Not sure if I completely understand the question, but...
Protobuf, Cap'n Proto, Flatbuffers, and anything else with a similar design gives you the ability to verify that two versions of the protocol are "compatible" insofar as:
- If a new version of the program reads a message from an older version which is missing some newly-added field, that field will assigned a default value or "null", but the rest of the message will parse fine.
- If an old version of the program reads a message from a newer version which has some new fields that the old version doesn't know about, it will ignore those fields, but can parse the rest of the message just fine.
Of course, just because you've verified that the fields line up doesn't prove that the old and new versions of the program are actually compatible. The interpretation of the protocol could change in an incompatible way without any change to the protocol itself. Verifying compatibility at that level is an AI-complete problem.
But in practice, it works very well. Enabling safe incremental, rolling updates of components in a distributed system is exactly what Protobuf was designed to do and has been doing for >15 years at Google.
Protobuf, Cap'n Proto, Flatbuffers, and anything else with a similar design gives you the ability to verify that two versions of the protocol are "compatible" insofar as:
- If a new version of the program reads a message from an older version which is missing some newly-added field, that field will assigned a default value or "null", but the rest of the message will parse fine.
- If an old version of the program reads a message from a newer version which has some new fields that the old version doesn't know about, it will ignore those fields, but can parse the rest of the message just fine.
Of course, just because you've verified that the fields line up doesn't prove that the old and new versions of the program are actually compatible. The interpretation of the protocol could change in an incompatible way without any change to the protocol itself. Verifying compatibility at that level is an AI-complete problem.
But in practice, it works very well. Enabling safe incremental, rolling updates of components in a distributed system is exactly what Protobuf was designed to do and has been doing for >15 years at Google.