Fix HEAD requests for static content

CHANGES/4809.bugfix

@@ -0,0 +1 @@
+Fix HEAD requests for static content.

CONTRIBUTORS.txt

@@ -52,6 +52,7 @@ Boyi Chen
 Brett Cannon
 Brian C. Lane
 Brian Muller
+Bruce Merry
 Bryan Kok
 Bryce Drennan
 Carl George

aiohttp/web_fileresponse.py

@@ -360,6 +360,9 @@ async def prepare(
             self.headers[hdrs.CONTENT_RANGE] = 'bytes {0}-{1}/{2}'.format(
                 real_start, real_start + count - 1, file_size)
 
+        if request.method == hdrs.METH_HEAD or self.status in [204, 304]:
+            return await super().prepare(request)
+
         fobj = await loop.run_in_executor(None, filepath.open, 'rb')
         if start:  # be aware that start could be None or int=0 here.
             offset = start

tests/test_web_urldispatcher.py

@@ -1,3 +1,4 @@
+import asyncio
 import pathlib
 from unittest import mock
 from unittest.mock import MagicMock
@@ -238,6 +239,33 @@ async def test_access_special_resource(tmp_path, aiohttp_client) -> None:
         assert r.status == 403
 
 
+async def test_static_head(tmp_path, aiohttp_client) -> None:
+    # Test HEAD on static route
+    my_file_path = tmp_path / 'test.txt'
+    with my_file_path.open('wb') as fw:
+        fw.write(b'should_not_see_this\n')
+
+    app = web.Application()
+    app.router.add_static('/', str(tmp_path))
+    client = await aiohttp_client(app)
+
+    r = await client.head('/test.txt')
+    assert r.status == 200
+
+    # Check that there is no content sent (see #4809). This can't easily be
+    # done with aiohttp_client because the buffering can consume the content.
+    reader, writer = await asyncio.open_connection(client.host, client.port)
+    writer.write(b'HEAD /test.txt HTTP/1.1\r\n')
+    writer.write(b'Host: localhost\r\n')
+    writer.write(b'Connection: close\r\n')
+    writer.write(b'\r\n')
+    while await reader.readline() != b'\r\n':
+        pass
+    content = await reader.read()
+    writer.close()
+    assert content == b''
+
+
 def test_system_route() -> None:
     route = SystemRoute(web.HTTPCreated(reason='test'))
     with pytest.raises(RuntimeError):