Re: [bitcoin-dev] Package Relay Proposal

From: <eric@voskuil•org>
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
Date: Wed, 25 May 2022 13:52:07 -0700	[thread overview]
Message-ID: <017501d87079$4c08f9c0$e41aed40$@voskuil.org> (raw)
In-Reply-To: <8FFE048D-854F-4D34-85DA-CE523C16EEB0@erisian.com.au>

> 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.
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