add version number query about cable HOT 4 CLOSED

Another option, I'm realizing, is to treat msg_type as a version. So a msg_type=1 message will ALWAYS look the way it's specified in the spec, as a data response, but of course that doesn't prevent us from specifying a data response v2 message type with a larger msg_type value that works differently. The same idea applies for post types.

This would prevent old nodes from breaking, and adds no extra data overhead. A downside is that a pair of peers will have no explicit knowledge that they're on different versions, but one side can infer they are when they receive a message of a type they aren't familiar with.

This logic also applies in the event that a message or post type has a security vulnerability discovered in it, where newer clients can choose to ignore older post and message types that are known to be deprecated and have newer replacement versions. Like the previous situation, here the newer client will detect there is a compatibility mismatch when they receive deprecated messages or posts.

from cable.

This is a good point. I think we need both of these: protocol versioning and post versioning. We're definitely not going to get everything right on the first try. 🙃

I like the idea of exchanging protocol version #s during handshake, primarily because even if we end up changing something very fundamental, like the shape of request headers, peers will know right away they aren't compatible with each other. This would mean us adding wire protocol for said initial handshake.

I think it would be reasonable to add one byte to the post header. Given the header's current size (129+ bytes), another byte only makes it 0.78% larger!

from cable.

If we treat each message type definition as immutable (i.e. msg_type=1 will ALWAYS have the given binary format), we don't need any other versioning across the protocol, right? Right now the cable protocol is made up exclusively from messages and posts, and if both are implicitly versioned, we're done, right?

I do think that, if we have a handshake specification, that ought to be versioned!

from cable.

we have a handshake with versioning now :) https://github.com/cabal-club/cable/blob/main/handshake.md

from cable.