htlcs: add flag to 'fail immediately'

If we're over the dust limit, we fail it immediatey *after* commiting
it, but we need a way to signal this throughout the lifecycle, so we add
it to htlc_in struct and persist it through to the database.

If it's supposed to be failed, we fail after the commit cycle is
completed.

Author: niftynei

channeld/channeld.c

@@ -738,7 +738,11 @@ static void handle_peer_add_htlc(struct peer *peer, const u8 *msg)
 #endif
 	add_err = channel_add_htlc(peer->channel, REMOTE, id, amount,
 				   cltv_expiry, &payment_hash,
-				   onion_routing_packet, blinding, &htlc, NULL);
+				   onion_routing_packet, blinding, &htlc, NULL,
+				   /* We don't immediately fail incoming htlcs,
+				    * instead we wait and fail them after
+				    * they've been committed */
+				   false);
 	if (add_err != CHANNEL_ERR_ADD_OK)
 		peer_failed_warn(peer->pps, &peer->channel_id,
 				 "Bad peer_add_htlc: %s",
@@ -1468,6 +1472,7 @@ static void marshall_htlc_info(const tal_t *ctx,
 				ecdh(a.blinding, &a.blinding_ss);
 			} else
 				a.blinding = NULL;
+			a.fail_immediate = htlc->fail_immediate;
 			tal_arr_expand(added, a);
 		} else if (htlc->state == RCVD_REMOVE_COMMIT) {
 			if (htlc->r) {
@@ -3299,7 +3304,8 @@ static void handle_offer_htlc(struct peer *peer, const u8 *inmsg)
 
 	e = channel_add_htlc(peer->channel, LOCAL, peer->htlc_id,
 			     amount, cltv_expiry, &payment_hash,
-			     onion_routing_packet, take(blinding), NULL, &htlc_fee);
+			     onion_routing_packet, take(blinding), NULL,
+			     &htlc_fee, true);
 	status_debug("Adding HTLC %"PRIu64" amount=%s cltv=%u gave %s",
 		     peer->htlc_id,
 		     type_to_string(tmpctx, struct amount_msat, &amount),

channeld/channeld_htlc.h

@@ -28,6 +28,9 @@ struct htlc {
 
 	/* Blinding (optional). */
 	struct pubkey *blinding;
+
+	/* Should we immediately fail this htlc? */
+	bool fail_immediate;
 };
 
 static inline bool htlc_has(const struct htlc *h, int flag)

channeld/full_channel.c

@@ -493,7 +493,8 @@ static enum channel_add_err add_htlc(struct channel *channel,
 				     const struct pubkey *blinding TAKES,
 				     struct htlc **htlcp,
 				     bool enforce_aggregate_limits,
-				     struct amount_sat *htlc_fee)
+				     struct amount_sat *htlc_fee,
+				     bool err_immediate_failures)
 {
 	struct htlc *htlc, *old;
 	struct amount_msat msat_in_htlcs, committed_msat, adding_msat, removing_msat;
@@ -508,6 +509,7 @@ static enum channel_add_err add_htlc(struct channel *channel,
 	htlc->id = id;
 	htlc->amount = amount;
 	htlc->state = state;
+	htlc->fail_immediate = false;
 
 	htlc->rhash = *payment_hash;
 	if (blinding)
@@ -768,7 +770,8 @@ enum channel_add_err channel_add_htlc(struct channel *channel,
 				      const u8 routing[TOTAL_PACKET_SIZE(ROUTING_INFO_SIZE)],
 				      const struct pubkey *blinding TAKES,
 				      struct htlc **htlcp,
-				      struct amount_sat *htlc_fee)
+				      struct amount_sat *htlc_fee,
+				      bool err_immediate_failures)
 {
 	enum htlc_state state;
 
@@ -786,7 +789,7 @@ enum channel_add_err channel_add_htlc(struct channel *channel,
 
 	return add_htlc(channel, state, id, amount, cltv_expiry,
 			payment_hash, routing, blinding,
-			htlcp, true, htlc_fee);
+			htlcp, true, htlc_fee, err_immediate_failures);
 }
 
 struct htlc *channel_get_htlc(struct channel *channel, enum side sender, u64 id)
@@ -1392,7 +1395,7 @@ bool channel_force_htlcs(struct channel *channel,
 			     &htlcs[i]->payment_hash,
 			     htlcs[i]->onion_routing_packet,
 			     htlcs[i]->blinding,
-			     &htlc, false, NULL);
+			     &htlc, false, NULL, false);
 		if (e != CHANNEL_ERR_ADD_OK) {
 			status_broken("%s HTLC %"PRIu64" failed error %u",
 				     htlc_state_owner(htlcs[i]->state) == LOCAL

channeld/full_channel.h

@@ -103,6 +103,10 @@ u32 actual_feerate(const struct channel *channel,
  * @routing: routing information (copied)
  * @blinding: optional blinding information for this HTLC.
  * @htlcp: optional pointer for resulting htlc: filled in if and only if CHANNEL_ERR_NONE.
+ * @err_immediate_failures: in some cases (dusty htlcs) we want to immediately
+ *                          fail the htlc; for peer incoming don't want to
+ *                          error, but rather mark it as failed and fail after
+ *                          it's been committed to (so set this to false)
  *
  * If this returns CHANNEL_ERR_NONE, the fee htlc was added and
  * the output amounts adjusted accordingly.  Otherwise nothing
@@ -117,7 +121,8 @@ enum channel_add_err channel_add_htlc(struct channel *channel,
 				      const u8 routing[TOTAL_PACKET_SIZE(ROUTING_INFO_SIZE)],
 				      const struct pubkey *blinding TAKES,
 				      struct htlc **htlcp,
-				      struct amount_sat *htlc_fee);
+				      struct amount_sat *htlc_fee,
+				      bool err_immediate_failures);
 
 /**
  * channel_get_htlc: find an HTLC

channeld/test/run-full_channel.c

@@ -165,7 +165,7 @@ static const struct htlc **include_htlcs(struct channel *channel, enum side side
 		memset(&preimage, i, sizeof(preimage));
 		sha256(&hash, &preimage, sizeof(preimage));
 		e = channel_add_htlc(channel, sender, i, msatoshi, 500+i, &hash,
-				     dummy_routing, NULL, NULL, NULL);
+				     dummy_routing, NULL, NULL, NULL, true);
 		assert(e == CHANNEL_ERR_ADD_OK);
 		htlcs[i] = channel_get_htlc(channel, sender, i);
 	}
@@ -257,7 +257,7 @@ static void send_and_fulfill_htlc(struct channel *channel,
 	sha256(&rhash, &r, sizeof(r));
 
 	assert(channel_add_htlc(channel, sender, 1337, msatoshi, 900, &rhash,
-				dummy_routing, NULL, NULL, NULL)
+				dummy_routing, NULL, NULL, NULL, true)
 	       == CHANNEL_ERR_ADD_OK);
 
 	changed_htlcs = tal_arr(channel, const struct htlc *, 0);

common/htlc_wire.c

@@ -78,6 +78,7 @@ void towire_added_htlc(u8 **pptr, const struct added_htlc *added)
 		towire_secret(pptr, &added->blinding_ss);
 	} else
 		towire_bool(pptr, false);
+	towire_bool(pptr, added->fail_immediate);
 }
 
 void towire_existing_htlc(u8 **pptr, const struct existing_htlc *existing)
@@ -171,6 +172,7 @@ void fromwire_added_htlc(const u8 **cursor, size_t *max,
 		fromwire_secret(cursor, max, &added->blinding_ss);
 	} else
 		added->blinding = NULL;
+	added->fail_immediate = fromwire_bool(cursor, max);
 }
 
 struct existing_htlc *fromwire_existing_htlc(const tal_t *ctx,

common/htlc_wire.h

@@ -15,6 +15,7 @@ struct added_htlc {
 	struct sha256 payment_hash;
 	u32 cltv_expiry;
 	u8 onion_routing_packet[TOTAL_PACKET_SIZE(ROUTING_INFO_SIZE)];
+	bool fail_immediate;
 
 	/* If this is non-NULL, secret is the resulting shared secret */
 	struct pubkey *blinding;

lightningd/htlc_end.c

@@ -130,7 +130,8 @@ struct htlc_in *new_htlc_in(const tal_t *ctx,
 			    const struct secret *shared_secret TAKES,
 			    const struct pubkey *blinding TAKES,
 			    const struct secret *blinding_ss,
-			    const u8 *onion_routing_packet)
+			    const u8 *onion_routing_packet,
+			    bool fail_immediate)
 {
 	struct htlc_in *hin = tal(ctx, struct htlc_in);
 
@@ -141,6 +142,7 @@ struct htlc_in *new_htlc_in(const tal_t *ctx,
 	hin->cltv_expiry = cltv_expiry;
 	hin->payment_hash = *payment_hash;
 	hin->status = NULL;
+	hin->fail_immediate = fail_immediate;
 	if (shared_secret)
 		hin->shared_secret = tal_dup(hin, struct secret, shared_secret);
 	else

lightningd/htlc_end.h

@@ -52,6 +52,8 @@ struct htlc_in {
 	struct secret blinding_ss;
 	/* true if we supplied the preimage */
 	bool *we_filled;
+	/* true if we immediately fail the htlc (too much dust) */
+	bool fail_immediate;
 
 	/* A simple text annotation shown in `listpeers` */
 	char *status;
@@ -154,7 +156,8 @@ struct htlc_in *new_htlc_in(const tal_t *ctx,
 			    const struct secret *shared_secret TAKES,
 			    const struct pubkey *blinding TAKES,
 			    const struct secret *blinding_ss,
-			    const u8 *onion_routing_packet);
+			    const u8 *onion_routing_packet,
+			    bool fail_immediate);
 
 /* You need to set the ID, then connect_htlc_out this! */
 struct htlc_out *new_htlc_out(const tal_t *ctx,

lightningd/peer_htlcs.c

@@ -1171,6 +1171,13 @@ static bool peer_accepted_htlc(const tal_t *ctx,
 		goto fail;
 	}
 
+	if (hin->fail_immediate && htlc_in_update_state(channel, hin, RCVD_ADD_ACK_REVOCATION)) {
+		log_debug(channel->log, "failing immediately, as requested");
+		/* Failing the htlc, typically done because of htlc dust */
+		*failmsg = towire_temporary_node_failure(ctx);
+		goto fail;
+	}
+
 	if (!replay && !htlc_in_update_state(channel, hin, RCVD_ADD_ACK_REVOCATION)) {
 		*failmsg = towire_temporary_node_failure(ctx);
 		goto fail;
@@ -1863,7 +1870,8 @@ static bool channel_added_their_htlc(struct channel *channel,
 			  added->cltv_expiry, &added->payment_hash,
 			  op ? &shared_secret : NULL,
 			  added->blinding, &added->blinding_ss,
-			  added->onion_routing_packet);
+			  added->onion_routing_packet,
+			  added->fail_immediate);
 
 	/* Save an incoming htlc to the wallet */
 	wallet_htlc_save_in(ld->wallet, channel, hin);