Port mtproto from grammers

client/src/telethon/_impl/mtproto/transport/full.py

@@ -0,0 +1,57 @@
+import struct
+from zlib import crc32
+
+from .abcs import Transport
+
+
+class Full(Transport):
+    __slots__ = ("_send_seq", "_recv_seq")
+
+    """
+    Implementation of the [full transport]:
+
+    ```text
+    +----+----+----...----+----+
+    | len| seq|  payload  | crc|
+    +----+----+----...----+----+
+     ^^^^ 4 bytes
+    ```
+
+    [full transport]: https://core.telegram.org/mtproto/mtproto-transports#full
+    """
+
+    def __init__(self) -> None:
+        self._send_seq = 0
+        self._recv_seq = 0
+
+    def pack(self, input: bytes, output: bytearray) -> None:
+        assert len(input) % 4 == 0
+
+        length = len(input) + 12
+        output += struct.pack("<ii", length, self._send_seq)
+        output += input
+        output += struct.pack("<i", crc32(memoryview(output)[-(length - 4) :]))
+        self._send_seq += 1
+
+    def unpack(self, input: bytes, output: bytearray) -> None:
+        if len(input) < 4:
+            raise ValueError(f"missing bytes, expected: 4, got: {len(input)}")
+
+        length = struct.unpack_from("<i", input)[0]
+        if length < 12:
+            raise ValueError(f"bad length, expected > 12, got: {length}")
+
+        if len(input) < length:
+            raise ValueError(f"missing bytes, expected: {length}, got: {len(input)}")
+
+        seq = struct.unpack_from("<i", input, 4)[0]
+        if seq != self._recv_seq:
+            raise ValueError(f"bad seq, expected: {self._recv_seq}, got: {seq}")
+
+        crc = struct.unpack_from("<I", input, length - 4)[0]
+        valid_crc = crc32(memoryview(input)[:-4])
+        if crc != valid_crc:
+            raise ValueError(f"bad crc, expected: {valid_crc}, got: {crc}")
+
+        self._recv_seq += 1
+        output += memoryview(input)[8:-4]