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43 lines
1.3 KiB
Python
43 lines
1.3 KiB
Python
import struct
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from zlib import crc32
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from .connection import Connection, PacketCodec
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from ...errors import InvalidChecksumError
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class FullPacketCodec(PacketCodec):
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tag = None
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def __init__(self, _conn):
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self._send_counter = 0 # Important or Telegram won't reply
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def encode_packet(self, data):
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# https://core.telegram.org/mtproto#tcp-transport
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# total length, sequence number, packet and checksum (CRC32)
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length = len(data) + 12
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data = struct.pack('<ii', length, self._send_counter) + data
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crc = struct.pack('<I', crc32(data))
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self._send_counter += 1
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return data + crc
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async def read_packet(self, reader):
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packet_len_seq = await reader.readexactly(8) # 4 and 4
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packet_len, seq = struct.unpack('<ii', packet_len_seq)
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body = await reader.readexactly(packet_len - 8)
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checksum = struct.unpack('<I', body[-4:])[0]
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body = body[:-4]
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valid_checksum = crc32(packet_len_seq + body)
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if checksum != valid_checksum:
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raise InvalidChecksumError(checksum, valid_checksum)
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return body
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class ConnectionTcpFull(Connection):
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"""
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Default Telegram mode. Sends 12 additional bytes and
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needs to calculate the CRC value of the packet itself.
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"""
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packet_codec = FullPacketCodec
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