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: Optional[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))  # type: ignore
 
     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
@@ -586,11 +587,11 @@ async def test_json_no_content(loop, session) -> None:
                               loop=loop,
                               session=session)
     response._headers = {
-        'Content-Type': 'data/octet-stream'}
+        'Content-Type': 'application/json'}
     response._body = b''
 
-    res = await response.json(content_type=None)
-    assert res is None
+    with pytest.raises(JSONDecodeError):
+        await response.json(content_type=None)
 
 
 async def test_json_override_encoding(loop, session) -> None: