add protocol version

This is distinct from the wire protocol version used in the websocket
framing of messages. Versioning the high level protocol will let later
features be added.

The user controls the protocol version, since they send the first
several messages. Developers that connect need to avoid using features
from newer protocol versions.

So, developers and servers will need to support the most recent version,
while the user can have an old version of debug-me and it will continue
to work.

This commit changes the protocol buffer encoding, and is the last such
free change. All changes past this point will need to be versioned.

This commit was sponsored by Jochen Bartl on Patreon.

1 files changed, 10 insertions, 0 deletions

diff --git a/doc/protocol.mdwn b/doc/protocol.mdwn
index 2c4887e..94f4ee1 100644
--- a/doc/protocol.mdwn
+++ b/doc/protocol.mdwn
@@ -107,3 +107,13 @@ The prevActivity and prevEntered hashes are actually not included in the
 data sent across the wire. They are left out to save space, and get
 added back in by the receiver. The receiver uses the signature of the
 message to tell when it's found the right hashes to add back in.
+
+## protocol versioning
+
+The SessionKey control messages include a field for the protocol version.
+Since the user starts by sending a SessionKey, the included version
+specifies the protocol version used by the rest of the protocol. When
+developers connect, their clients will need to check that version,
+and avoid sending any messages using features from a later version.
+
+The current protocol version is "1".