Telethon/telethon/network/connection/tcpintermediate.py

import struct
import random
import os

from .connection import Connection, PacketCodec


class IntermediatePacketCodec(PacketCodec):
    tag = b'\xee\xee\xee\xee'
    obfuscate_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 RandomizedIntermediatePacketCodec(IntermediatePacketCodec):
    """
    Data packets are aligned to 4bytes. This codec adds random bytes of size
    from 0 to 3 bytes, which are ignored by decoder.
    """
    tag = None
    obfuscate_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


class ConnectionTcpIntermediate(Connection):
    """
    Intermediate mode between `ConnectionTcpFull` and `ConnectionTcpAbridged`.
    Always sends 4 extra bytes for the packet length.
    """
    packet_codec = IntermediatePacketCodec