Make space in the session pickle for chain index

Keeping track of the chain index is a useful thing to do, but is only required
if we've enabled diagnostics. Extend the session pickle format to make a space
for it, so that pickles can be transferred between the logging_enabled branch
and the master branch without loss of information.

Also add some tests for session pickling which explicitly check that we can
unpickle both formats of pickle.

1 files changed, 17 insertions, 1 deletions

diff --git a/src/ratchet.cpp b/src/ratchet.cpp
index dd1d42c..671d260 100644
--- a/src/ratchet.cpp
+++ b/src/ratchet.cpp
@@ -363,6 +363,10 @@ std::size_t olm::pickle_length(
     length += olm::pickle_length(value.sender_chain);
     length += olm::pickle_length(value.receiver_chains);
     length += olm::pickle_length(value.skipped_message_keys);
+
+    // the logging_enabled branch includes a 'chain_index' field
+    length += olm::pickle_length(std::uint32_t(0));
+
     return length;
 }
 
@@ -374,18 +378,30 @@ std::uint8_t * olm::pickle(
     pos = pickle(pos, value.sender_chain);
     pos = pickle(pos, value.receiver_chains);
     pos = pickle(pos, value.skipped_message_keys);
+
+    // the logging_enabled branch includes a 'chain_index' field; for us, it is
+    // empty.
+    pos = pickle(pos, std::uint32_t(0));
+
     return pos;
 }
 
 
 std::uint8_t const * olm::unpickle(
     std::uint8_t const * pos, std::uint8_t const * end,
-    olm::Ratchet & value
+    olm::Ratchet & value,
+    bool includes_chain_index
 ) {
     pos = unpickle(pos, end, value.root_key);
     pos = unpickle(pos, end, value.sender_chain);
     pos = unpickle(pos, end, value.receiver_chains);
     pos = unpickle(pos, end, value.skipped_message_keys);
+
+    // pickle v2 includes a chain index; pickle v1 did not.
+    if (includes_chain_index) {
+        std::uint32_t dummy;
+        pos = unpickle(pos, end, dummy);
+    }
     return pos;
 }