Service bits are advertised, protocol support is not. https://en.bitcoin.it/wiki/Protocol_documentation#Network_address
e > On Aug 21, 2020, at 14:08, Jeremy <jlru...@mit.edu> wrote: > > > Actually we already have service bits (which are sadly limited) which allow > negotiation of non bilateral feature support, so this would supercede that. > -- > @JeremyRubin > > >> On Fri, Aug 21, 2020 at 1:45 PM Matt Corallo <lf-li...@mattcorallo.com> >> wrote: >> 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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