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onchaind: use lightningd to sign and broadcast htlc expired txs.
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This is when they closed the channel, we can simply make our own tx to
expire the HTLC.  (The other case is where we closed the channel, and
we have a special htlc_timeout tx which we have their signature for).

Signed-off-by: Rusty Russell <[email protected]>
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@rustyrussell
rustyrussell committed Apr 7, 2023
1 parent 5bdd532 commit 0c27acc
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Showing 9 changed files with 169 additions and 181 deletions.
77 changes: 77 additions & 0 deletions lightningd/onchain_control.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -567,6 +567,10 @@ struct onchain_signing_info {
struct pubkey remote_per_commitment_point;
struct preimage preimage;
} fulfill;
/* WIRE_ONCHAIND_SPEND_HTLC_EXPIRED */
struct {
struct pubkey remote_per_commitment_point;
} htlc_expired;
} u;
};

Expand Down Expand Up @@ -660,6 +664,22 @@ static u8 *sign_fulfill(const tal_t *ctx,
info->channel->dbid);
}

static u8 *sign_htlc_expired(const tal_t *ctx,
const struct bitcoin_tx *tx,
const struct onchain_signing_info *info)
{
const bool anchor_outputs = channel_has(info->channel, OPT_ANCHOR_OUTPUTS);

assert(info->msgtype == WIRE_ONCHAIND_SPEND_HTLC_EXPIRED);
return towire_hsmd_sign_any_remote_htlc_to_us(ctx,
&info->u.htlc_expired.remote_per_commitment_point,
tx, info->wscript,
anchor_outputs,
0,
&info->channel->peer->id,
info->channel->dbid);
}

/* Matches bitcoin_witness_sig_and_element! */
static const struct onchain_witness_element **
onchain_witness_sig_and_element(const tal_t *ctx, u8 **witness)
Expand Down Expand Up @@ -1172,6 +1192,59 @@ static void handle_onchaind_spend_htlc_timeout(struct channel *channel,
subd_send_msg(channel->owner, take(msg));
}

static void handle_onchaind_spend_htlc_expired(struct channel *channel,
const u8 *msg)
{
struct lightningd *ld = channel->peer->ld;
struct onchain_signing_info *info;
struct bitcoin_outpoint out;
struct amount_sat out_sats;
u64 htlc_id;
u32 cltv_expiry, initial_feerate;
const bool anchor_outputs = channel_has(channel, OPT_ANCHOR_OUTPUTS);

info = new_signing_info(msg, channel, WIRE_ONCHAIND_SPEND_HTLC_EXPIRED);

/* BOLT #5:
*
* ## HTLC Output Handling: Remote Commitment, Local Offers
* ...
*
* - if the commitment transaction HTLC output has *timed out* AND NOT
* been *resolved*:
* - MUST *resolve* the output, by spending it to a convenient
* address.
*/
info->stack_elem = NULL;

if (!fromwire_onchaind_spend_htlc_expired(info, msg,
&out, &out_sats,
&htlc_id,
&cltv_expiry,
&info->u.htlc_expired.remote_per_commitment_point,
&info->wscript)) {
channel_internal_error(channel, "Invalid onchaind_spend_htlc_expired %s",
tal_hex(tmpctx, msg));
return;
}

/* nLocktime: we have to be *after* that block! */
info->minblock = cltv_expiry + 1;

/* FIXME: Be more sophisticated! */
initial_feerate = htlc_resolution_feerate(ld->topology);
if (!initial_feerate)
initial_feerate = tx_feerate(channel->last_tx);

/* We have to spend it before we can close incoming */
info->deadline_block = htlc_outgoing_incoming_deadline(channel, htlc_id);
create_onchain_tx(channel, &out, out_sats,
anchor_outputs ? 1 : 0,
cltv_expiry,
initial_feerate, sign_htlc_expired, info,
__func__);
}

static unsigned int onchain_msg(struct subd *sd, const u8 *msg, const int *fds UNUSED)
{
enum onchaind_wire t = fromwire_peektype(msg);
Expand Down Expand Up @@ -1241,6 +1314,10 @@ static unsigned int onchain_msg(struct subd *sd, const u8 *msg, const int *fds U
handle_onchaind_spend_fulfill(sd->channel, msg);
break;

case WIRE_ONCHAIND_SPEND_HTLC_EXPIRED:
handle_onchaind_spend_htlc_expired(sd->channel, msg);
break;

/* We send these, not receive them */
case WIRE_ONCHAIND_INIT:
case WIRE_ONCHAIND_SPENT:
Expand Down
122 changes: 14 additions & 108 deletions onchaind/onchaind.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -607,105 +607,6 @@ static struct amount_sat get_htlc_success_fee(struct tracked_output *out)
return fee;
}

static u8 *remote_htlc_to_us(const tal_t *ctx,
struct bitcoin_tx *tx,
const u8 *wscript)
{
return towire_hsmd_sign_remote_htlc_to_us(ctx,
remote_per_commitment_point,
tx, wscript,
option_anchor_outputs);
}

/*
* This covers:
* 1. to-us output spend (`<local_delayedsig> 0`)
* 2. the their-commitment, our HTLC timeout case (`<remotehtlcsig> 0`),
* 3. the their-commitment, our HTLC redeem case (`<remotehtlcsig> <payment_preimage>`)
* 4. the their-revoked-commitment, to-local (`<revocation_sig> 1`)
* 5. the their-revoked-commitment, htlc (`<revocation_sig> <revocationkey>`)
*
* Overrides *tx_type if it all turns to dust.
*/
static struct bitcoin_tx *tx_to_us(const tal_t *ctx,
u8 *(*hsm_sign_msg)(const tal_t *ctx,
struct bitcoin_tx *tx,
const u8 *wscript),
struct tracked_output *out,
u32 to_self_delay,
u32 locktime,
const void *elem, size_t elemsize,
const u8 *wscript,
enum tx_type *tx_type,
u32 feerate)
{
struct bitcoin_tx *tx;
struct amount_sat fee, min_out, amt;
struct bitcoin_signature sig;
size_t weight;
u8 *msg;
u8 **witness;

tx = bitcoin_tx(ctx, chainparams, 1, 1, locktime);
bitcoin_tx_add_input(tx, &out->outpoint, to_self_delay,
NULL, out->sat, NULL, wscript);

bitcoin_tx_add_output(
tx, scriptpubkey_p2wpkh(tmpctx, &our_wallet_pubkey), NULL, out->sat);
psbt_add_keypath_to_last_output(tx, our_wallet_index, &our_wallet_ext_key);

/* Worst-case sig is 73 bytes */
weight = bitcoin_tx_weight(tx) + 1 + 3 + 73 + 0 + tal_count(wscript);
weight += elements_tx_overhead(chainparams, 1, 1);
fee = amount_tx_fee(feerate, weight);

/* Result is trivial? Spend with small feerate, but don't wait
* around for it as it might not confirm. */
if (!amount_sat_add(&min_out, dust_limit, fee))
status_failed(STATUS_FAIL_INTERNAL_ERROR,
"Cannot add dust_limit %s and fee %s",
type_to_string(tmpctx, struct amount_sat, &dust_limit),
type_to_string(tmpctx, struct amount_sat, &fee));

if (amount_sat_less(out->sat, min_out)) {
/* FIXME: We should use SIGHASH_NONE so others can take it */
fee = amount_tx_fee(feerate_floor(), weight);
status_unusual("TX %s amount %s too small to"
" pay reasonable fee, using minimal fee"
" and ignoring",
tx_type_name(*tx_type),
type_to_string(tmpctx, struct amount_sat, &out->sat));
*tx_type = IGNORING_TINY_PAYMENT;
}

/* This can only happen if feerate_floor() is still too high; shouldn't
* happen! */
if (!amount_sat_sub(&amt, out->sat, fee)) {
amt = dust_limit;
status_broken("TX %s can't afford minimal feerate"
"; setting output to %s",
tx_type_name(*tx_type),
type_to_string(tmpctx, struct amount_sat,
&amt));
}
bitcoin_tx_output_set_amount(tx, 0, amt);
bitcoin_tx_finalize(tx);

if (!wire_sync_write(HSM_FD, take(hsm_sign_msg(NULL, tx, wscript))))
status_failed(STATUS_FAIL_HSM_IO, "Writing sign request to hsm");
msg = wire_sync_read(tmpctx, HSM_FD);
if (!msg || !fromwire_hsmd_sign_tx_reply(msg, &sig)) {
status_failed(STATUS_FAIL_HSM_IO,
"Reading sign_tx_reply: %s",
tal_hex(tmpctx, msg));
}

witness = bitcoin_witness_sig_and_element(tx, &sig, elem,
elemsize, wscript);
bitcoin_tx_input_set_witness(tx, 0, take(witness));
return tx;
}

static void hsm_get_per_commitment_point(struct pubkey *per_commitment_point)
{
u8 *msg = towire_hsmd_get_per_commitment_point(NULL, commit_num);
Expand Down Expand Up @@ -1944,6 +1845,7 @@ static void wait_for_resolved(struct tracked_output **outs)
case WIRE_ONCHAIND_SPEND_HTLC_SUCCESS:
case WIRE_ONCHAIND_SPEND_HTLC_TIMEOUT:
case WIRE_ONCHAIND_SPEND_FULFILL:
case WIRE_ONCHAIND_SPEND_HTLC_EXPIRED:
break;
}
master_badmsg(-1, msg);
Expand Down Expand Up @@ -2201,9 +2103,10 @@ static size_t resolve_our_htlc_theircommit(struct tracked_output *out,
const struct htlc_stub *htlcs,
u8 **htlc_scripts)
{
struct bitcoin_tx *tx;
enum tx_type tx_type = OUR_HTLC_TIMEOUT_TO_US;
const u8 *msg;
u32 cltv_expiry = matches_cltv(matches, htlcs);
/* They're all equivalent: might as well use first one. */
const struct htlc_stub *htlc = &htlcs[matches[0]];

/* BOLT #5:
*
Expand All @@ -2215,14 +2118,17 @@ static size_t resolve_our_htlc_theircommit(struct tracked_output *out,
* - MUST *resolve* the output, by spending it to a convenient
* address.
*/
tx = tx_to_us(out, remote_htlc_to_us, out,
option_anchor_outputs ? 1 : 0,
cltv_expiry, NULL, 0,
htlc_scripts[matches[0]], &tx_type, htlc_feerate);

propose_resolution_at_block(out, tx, cltv_expiry, tx_type);
msg = towire_onchaind_spend_htlc_expired(NULL,
&out->outpoint, out->sat,
htlc->id,
cltv_expiry,
remote_per_commitment_point,
htlc_scripts[matches[0]]);
propose_resolution_to_master(out, take(msg),
/* nLocktime: we have to be *after* that block! */
cltv_expiry + 1,
OUR_HTLC_TIMEOUT_TO_US);

/* They're all equivalent: might as well use first one. */
return matches[0];
}

Expand Down
11 changes: 11 additions & 0 deletions onchaind/onchaind_wire.csv
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Original file line number Diff line number Diff line change
Expand Up @@ -197,6 +197,17 @@ msgdata,onchaind_spend_htlc_timeout,wscript,u8,wscript_len
msgdata,onchaind_spend_htlc_timeout,htlc_wscript_len,u32,
msgdata,onchaind_spend_htlc_timeout,htlc_wscript,u8,htlc_wscript_len

# We tell lightningd to create, sign and broadcast this tx to collect our
# expired htlc in their unilateral close:
msgtype,onchaind_spend_htlc_expired,5045
msgdata,onchaind_spend_htlc_expired,outpoint,bitcoin_outpoint,
msgdata,onchaind_spend_htlc_expired,outpoint_amount,amount_sat,
msgdata,onchaind_spend_htlc_expired,htlc_id,u64,
msgdata,onchaind_spend_htlc_expired,cltv_expiry,u32,
msgdata,onchaind_spend_htlc_expired,remote_per_commitment_point,pubkey,
msgdata,onchaind_spend_htlc_expired,wscript_len,u32,
msgdata,onchaind_spend_htlc_expired,wscript,u8,wscript_len

subtype,onchain_witness_element
subtypedata,onchain_witness_element,is_signature,bool,
subtypedata,onchain_witness_element,len,u32,
Expand Down
3 changes: 0 additions & 3 deletions onchaind/test/run-grind_feerate-bug.c
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Original file line number Diff line number Diff line change
Expand Up @@ -211,9 +211,6 @@ void towire_ext_key(u8 **pptr UNNEEDED, const struct ext_key *bip32 UNNEEDED)
/* Generated stub for towire_hsmd_get_per_commitment_point */
u8 *towire_hsmd_get_per_commitment_point(const tal_t *ctx UNNEEDED, u64 n UNNEEDED)
{ fprintf(stderr, "towire_hsmd_get_per_commitment_point called!\n"); abort(); }
/* Generated stub for towire_hsmd_sign_remote_htlc_to_us */
u8 *towire_hsmd_sign_remote_htlc_to_us(const tal_t *ctx UNNEEDED, const struct pubkey *remote_per_commitment_point UNNEEDED, const struct bitcoin_tx *tx UNNEEDED, const u8 *wscript UNNEEDED, bool option_anchor_outputs UNNEEDED)
{ fprintf(stderr, "towire_hsmd_sign_remote_htlc_to_us called!\n"); abort(); }
/* Generated stub for towire_htlc_stub */
void towire_htlc_stub(u8 **pptr UNNEEDED, const struct htlc_stub *htlc_stub UNNEEDED)
{ fprintf(stderr, "towire_htlc_stub called!\n"); abort(); }
Expand Down
9 changes: 3 additions & 6 deletions onchaind/test/run-grind_feerate.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -41,9 +41,6 @@ void *fromwire_fail(const u8 **cursor UNNEEDED, size_t *max UNNEEDED)
/* Generated stub for fromwire_hsmd_get_per_commitment_point_reply */
bool fromwire_hsmd_get_per_commitment_point_reply(const tal_t *ctx UNNEEDED, const void *p UNNEEDED, struct pubkey *per_commitment_point UNNEEDED, struct secret **old_commitment_secret UNNEEDED)
{ fprintf(stderr, "fromwire_hsmd_get_per_commitment_point_reply called!\n"); abort(); }
/* Generated stub for fromwire_hsmd_sign_tx_reply */
bool fromwire_hsmd_sign_tx_reply(const void *p UNNEEDED, struct bitcoin_signature *sig UNNEEDED)
{ fprintf(stderr, "fromwire_hsmd_sign_tx_reply called!\n"); abort(); }
/* Generated stub for fromwire_onchaind_depth */
bool fromwire_onchaind_depth(const void *p UNNEEDED, struct bitcoin_txid *txid UNNEEDED, u32 *depth UNNEEDED)
{ fprintf(stderr, "fromwire_onchaind_depth called!\n"); abort(); }
Expand Down Expand Up @@ -272,9 +269,6 @@ void towire_bool(u8 **pptr UNNEEDED, bool v UNNEEDED)
/* Generated stub for towire_hsmd_get_per_commitment_point */
u8 *towire_hsmd_get_per_commitment_point(const tal_t *ctx UNNEEDED, u64 n UNNEEDED)
{ fprintf(stderr, "towire_hsmd_get_per_commitment_point called!\n"); abort(); }
/* Generated stub for towire_hsmd_sign_remote_htlc_to_us */
u8 *towire_hsmd_sign_remote_htlc_to_us(const tal_t *ctx UNNEEDED, const struct pubkey *remote_per_commitment_point UNNEEDED, const struct bitcoin_tx *tx UNNEEDED, const u8 *wscript UNNEEDED, bool option_anchor_outputs UNNEEDED)
{ fprintf(stderr, "towire_hsmd_sign_remote_htlc_to_us called!\n"); abort(); }
/* Generated stub for towire_onchaind_add_utxo */
u8 *towire_onchaind_add_utxo(const tal_t *ctx UNNEEDED, const struct bitcoin_outpoint *prev_out UNNEEDED, const struct pubkey *per_commit_point UNNEEDED, struct amount_sat value UNNEEDED, u32 blockheight UNNEEDED, const u8 *scriptpubkey UNNEEDED, u32 csv_lock UNNEEDED)
{ fprintf(stderr, "towire_onchaind_add_utxo called!\n"); abort(); }
Expand Down Expand Up @@ -311,6 +305,9 @@ u8 *towire_onchaind_notify_coin_mvt(const tal_t *ctx UNNEEDED, const struct chai
/* Generated stub for towire_onchaind_spend_fulfill */
u8 *towire_onchaind_spend_fulfill(const tal_t *ctx UNNEEDED, const struct bitcoin_outpoint *outpoint UNNEEDED, struct amount_sat outpoint_amount UNNEEDED, u64 htlc_id UNNEEDED, const struct pubkey *remote_per_commitment_point UNNEEDED, const struct preimage *preimage UNNEEDED, const u8 *wscript UNNEEDED)
{ fprintf(stderr, "towire_onchaind_spend_fulfill called!\n"); abort(); }
/* Generated stub for towire_onchaind_spend_htlc_expired */
u8 *towire_onchaind_spend_htlc_expired(const tal_t *ctx UNNEEDED, const struct bitcoin_outpoint *outpoint UNNEEDED, struct amount_sat outpoint_amount UNNEEDED, u64 htlc_id UNNEEDED, u32 cltv_expiry UNNEEDED, const struct pubkey *remote_per_commitment_point UNNEEDED, const u8 *wscript UNNEEDED)
{ fprintf(stderr, "towire_onchaind_spend_htlc_expired called!\n"); abort(); }
/* Generated stub for towire_onchaind_spend_htlc_success */
u8 *towire_onchaind_spend_htlc_success(const tal_t *ctx UNNEEDED, const struct bitcoin_outpoint *outpoint UNNEEDED, struct amount_sat outpoint_amount UNNEEDED, struct amount_sat fee UNNEEDED, u64 htlc_id UNNEEDED, u64 commit_num UNNEEDED, const struct bitcoin_signature *remote_htlc_sig UNNEEDED, const struct preimage *preimage UNNEEDED, const u8 *wscript UNNEEDED, const u8 *htlc_wscript UNNEEDED)
{ fprintf(stderr, "towire_onchaind_spend_htlc_success called!\n"); abort(); }
Expand Down
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