Don't remount if file is deleted before data sent

When a file with a '.bin' or '.hex' extension is found then the remount
timer starts. Abort the remount if the file is deleted before any data
is sent.

When copying files with attributes that do not exist on FAT16 windows
goes through the following steps:
1. Create an uninitialized file of the correct size
2. Delete the file created in step 1
3. Create new file with size 0
4. Prompt user:
    "Are you sure you want to copy this file without its properties"
5. If yes then send file data, if no the delete file

This causes problems because after the file in step 1 is deleted
DAPLink detects this as a transfer error and remounts. By aborting
the transfer instead of triggering an error files with incompatible
attributes can be properly copied.

This problem can be reproduced by saving a target binary to Dropbox's
sync folder and then from there copying it to DAPLink.

Author: c1728p9

source/daplink/drag-n-drop/vfs_manager.c

@@ -140,8 +140,10 @@ static void build_filesystem(void);
 static void file_change_handler(const vfs_filename_t filename, vfs_file_change_t change, vfs_file_t file, vfs_file_t new_file_data);
 static void file_data_handler(uint32_t sector, const uint8_t *buf, uint32_t num_of_sectors);
 static bool ready_for_state_change(void);
+static void abort_remount(void);
 
 static void transfer_update_file_info(vfs_file_t file, uint32_t start_sector, uint32_t size, stream_type_t stream);
+static void transfer_reset_file_info(void);
 static void transfer_stream_open(stream_type_t stream, uint32_t start_sector);
 static void transfer_stream_data(uint32_t sector, const uint8_t *data, uint32_t size);
 static void transfer_update_state(error_t status);
@@ -408,7 +410,10 @@ static void file_change_handler(const vfs_filename_t filename, vfs_file_change_t
     }
 
     if (VFS_FILE_DELETED == change) {
-        // Unused
+        if (file == file_transfer_state.file_to_program) {
+            // The file that was being transferred has been deleted
+            transfer_reset_file_info();
+        }
     }
 }
 
@@ -521,6 +526,19 @@ static bool ready_for_state_change(void)
     return time_usb_idle > timeout_ms ? true : false;
 }
 
+// Abort a remount if one is pending
+void abort_remount(void)
+{
+    sync_lock();
+
+    // Only abort a remount if in the connected state and reconnecting is the next state
+    if ((VFS_MNGR_STATE_RECONNECTING == vfs_state_next) && (VFS_MNGR_STATE_CONNECTED == vfs_state)) {
+        vfs_state_next = VFS_MNGR_STATE_CONNECTED;
+    }
+
+    sync_unlock();
+}
+
 // Update the tranfer state with file information
 static void transfer_update_file_info(vfs_file_t file, uint32_t start_sector, uint32_t size, stream_type_t stream)
 {
@@ -558,8 +576,8 @@ static void transfer_update_file_info(vfs_file_t file, uint32_t start_sector, ui
         }
     }
 
-    // Check - File size must be the same or bigger
-    if (size < file_transfer_state.file_size) {
+    // Check - File size must either grow or be smaller than the size already transferred
+    if ((size < file_transfer_state.file_size) && (size < file_transfer_state.size_transferred)) {
         vfs_mngr_printf("    error: file size changed from %i to %i\r\n", file_transfer_state.file_size, size);
         transfer_update_state(ERROR_ERROR_DURING_TRANSFER);
         return;
@@ -579,15 +597,25 @@ static void transfer_update_file_info(vfs_file_t file, uint32_t start_sector, ui
         return;
     }
 
-    // Update values - Size is the only value that can change and it can only increase.
-    if (size > file_transfer_state.file_size) {
-        file_transfer_state.file_size = size;
-        vfs_mngr_printf("    updated size=%i\r\n", size);
-    }
+    // Update values - Size is the only value that can change
+    file_transfer_state.file_size = size;
+    vfs_mngr_printf("    updated size=%i\r\n", size);
 
     transfer_update_state(ERROR_SUCCESS);
 }
 
+// Reset the transfer information or error if transfer is already in progress
+static void transfer_reset_file_info()
+{
+    vfs_mngr_printf("vfs_manager transfer_reset_file_info()\r\n");
+    if (file_transfer_state.stream_open) {
+        transfer_update_state(ERROR_ERROR_DURING_TRANSFER);
+    } else {
+        file_transfer_state = default_transfer_state;
+        abort_remount();
+    }
+}
+
 // Update the tranfer state with new information
 static void transfer_stream_open(stream_type_t stream, uint32_t start_sector)
 {