Raise MultiPartException when missing "name" field on Content-Disposition header

setup.cfg

@@ -30,6 +30,7 @@ filterwarnings=
     error
     ignore: run_until_first_complete is deprecated and will be removed in a future version.:DeprecationWarning
     ignore: starlette\.middleware\.wsgi is deprecated and will be removed in a future release\.*:DeprecationWarning
+    ignore: Async generator 'starlette\.requests\.Request\.stream' was garbage collected before it had been exhausted.*:ResourceWarning
 
 [coverage:run]
 source_pkgs = starlette, tests

starlette/formparsers.py

@@ -220,7 +220,13 @@ async def parse(self) -> FormData:
                     header_value = b""
                 elif message_type == MultiPartMessage.HEADERS_FINISHED:
                     disposition, options = parse_options_header(content_disposition)
-                    field_name = _user_safe_decode(options[b"name"], charset)
+                    try:
+                        field_name = _user_safe_decode(options[b"name"], charset)
+                    except KeyError:
+                        raise MultiPartException(
+                            'The Content-Disposition header field "name" must be '
+                            "provided."
+                        )
                     if b"filename" in options:
                         filename = _user_safe_decode(options[b"filename"], charset)
                         file = UploadFile(

tests/test_formparsers.py

@@ -418,3 +418,35 @@ def test_missing_boundary_parameter(
         )
         assert res.status_code == 400
         assert res.text == "Missing boundary in multipart."
+
+
+@pytest.mark.parametrize(
+    "app,expectation",
+    [
+        (app, pytest.raises(MultiPartException)),
+        (Starlette(routes=[Mount("/", app=app)]), does_not_raise()),
+    ],
+)
+def test_missing_name_parameter_on_content_disposition(
+    app, expectation, test_client_factory: typing.Callable[..., TestClient]
+):
+    client = test_client_factory(app)
+    with expectation:
+        res = client.post(
+            "/",
+            data=(
+                # data
+                b"--a7f7ac8d4e2e437c877bb7b8d7cc549c\r\n"
+                b'Content-Disposition: form-data; ="field0"\r\n\r\n'
+                b"value0\r\n"
+            ),
+            headers={
+                "Content-Type": (
+                    "multipart/form-data; boundary=a7f7ac8d4e2e437c877bb7b8d7cc549c"
+                )
+            },
+        )
+        assert res.status_code == 400
+        assert (
+            res.text == 'The Content-Disposition header field "name" must be provided.'
+        )