From: Eric Voskuil <eric@voskuil•org>
To: Jeremy <jlrubin@mit•edu>
Cc: Bitcoin Protocol Discussion <bitcoin-dev@lists•linuxfoundation.org>
Subject: Re: [bitcoin-dev] Generalizing feature negotiation when new p2p connections are setup
Date: Fri, 21 Aug 2020 14:17:55 -0700 [thread overview]
Message-ID: <C9CB03D3-2328-4FEB-96EF-4FB297C78BC6@voskuil.org> (raw)
In-Reply-To: <CAD5xwhhrz8SMQ4bA6eD2VRwqmMEzVv7NmrD8kDnPfqJy092bKQ@mail.gmail.com>
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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 <jlrubin@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-lists@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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next prev parent reply other threads:[~2020-08-21 21:18 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-14 19:28 Suhas Daftuar
2020-08-16 17:24 ` Jeremy
2020-08-16 19:06 ` Eric Voskuil
2020-08-17 20:40 ` Suhas Daftuar
2020-08-17 21:21 ` Eric Voskuil
2020-08-20 14:13 ` David A. Harding
2020-08-18 14:59 ` Matt Corallo
2020-08-18 16:54 ` Eric Voskuil
2020-08-18 17:26 ` Matt Corallo
2020-08-18 18:11 ` Eric Voskuil
2020-08-18 18:25 ` Matt Corallo
2020-08-18 18:56 ` Eric Voskuil
2020-08-21 2:36 ` Anthony Towns
2020-08-21 4:25 ` Eric Voskuil
2020-08-21 14:15 ` lf-lists
2020-08-21 16:42 ` Eric Voskuil
2020-08-21 19:50 ` Jeremy
2020-08-21 20:45 ` Matt Corallo
2020-08-21 21:08 ` Jeremy
2020-08-21 21:17 ` Jeremy
2020-08-21 22:16 ` Matt Corallo
2020-08-23 17:49 ` Eric Voskuil
2020-08-24 9:44 ` Suhas Daftuar
2020-08-24 13:59 ` G. Andrew Stone
2020-08-24 19:58 ` Jeremy
2020-08-24 20:17 ` Eric Voskuil
2020-08-24 20:21 ` Jeremy
2020-08-24 20:33 ` Eric Voskuil
2020-08-21 21:17 ` Eric Voskuil [this message]
2020-08-23 17:45 ` Eric Voskuil
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