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From: Matt Corallo <lf-lists@mattcorallo.com>
To: Jeremy <jlrubin@mit.edu>, Eric Voskuil <eric@voskuil.org>,
	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 16:45:26 -0400	[thread overview]
Message-ID: <b6198e1a-c30b-358a-9673-247a7c305913@mattcorallo.com> (raw)
In-Reply-To: <CAD5xwhi9zVp3nOhFy3Hia_Md++Gdz+F5Kat_bbbZwBcmPhMGZA@mail.gmail.com>

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>


  reply	other threads:[~2020-08-21 20:45 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-14 19:28 [bitcoin-dev] Generalizing feature negotiation when new p2p connections are setup 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 [this message]
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
2020-08-23 17:45           ` Eric Voskuil

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