asyncio.streams.StreamReader: Add 'at_eof()' method

Lib/asyncio/streams.py

@@ -293,6 +293,10 @@ class StreamReader:
             if not waiter.cancelled():
                 waiter.set_result(True)
 
+    def at_eof(self):
+        """Return True if the buffer is empty and 'feed_eof' was called."""
+        return self._eof and not self._buffer
+
     def feed_data(self, data):
         assert not self._eof, 'feed_data after feed_eof'
 

Lib/test/test_asyncio/test_streams.py

@@ -204,6 +204,21 @@ class StreamReaderTests(unittest.TestCase):
         # expected to be empty now.
         self.assertEqual(b'', stream._buffer)
 
+    def test_at_eof(self):
+        stream = asyncio.StreamReader(loop=self.loop)
+        self.assertFalse(stream.at_eof())
+
+        stream.feed_data(b'some data\n')
+        self.assertFalse(stream.at_eof())
+
+        self.loop.run_until_complete(stream.readline())
+        self.assertFalse(stream.at_eof())
+
+        stream.feed_data(b'some data\n')
+        stream.feed_eof()
+        self.loop.run_until_complete(stream.readline())
+        self.assertTrue(stream.at_eof())
+
     def test_readline_limit(self):
         # Read one line. StreamReaders are fed with data after
         # their 'readline' methods are called.