Pass whole File object to Client

Every `Client` can handle torrent files in different ways.  One can work
with `bytearrays` while the other one can only with a `path`.

By passing raw `File` object we let the `Client` handle operations that
it supports.

backends/transmission.py

@@ -1,3 +1,5 @@
+import base64
+
 import transmissionrpc
 
 
@@ -15,7 +17,15 @@ def __init__(self, config):
                                                    config['port'])
 
     def add_torrent(self, torrent, timeout=None, **kwargs):
-        return Torrent(self.transmission.add_torrent(torrent, timeout, **kwargs))
+        """Adds new torrent to download list.
+
+        Args:
+            torrent (telegram.File): File torrent object.
+            timeout (int): Drop connection after timeout seconds.
+        """
+        barray = torrent.download_as_bytearray()
+        filedump = base64.b64encode(barray).decode('utf-8')
+        self.transmission.add_torrent(filedump, timeout, **kwargs)
 
     def get_torrents(self):
         """Yields Torrents objects."""

handlers/message_handlers.py

@@ -1,4 +1,3 @@
-import base64
 import logging
 
 from telegram.ext import Filters, MessageHandler
@@ -13,9 +12,8 @@ def __init__(self, client):
         super().__init__(self.filters, self.callback)
 
     def callback(self, update, context):
-        torrent = update.message.document.get_file().download_as_bytearray()
-        filedump = base64.b64encode(torrent).decode('utf-8')
-        self.client.add_torrent(filedump)
+        torrent = update.message.document.get_file()
+        self.client.add_torrent(torrent)
         logging.info('Added new torrent file %s',
                      update.message.document.file_name)
         context.bot.send_message(