Restrict to one open file of each type at a time

blefs/error.go

@@ -11,6 +11,8 @@ var (
 	ErrFileWriteOnly = errors.New("file is write only")
 	ErrInvalidOffset = errors.New("invalid file offset")
 	ErrOffsetChanged = errors.New("offset has already been changed")
+	ErrReadOpen      = errors.New("only one file can be opened for reading at a time")
+	ErrWriteOpen     = errors.New("only one file can be opened for writing at a time")
 )
 
 // FSError represents an error returned by BLE FS

blefs/file.go

@@ -24,6 +24,10 @@ type File struct {
 // Open opens a file and returns it as an fs.File to
 // satisfy the fs.FS interface
 func (blefs *FS) Open(path string) (*File, error) {
+	if blefs.readOpen {
+		return nil, ErrReadOpen
+	}
+	blefs.readOpen = true
 	// Make a read file request. This opens the file for reading.
 	err := blefs.request(
 		FSCmdReadFile,
@@ -49,6 +53,10 @@ func (blefs *FS) Open(path string) (*File, error) {
 
 // Create makes a new file on the BLE file system and returns it.
 func (blefs *FS) Create(path string, size uint32) (*File, error) {
+	if blefs.writeOpen {
+		return nil, ErrWriteOpen
+	}
+	blefs.writeOpen = true
 	// Make a write file request. This will create and open a file for writing.
 	err := blefs.request(
 		FSCmdWriteFile,
@@ -316,9 +324,14 @@ func (fl *File) Seek(offset int64, whence int) (int64, error) {
 	return int64(newOffset), nil
 }
 
-// Close implements the fs.File interface.
-// It just returns nil.
+// Close must be called before opening another file
 func (fl *File) Close() error {
+	if fl.isReadOnly {
+		fl.fs.readOpen = false
+	} else if fl.isWriteOnly {
+		fl.fs.writeOpen = false
+	}
+
 	return nil
 }
 

blefs/fs.go

@@ -50,6 +50,8 @@ var btOptsCmd = map[string]interface{}{"type": "command"}
 type FS struct {
 	transferChar   *gatt.GattCharacteristic1
 	transferRespCh <-chan *bluez.PropertyChanged
+	readOpen       bool
+	writeOpen      bool
 }
 
 // New creates a new fs given the transfer characteristic