Improve error handling in transports

client/src/telethon/_impl/mtproto/__init__.py

@@ -3,7 +3,7 @@ from .authentication import step1 as auth_step1
 from .authentication import step2 as auth_step2
 from .authentication import step3 as auth_step3
 from .mtp import BadMessage, Deserialization, Encrypted, MsgId, Mtp, Plain, RpcError
-from .transport import Abridged, Full, Intermediate, MissingBytes, Transport
+from .transport import Abridged, BadStatus, Full, Intermediate, MissingBytes, Transport
 from .utils import DEFAULT_COMPRESSION_THRESHOLD
 
 __all__ = [
@@ -23,6 +23,7 @@ __all__ = [
     "Plain",
     "RpcError",
     "Abridged",
+    "BadStatus",
     "Full",
     "Intermediate",
     "MissingBytes",

client/src/telethon/_impl/mtproto/mtp/types.py

@@ -1,3 +1,4 @@
+import logging
 import re
 from abc import ABC, abstractmethod
 from dataclasses import dataclass
@@ -80,6 +81,25 @@ class RpcError(ValueError):
         )
 
 
+# https://core.telegram.org/mtproto/service_messages_about_messages
+BAD_MSG_DESCRIPTIONS = {
+    16: "msg_id too low",
+    17: "msg_id too high",
+    18: "incorrect two lower order msg_id bits",
+    19: "container msg_id is the same as msg_id of a previously received message",
+    20: "message too old, and it cannot be verified whether the server has received a message with this msg_id or not",
+    32: "msg_seqno too low",
+    33: "msg_seqno too high",
+    34: "an even msg_seqno expected, but odd received",
+    35: "odd msg_seqno expected, but even received",
+    48: "incorrect server salt",
+    64: "invalid container",
+}
+
+RETRYABLE_MSG_IDS = {16, 17, 48}
+NON_FATAL_MSG_IDS = RETRYABLE_MSG_IDS & {32, 33}
+
+
 class BadMessage(ValueError):
     def __init__(
         self,
@@ -87,15 +107,27 @@ class BadMessage(ValueError):
         code: int,
         caused_by: Optional[int] = None,
     ) -> None:
-        super().__init__(f"bad msg: {code}")
+        description = BAD_MSG_DESCRIPTIONS.get(code) or "no description available"
+        super().__init__(f"bad msg={code}: {description}")
 
         self._code = code
         self._caused_by = caused_by
+        self.severity = (
+            logging.WARNING if self._code in NON_FATAL_MSG_IDS else logging.ERROR
+        )
 
     @property
     def code(self) -> int:
         return self._code
 
+    @property
+    def retryable(self) -> bool:
+        return self._code in RETRYABLE_MSG_IDS
+
+    @property
+    def fatal(self) -> bool:
+        return self._code not in NON_FATAL_MSG_IDS
+
     def __eq__(self, other: object) -> bool:
         if not isinstance(other, self.__class__):
             return NotImplemented

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

@@ -1,6 +1,6 @@
-from .abcs import MissingBytes, Transport
+from .abcs import BadStatus, MissingBytes, Transport
 from .abridged import Abridged
 from .full import Full
 from .intermediate import Intermediate
 
-__all__ = ["MissingBytes", "Transport", "Abridged", "Full", "Intermediate"]
+__all__ = ["BadStatus", "MissingBytes", "Transport", "Abridged", "Full", "Intermediate"]

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

@@ -19,3 +19,9 @@ class Transport(ABC):
 class MissingBytes(ValueError):
     def __init__(self, *, expected: int, got: int) -> None:
         super().__init__(f"missing bytes, expected: {expected}, got: {got}")
+
+
+class BadStatus(ValueError):
+    def __init__(self, *, status: int) -> None:
+        super().__init__(f"transport reported bad status: {status}")
+        self.status = status

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

@@ -1,6 +1,6 @@
 import struct
 
-from .abcs import MissingBytes, OutFn, Transport
+from .abcs import BadStatus, MissingBytes, OutFn, Transport
 
 
 class Abridged(Transport):
@@ -41,7 +41,7 @@ class Abridged(Transport):
             raise MissingBytes(expected=1, got=0)
 
         length = input[0]
-        if length < 127:
+        if 1 < length < 127:
             header_len = 1
         elif len(input) < 4:
             raise MissingBytes(expected=4, got=len(input))
@@ -49,6 +49,11 @@ class Abridged(Transport):
             header_len = 4
             length = struct.unpack_from("<i", input)[0] >> 8
 
+        if length <= 0:
+            if length < 0:
+                raise BadStatus(status=-length)
+            raise ValueError(f"bad length, expected > 0, got: {length}")
+
         length *= 4
         if len(input) < header_len + length:
             raise MissingBytes(expected=header_len + length, got=len(input))

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

@@ -1,7 +1,7 @@
 import struct
 from zlib import crc32
 
-from .abcs import MissingBytes, OutFn, Transport
+from .abcs import BadStatus, MissingBytes, OutFn, Transport
 
 
 class Full(Transport):
@@ -42,6 +42,8 @@ class Full(Transport):
         length = struct.unpack_from("<i", input)[0]
         assert isinstance(length, int)
         if length < 12:
+            if length < 0:
+                raise BadStatus(status=-length)
             raise ValueError(f"bad length, expected > 12, got: {length}")
 
         if len(input) < length:

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

@@ -1,6 +1,6 @@
 import struct
 
-from .abcs import MissingBytes, OutFn, Transport
+from .abcs import BadStatus, MissingBytes, OutFn, Transport
 
 
 class Intermediate(Transport):
@@ -41,5 +41,14 @@ class Intermediate(Transport):
         if len(input) < length:
             raise MissingBytes(expected=length, got=len(input))
 
+        if length <= 4:
+            if (
+                length >= 4
+                and (status := struct.unpack("<i", input[4 : 4 + length])[0]) < 0
+            ):
+                raise BadStatus(status=-status)
+
+            raise ValueError(f"bad length, expected > 0, got: {length}")
+
         output += memoryview(input)[4 : 4 + length]
         return length + 4

client/src/telethon/_impl/mtproto/utils.py

@@ -1,5 +1,4 @@
 import gzip
-import struct
 from typing import Optional
 
 from ..tl.mtproto.types import GzipPacked, Message
@@ -12,10 +11,7 @@ MESSAGE_SIZE_OVERHEAD = 8 + 4 + 4  # msg_id, seq_no, bytes
 
 
 def check_message_buffer(message: bytes) -> None:
-    if len(message) == 4:
-        neg_http_code = struct.unpack("<i", message)[0]
-        raise ValueError(f"transport error: {neg_http_code}")
-    elif len(message) < 20:
+    if len(message) < 20:
         raise ValueError(
             f"server payload is too small to be a valid message: {message.hex()}"
         )