We don't want to use pickle as it can execute arbitrary code. JSON is
safer. However, note that it supports serialization for only some
specific subset of object types; this should be enough for what we need,
though.
To avoid issues on upgrades (unability to read pickled values, and cache
poisoning for old servers not understanding JSON), we add a
memcache_serialization_support configuration option, with the following
values:
0 = older, insecure pickle serialization
1 = json serialization but pickles can still be read (still insecure)
2 = json serialization only (secure and the default)
To avoid an instant full cache flush, existing installations should
upgrade with 0, then set to 1 and reload, then after some time (24
hours) set to 2 and reload. Support for 0 and 1 will be removed in
future versions.
Part of bug 1006414.
Change-Id: Id7d6d547b103b4f23ebf5be98b88f09ec6027ce4
e1ff51c045