Fixed 7616: EmptyStreamReader.iter_chunks() never ends (#7644)

## What do these changes do?

Fixes an issue reported in
[7616](#7616) - An iteration
of the chunks of an EmptyStreamReader with iter_chunks() never ends.
## Are there changes in behavior for the user?

- `EmptyStreamReader` `iter_chunks()` does not get stuck
- First call of `EmptyStreamReader` `readchunk()` now returns `(b"",
False)`. All the subsequent calls return `(b"", True)`. Before this PR
it was always `(b"", True)`.

## Related issue number

[7616](#7616)

CHANGES/7616.bugfix

@@ -0,0 +1 @@
+Fixed ``EmptyStreamReader.iter_chunks()`` never ending -- by :user:`mind1m`

aiohttp/streams.py

@@ -491,7 +491,7 @@ def _read_nowait(self, n: int) -> bytes:
 
 class EmptyStreamReader(StreamReader):  # lgtm [py/missing-call-to-init]
     def __init__(self) -> None:
-        pass
+        self._read_eof_chunk = False
 
     def __repr__(self) -> str:
         return "<%s>" % self.__class__.__name__
@@ -535,6 +535,10 @@ async def readany(self) -> bytes:
         return b""
 
     async def readchunk(self) -> Tuple[bytes, bool]:
+        if not self._read_eof_chunk:
+            self._read_eof_chunk = True
+            return (b"", False)
+
         return (b"", True)
 
     async def readexactly(self, n: int) -> bytes:

tests/test_streams.py

@@ -1109,12 +1109,22 @@ async def test_empty_stream_reader() -> None:
     assert await s.read() == b""
     assert await s.readline() == b""
     assert await s.readany() == b""
+    assert await s.readchunk() == (b"", False)
     assert await s.readchunk() == (b"", True)
     with pytest.raises(asyncio.IncompleteReadError):
         await s.readexactly(10)
     assert s.read_nowait() == b""
 
 
+async def test_empty_stream_reader_iter_chunks() -> None:
+    s = streams.EmptyStreamReader()
+
+    # check that iter_chunks() does not cause infinite loop
+    iter_chunks = s.iter_chunks()
+    with pytest.raises(StopAsyncIteration):
+        await iter_chunks.__anext__()
+
+
 @pytest.fixture
 async def buffer(loop: Any):
     return streams.DataQueue(loop)