time | encoding/json: time value not the same after encoding/decoding

[pierrre]

What version of Go are you using (go version)?

go1.7.3 linux/amd64

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/pierre/Go"
GORACE=""
GOROOT="/home/pierre/.gimme/versions/go1.7.3.src"
GOTOOLDIR="/home/pierre/.gimme/versions/go1.7.3.src/pkg/tool/linux_amd64"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build879209547=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"

What did you do?

My code

func TestTime(t *testing.T) {
	type A struct {
		T time.Time
	}
	v1 := A{
		T: time.Now(),
	}
	b, err := json.Marshal(v1)
	if err != nil {
		t.Fatal(err)
	}
	t.Log(string(b))
	var v2 A
	err = json.Unmarshal(b, &v2)
	if err != nil {
		t.Fatal(err)
	}
	t.Log(reflect.DeepEqual(v1, v2))
	t.Logf("%s %#v %s", v1.T, v1.T, v1.T.Location())
	t.Logf("%s %#v %s", v2.T, v2.T, v2.T.Location())
}

What did you expect to see?

On my local computer (I live in France)

	http_test.go:28: {"T":"2016-11-10T15:22:49.975623925+01:00"}
	http_test.go:34: true
	http_test.go:35: 2016-11-10 15:22:49.975623925 +0100 CET time.Time{sec:63614384569, nsec:975623925, loc:(*time.Location)(0x9bfc60)} Local
	http_test.go:36: 2016-11-10 15:22:49.975623925 +0100 CET time.Time{sec:63614384569, nsec:975623925, loc:(*time.Location)(0x9bfc60)} Local

What did you see instead?

On Travis CI

	http_test.go:28: {"T":"2016-11-10T14:15:29.853905878Z"}
	http_test.go:34: false
	http_test.go:35: 2016-11-10 14:15:29.853905878 +0000 UTC time.Time{sec:63614384129, nsec:853905878, loc:(*time.Location)(0x9c5aa0)} Local
	http_test.go:36: 2016-11-10 14:15:29.853905878 +0000 UTC time.Time{sec:63614384129, nsec:853905878, loc:(*time.Location)(0x9adda0)} UTC

The locations in the time are not equal.

Is it expected ?
Is it a bug ?
What should I do instead ? (I want my 2 structs to be equal with reflect.DeepEqual())

[quentinmit]

This is working as intended. You need to use t1.Equal(t2) to compare times. reflect.DeepEqual and the == operator do not work.

[pierrre]

Thank you for your answer.

Unfortunately it will be very difficult to me to use time.Time.Equal(), because my struct (in my real code) has several fields.
reflect.DeepEqual() is more convenient. (I want to compare all the struct values)

Is it possible to change reflect.DeepEqual to make it use time.Time.Equal() ?
I understand perfectly if you don't want to do it.

Do you know a third party library that support it ?

Is comparing JSON encoded values a valid alternative ?
Is the JSON encoding deterministic ? (fields order)

In the mean time I found a "fix" for my code:
I force the time's location with .In(time.UTC).

[bradfitz]

For questions about Go, see https://golang.org/wiki/Questions