(carbon.Sunday)
    carbon.SetLocale("en")

    log.Printf("  UTC String()            now=[%s]\n", now.String())
    log.Printf("  UTC ToString()          now=[%s]\n", now.ToString())
    log.Printf("  UTC ToDateTimeString    now=[%s]\n", now.ToDateTimeString())

    log.Printf("  EST now=[%s]\n", now.SetTimezone(carbon.EST))
    log.Printf("  EST String()            now=[%s]\n", now.String())
    log.Printf("  EST ToString()          now=[%s]\n", now.ToString())
    log.Printf("  EST ToDateTimeString()  now=[%s]\n", now.ToDateTimeString())
}

The code gets the default carbon time in UTC, then converts it to EST, I would have expected carbon to have converted the EST time with the fact that Daylight Savings Time is currently happening.

  UTC String()            now=[2025-03-27T11:44:13+00:00]
  UTC ToString()          now=[2025-03-27 11:44:13.19295 +0000 UTC]
  UTC ToDateTimeString    now=[2025-03-27 11:44:13]
  EST now=[2025-03-27T06:44:13-05:00]
  EST String()            now=[2025-03-27T06:44:13-05:00]
  EST ToString()          now=[2025-03-27 06:44:13.19295 -0500 EST]
  EST ToDateTimeString()  now=[2025-03-27 06:44:13]

However, the actual date/time is 2025-03-27 07:44:13.19295, this is 1 hours off because we are now in Daylight Savings Time.

With version 2.6.0 of carbon, how to I handle Daylight Savings Time?

Thanks,

[kuafuRace]

Try using v2.6.1

[jlanzarotta]

Thanks, I will give that a try.

[jlanzarotta]

I rebuilt the sample program using v2.6.1; however, that did not seem to change anything.

  UTC String()            now=[2025-03-27T13:23:32+00:00]
  UTC ToString()          now=[2025-03-27 13:23:32.8907113 +0000 UTC]
  UTC ToDateTimeString    now=[2025-03-27 13:23:32]
  EST now=[2025-03-27T08:23:32-05:00]
  EST String()            now=[2025-03-27T08:23:32-05:00]
  EST ToString()          now=[2025-03-27 08:23:32.8907113 -0500 EST]
  EST ToDateTimeString()  now=[2025-03-27 08:23:32]

Carbon is telling me it is 08:23.32 while the actual time is 09:23.32...

[kuafuRace]

Which city are you in?

[jlanzarotta]

East Coast of USA. We are Eastern time; however, we are now in Daylight Savings Time.

[kuafuRace]

I know where the problem is. You first set the global timezone UTC. After setting it, carbon.Local becomes UTC, not your current timezone EDT/EST .
If you want to get your current date/time, you can set the global timezone to Local, or specify a specific location as the local timezone, such as

carbon.SetTimezone(carbon.Local)

or
carbon.Now().SetTimezone(carbon.NewYork)

or 
carbon.Now(carbon.NewYork)

[jlanzarotta]

Hello,
Thanks for the information. I think I am still stuck though. Let me explain my situation a bit differently.

package main

import (
    "log"
    "github.com/dromara/carbon/v2"
)

func main() {
    log.SetFlags(0)

    log.Printf("UTC[%s]\n", "2025-03-28T12:03:25+00:00")
    log.Printf("EST[%s]\n", carbon.Parse("2025-03-28T12:03:25+00:00").SetTimezone(carbon.EST).ToIso8601String())
}

Take this situation. I have an ISO8601 formatted date/time and I want to convert that to EST. In this situation, I get this:

UTC[2025-03-28T12:03:25+00:00]
EST[2025-03-28T07:03:25-05:00]

Again, the EST time is 1 hour off because of Daylight Savings Time. I store the date/time in UTC in a database and then convert it to the local timezone the application is running. In this case, it is EST.

Any idea on how I can get the correct conversion?

Thanks,

[kuafuRace]

fmt.Println(carbon.Parse("2025-03-28T12:03:25+00:00").SetTimezone(carbon.EST).ToString(carbon.NewYork))

or 

fmt.Println(carbon.Parse("2025-03-28T12:03:25+00:00", carbon.EST).ToString(carbon.NewYork))

// 2025-03-28 08:03:25 -0400 EDT

[kuafuRace]

The next version will fix this issue by no longer updating time.Local when setting the global default time zone.

[jlanzarotta]

Many thanks and much appreciated.

[kuafuRace]

v2.6.2-rc1 has been released, you can try it

[jlanzarotta]

I tried that version. Still seeing the same outcome. Maybe I am doing it wrong. Here is a simplified test..

package main

import (
    "log"

    "github.com/dromara/carbon/v2"
)

func main() {
    log.SetFlags(0)

    log.Printf("UTC[%s]\n", "2025-03-28T12:03:25+00:00")
    log.Printf("EST[%s]\n", carbon.Parse("2025-03-28T12:03:25+00:00").SetTimezone(carbon.EST).ToIso8601String())
}

With the output of...

UTC[2025-03-28T12:03:25+00:00]
EST[2025-03-28T07:03:25-05:00]

I would have expected the EST date/time to be...

EST[2025-03-28T08:03:25-04:00]