From: <eric@voskuil.org>
To: "'Anthony Towns'" <aj@erisian.com.au>,
 "'Bitcoin Protocol Discussion'" <bitcoin-dev@lists.linuxfoundation.org>,
 "'Gloria Zhao'" <gloriajzhao@gmail.com>
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In-Reply-To: <017501d87079$4c08f9c0$e41aed40$@voskuil.org>
Date: Wed, 25 May 2022 19:59:01 -0700
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Subject: Re: [bitcoin-dev] Package Relay Proposal
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Given that packages have no header, the package requires identity in a
BIP152 scheme. For example 'header' and 'blockhash' fields can be replaced
with a Merkle root (e.g. "identity" field) for the package, uniquely
identifying the partially-ordered set of txs. And use of 'getdata' (to
obtain a package by hash) can be eliminated (not a use case).

e

> -----Original Message-----
> From: eric@voskuil.org <eric@voskuil.org>
> Sent: Wednesday, May 25, 2022 1:52 PM
> To: 'Anthony Towns' <aj@erisian.com.au>; 'Bitcoin Protocol Discussion'
> <bitcoin-dev@lists.linuxfoundation.org>; 'Gloria Zhao'
> <gloriajzhao@gmail.com>
> Subject: RE: [bitcoin-dev] Package Relay Proposal
> 
> > From: bitcoin-dev <bitcoin-dev-bounces@lists.linuxfoundation.org> On
> Behalf
> > Of Anthony Towns via bitcoin-dev
> > Sent: Wednesday, May 25, 2022 11:56 AM
> 
> > So the other thing is what happens if the peer announcing packages to us
> is
> > dishonest?
> >
> > They announce pkg X, say X has parents A B C and the fee rate is
garbage.
> But
> > actually X has parent D and the fee rate is excellent. Do we request the
> > package from another peer, or every peer, to double check? Otherwise
> we're
> > allowing the first peer we ask about a package to censor that tx from
us?
> >
> > I think the fix for that is just to provide the fee and weight when
> announcing
> > the package rather than only being asked for its info? Then if one peer
> makes
> > it sound like a good deal you ask for the parent txids from them,
dedupe,
> > request, and verify they were honest about the parents.
> 
> Single tx broadcasts do not carry an advertised fee rate, however the'
> feefilter' message (BIP133) provides this distinction. This should be
> interpreted as applicable to packages. Given this message there is no
reason
> to send a (potentially bogus) fee rate with every package. It can only be
> validated by obtaining the full set of txs, and the only recourse is
> dropping (etc.) the peer, as is the case with single txs. Relying on the
> existing message is simpler, more consistent, and more efficient.
> 
> > >> Is it plausible to add the graph in?
> >
> > Likewise, I think you'd have to have the graph info from many nodes if
> you're
> > going to make decisions based on it and don't want hostile peers to be
> able to
> > trick you into ignoring txs.
> >
> > Other idea: what if you encode the parent txs as a short hash of the
wtxid
> > (something like bip152 short ids? perhaps seeded per peer so collisions
> will
> > be different per peer?) and include that in the inv announcement? Would
> > that work to avoid a round trip almost all of the time, while still
giving
> you
> > enough info to save bw by deduping parents?
> 
> As I suggested earlier, a package is fundamentally a compact block (or
> block) announcement without the header. Compact block (BIP152)
> announcement
> is already well-defined and widely implemented. A node should never be
> required to retain an orphan, and BIP152 ensures this is not required.
> 
> Once a validated set of txs within the package has been obtained with
> sufficient fee, a fee-optimal node would accept the largest subgraph of
the
> package that conforms to fee constraints and drop any peer that provides a
> package for which the full graph does not.
> 
> Let us not reinvent the wheel and/or introduce accidental complexity. I
see
> no reason why packaging is not simply BIP152 without the 'header' field,
an
> updated protocol version, and the following sort of changes to names:
> 
> sendpkg
> MSG_CMPCT_PKG
> cmpctpkg
> getpkgtxn
> pkgtxn
> 
> > > For a maximum 25 transactions,
> > >23*24/2 = 276, seems like 36 bytes for a child-with-parents package.
> >
> > If you're doing short ids that's maybe 25*4B=100B already, then the
above
> is
> > up to 36% overhead, I guess. Might be worth thinking more about, but
> maybe
> > more interesting with ancestors than just parents.
> >
> > >Also side note, since there are no size/count params,
> 
> Size is restricted in the same manner as block and transaction broadcasts,
> by consensus. If the fee rate is sufficient there would be no reason to
> preclude any valid size up to what can be mined in one block (packaging
> across blocks is not economically rational under the assumption that one
> miner cannot expect to mine multiple blocks in a row). Count is
incorporated
> into BIP152 as 'shortids_length'.
> 
> > > wondering if we
> > >should just have "version" in "sendpackages" be a bit field instead of
> > >sending a message for each version. 32 versions should be enough right?
> 
> Adding versioning to individual protocols is just a reflection of the
> insufficiency of the initial protocol versioning design, and that of the
> various ad-hoc changes to it (including yet another approach in this
> proposal) that have been introduced to compensate for it, though I'll
> address this in an independent post at some point.
> 
> Best,
> e
> 
> > Maybe but a couple of messages per connection doesn't really seem worth
> > arguing about?
> >
> > Cheers,
> > aj
> >
> >
> > --
> > Sent from my phone.
> > _______________________________________________
> > bitcoin-dev mailing list
> > bitcoin-dev@lists.linuxfoundation.org
> > https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev