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splice: Sign shared output early

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When doing a multi channel splice, we need to break the deadlock by signing the shared output early (even though it is not sent to the peer until later).
This commit is contained in:
Dusty Daemon
2025-06-18 16:11:01 -04:00
committed by Rusty Russell
parent dd1e183b8a
commit e3e0813552
1 changed files with 41 additions and 0 deletions
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41
channeld/channeld.c
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@@ -4277,6 +4277,8 @@ static void splice_initiator_user_finalized(struct peer *peer)
u8 *outmsg;
struct interactivetx_context *ictx;
struct bitcoin_tx *prev_tx;
struct bitcoin_tx *bitcoin_tx;
struct bitcoin_signature splice_sig;
bool sign_first;
char *error;
u32 chan_output_index, splice_funding_index;
@@ -4288,6 +4290,7 @@ static void splice_initiator_user_finalized(struct peer *peer)
struct amount_msat current_push_val;
const enum tx_role our_role = TX_INITIATOR;
u8 *abort_msg;
const u8* msg;
/* We must loading the funding tx as our previous utxo */
prev_tx = bitcoin_tx_from_txid(peer, peer->channel->funding.txid);
@@ -4336,6 +4339,44 @@ static void splice_initiator_user_finalized(struct peer *peer)
psbt_elements_normalize_fees(ictx->current_psbt);
/* We have to sign the shared output early (here) for cases where we are
* splicing between multiple channels simultaneously. This is so the
* we can build a complete `tx_signatures` message when there are two
* or more shared outputs between mulitple peers */
splice_sig.sighash_type = SIGHASH_ALL;
bitcoin_tx = bitcoin_tx_with_psbt(tmpctx, ictx->current_psbt);
status_info("Splice pre-signing tx: %s",
tal_hex(tmpctx, linearize_tx(tmpctx, bitcoin_tx)));
msg = towire_hsmd_sign_splice_tx(tmpctx, bitcoin_tx,
&peer->channel->funding_pubkey[REMOTE],
splice_funding_index);
msg = hsm_req(tmpctx, take(msg));
if (!fromwire_hsmd_sign_tx_reply(msg, &splice_sig))
status_failed(STATUS_FAIL_HSM_IO,
"Reading sign_splice_tx reply: %s",
tal_hex(tmpctx, msg));
/* Set the splice_sig on the splice funding tx psbt */
if (!psbt_input_set_signature(ictx->current_psbt, splice_funding_index,
&peer->channel->funding_pubkey[LOCAL],
&splice_sig))
status_failed(STATUS_FAIL_INTERNAL_ERROR,
"Unable to pre-set signature internally "
"funding_index: %d "
"my pubkey: %s "
"my signature: %s "
"psbt: %s",
splice_funding_index,
fmt_pubkey(tmpctx,
&peer->channel->funding_pubkey[LOCAL]),
fmt_bitcoin_signature(tmpctx, &splice_sig),
fmt_wally_psbt(tmpctx, ictx->current_psbt));
status_debug("Splice adding inflight: %s",
fmt_wally_psbt(tmpctx, ictx->current_psbt));