Pipelined identify protocol "negotiation"

[Stebalien]

Now that we're going to introduce multiple identify protocols, we'll need to negotiate to pick the right one. This could cost us multiple round-trips.

However, there's a simple hack to work around this: just send all protocols we speak up-front!

That is, instead of:

> /multistream/1.0.0\n
> /p2p/id/1.1.0
< /multistream/1.0.0\n
< na
> /ipfs/id/1.0.0\n
< /ipfs/id/1.0.0\n
< Identify Message

Send all protocols we speak together:

> /multistream/1.0.0\n
> /p2p/id/1.1.0
> /ipfs/id/1.0.0\n
< /multistream/1.0.0\n
< na
< /ipfs/id/1.0.0\n
< Identify Message

The trick here is that the receiver will ignore any data from the initiator of the identify request.

[raulk]

Can't we just make the identify message for /p2p/id/1.1.0 backwards compatible? Unless I'm missing something (which I probably am), it should be easily doable with Protobuf.

[Stebalien]

We can. But in that case, we'd need to keep the same protocol name.

[Stebalien]

(i.e., /ipfs/id/1.0.0)

[raulk]

Exactly, that’s precisely what I mean. Versioning protocols by outer protocol identifiers is one way to version protocol. It’s practicable when it’s accompanied by an efficient protocol negotiation scheme. Multistream-select 1.0 is not that, it’s pretty wasteful, and working around it with a bespoke flow is something I’d like to avoid. Let’s version the protocol from inside the protocol in this case. When we introduce a HELLO message in ms2.0, all this will become much better.

[Stebalien]

This is no longer an issue.