Splicing problem with VLS Integration

[enaples]

Starting from v26.04 splicing is enabled by default which causes VLS to fire the following error message:

ERROR connect: vlsd/src/grpc/signer.rs:508: error on stream: status: Unknown, message: 
"h2 protocol error: error reading a body from connection", details: [], metadata: 
MetadataMap { headers: {} } datadir="/path/to/vls" uri=http://localhost:<vlsd_port>/

Moreover, in v26.04 lightningd --help is still present a reference to the flag experimental-splicing, which if added as flag (or to the config file) makes the node crash with the error:

lightningd: Config file /path/to/config/file line 8: experimental-splicing: --experimental-splicing 
is now enabled by default enabled by default

Conversely, VLS does not have (yet) implemented (in any branch afaik) advertising for splicing which causes the h2 protocol error.

Given that, is there any way to disable splicing?

[enaples]

A work around could be to strip the optional splice bit with the option dev-force-feature=-63

[ddustin]

Without being familiar with how VLS handles all this, a wild guess is VLS is expecting the feature bit for splicing to be something else. The splicing feature numbers internal to lightning changed a fair bit as the spec was being settled. Now it should be locked in:

/* BOLT-splice #9:
 * | 62/63 | `option_splice`                   |... IN ...
 */

...

#define OPT_SPLICE				62

Seperate from the feature bit is the HSM splice permission bitfield:

#define HSM_PERM_SIGN_SPLICE_TX 128

It would be great to get VLS locked in on this! I think all the code is there it probably just needs these values locked in.

[ddustin]

ping: @ksedgwic

[ksedgwic]

@king-11 ^^

[jackronaldi]

VLS doesn't support splicing yet. Planning to start work on splicing support in July. In the meantime, we'll look into a better error message.