[Python-checkins] bpo-32622: Enforce sendfile fallback policy for FALLBACK transports (#5364)

[Yury Selivanov]

https://github.com/python/cpython/commit/b1a6ac4c4026d648b3d948945b734a4d0f175a3c
commit: b1a6ac4c4026d648b3d948945b734a4d0f175a3c
branch: master
author: Yury Selivanov <yury at magic.io>
committer: GitHub <noreply at github.com>
date: 2018-01-27T15:52:52-05:00
summary:

bpo-32622: Enforce sendfile fallback policy for FALLBACK transports (#5364)

files:
M Lib/asyncio/base_events.py
M Lib/test/test_asyncio/test_events.py

diff --git a/Lib/asyncio/base_events.py b/Lib/asyncio/base_events.py
index f532dc42132..7442bf28b03 100644
--- a/Lib/asyncio/base_events.py
+++ b/Lib/asyncio/base_events.py
@@ -1035,7 +1035,12 @@ def _check_sendfile_params(self, sock, file, offset, count):
             except events.SendfileNotAvailableError as exc:
                 if not fallback:
                     raise
-        # the mode is FALLBACK or fallback is True
+
+        if not fallback:
+            raise RuntimeError(
+                f"fallback is disabled and native sendfile is not "
+                f"supported for transport {transport!r}")
+
         return await self._sendfile_fallback(transport, file,
                                              offset, count)
 
diff --git a/Lib/test/test_asyncio/test_events.py b/Lib/test/test_asyncio/test_events.py
index 0981bd6ac91..b66d91d415e 100644
--- a/Lib/test/test_asyncio/test_events.py
+++ b/Lib/test/test_asyncio/test_events.py
@@ -27,6 +27,7 @@
 
 import asyncio
 from asyncio import base_events
+from asyncio import constants
 from asyncio import coroutines
 from asyncio import events
 from asyncio import proactor_events
@@ -2381,6 +2382,14 @@ def test_sendfile_prevents_bare_write(self):
         ret = self.run_loop(t)
         self.assertEqual(ret, len(self.DATA))
 
+    def test_sendfile_no_fallback_for_fallback_transport(self):
+        transport = mock.Mock()
+        transport.is_closing.side_effect = lambda: False
+        transport._sendfile_compatible = constants._SendfileMode.FALLBACK
+        with self.assertRaisesRegex(RuntimeError, 'fallback is disabled'):
+            self.loop.run_until_complete(
+                self.loop.sendfile(transport, None, fallback=False))
+
 
 if sys.platform == 'win32':