Register a static directory handler with Mach9 by adding a route to the
    router and registering a handler.

    :param app: Mach9
    :param file_or_directory: File or directory path to serve from
    :param uri: URL to serve from
    :param pattern: regular expression used to match files in the URL
    :param use_modified_since: If true, send file modified time, and return
                               not modified if the browser's matches the
                               server's
    :param use_content_range: If true, process header for range requests
                              and sends the file part that is requested

def register(app, uri, file_or_directory, pattern,
             use_modified_since, use_content_range):
    # TODO: Though mach9 is not a file server, I feel like we should at least
    #       make a good effort here.  Modified-since is nice, but we could
    #       also look into etags, expires, and caching
    """
    Register a static directory handler with Mach9 by adding a route to the
    router and registering a handler.

    :param app: Mach9
    :param file_or_directory: File or directory path to serve from
    :param uri: URL to serve from
    :param pattern: regular expression used to match files in the URL
    :param use_modified_since: If true, send file modified time, and return
                               not modified if the browser's matches the
                               server's
    :param use_content_range: If true, process header for range requests
                              and sends the file part that is requested
    """
    # If we're not trying to match a file directly,
    # serve from the folder
    if not path.isfile(file_or_directory):
        uri += '<file_uri:' + pattern + '>'

    async def _handler(request, file_uri=None):
        # Using this to determine if the URL is trying to break out of the path
        # served.  os.path.realpath seems to be very slow
        if file_uri and '../' in file_uri:
            raise InvalidUsage("Invalid URL")
        # Merge served directory and requested file if provided
        # Strip all / that in the beginning of the URL to help prevent python
        # from herping a derp and treating the uri as an absolute path
        root_path = file_path = file_or_directory
        if file_uri:
            file_path = path.join(
                file_or_directory, sub('^[/]*', '', file_uri))

        # URL decode the path sent by the browser otherwise we won't be able to
        # match filenames which got encoded (filenames with spaces etc)
        file_path = path.abspath(unquote(file_path))
        if not file_path.startswith(path.abspath(unquote(root_path))):
            raise FileNotFound('File not found',
                               path=file_or_directory,
                               relative_url=file_uri)
        try:
            headers = {}
            # Check if the client has been sent this file before
            # and it has not been modified since
            stats = None
            if use_modified_since:
                stats = await stat(file_path)
                modified_since = strftime(
                    '%a, %d %b %Y %H:%M:%S GMT', gmtime(stats.st_mtime))
                if request.headers.get('If-Modified-Since') == modified_since:
                    return HTTPResponse(status=304)
                headers['Last-Modified'] = modified_since
            _range = None
            if use_content_range:
                _range = None
                if not stats:
                    stats = await stat(file_path)
                headers['Accept-Ranges'] = 'bytes'
                headers['Content-Length'] = str(stats.st_size)
                if request.method != 'HEAD':
                    try:
                        _range = ContentRangeHandler(request, stats)
                    except HeaderNotFound:
                        pass
                    else:
                        del headers['Content-Length']
                        for key, value in _range.headers.items():
                            headers[key] = value
            if request.method == 'HEAD':
                return HTTPResponse(
                    headers=headers,
                    content_type=guess_type(file_path)[0] or 'text/plain')
            else:
                return await file(file_path, headers=headers, _range=_range)
        except ContentRangeError:
            raise
        except Exception:
            raise FileNotFound('File not found',
                               path=file_or_directory,
                               relative_url=file_uri)

    app.route(uri, methods=['GET', 'HEAD'])(_handler)