Implement different mtproto proxy protocols; refactor obfuscated2

telethon/network/connection/tcpintermediate.py

@@ -1,4 +1,6 @@
 import struct
+import random
+import os
 
 from .connection import Connection
 
@@ -8,12 +10,47 @@ class ConnectionTcpIntermediate(Connection):
     Intermediate mode between `ConnectionTcpFull` and `ConnectionTcpAbridged`.
     Always sends 4 extra bytes for the packet length.
     """
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self._codec = IntermediatePacket()
+
     def _init_conn(self):
-        self._writer.write(b'\xee\xee\xee\xee')
+        self._writer.write(self._codec.tag)
 
     def _send(self, data):
-        self._writer.write(struct.pack('<i', len(data)) + data)
+        self._writer.write(self._codec.encode_packet(data))
 
     async def _recv(self):
-        return await self._reader.readexactly(
-            struct.unpack('<i', await self._reader.readexactly(4))[0])
+        return await self.codec.read_packet(self._reader)
+
+
+class IntermediatePacket:
+    tag = b'\xee\xee\xee\xee'
+    mtproto_proxy_tag = tag
+
+    def encode_packet(self, data):
+        return struct.pack('<i', len(data)) + data
+
+    async def read_packet(self, reader):
+        length = struct.unpack('<i', await reader.readexactly(4))[0]
+        return await reader.readexactly(length)
+
+
+class RandomizedIntermediatePacket(IntermediatePacket):
+    """
+    Data packets are aligned to 4bytes. This codec adds random bytes of size
+    from 0 to 3 bytes, which are ignored by decoder.
+    """
+    mtproto_proxy_tag = b'\xdd\xdd\xdd\xdd'
+
+    def encode_packet(self, data):
+        pad_size = random.randint(0, 3)
+        padding = os.urandom(pad_size)
+        return super().encode_packet(data + padding)
+
+    async def read_packet(self, reader):
+        packet_with_padding = await super().read_packet(reader)
+        pad_size = len(packet_with_padding) % 4
+        if pad_size > 0:
+            return packet_with_padding[:-pad_size]
+        return packet_with_padding