Merge lp:~cjwatson/loggerhead/marshal-version into lp:loggerhead

[Colin Watson]

Make RevInfoDiskCache use a marshal version supported by Python 2.

Otherwise we run into trouble in the middle of an upgrade to Python 3, as marshal.dumps produces output that Python 2's marshal.loads can't read.

Since we now have some existing cached data unreadable by Python 2, I also made marshal.loads errors non-fatal and we just pretend we have no cache in such cases; this is OK because it's a cache.

[Tom Wardill (twom)]

review: Approve

=== modified file 'loggerhead/changecache.py'
--- loggerhead/changecache.py	2018-10-20 15:14:09 +0000
+++ loggerhead/changecache.py	2021-07-28 10:25:43 +0000
@@ -130,7 +130,10 @@
         elif str(row[0]) != revid:
             return None
         else:
-            return marshal.loads(zlib.decompress(row[1]))
+            try:
+                return marshal.loads(zlib.decompress(row[1]))
+            except (EOFError, ValueError, TypeError):
+                return None
 
     def set(self, key, revid, data):
         if not isinstance(key, bytes):
@@ -140,7 +143,7 @@
         try:
             self.cursor.execute(
                 'delete from data where key = ?', (dbapi2.Binary(key), ))
-            blob = zlib.compress(marshal.dumps(data))
+            blob = zlib.compress(marshal.dumps(data, version=2))
             self.cursor.execute(
                 "insert into data (key, revid, data) values (?, ?, ?)",
                 list(map(dbapi2.Binary, [key, revid, blob])))