convert events.DataReceived into a dataclass

Author: mhils

src/h2/events.py

@@ -13,7 +13,7 @@
 import binascii
 import sys
 from dataclasses import dataclass
-from typing import TYPE_CHECKING
+from typing import Any, TYPE_CHECKING
 
 from .settings import ChangedSetting, SettingCodes, Settings, _setting_code_from_int
 
@@ -30,6 +30,15 @@
     kw_only = {"kw_only": True}
 
 
+_LAZY_INIT: Any = object()
+"""
+Some h2 events are instantiated by the state machine, but its attributes are
+subsequently populated by H2Stream. To make this work with strict type annotations
+on the events, they are temporarily set to this placeholder value.
+This value should never be exposed to users.
+"""
+
+
 class Event:
     """
     Base class for h2 events.
@@ -258,6 +267,7 @@ def __repr__(self) -> str:
         return f"<InformationalResponseReceived stream_id:{self.stream_id}, headers:{self.headers}>"
 
 
+@dataclass(**kw_only)
 class DataReceived(Event):
     """
     The DataReceived event is fired whenever data is received on a stream from
@@ -268,25 +278,28 @@ class DataReceived(Event):
        Added ``stream_ended`` property.
     """
 
-    def __init__(self) -> None:
-        #: The Stream ID for the stream this data was received on.
-        self.stream_id: int | None = None
+    stream_id: int
+    """The Stream ID for the stream this data was received on."""
+
+    data: bytes = _LAZY_INIT
+    """The data itself."""
 
-        #: The data itself.
-        self.data: bytes | None = None
+    flow_controlled_length: int = _LAZY_INIT
+    """
+    The amount of data received that counts against the flow control
+    window. Note that padding counts against the flow control window, so
+    when adjusting flow control you should always use this field rather
+    than ``len(data)``.
+    """
 
-        #: The amount of data received that counts against the flow control
-        #: window. Note that padding counts against the flow control window, so
-        #: when adjusting flow control you should always use this field rather
-        #: than ``len(data)``.
-        self.flow_controlled_length: int | None = None
+    stream_ended: StreamEnded | None = None
+    """
+    If this data chunk also completed the stream, the associated
+    :class:`StreamEnded <h2.events.StreamEnded>` event will be available
+    here.
 
-        #: If this data chunk also completed the stream, the associated
-        #: :class:`StreamEnded <h2.events.StreamEnded>` event will be available
-        #: here.
-        #:
-        #: .. versionadded:: 2.4.0
-        self.stream_ended: StreamEnded | None = None
+    .. versionadded:: 2.4.0
+    """
 
     def __repr__(self) -> str:
         return (

src/h2/stream.py

@@ -224,8 +224,7 @@ def data_received(self, previous_state: StreamState) -> list[Event]:
         if not self.headers_received:
             msg = "cannot receive data before headers"
             raise ProtocolError(msg)
-        event = DataReceived()
-        event.stream_id = self.stream_id
+        event = DataReceived(stream_id=self.stream_id)
         return [event]
 
     def window_updated(self, previous_state: StreamState) -> list[Event]:

tests/test_events.py

@@ -172,10 +172,11 @@ def test_datareceived_repr(self) -> None:
         """
         DataReceived has a useful debug representation.
         """
-        e = h2.events.DataReceived()
-        e.stream_id = 888
-        e.data = b"abcdefghijklmnopqrstuvwxyz"
-        e.flow_controlled_length = 88
+        e = h2.events.DataReceived(
+            stream_id=888,
+            data=b"abcdefghijklmnopqrstuvwxyz",
+            flow_controlled_length=88,
+        )
 
         assert repr(e) == (
             "<DataReceived stream_id:888, flow_controlled_length:88, "