Fix for BufferedReader sets is_zero_size true for a chunk

When the image is size larger than chunk size, swift store
uploads 0 bytes for swift_buffered_upload enabled.

Closes-Bug: #1863691

Change-Id: I272d380d8fc093e946ecd6bd5ba99b5bbe2409b2

glance_store/_drivers/swift/buffered.py

@@ -137,7 +137,7 @@ class BufferedReader(object):
     def _buffer(self):
         to_buffer = self.total
         LOG.debug("Buffering %s bytes of image segment" % to_buffer)
-
+        buffer_read_count = 0
         while not self._buffered:
             read_size = min(to_buffer, READ_SIZE)
             try:
@@ -156,6 +156,9 @@ class BufferedReader(object):
                 break
             self._tmpfile.write(buf)
             to_buffer -= len(buf)
+            buffer_read_count = buffer_read_count + 1
+        if buffer_read_count == 0:
+            self.is_zero_size = True
 
     # NOTE(belliott) seek and tell get used by python-swiftclient to "reset"
     # if there is a put_object error

glance_store/tests/unit/test_swift_store.py

@@ -2239,3 +2239,37 @@ class TestBufferedReader(base.StoreBaseTest):
         # file objects are not required to have a 'close' attribute
         if getattr(self.reader._tmpfile, 'closed'):
             self.assertTrue(self.reader._tmpfile.closed)
+
+    def test_read_all_data(self):
+        """
+        Replicate what goes on in the Swift driver with the
+        repeated creation of the BufferedReader object
+        """
+        CHUNKSIZE = 100
+        data = b'*' * units.Ki
+        expected_checksum = hashlib.md5(data).hexdigest()
+        expected_multihash = hashlib.sha256(data).hexdigest()
+        data_file = tempfile.NamedTemporaryFile()
+        data_file.write(data)
+        data_file.flush()
+        infile = open(data_file.name, 'rb')
+        bytes_read = 0
+        checksum = hashlib.md5()
+        os_hash_value = hashlib.sha256()
+        while True:
+            cr = buffered.BufferedReader(infile, checksum, os_hash_value,
+                                         CHUNKSIZE)
+            chunk = cr.read(CHUNKSIZE)
+            if len(chunk) == 0:
+                self.assertEqual(True, cr.is_zero_size)
+                break
+            else:
+                self.assertEqual(False, cr.is_zero_size)
+            bytes_read += len(chunk)
+        self.assertEqual(units.Ki, bytes_read)
+        self.assertEqual(expected_checksum,
+                         cr.checksum.hexdigest())
+        self.assertEqual(expected_multihash,
+                         cr.os_hash_value.hexdigest())
+        data_file.close()
+        infile.close()