[bitcoin-dev] SegWit GBT updates

[Cory Fields]

Thanks for getting this started, Luke.

Noticeably absent here is the "default_witness_commitment" key, as
added by the current reference implementation[0].

I assume (please correct me if I'm wrong) that this has been omitted
for the sake of having clients create the commitment themselves as
opposed to having it provided to them.

I don't think that the two approaches (providing the default
commitment for the complete tx set as well as the ability to create it
from chosen transactions) are at odds with each-other, rather it
merely allows for a simpler approach for those who are taking tx's
as-is from bitcoind. It's obviously important for the clients to be
able to chose tx's and create commitments as they desire, but it's
equally important to allow for simpler use-cases.

The issue in particular here is that a non-trivial burden is thrust
upon mining software, increasing the odds of bugs in the process. I'd
like to point out that this is not a theoretical argument. I've
already fixed a handful of bugs relating to serialization or
commitment creation in the mining/pool software that I've worked on
for segwit [1][2][3][4]. Asking them to handle more serialization and
calculation of complex structures needlessly increases the complexity
for zero benefit in the case where the tx's are to be used as-is.

I'll PR this change to the BIP, as I can't really come up with an
argument against. At worst, it can simply be ignored.

[0]: https://github.com/sipa/bitcoin/blob/segwit/src/rpcmining.cpp#L590
[1]: https://github.com/bitcoin/libblkmaker/commit/22f6e42844aa14ed0037ebf12a734f07e63533d7
[2]: https://github.com/bitcoin/libblkmaker/commit/15e2c35bf69c997488e37147cf062dfa925b4912
[3]: https://github.com/bitcoin/libblkmaker/commit/9a5799891e0f3590779b8e5a993a7b306088e2fa
[4]: https://github.com/theuni/ckpool/commit/7d84b1d76b39591cc1c1ef495ebec513cb19a08e

Regards,
Cory

On Sat, Jan 30, 2016 at 1:50 PM, Luke Dashjr via bitcoin-dev
<bitcoin-dev at lists.linuxfoundation.org> wrote:
> I've completed an initial draft of a BIP for updating getblocktemplate for
> segregated witness here:
>     https://github.com/luke-jr/bips/blob/segwit_gbt/bip-segwit-gbt.mediawiki
>
> Please review and comment (especially with regard to the changes in the
> sigoplimits handling).
>
> (Note: libblkmaker's reference implementation is at this time incompatible
> with the "last output" rule in this BIP.)
>
> Thanks,
>
> Luke
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