> Instead, would you consider to use ANYONECANPAY to sign the tx, so it is
> possible add more inputs for fees? The total tx size is bigger than the
> OP_TRUE approach, but you don’t need to ask for any protocol change.
If one has a "root" commitment with other nested descendent
multi-transaction contracts, then changing the txid of the root commitment
will invalidated all the nested multi tx contracts. In our specific case, we
have pre-signed 2-stage HTLC transaction which rely on a stable txid. As a
result, we can't use the ANYONECANPAY approach atm.
> In long-term, I think the right way is to have a more flexible SIGHASH
> system to allow people to add more inputs and outputs easily.
Agreed, see the recent proposal to introduce SIGHASH_NOINPUT as a new
sighash type. IMO it presents an opportunity to introduce more flexible fine
grained sighash inclusion control.
-- Laolu
You should make a “0 fee tx with exactly one OP_TRUE output” standard, but nothing else. This makes sure CPFP will always be needed, so the OP_TRUE output won’t pollute the UTXO set
Instead, would you consider to use ANYONECANPAY to sign the tx, so it is possible add more inputs for fees? The total tx size is bigger than the OP_TRUE approach, but you don’t need to ask for any protocol change.
In long-term, I think the right way is to have a more flexible SIGHASH system to allow people to add more inputs and outputs easily.
> On 9 May 2018, at 7:57 AM, Rusty Russell via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:
>
> Hi all,
>
> The largest problem we are having today with the lightning
> protocol is trying to predict future fees. Eltoo solves this elegantly,
> but meanwhile we would like to include a 546 satoshi OP_TRUE output in
> commitment transactions so that we use minimal fees and then use CPFP
> (which can't be done at the moment due to CSV delays on outputs).
>
> Unfortunately, we'd have to P2SH it at the moment as a raw 'OP_TRUE' is
> non-standard. Are there any reasons not to suggest such a policy
> change?
>
> Thanks!
> Rusty.
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