utils.FromUnixMilli: Replace logic by time.UnixMilli

Required for incremental configurations in icinga-notifications as it
introduces time comparisons: Icinga/icinga-notifications#5

References #753.

pkg/types/unix_milli_test.go

@@ -1,6 +1,7 @@
 package types
 
 import (
+	"github.com/icinga/icingadb/pkg/utils"
 	"github.com/stretchr/testify/require"
 	"testing"
 	"time"
@@ -16,6 +17,7 @@ func TestUnixMilli_MarshalJSON(t *testing.T) {
 		{"zero", UnixMilli{}, `null`},
 		{"epoch", UnixMilli(time.Unix(0, 0)), `0`},
 		{"nonzero", UnixMilli(time.Unix(1234567890, 62500000)), `1234567890062`},
+		{"ilovefloats", UnixMilli(utils.FromUnixMilli(1714489037339)), `1714489037339`},
 	}
 
 	for _, st := range subtests {

pkg/utils/utils.go

@@ -9,7 +9,6 @@ import (
 	"github.com/lib/pq"
 	"github.com/pkg/errors"
 	"golang.org/x/exp/utf8string"
-	"math"
 	"net"
 	"os"
 	"path/filepath"
@@ -21,9 +20,7 @@ import (
 // FromUnixMilli creates and returns a time.Time value
 // from the given milliseconds since the Unix epoch ms.
 func FromUnixMilli(ms int64) time.Time {
-	sec, dec := math.Modf(float64(ms) / 1e3)
-
-	return time.Unix(int64(sec), int64(dec*(1e9)))
+	return time.UnixMilli(ms)
 }
 
 // Name returns the declared name of type t.

pkg/utils/utils_test.go

@@ -3,6 +3,7 @@ package utils
 import (
 	"github.com/stretchr/testify/require"
 	"testing"
+	"time"
 )
 
 func TestChanFromSlice(t *testing.T) {
@@ -52,3 +53,8 @@ func requireClosedEmpty(t *testing.T, ch <-chan int) {
 		require.Fail(t, "receiving should not block")
 	}
 }
+
+func TestFromUnixMilli_Float(t *testing.T) {
+	const ms = 1714489037339
+	require.Equal(t, time.UnixMilli(ms), FromUnixMilli(ms))
+}