Be more tolerant of badly formed blocks in LLUDP

This helps us deal with badly formed ImprovedInstantMessage
messages sent by newer viewers.

Author: SaladDais

hippolyzer/lib/base/message/udpdeserializer.py

@@ -168,6 +168,7 @@ def parse_message_body(self, msg: Message):
         current_template = self.template_dict.get_template_by_name(msg.name)
         reader.seek(current_template.get_msg_freq_num_len() + msg.offset)
 
+        ran_off_end = False
         for tmpl_block in current_template.blocks:
             # EOF?
             if not len(reader):
@@ -200,9 +201,21 @@ def parse_message_body(self, msg: Message):
                             reader=reader,
                             tmpl_variable=tmpl_variable,
                         )
-                    except:
+                    except se.ReadPastEndError:
+                        # Ran off end of packet. Remove the partially-created
+                        # block and bail out so reserialization doesn't include
+                        # blocks that weren't in the original message.
+                        LOG.debug(f"Ran off end of {msg.name} while parsing {context_str}")
+                        msg.blocks[tmpl_block.name].pop()
+                        ran_off_end = True
+                        break
+                    except Exception:
                         LOG.exception(f"Raised while parsing var in {context_str}")
                         raise
+                if ran_off_end:
+                    break
+            if ran_off_end:
+                break
 
         if not msg.blocks and current_template.blocks:
             raise exc.MessageDeserializationError("message", "message is empty")

hippolyzer/lib/base/serialization.py

@@ -18,6 +18,10 @@
 from hippolyzer.lib.base.multidict import OrderedMultiDict
 
 
+class ReadPastEndError(ValueError):
+    """Raised when a read would go past the end of the buffer"""
+
+
 SERIALIZABLE_TYPE = Union["SerializableBase", Type["SerializableBase"]]
 SUBFIELD_SERIALIZERS: Dict[Tuple[str, str, str], "BaseSubfieldSerializer"] = {}
 HTTP_SERIALIZERS: Dict[str, "BaseHTTPSerializer"] = {}
@@ -224,7 +228,7 @@ def seek(self, pos: int, whence: int = SEEK_SET):
     def read_bytes(self, num_bytes, peek=False, to_bytes=False, check_len=True):
         end_pos = self._pos + num_bytes
         if end_pos > self._len and check_len:
-            raise ValueError(f"{len(self)} bytes left, needed {num_bytes}")
+            raise ReadPastEndError(f"{len(self)} bytes left, needed {num_bytes}")
 
         read_bytes = self._buffer[self._pos:end_pos]
         if to_bytes: