fix(connection): Fix creation of FormMultiDict in Request.form to pro…

…perly handle multi-keys (litestar-org#3639)

Fix creation of FormMultiDict in Request.form to properly handle multi-keys

litestar/connection/request.py

@@ -74,7 +74,7 @@ def __init__(self, scope: Scope, receive: Receive = empty_receive, send: Send =
         super().__init__(scope, receive, send)
         self.is_connected: bool = True
         self._body: bytes | EmptyType = Empty
-        self._form: dict[str, str | list[str]] | EmptyType = Empty
+        self._form: FormMultiDict | EmptyType = Empty
         self._json: Any = Empty
         self._msgpack: Any = Empty
         self._content_type: tuple[str, dict[str, str]] | EmptyType = Empty
@@ -205,26 +205,36 @@ async def form(self) -> FormMultiDict:
             A FormMultiDict instance
         """
         if self._form is Empty:
-            if (form := self._connection_state.form) is not Empty:
-                self._form = form
-            else:
+            if (form_data := self._connection_state.form) is Empty:
                 content_type, options = self.content_type
                 if content_type == RequestEncodingType.MULTI_PART:
-                    self._form = parse_multipart_form(
+                    form_data = parse_multipart_form(
                         body=await self.body(),
                         boundary=options.get("boundary", "").encode(),
                         multipart_form_part_limit=self.app.multipart_form_part_limit,
                     )
                 elif content_type == RequestEncodingType.URL_ENCODED:
-                    self._form = parse_url_encoded_form_data(
+                    form_data = parse_url_encoded_form_data(
                         await self.body(),
                     )
                 else:
-                    self._form = {}
-
-                self._connection_state.form = self._form
+                    form_data = {}
+
+                self._connection_state.form = form_data
+
+            # form_data is a dict[str, list[str] | str | UploadFile]. Convert it to a
+            # list[tuple[str, str | UploadFile]] before passing it to FormMultiDict so
+            # multi-keys can be accessed properly
+            items = []
+            for k, v in form_data.items():
+                if isinstance(v, list):
+                    for sv in v:
+                        items.append((k, sv))
+                else:
+                    items.append((k, v))
+            self._form = FormMultiDict(items)
 
-        return FormMultiDict(self._form)
+        return self._form
 
     async def send_push_promise(self, path: str, raise_if_unavailable: bool = False) -> None:
         """Send a push promise.

tests/unit/test_connection/test_request.py

@@ -11,7 +11,7 @@
 
 import pytest
 
-from litestar import MediaType, Request, asgi, get
+from litestar import MediaType, Request, asgi, get, post
 from litestar.connection.base import empty_send
 from litestar.datastructures import Address, Cookie
 from litestar.exceptions import (
@@ -282,6 +282,24 @@ async def app(scope: Scope, receive: Receive, send: Send) -> None:
     assert response.json() == {"form": {"abc": "123 @"}}
 
 
+def test_request_form_urlencoded_multi_keys() -> None:
+    @post("/")
+    async def handler(request: Request) -> Any:
+        return (await request.form()).getall("foo")
+
+    with create_test_client(handler) as client:
+        assert client.post("/", data={"foo": ["1", "2"]}).json() == ["1", "2"]
+
+
+def test_request_form_multipart_multi_keys() -> None:
+    @post("/")
+    async def handler(request: Request) -> int:
+        return len((await request.form()).getall("foo"))
+
+    with create_test_client(handler) as client:
+        assert client.post("/", data={"foo": "1"}, files={"foo": b"a"}).json() == 2
+
+
 def test_request_body_then_stream() -> None:
     async def app(scope: Any, receive: Receive, send: Send) -> None:
         request = Request[Any, Any, Any](scope, receive)

tests/unit/test_kwargs/test_multipart_data.py

@@ -51,18 +51,17 @@ async def form_multi_item_handler(request: Request) -> DefaultDict[str, list]:
     data = await request.form()
     output = defaultdict(list)
     for key, value in data.multi_items():
-        for v in value:
-            if isinstance(v, UploadFile):
-                content = await v.read()
-                output[key].append(
-                    {
-                        "filename": v.filename,
-                        "content": content.decode(),
-                        "content_type": v.content_type,
-                    }
-                )
-            else:
-                output[key].append(v)
+        if isinstance(value, UploadFile):
+            content = await value.read()
+            output[key].append(
+                {
+                    "filename": value.filename,
+                    "content": content.decode(),
+                    "content_type": value.content_type,
+                }
+            )
+        else:
+            output[key].append(value)
     return output