Create a new MTProtoSender structure and its foundation

This means that the TcpClient and the Connection (currently only
ConnectionTcpFull) will no longer be concerned about handling
errors, but the MTProtoSender will.

The foundation of the library will now be based on asyncio.

telethon/helpers.py

@@ -3,9 +3,9 @@ import os
 import struct
 from hashlib import sha1, sha256
 
-from telethon.crypto import AES
-from telethon.errors import SecurityError
-from telethon.extensions import BinaryReader
+from .crypto import AES
+from .errors import SecurityError, BrokenAuthKeyError
+from .extensions import BinaryReader
 
 
 # region Multiple utilities
@@ -46,15 +46,22 @@ def pack_message(session, message):
     return key_id + msg_key + AES.encrypt_ige(data + padding, aes_key, aes_iv)
 
 
-def unpack_message(session, reader):
+def unpack_message(session, body):
     """Unpacks a message following MtProto 2.0 guidelines"""
     # See https://core.telegram.org/mtproto/description
-    if reader.read_long(signed=False) != session.auth_key.key_id:
+    if len(body) < 8:
+        if body == b'l\xfe\xff\xff':
+            raise BrokenAuthKeyError()
+        else:
+            raise BufferError("Can't decode packet ({})".format(body))
+
+    key_id = struct.unpack('<Q', body[:8])[0]
+    if key_id != session.auth_key.key_id:
         raise SecurityError('Server replied with an invalid auth key')
 
-    msg_key = reader.read(16)
+    msg_key = body[8:24]
     aes_key, aes_iv = calc_key(session.auth_key.key, msg_key, False)
-    data = BinaryReader(AES.decrypt_ige(reader.read(), aes_key, aes_iv))
+    data = BinaryReader(AES.decrypt_ige(body[24:], aes_key, aes_iv))
 
     data.read_long()  # remote_salt
     if data.read_long() != session.id: