Do not strip body before JSON decoding + do not return None on empty …

…body (#3482)

This commit actually reverts 6a19364

CHANGES/3482.bugfix

@@ -0,0 +1 @@
+Do not return `None` on `await response.json()` when body is empty. Instead, raise `json.JSONDecodeError` as expected.

aiohttp/client_reqrep.py

@@ -692,7 +692,7 @@ def __init__(self, method: str, url: URL, *,
 
         self._real_url = url
         self._url = url.with_fragment(None)
-        self._body = None  # type: Any
+        self._body = None  # type: bytes
         self._writer = writer  # type: Optional[asyncio.Task[None]]
         self._continue = continue100  # None by default
         self._closed = True
@@ -1028,14 +1028,10 @@ async def json(self, *, encoding: str=None,
                              'unexpected mimetype: %s' % ctype),
                     headers=self.headers)
 
-        stripped = self._body.strip()  # type: ignore
-        if not stripped:
-            return None
-
         if encoding is None:
             encoding = self.get_encoding()
 
-        return loads(stripped.decode(encoding))
+        return loads(self._body.decode(encoding))
 
     async def __aenter__(self) -> 'ClientResponse':
         return self

tests/test_client_response.py

@@ -3,6 +3,7 @@
 
 import gc
 import sys
+from json import JSONDecodeError
 from unittest import mock
 
 import pytest
@@ -486,6 +487,31 @@ def side_effect(*args, **kwargs):
     assert response._connection is None
 
 
+async def test_json_empty_body(loop, session) -> None:
+    response = ClientResponse('get', URL('http://def-cl-resp.org'),
+                              request_info=mock.Mock(),
+                              writer=mock.Mock(),
+                              continue100=None,
+                              timer=TimerNoop(),
+                              traces=[],
+                              loop=loop,
+                              session=session)
+
+    def side_effect(*args, **kwargs):
+        fut = loop.create_future()
+        fut.set_result(b'')
+        return fut
+
+    response._headers = {'Content-Type': 'application/json'}
+    content = response.content = mock.Mock()
+    content.read.side_effect = side_effect
+
+    with pytest.raises(JSONDecodeError):
+        res = await response.json()
+
+    assert response._connection is None
+
+
 async def test_json_extended_content_type(loop, session) -> None:
     response = ClientResponse('get', URL('http://def-cl-resp.org'),
                               request_info=mock.Mock(),