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Add ToTimeInDefaultLocation/E
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Go's time parsing uses UTC when the format doesn't have a tiemzone, and
has even weirder behavior when it has a zone name but no numeric offset.
A caller to `cast.ToTime` won't know if the returned time was explicitly
in UTC, or defaulted there, so the caller cannot fix it. These new
functions allow a user to supply a different timezone to default to,
with nil using the local zone.
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heewa authored and bep committed Jul 27, 2021
1 parent c3e59ce commit e4dda5f
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Showing 3 changed files with 242 additions and 30 deletions.
5 changes: 5 additions & 0 deletions cast.go
Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,11 @@ func ToTime(i interface{}) time.Time {
return v
}

func ToTimeInDefaultLocation(i interface{}, location *time.Location) time.Time {
v, _ := ToTimeInDefaultLocationE(i, location)
return v
}

// ToDuration casts an interface to a time.Duration type.
func ToDuration(i interface{}) time.Duration {
v, _ := ToDurationE(i)
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169 changes: 169 additions & 0 deletions cast_test.go
Original file line number Diff line number Diff line change
Expand Up @@ -1293,3 +1293,172 @@ func TestToDurationE(t *testing.T) {
assert.Equal(t, test.expect, v, errmsg)
}
}

func TestToTime(t *testing.T) {
est, err := time.LoadLocation("EST")
if !assert.NoError(t, err) {
return
}

irn, err := time.LoadLocation("Iran")
if !assert.NoError(t, err) {
return
}

swd, err := time.LoadLocation("Europe/Stockholm")
if !assert.NoError(t, err) {
return
}

// time.Parse*() fns handle the target & local timezones being the same
// differently, so make sure we use one of the timezones as local by
// temporarily change it.
if !locationEqual(time.Local, swd) {
var originalLocation *time.Location
originalLocation, time.Local = time.Local, swd
defer func() {
time.Local = originalLocation
}()
}

// Test same local time in different timezones
utc2016 := time.Date(2016, time.January, 1, 0, 0, 0, 0, time.UTC)
est2016 := time.Date(2016, time.January, 1, 0, 0, 0, 0, est)
irn2016 := time.Date(2016, time.January, 1, 0, 0, 0, 0, irn)
swd2016 := time.Date(2016, time.January, 1, 0, 0, 0, 0, swd)

for _, format := range timeFormats {
t.Logf("Checking time format '%s', has timezone: %v", format.format, format.hasTimezone)

est2016str := est2016.Format(format.format)
if !assert.NotEmpty(t, est2016str) {
continue
}

swd2016str := swd2016.Format(format.format)
if !assert.NotEmpty(t, swd2016str) {
continue
}

// Test conversion without a default location
converted, err := ToTimeE(est2016str)
if assert.NoError(t, err) {
if format.hasTimezone {
// Converting inputs with a timezone should preserve it
assertTimeEqual(t, est2016, converted)
assertLocationEqual(t, est, converted.Location())
} else {
// Converting inputs without a timezone should be interpreted
// as a local time in UTC.
assertTimeEqual(t, utc2016, converted)
assertLocationEqual(t, time.UTC, converted.Location())
}
}

// Test conversion of a time in the local timezone without a default
// location
converted, err = ToTimeE(swd2016str)
if assert.NoError(t, err) {
if format.hasTimezone {
// Converting inputs with a timezone should preserve it
assertTimeEqual(t, swd2016, converted)
assertLocationEqual(t, swd, converted.Location())
} else {
// Converting inputs without a timezone should be interpreted
// as a local time in UTC.
assertTimeEqual(t, utc2016, converted)
assertLocationEqual(t, time.UTC, converted.Location())
}
}

// Conversion with a nil default location sould have same behavior
converted, err = ToTimeInDefaultLocationE(est2016str, nil)
if assert.NoError(t, err) {
if format.hasTimezone {
// Converting inputs with a timezone should preserve it
assertTimeEqual(t, est2016, converted)
assertLocationEqual(t, est, converted.Location())
} else {
// Converting inputs without a timezone should be interpreted
// as a local time in the local timezone.
assertTimeEqual(t, swd2016, converted)
assertLocationEqual(t, swd, converted.Location())
}
}

// Test conversion with a default location that isn't UTC
converted, err = ToTimeInDefaultLocationE(est2016str, irn)
if assert.NoError(t, err) {
if format.hasTimezone {
// Converting inputs with a timezone should preserve it
assertTimeEqual(t, est2016, converted)
assertLocationEqual(t, est, converted.Location())
} else {
// Converting inputs without a timezone should be interpreted
// as a local time in the given location.
assertTimeEqual(t, irn2016, converted)
assertLocationEqual(t, irn, converted.Location())
}
}

// Test conversion of a time in the local timezone with a default
// location that isn't UTC
converted, err = ToTimeInDefaultLocationE(swd2016str, irn)
if assert.NoError(t, err) {
if format.hasTimezone {
// Converting inputs with a timezone should preserve it
assertTimeEqual(t, swd2016, converted)
assertLocationEqual(t, swd, converted.Location())
} else {
// Converting inputs without a timezone should be interpreted
// as a local time in the given location.
assertTimeEqual(t, irn2016, converted)
assertLocationEqual(t, irn, converted.Location())
}
}
}
}

func assertTimeEqual(t *testing.T, expected, actual time.Time, msgAndArgs ...interface{}) bool {
if !expected.Equal(actual) {
return assert.Fail(t, fmt.Sprintf("Expected time '%s', got '%s'", expected, actual), msgAndArgs...)
}
return true
}

func assertLocationEqual(t *testing.T, expected, actual *time.Location, msgAndArgs ...interface{}) bool {
if !locationEqual(expected, actual) {
return assert.Fail(t, fmt.Sprintf("Expected location '%s', got '%s'", expected, actual), msgAndArgs...)
}
return true
}

func locationEqual(a, b *time.Location) bool {
// A note about comparring time.Locations:
// - can't only compare pointers
// - can't compare loc.String() because locations with the same
// name can have different offsets
// - can't use reflect.DeepEqual because time.Location has internal
// caches

if a == b {
return true
} else if a == nil || b == nil {
return false
}

// Check if they're equal by parsing times with a format that doesn't
// include a timezone, which will interpret it as being a local time in
// the given zone, and comparing the resulting local times.
tA, err := time.ParseInLocation("2006-01-02", "2016-01-01", a)
if err != nil {
return false
}

tB, err := time.ParseInLocation("2006-01-02", "2016-01-01", b)
if err != nil {
return false
}

return tA.Equal(tB)
}
98 changes: 68 additions & 30 deletions caste.go
Original file line number Diff line number Diff line change
Expand Up @@ -20,13 +20,20 @@ var errNegativeNotAllowed = errors.New("unable to cast negative value")

// ToTimeE casts an interface to a time.Time type.
func ToTimeE(i interface{}) (tim time.Time, err error) {
return ToTimeInDefaultLocationE(i, time.UTC)
}

// ToTimeInDefaultLocationE casts an empty interface to time.Time,
// interpreting inputs without a timezone to be in the given location,
// or the local timezone if nil.
func ToTimeInDefaultLocationE(i interface{}, location *time.Location) (tim time.Time, err error) {
i = indirect(i)

switch v := i.(type) {
case time.Time:
return v, nil
case string:
return StringToDate(v)
return StringToDateInDefaultLocation(v, location)
case int:
return time.Unix(int64(v), 0), nil
case int64:
Expand Down Expand Up @@ -1239,37 +1246,68 @@ func ToDurationSliceE(i interface{}) ([]time.Duration, error) {
// predefined list of formats. If no suitable format is found, an error is
// returned.
func StringToDate(s string) (time.Time, error) {
return parseDateWith(s, []string{
time.RFC3339,
"2006-01-02T15:04:05", // iso8601 without timezone
time.RFC1123Z,
time.RFC1123,
time.RFC822Z,
time.RFC822,
time.RFC850,
time.ANSIC,
time.UnixDate,
time.RubyDate,
"2006-01-02 15:04:05.999999999 -0700 MST", // Time.String()
"2006-01-02",
"02 Jan 2006",
"2006-01-02T15:04:05-0700", // RFC3339 without timezone hh:mm colon
"2006-01-02 15:04:05 -07:00",
"2006-01-02 15:04:05 -0700",
"2006-01-02 15:04:05Z07:00", // RFC3339 without T
"2006-01-02 15:04:05Z0700", // RFC3339 without T or timezone hh:mm colon
"2006-01-02 15:04:05",
time.Kitchen,
time.Stamp,
time.StampMilli,
time.StampMicro,
time.StampNano,
})
return StringToDateInDefaultLocation(s, time.UTC)
}

// StringToDateInDefaultLocation casts an empty interface to a time.Time,
// interpreting inputs without a timezone to be in the given location,
// or the local timezone if nil.
func StringToDateInDefaultLocation(s string, location *time.Location) (time.Time, error) {
if location == nil {
location = time.Local
}
return parseDateWith(s, location, timeFormats)
}

type timeFormat struct {
format string
hasTimezone bool
}

func parseDateWith(s string, dates []string) (d time.Time, e error) {
for _, dateType := range dates {
if d, e = time.Parse(dateType, s); e == nil {
var (
timeFormats = []timeFormat{
timeFormat{time.RFC3339, true},
timeFormat{"2006-01-02T15:04:05", false}, // iso8601 without timezone
timeFormat{time.RFC1123Z, true},
timeFormat{time.RFC1123, false},
timeFormat{time.RFC822Z, true},
timeFormat{time.RFC822, false},

timeFormat{time.RFC850, true},
timeFormat{"2006-01-02 15:04:05.999999999 -0700 MST", true}, // Time.String()
timeFormat{"2006-01-02T15:04:05-0700", true}, // RFC3339 without timezone hh:mm colon
timeFormat{"2006-01-02 15:04:05Z0700", true}, // RFC3339 without T or timezone hh:mm colon
timeFormat{"2006-01-02 15:04:05", false},

timeFormat{time.ANSIC, false},
timeFormat{time.UnixDate, false},
timeFormat{time.RubyDate, true},
timeFormat{"2006-01-02 15:04:05Z07:00", true},
timeFormat{"2006-01-02", false},
timeFormat{"02 Jan 2006", false},
timeFormat{"2006-01-02 15:04:05 -07:00", true},
timeFormat{"2006-01-02 15:04:05 -0700", true},
timeFormat{time.Kitchen, false},
timeFormat{time.Stamp, false},
timeFormat{time.StampMilli, false},
timeFormat{time.StampMicro, false},
timeFormat{time.StampNano, false},
}
)

func parseDateWith(s string, defaultLocation *time.Location, formats []timeFormat) (d time.Time, e error) {
for _, format := range formats {
if d, e = time.Parse(format.format, s); e == nil {

// Some time formats have a zone name, but no offset, so it gets
// put in that zone name (not the default one passed in to us), but
// without that zone's offset. So set the location manually.
if !format.hasTimezone && defaultLocation != nil {
year, month, day := d.Date()
hour, min, sec := d.Clock()
d = time.Date(year, month, day, hour, min, sec, d.Nanosecond(), defaultLocation)
}

return
}
}
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