Fix Tacview continuation-line parsing in telemetry stream (#693)

## Summary

This fixes telemetry parsing for ACMI streams containing multi-line
continuation
records, such as long global `Comments` values in Tacview exports and
realtime
streams.

## Root Cause

`pkg/telemetry/streamer.go` was reading from the same `bufio.Reader` in
two
different places:

- the background goroutine in `handleLines()`
- `handleLine()` when it detected a continuation line ending with `\`

That allowed reads to interleave. When a multi-line global property was
present,
part of the continuation block and the following record could be spliced
together, leading to parse errors like:

`strconv.ParseUint: parsing "====================0": invalid syntax`

## Changes

- make the background reader goroutine the sole owner of ACMI stream
reads
- add `readACMILine()` to assemble full logical ACMI records, including
  continuation lines, before parsing
- simplify `handleLine()` so it only parses an already-assembled record
- add regression tests for a sample-like multi-line `Comments` record
followed
  by the next global update

## Validation

- `make test`

Author: red-one1

pkg/telemetry/streamer.go

@@ -218,7 +218,7 @@ func (c *streamingClient) handleLines(ctx context.Context, reader *bufio.Reader)
 	go func() {
 		defer close(lines)
 		for {
-			line, err := reader.ReadString('\n')
+			line, err := readACMILine(reader)
 			select {
 			case lines <- result{line, err}:
 			case <-ctx.Done():
@@ -252,29 +252,37 @@ func (c *streamingClient) handleLines(ctx context.Context, reader *bufio.Reader)
 				}
 				return fmt.Errorf("error reading line: %w", r.err)
 			}
-			if err := c.handleLine(r.line, reader); err != nil {
+			if err := c.handleLine(r.line); err != nil {
 				return fmt.Errorf("error reading ACMI stream: %w", err)
 			}
 		}
 	}
 }
 
-func (c *streamingClient) handleLine(line string, reader *bufio.Reader) error {
-	if strings.HasSuffix(line, "\\\n") {
-		var sb strings.Builder
-		sb.WriteString(line[:len(line)-2])
-		for {
-			next, err := reader.ReadString('\n')
-			if err != nil {
-				return fmt.Errorf("error reading continuation line: %w", err)
-			}
-			sb.WriteString(next)
-			if !strings.HasSuffix(next, "\\\n") {
-				break
-			}
+func readACMILine(reader *bufio.Reader) (string, error) {
+	line, err := reader.ReadString('\n')
+	if err != nil {
+		return line, err
+	}
+	if !strings.HasSuffix(line, "\\\n") {
+		return line, nil
+	}
+
+	var sb strings.Builder
+	sb.WriteString(line[:len(line)-2])
+	for {
+		next, readErr := reader.ReadString('\n')
+		if readErr != nil {
+			return "", fmt.Errorf("error reading continuation line: %w", readErr)
+		}
+		sb.WriteString(next)
+		if !strings.HasSuffix(next, "\\\n") {
+			return sb.String(), nil
 		}
-		line = sb.String()
 	}
+}
+
+func (c *streamingClient) handleLine(line string) error {
 	line = strings.TrimSpace(line)
 	if line == "" {
 		return nil

pkg/telemetry/streamer_test.go

@@ -0,0 +1,56 @@
+package telemetry
+
+import (
+	"bufio"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestReadACMILineContinuationPreservesNextRecord(t *testing.T) {
+	t.Parallel()
+
+	reader := bufio.NewReader(strings.NewReader(strings.Join([]string{
+		"0,Comments=DCS Retribution Turn 6\\",
+		"====================\\",
+		"Most briefing information can be found on your kneeboard.",
+		"0,ReferenceTime=1989-09-13T10:08:31Z",
+	}, "\n") + "\n"))
+
+	first, err := readACMILine(reader)
+	require.NoError(t, err)
+	assert.Equal(
+		t,
+		"0,Comments=DCS Retribution Turn 6====================\\\nMost briefing information can be found on your kneeboard.\n",
+		first,
+	)
+
+	second, err := readACMILine(reader)
+	require.NoError(t, err)
+	assert.Equal(t, "0,ReferenceTime=1989-09-13T10:08:31Z\n", second)
+}
+
+func TestHandleLineAcceptsContinuationRecordBeforeNextObject(t *testing.T) {
+	t.Parallel()
+
+	client := newStreamingClient(time.Second)
+	reader := bufio.NewReader(strings.NewReader(strings.Join([]string{
+		"0,Comments=DCS Retribution Turn 6\\",
+		"====================\\",
+		"Most briefing information can be found on your kneeboard.",
+		"0,ReferenceTime=1989-09-13T10:08:31Z",
+	}, "\n") + "\n"))
+
+	line, err := readACMILine(reader)
+	require.NoError(t, err)
+	require.NoError(t, client.handleLine(line))
+
+	line, err = readACMILine(reader)
+	require.NoError(t, err)
+	require.NoError(t, client.handleLine(line))
+
+	assert.Equal(t, time.Date(1989, 9, 13, 10, 8, 31, 0, time.UTC), client.Time())
+}