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splice: add zero-conf splice support per BOLT #2 #8985

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splice: add zero-conf splice support per BOLT #2 #8985

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7ca893f
splice: add zero-conf splice support per BOLT #2
vincenzopalazzo Mar 25, 2026
a0aa161
tests: add test_splice_zeroconf for zero-conf splice support
vincenzopalazzo Mar 25, 2026
32471fa
fix: resolve zeroconf splice and gossip CI failures
vincenzopalazzo Mar 25, 2026
7931c83
fix: address PR review feedback
vincenzopalazzo Mar 25, 2026
7bd121c
fix: handle zeroconf splice reestablish
vincenzopalazzo Mar 25, 2026
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20 changes: 20 additions & 0 deletions channeld/channeld.c
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Original file line number Diff line number Diff line change
Expand Up @@ -4224,6 +4224,16 @@ static void splice_accepter(struct peer *peer, const u8 *inmsg)
}
}
else if (type == WIRE_TX_INIT_RBF) {
/* BOLT #2:
* The sender:
* - MUST NOT send `tx_init_rbf` if `option_zeroconf`
* has been negotiated.
*/
if (channel_type_has(peer->channel->type, OPT_ZEROCONF))
peer_failed_warn(peer->pps, &peer->channel_id,
"Peer sent tx_init_rbf but channel"
" uses option_zeroconf");

if (!fromwire_tx_init_rbf(tmpctx, inmsg,
&channel_id,
&locktime,
Expand Down Expand Up @@ -4918,6 +4928,16 @@ static void handle_splice_stfu_success(struct peer *peer)
&peer->channel->funding_pubkey[LOCAL]);
}
else { /* RBF attempt */
/* BOLT #2:
* The sender:
* - MUST NOT send `tx_init_rbf` if `option_zeroconf`
* has been negotiated.
*/
if (channel_type_has(peer->channel->type, OPT_ZEROCONF))
peer_failed_warn(peer->pps, &peer->channel_id,
"Cannot RBF splice: channel uses"
" option_zeroconf");

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init_rbf_tlvs = tlv_tx_init_rbf_tlvs_new(tmpctx);
init_rbf_tlvs->funding_output_contribution = tal(init_rbf_tlvs, s64);
*init_rbf_tlvs->funding_output_contribution = peer->splicing->opener_relative;
Expand Down
7 changes: 7 additions & 0 deletions lightningd/channel_control.c
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Original file line number Diff line number Diff line change
Expand Up @@ -699,6 +699,13 @@ static enum watch_result splice_depth_cb(struct lightningd *ld,
return DELETE_WATCH;
}

/* Reorged out? OK, we're not committed yet.
* But for zero-conf channels (minimum_depth == 0), depth 0 means
* we should send splice_locked immediately per BOLT #2. */
if (depth == 0 && inflight->channel->minimum_depth != 0) {
return KEEP_WATCHING;
}

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@ddustin ddustin Mar 25, 2026

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This is not the right place to be trying to do zero-conf. Instead we should initiate splice_locked in channeld right after sending tx_signatures which occurs in resume_splice_negotiation.

This needs to be done with extra care because this flow can occur from initiate, accepter, or during the reestablish flow. We need to make sure it's behaving correctly in each of these flows.

Probably the best approach is to take the code in handle_funding_depth that confirms the splice and move it out into it's own function so that we can additionally call it from resume_splice_negotiation.

It would be very important to duplicate the tests in test_splicing_disconnect.py with this new zero conf splice setting enabled.

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@vincenzopalazzo vincenzopalazzo Mar 25, 2026

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Addressed in 7bd121c.

I moved zero-conf splice_locked initiation into resume_splice_negotiation() so we send it immediately after each local tx_signatures write, which covers the initiator, accepter, and reestablish paths in one place. For the reconnect cases I also persist i_sent_sigs, cache early splice_locked until the local signature path is complete, and treat channel_ready during zero-conf reestablish as an implied peer splice_locked once we have already sent ours.

I also duplicated the disconnect regressions for zero-conf in tests/test_splicing_disconnect.py and re-ran the zero-conf happy-path splice test. Verified with targeted runs of test_splice_zeroconf, test_splice_disconnect_sig_zeroconf, and test_splice_disconnect_commit_zeroconf.

if (inflight->channel->owner) {
log_debug(inflight->channel->log, "splice_depth_cb: sending funding depth scid: %s",
fmt_short_channel_id(tmpctx, *inflight->scid));
Expand Down
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