Possible foundation changes desired for usb drive fix.

[Xavron]

Issue related https://github.com/ppareit/swiftp/issues/192

This pull request can remain open or accepted into the code if wanting the desired changes. If left open or accepted, I will slowly switch over more classes in time (years) or someone else can jump in. The code is set up with one class done as an example to go on for switching more over. The rest of the classes can be switched over time.

This pull request seeks to improve the foundation on which to deal with the USB drive fix. The code in the CmdDELE class is more readable, improved, and slimmed down like it once was when there was only File in use.

The tests I've run on it are successful.

I've only implemented it as a trial example to see if it is good to continue with. Other ways are indeed possible.

Example block side by side:

This pull request

        if (file == null) {
            errString = "550 Invalid name or chroot violation\r\n";
        } else {
            final String path = FileUtil.getScopedClientPath(param, null, null);
            if (file.violatesChroot(this, path)) {
                errString = "550 Invalid name or chroot violation\r\n";
            } else if (file.isDirectory()) {
                errString = "550 Can't DELE a directory\r\n";
            } else if (!file.delete(App.getAppContext())) {
                errString = "450 Error deleting file\r\n";
            }
        }

Current

        if (storeFile == null || storeFile.getOb() == null) {
            errString = "550 Invalid name or chroot violation\r\n";
        } else {
            final boolean isDocumentFile = storeFile.getOb() instanceof DocumentFile;
            final boolean isFile = !isDocumentFile;
            final String path = FileUtil.getScopedClientPath(param, null, null);
            if ((isDocumentFile && violatesChroot((DocumentFile) storeFile.getOb(), path))
                    || (isFile && violatesChroot((File) storeFile.getOb()))) {
                errString = "550 Invalid name or chroot violation\r\n";
            } else if (storeFile.isDirectory()) {
                errString = "550 Can't DELE a directory\r\n";
            } else if ((isDocumentFile && !((DocumentFile) storeFile.getOb()).delete())
                    || (isFile && !FileUtil.deleteFile((File) storeFile.getOb(), App.getAppContext()))) {
                errString = "450 Error deleting file\r\n";
            }
        }

Before DocumentFile

        if (violatesChroot(storeFile)) {
            errString = "550 Invalid name or chroot violation\r\n";
        } else if (storeFile.isDirectory()) {
            errString = "550 Can't DELE a directory\r\n";
        } else if (!FileUtil.deleteFile(storeFile, App.getAppContext())) {
            errString = "450 Error deleting file\r\n";
        }

[Xavron]

I see a thumbs up =)

Will look into this more in time.