fix empty response into webhook (#1665)

CHANGES/1664.bugfix.rst

@@ -0,0 +1,25 @@
+Fix empty response into webhook.
+
+We need to return something “empty”, and “empty” form doesn’t work since
+it’s sending only “end” boundary w/o “start”.
+
+An empty formdata should look smth like this for Telegram to understand:
+
+::
+
+   --webhookBoundaryvsF_aMHhspPjfOq7O0JNRg
+   --webhookBoundaryvsF_aMHhspPjfOq7O0JNRg--
+
+But aiohttp sends only the ending boundary:
+
+::
+
+   --webhookBoundaryvsF_aMHhspPjfOq7O0JNRg--
+
+Such response doesn't suit Telegram servers.
+
+The fix replaces empty response with empty JSON response:
+
+::
+
+   {}

aiogram/webhook/aiohttp_server.py

@@ -4,7 +4,7 @@ from abc import ABC, abstractmethod
 from asyncio import Transport
 from typing import Any, Awaitable, Callable, Dict, Optional, Set, Tuple, cast
 
-from aiohttp import MultipartWriter, web
+from aiohttp import JsonPayload, MultipartWriter, Payload, web
 from aiohttp.abc import Application
 from aiohttp.typedefs import Handler
 from aiohttp.web_middlewares import middleware
@@ -151,13 +151,17 @@ class BaseRequestHandler(ABC):
 
     def _build_response_writer(
         self, bot: Bot, result: Optional[TelegramMethod[TelegramType]]
-    ) -> MultipartWriter:
+    ) -> Payload:
+        if not result:
+            # we need to return something "empty"
+            # and "empty" form doesn't work
+            # since it's sending only "end" boundary w/o "start"
+            return JsonPayload({})
+
         writer = MultipartWriter(
             "form-data",
             boundary=f"webhookBoundary{secrets.token_urlsafe(16)}",
         )
-        if not result:
-            return writer
 
         payload = writer.append(result.__api_method__)
         payload.set_content_disposition("form-data", name="method")

tests/test_webhook/test_aiohtt_server.py

@@ -150,13 +150,9 @@ class TestSimpleRequestHandler:
 
         resp = await self.make_reqest(client=client, text="spam")
         assert resp.status == 200
-        assert resp.content_type == "multipart/form-data"
-        result = {}
-        reader = MultipartReader.from_response(resp)
-        while part := await reader.next():
-            value = await part.read()
-            result[part.name] = value.decode()
-        assert not result
+        assert resp.content_type == "application/json"
+        expected_result = {}
+        assert await resp.json() == expected_result
 
     async def test_reply_into_webhook_background(self, bot: MockedBot, aiohttp_client):
         app = Application()