Fix crash loop when ACMI stream sends zero ReferenceTime

pkg/telemetry/streamer.go

@@ -34,6 +34,10 @@ type streamingClient struct {
 
 	// referenceTime is the reference point provided in the ACMI data.
 	referenceTime time.Time
+	// referenceTimeSet tracks whether a ReferenceTime property has been received. It must not be
+	// replaced by referenceTime.IsZero() because 0001-01-01T00:00:00Z is a valid reference time
+	// used by some ACMI recorders (e.g. DCS2ACMI) and is also Go's zero time.Time value.
+	referenceTimeSet bool
 	// referencePoint is the reference point provided in the ACMI data.
 	referencePoint orb.Point
 	// cursorTime is the current frame time, computed by adding the current time frame to the reference time.
@@ -333,7 +337,7 @@ func (c *streamingClient) handleTimeFrame(line string) error {
 	if err != nil {
 		return fmt.Errorf("error parsing time frame: %w", err)
 	}
-	if c.referenceTime.IsZero() {
+	if !c.referenceTimeSet {
 		return errors.New("time frame received before reference time")
 	}
 	c.cursorTime = c.referenceTime.Add(offset)
@@ -353,6 +357,7 @@ func (c *streamingClient) updateGlobalObject(update *objects.Update) error {
 			return fmt.Errorf("error parsing reference time: %w", err)
 		}
 		c.referenceTime = referenceTime
+		c.referenceTimeSet = true
 		if c.cursorTime.IsZero() {
 			c.cursorTime = c.referenceTime
 		}
@@ -450,6 +455,7 @@ func (c *streamingClient) reset() {
 	defer c.lock.Unlock()
 
 	c.referenceTime = time.Time{}
+	c.referenceTimeSet = false
 	c.referencePoint = orb.Point{}
 	c.cursorTime = time.Time{}
 	c.state = map[uint64]*objects.Object{}

pkg/telemetry/streamer_test.go

@@ -6,10 +6,41 @@ import (
 	"testing"
 	"time"
 
+	"github.com/dharmab/goacmi/v2/parsing"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
+// TestHandleLineAcceptsZeroReferenceTime verifies that a zero-valued
+// ReferenceTime (0001-01-01T00:00:00Z) is accepted and does not cause
+// subsequent time frames to be rejected. This is regression test for
+// a case that sometimes happens on Lima Kilo.
+func TestHandleLineAcceptsZeroReferenceTime(t *testing.T) {
+	t.Parallel()
+
+	const timeFrame = "#62754967308.46" // Observed value from eu.limakilo.net sometimes
+	lines := []string{
+		"FileType=text/acmi/tacview",
+		"FileVersion=2.2",
+		"0,ReferenceTime=0001-01-01T00:00:00Z",
+		"0,ReferenceLongitude=30",
+		"0,ReferenceLatitude=30",
+		timeFrame,
+	}
+
+	client := newStreamingClient(time.Second)
+	reader := bufio.NewReader(strings.NewReader(strings.Join(lines, "\n") + "\n"))
+	for range lines {
+		line, err := readACMILine(reader)
+		require.NoError(t, err)
+		require.NoError(t, client.handleLine(line))
+	}
+
+	offset, err := parsing.ParseTimeFrame(timeFrame)
+	require.NoError(t, err)
+	assert.Equal(t, time.Time{}.Add(offset), client.Time())
+}
+
 func TestReadACMILineContinuationPreservesNextRecord(t *testing.T) {
 	t.Parallel()