fix(time): correct export data timestamp conversions (#586)

browser/chromium/chromium.go

@@ -348,17 +348,19 @@ func isSkippedDir(name string) bool {
 	return false
 }
 
-// timeEpoch converts a WebKit/Chromium epoch timestamp (microseconds since
-// 1601-01-01) to a time.Time.
+// Offset from the Chromium epoch (1601-01-01 UTC) to the Unix epoch,
+// matching base::Time::kTimeTToMicrosecondsOffset in Chromium.
+const chromiumEpochOffsetMicros int64 = 11644473600000000
+
+// timeEpoch converts a Chromium base::Time (μs since 1601 UTC) to UTC.
+// Returns zero for non-positive input or out-of-JSON-range values.
 func timeEpoch(epoch int64) time.Time {
-	maxTime := int64(99633311740000000)
-	if epoch > maxTime {
-		return time.Date(2049, 1, 1, 1, 1, 1, 1, time.Local)
+	if epoch <= 0 {
+		return time.Time{}
 	}
-	t := time.Date(1601, 1, 1, 0, 0, 0, 0, time.Local)
-	d := time.Duration(epoch)
-	for i := 0; i < 1000; i++ {
-		t = t.Add(d)
+	t := time.UnixMicro(epoch - chromiumEpochOffsetMicros).UTC()
+	if t.Year() < 1 || t.Year() > 9999 {
+		return time.Time{}
 	}
 	return t
 }

browser/chromium/chromium_test.go

@@ -4,6 +4,7 @@ import (
 	"os"
 	"path/filepath"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -720,3 +721,47 @@ func TestSetKeyRetrievers_SatisfiesInterface(t *testing.T) {
 		SetKeyRetrievers(keyretriever.Retrievers)
 	} = (*Browser)(nil)
 }
+
+// Anchor: 2024-01-15T10:30:00Z as Chromium microseconds since 1601 UTC.
+const anchorUnixSeconds = int64(1705314600)
+
+var anchorChromiumMicros = (anchorUnixSeconds + 11644473600) * 1_000_000
+
+func TestTimeEpoch_AnchorDate(t *testing.T) {
+	got := timeEpoch(anchorChromiumMicros)
+	want := time.Date(2024, 1, 15, 10, 30, 0, 0, time.UTC)
+	assert.Equal(t, want, got)
+	assert.Equal(t, anchorUnixSeconds, got.Unix())
+}
+
+func TestTimeEpoch_ZeroReturnsZeroTime(t *testing.T) {
+	assert.True(t, timeEpoch(0).IsZero())
+}
+
+func TestTimeEpoch_NegativeReturnsZeroTime(t *testing.T) {
+	assert.True(t, timeEpoch(-1).IsZero())
+}
+
+func TestTimeEpoch_AlwaysUTC(t *testing.T) {
+	// assert.Same checks pointer equality: time.UTC and time.Local are
+	// distinct *Location globals, so this catches any regression that
+	// drops .UTC() even when the runner's TZ happens to be UTC.
+	got := timeEpoch(anchorChromiumMicros)
+	assert.Same(t, time.UTC, got.Location())
+}
+
+func TestTimeEpoch_MicrosecondPrecisionPreserved(t *testing.T) {
+	got := timeEpoch(anchorChromiumMicros + 123456)
+	assert.Equal(t, 123456*int64(time.Microsecond), int64(got.Nanosecond()))
+}
+
+func TestTimeEpoch_UnixEpochBoundary(t *testing.T) {
+	got := timeEpoch(chromiumEpochOffsetMicros)
+	assert.Equal(t, time.Unix(0, 0).UTC(), got)
+}
+
+func TestTimeEpoch_OutOfJSONRangeReturnsZero(t *testing.T) {
+	jsonBytes, err := timeEpoch(1 << 62).MarshalJSON()
+	require.NoError(t, err)
+	assert.JSONEq(t, `"0001-01-01T00:00:00Z"`, string(jsonBytes))
+}