slo_preservs.diff

diff --git a/swift/obj/mem_diskfile.py b/swift/obj/mem_diskfile.py
index a3b37f4..4456fa3 100644
--- a/swift/obj/mem_diskfile.py
+++ b/swift/obj/mem_diskfile.py
@@ -27,8 +27,7 @@ from swift.common.exceptions import DiskFileQuarantined, DiskFileNotExist, \
     DiskFileCollision, DiskFileDeleted, DiskFileNotOpen
 from swift.common.request_helpers import is_sys_meta
 from swift.common.swob import multi_range_iterator
-from swift.obj.diskfile import DATAFILE_SYSTEM_META
-
+from swift.obj.diskfile import DATAFILE_SYSTEM_META, RESERVED_DATAFILE_META
 
 class InMemoryFileSystem(object):
     """
@@ -433,7 +432,8 @@ class DiskFile(object):
             # with the object data.
             immutable_metadata = dict(
                 [(key, val) for key, val in cur_mdata.items()
-                 if key.lower() in DATAFILE_SYSTEM_META
+                 if key.lower() in (RESERVED_DATAFILE_META |
+                                    DATAFILE_SYSTEM_META)
                  or is_sys_meta('object', key)])
             metadata.update(immutable_metadata)
             metadata['name'] = self._name
diff --git a/test/unit/obj/test_diskfile.py b/test/unit/obj/test_diskfile.py
index 2a18478..2b1c43f 100644
--- a/test/unit/obj/test_diskfile.py
+++ b/test/unit/obj/test_diskfile.py
@@ -2412,6 +2412,23 @@ class DiskFileMixin(BaseDiskFileTestMixin):
             # original sysmeta keys are preserved
             self.assertEqual('Value1', df._metadata['X-Object-Sysmeta-Key1'])
 
+    def test_disk_file_preserves_slo(self):
+        # build an object with some meta (at t0)
+        orig_metadata = {'X-Static-Large-Object': 'True',
+                         'Content-Type': 'text/garbage'}
+        df = self._get_open_disk_file(ts=self.ts().internal,
+                                      extra_metadata=orig_metadata)
+        with df.open():
+            self.assertEqual('1024', df._metadata['Content-Length'])
+        # write some new metadata (fast POST, don't send orig meta, at t0+1s)
+        df = self._simple_get_diskfile()
+        df.write_metadata({'X-Timestamp': self.ts().internal})
+        df = self._simple_get_diskfile()
+        with df.open():
+            # non-fast-post updateable keys are preserved
+            self.assertEqual('text/garbage', df._metadata['Content-Type'])
+            self.assertEqual('True', df._metadata['X-Static-Large-Object'])
+
     def test_disk_file_reader_iter(self):
         df = self._create_test_file('1234567890')
         quarantine_msgs = []