schema: add UnknownLocation and IsZoneKnown

Change-Id: Ia056d03a367502ea4d06e5748cc7de7072c3e12c

pkg/schema/schema.go

@@ -828,14 +828,40 @@ func NewDeleteClaim(target blob.Ref) *Builder {
 // This is the "send a link to a friend" access model.
 const ShareHaveRef = "haveref"
 
-// RFC3339FromTime returns an RFC3339-formatted time in UTC.
+// UnknownLocation is a magic timezone value used when the actual location
+// of a time is unknown. For instance, EXIF files commonly have a time without
+// a corresponding location or timezone offset.
+var UnknownLocation = time.FixedZone("Unknown", -60) // 1 minute west
+
+// IsZoneKnown reports whether t is in a known timezone.
+// Camlistore uses the magic timezone offset of 1 minute west of UTC
+// to mean that the timezone wasn't known.
+func IsZoneKnown(t time.Time) bool {
+	if t.Location() == UnknownLocation {
+		return false
+	}
+	if _, off := t.Zone(); off == -60 {
+		return false
+	}
+	return true
+}
+
+// RFC3339FromTime returns an RFC3339-formatted time.
+//
+// If the timezone is known, the time will be converted to UTC and
+// returned with a "Z" suffix. For unknown zones, the timezone will be
+// "-00:01" (1 minute west of UTC).
+//
 // Fractional seconds are only included if the time has fractional
 // seconds.
 func RFC3339FromTime(t time.Time) string {
-	if t.UnixNano()%1e9 == 0 {
-		return t.UTC().Format(time.RFC3339)
+	if IsZoneKnown(t) {
+		t = t.UTC()
 	}
-	return t.UTC().Format(time.RFC3339Nano)
+	if t.UnixNano()%1e9 == 0 {
+		return t.Format(time.RFC3339)
+	}
+	return t.Format(time.RFC3339Nano)
 }
 
 var bytesCamliVersion = []byte("camliVersion")

pkg/schema/schema_test.go

@@ -158,11 +158,27 @@ func TestStringFromMixedArray(t *testing.T) {
 	}
 }
 
+func TestIsZoneKnown(t *testing.T) {
+	if !IsZoneKnown(time.Now()) {
+		t.Errorf("should know Now's zone")
+	}
+	if !IsZoneKnown(time.Now().UTC()) {
+		t.Errorf("UTC should be known")
+	}
+	if IsZoneKnown(time.Now().In(UnknownLocation)) {
+		t.Errorf("with explicit unknown location, should be false")
+	}
+	if IsZoneKnown(time.Now().In(time.FixedZone("xx", -60))) {
+		t.Errorf("with other fixed zone at -60, should be false")
+	}
+}
+
 func TestRFC3339(t *testing.T) {
 	tests := []string{
 		"2012-05-13T15:02:47Z",
 		"2012-05-13T15:02:47.1234Z",
 		"2012-05-13T15:02:47.123456789Z",
+		"2012-05-13T15:02:47-00:01",
 	}
 	for _, in := range tests {
 		tm, err := time.Parse(time.RFC3339, in)
@@ -170,9 +186,19 @@ func TestRFC3339(t *testing.T) {
 			t.Errorf("error parsing %q", in)
 			continue
 		}
-		if out := RFC3339FromTime(tm); in != out {
+		knownZone := IsZoneKnown(tm)
+		out := RFC3339FromTime(tm)
+		if in != out {
 			t.Errorf("RFC3339FromTime(%q) = %q; want %q", in, out, in)
 		}
+
+		sub := "Z"
+		if !knownZone {
+			sub = "-00:01"
+		}
+		if !strings.Contains(out, sub) {
+			t.Errorf("expected substring %q in %q", sub, out)
+		}
 	}
 }