Handle edge case (read 0 bytes) in read function. Fix #171 (#193)

* Resolve issue #171: handle edge case in read function

* get rid of unneeded parameter in test

smart_open/s3.py

@@ -179,7 +179,9 @@ def detach(self):
 
     def read(self, size=-1):
         """Read up to size bytes from the object and return them."""
-        if size <= 0:
+        if size == 0:
+            return b''
+        elif size < 0:
             if len(self._buffer):
                 from_buf = self._read_from_buffer(len(self._buffer))
             else:

smart_open/tests/test_s3.py

@@ -212,6 +212,15 @@ def test_readline_tiny_buffer(self):
         expected = [b'englishman\n', b'in\n', b'new\n', b'york\n']
         self.assertEqual(expected, actual)
 
+    def test_read0_does_not_return_data(self):
+        content = b'englishman\nin\nnew\nyork\n'
+        create_bucket_and_key(contents=content)
+
+        with smart_open.s3.BufferedInputBase(BUCKET_NAME, KEY_NAME) as fin:
+            data = fin.read(0)
+
+        self.assertEqual(data, b'')
+
 
 @maybe_mock_s3
 class BufferedOutputBaseTest(unittest.TestCase):