This seems to be pretty overengineered. Do you have a specific use-case in mind for anything more than simply continuing
the pattern we've been using of sending a message indicating support for a given feature? If we find some in the future,
we could deploy something like this, though the current proposal makes it possible to do it on a per-feature case.
The great thing about Suhas' proposal is the diff is about -1/+1 (not including tests), while still getting all the
flexibility we need. Even better, the code already exists.
Matt
On 8/21/20 3:50 PM, Jeremy wrote:
I have a proposal:
Protocol >= 70016 cease to send or process VERACK, and instead use HANDSHAKEACK, which is completed after feature
negotiation.
This should make everyone happy/unhappy, as in a new protocol number it's fair game to change these semantics to be
clear that we're acking more than version.
I don't care about when or where these messages are sequenced overall, it seems to have minimal impact. If I had free
choice, I slightly agree with Eric that verack should come before feature negotiation, as we want to divorce the idea
that protocol number and feature support are tied.
But once this is done, we can supplant Verack with HANDSHAKENACK or HANDSHAKEACK to signal success or failure to agree
on a connection. A NACK reason (version too high/low or an important feature missing) could be optional. Implicit NACK
would be disconnecting, but is discouraged because a peer doesn't know if it should reconnect or the failure was
intentional.
------
AJ: I think I generally do prefer to have a FEATURE wrapper as you suggested, or a rule that all messages in this period
are interpreted as features (and may be redundant with p2p message types -- so you can literally just use the p2p
message name w/o any data).
I think we would want a semantic (which could be based just on message names, but first-class support would be nice) for
ACKing that a feature is enabled. This is because a transcript of:
NODE0:
FEATURE A
FEATURE B
VERACK
NODE1:
FEATURE A
VERACK
It remains unclear if Node 1 ignored B because it's an unknown feature, or
because it is disabled. A transcript like:
NODE0:
FEATURE A
FEATURE B
FEATURE C
ACK A
VERACK
NODE1:
FEATURE A
ACK A
NACK B
VERACK
would make it clear that A and B are known, B is disabled, and C is unknown. C has 0 support, B Node 0 should support
inbound messages but knows not to send to Node 1, and A has full bilateral support. Maybe instead it could a message
FEATURE SEND A and FEATURE RECV A, so we can make the split explicit rather than inferred from ACK/NACK.
------
I'd also propose that we add a message which is SYNC, which indicates the end of a list of FEATURES and a request to
send ACKS or NACKS back (which are followed by a SYNC). This allows multi-round negotiation where based on the presence
of other features, I may expand the set of features I am offering. I think you could do without SYNC, but there are more
edge cases and the explicitness is nice given that this already introduces future complexity.
This multi-round makes it an actual negotiation rather than a pure announcement system. I don't think it would be used
much in the near term, but it makes sense to define it correctly now. Build for the future and all...
--
@JeremyRubin <https://twitter.com/JeremyRubin><https://twitter.com/JeremyRubin>
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