Fix _transport_sockname request initialization warning

CHANGES/13029.bugfix.rst

@@ -0,0 +1,3 @@
+Fixed a deprecation warning during request initialization by allowing
+``BaseRequest`` to assign ``_transport_sockname``.
+-- by :user:`nightcityblade`.

aiohttp/web_request.py

@@ -132,6 +132,7 @@ class BaseRequest(MutableMapping[str | RequestKey[Any], Any], HeadersMixin):
             "_loop",
             "_transport_sslcontext",
             "_transport_peername",
+            "_transport_sockname",
         ]
     )
     _post: MultiDictProxy[_Post] | None = None

tests/test_web_request.py

@@ -167,6 +167,29 @@ def test_host_with_no_transport_sockname() -> None:
     assert req.host == ""
 
 
+def test_request_init_allows_transport_sockname_assignment() -> None:
+    message = make_mocked_request("GET", "/")._message
+    payload = mock.Mock()
+    payload_writer = mock.Mock()
+    task = mock.Mock()
+    loop = mock.Mock()
+    protocol = mock.Mock()
+    protocol.ssl_context = None
+    protocol.peername = None
+    protocol.sockname = ("127.0.0.1", 8080)
+
+    req = BaseRequest(
+        message,
+        payload,
+        protocol,
+        payload_writer,
+        task,
+        loop,
+    )
+
+    assert req._transport_sockname == ("127.0.0.1", 8080)
+
+
 def test_doubleslashes() -> None:
     # NB: //foo/bar is an absolute URL with foo netloc and /bar path
     req = make_mocked_request("GET", "/bar//foo/")