Reserve recording paths atomically

recording/recorder.go

@@ -57,14 +57,19 @@ func New(directory string, format string, now time.Time, frameSize int, interval
 	if err := os.MkdirAll(directory, 0755); err != nil {
 		return nil, err
 	}
-	path := UniquePath(directory, now, format)
+	path, err := reservePath(directory, now, format)
+	if err != nil {
+		return nil, err
+	}
 	args := ffmpegArgs(format, path)
 	cmd := exec.Command("ffmpeg", args...)
 	stdin, err := cmd.StdinPipe()
 	if err != nil {
+		_ = os.Remove(path)
 		return nil, err
 	}
 	if err := cmd.Start(); err != nil {
+		_ = os.Remove(path)
 		return nil, err
 	}
 	recorder := &Recorder{
@@ -91,6 +96,24 @@ func NormalizeFormat(format string) string {
 	return format
 }
 
+func reservePath(directory string, now time.Time, format string) (string, error) {
+	for {
+		path := UniquePath(directory, now, format)
+		file, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0600)
+		if os.IsExist(err) {
+			continue
+		}
+		if err != nil {
+			return "", err
+		}
+		if err := file.Close(); err != nil {
+			_ = os.Remove(path)
+			return "", err
+		}
+		return path, nil
+	}
+}
+
 func UniquePath(directory string, now time.Time, format string) string {
 	base := fmt.Sprintf("barnard-recording-%s", now.Format("20060102-150405"))
 	path := filepath.Join(directory, base+"."+format)