I was assuming, largely, that Bitcoin Core will eventually get what you describe here (which is generally termed
"package relay", implying we relay, and process, groups of transactions as one).
What we'd need for SIGHASH_ANYPREVOUT is a relay network that isn't just smart about fee calculation, but can actually
rewrite the transactions themselves before passing them on to a local bitcoind.
eg such a network would need to be able to relay
"I have transaction A, with one input, which is valid for any output-idx-0 in a
transaction spending output B".
and then have the receiver go look up which transaction in its mempool/chain spends output B, then fill in the input
with that outpoint and hand the now-fully-formed transaction to their local bitcoind for processing.
Matt
On 8/7/20 11:34 AM, Richard Myers wrote:
When you say that a special relay network might be more "smart about replacement" in the context of ANYPREVOUT*, do you
mean these nodes could RBF parts of a package like this:
Given:
- Package A = UpdateTx_A(n=1): txin: AnchorTx, txout: SettlementTx_A(n=1) -> HtlcTxs(n=1)_A -> .chain of transactions
that pin UpdateTx_A(n=1) with high total fee, etc.
And a new package with higher fee rate versions of ANYPREVOUT* transactions in
the package, but otherwise lower total fee:
- Package B = UpdateTx_B(n=1): txin: AnchorTx, txout: SettlementTx_B(n=1) ->
HtlcTxs(n=1)_B -> low total fee package
Relay just the higher up-front fee-rate transactions from package B which get spent by the high absolute fee child
transactions from package A:
- Package A' = UpdateTx_B(n=1): txin: AnchorTx, txout: SettlementTx_B(n=1) -> HtlcTxs(n=1)_A -> ...chain of up to 25
txs that pin UpdateTx(n=1) with high total fee, etc.
On Thu, Aug 6, 2020 at 5:59 PM Matt Corallo via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org
<mailto:bitcoin-dev@lists.linuxfoundation.org>> wrote:
In general, SIGHASH_NOINPUT makes these issues much, much simpler to
address, but only if we assume that nodes can
somehow be "smart" about replacement when they see a SIGHASH_NOINPUT spend
which can spend an output that something else
in the mempool already spends (potentially a different input than the
relaying node thinks the transaction should
spend). While ideally we'd be able to shove that (significant) complexity
into the Bitcoin P2P network, that may not be
feasible, but we could imagine a relay network of lightning nodes doing
that calculation and then passing the
transactions to their local full nodes.
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