add: added basic structure of forward failure reasons

.msggen.json

@@ -242,6 +242,23 @@
         "ListconfigsConfigsConfSource": {
             "cmdline": 0
         },
+        "ListforwardsForwardsFailureReason": {
+            "channel_failed_permanent": 11,
+            "channel_shutting_down": 13,
+            "cltv_expiry_too_far": 8,
+            "cltv_expiry_too_soon": 7,
+            "cltv_incorrect": 6,
+            "dust_limit": 2,
+            "fee_insufficient": 5,
+            "htlc_above_maximum": 4,
+            "htlc_below_minimum": 3,
+            "insufficient_outgoing_liquidity": 0,
+            "invalid_onion": 12,
+            "max_htlc_value_in_flight": 14,
+            "outgoing_peer_offline": 10,
+            "too_many_htlcs": 1,
+            "unknown_next_peer": 9
+        },
         "ListforwardsForwardsStatus": {
             "failed": 3,
             "local_failed": 2,
@@ -3066,6 +3083,7 @@
             "ListForwards.forwards[].created_index": 12,
             "ListForwards.forwards[].failcode": 15,
             "ListForwards.forwards[].failreason": 16,
+            "ListForwards.forwards[].failure_reason": 17,
             "ListForwards.forwards[].fee_msat": 7,
             "ListForwards.forwards[].in_channel": 1,
             "ListForwards.forwards[].in_htlc_id": 10,
@@ -11156,6 +11174,10 @@
             "added": "pre-v0.10.1",
             "deprecated": null
         },
+        "ListForwards.forwards[].failure_reason": {
+            "added": "pre-v0.10.1",
+            "deprecated": null
+        },
         "ListForwards.forwards[].fee_msat": {
             "added": "pre-v0.10.1",
             "deprecated": null

channeld/channeld.c

@@ -23,6 +23,7 @@
 #include <channeld/watchtower.h>
 #include <common/billboard.h>
 #include <common/ecdh_hsmd.h>
+#include <common/forward_failure_reason.h>
 #include <common/interactivetx.h>
 #include <common/key_derive.h>
 #include <common/memleak.h>
@@ -6370,6 +6371,7 @@ static void handle_offer_htlc(struct peer *peer, const u8 *inmsg)
 	enum channel_add_err e;
 	const u8 *failwiremsg;
 	const char *failstr;
+	enum forward_failure_reason reason = FORWARD_FAIL_UNKNOWN;
 	struct amount_sat htlc_fee;
 	struct pubkey *path_key;
 	struct tlv_field *extra_tlvs;
@@ -6432,13 +6434,14 @@ static void handle_offer_htlc(struct peer *peer, const u8 *inmsg)
 		start_commit_timer(peer);
 		/* Tell the master. */
 		msg = towire_channeld_offer_htlc_reply(NULL, peer->htlc_id,
-						      0, "");
+						      0, "", FORWARD_FAIL_UNKNOWN);
 		wire_sync_write(MASTER_FD, take(msg));
 		peer->htlc_id++;
 		return;
 	case CHANNEL_ERR_INVALID_EXPIRY:
 		failwiremsg = towire_incorrect_cltv_expiry(inmsg, cltv_expiry, NULL);
 		failstr = tal_fmt(inmsg, "Invalid cltv_expiry %u", cltv_expiry);
+		reason = FORWARD_FAIL_CLTV_INCORRECT;
 		goto failed;
 	case CHANNEL_ERR_DUPLICATE:
 	case CHANNEL_ERR_DUPLICATE_ID_DIFFERENT:
@@ -6448,21 +6451,30 @@ static void handle_offer_htlc(struct peer *peer, const u8 *inmsg)
 	case CHANNEL_ERR_MAX_HTLC_VALUE_EXCEEDED:
 		failwiremsg = towire_required_node_feature_missing(inmsg);
 		failstr = "Mini mode: maximum value exceeded";
+		reason = FORWARD_FAIL_HTLC_ABOVE_MAXIMUM;
+		goto failed;
+	case CHANNEL_ERR_MAX_HTLC_VALUE_IN_FLIGHT_EXCEEDED:
+		failwiremsg = towire_temporary_channel_failure(inmsg, NULL);
+		failstr = "Aggregate value of committed HTLCs would exceed max_htlc_value_in_flight_msat";
+		reason = FORWARD_FAIL_MAX_HTLC_VALUE_IN_FLIGHT;
 		goto failed;
 	/* FIXME: Fuzz the boundaries a bit to avoid probing? */
 	case CHANNEL_ERR_CHANNEL_CAPACITY_EXCEEDED:
 		failwiremsg = towire_temporary_channel_failure(inmsg, NULL);
 		failstr = tal_fmt(inmsg, "Capacity exceeded - HTLC fee: %s", fmt_amount_sat(inmsg, htlc_fee));
+		reason = FORWARD_FAIL_INSUFFICIENT_OUTGOING_LIQUIDITY;
 		goto failed;
 	case CHANNEL_ERR_HTLC_BELOW_MINIMUM:
 		failwiremsg = towire_amount_below_minimum(inmsg, amount, NULL);
 		failstr = tal_fmt(inmsg, "HTLC too small (%s minimum)",
 				  fmt_amount_msat(tmpctx,
 						  peer->channel->config[REMOTE].htlc_minimum));
+		reason = FORWARD_FAIL_HTLC_BELOW_MINIMUM;
 		goto failed;
 	case CHANNEL_ERR_TOO_MANY_HTLCS:
 		failwiremsg = towire_temporary_channel_failure(inmsg, NULL);
 		failstr = "Too many HTLCs";
+		reason = FORWARD_FAIL_TOO_MANY_HTLCS;
 		goto failed;
 	case CHANNEL_ERR_DUST_FAILURE:
 		/* BOLT-919 #2:
@@ -6473,14 +6485,15 @@ static void handle_offer_htlc(struct peer *peer, const u8 *inmsg)
 		 */
 		failwiremsg = towire_temporary_channel_failure(inmsg, NULL);
 		failstr = "HTLC too dusty, allowed dust limit reached";
+		reason = FORWARD_FAIL_DUST_LIMIT;
 		goto failed;
 	}
 	/* Shouldn't return anything else! */
 	abort();
 
 failed:
 	/* lightningd appends update to this for us */
-	msg = towire_channeld_offer_htlc_reply(NULL, 0, failwiremsg, failstr);
+	msg = towire_channeld_offer_htlc_reply(NULL, 0, failwiremsg, failstr, reason);
 	wire_sync_write(MASTER_FD, take(msg));
 }
 

channeld/channeld_wire.csv

@@ -107,6 +107,9 @@ msgdata,channeld_offer_htlc_reply,id,u64,
 msgdata,channeld_offer_htlc_reply,len,u16,
 msgdata,channeld_offer_htlc_reply,failuremsg,u8,len
 msgdata,channeld_offer_htlc_reply,failurestr,wirestring,
+# enum forward_failure_reason (common/forward_failure_reason.h) - root cause
+# of the failure, 0 (FORWARD_FAIL_UNKNOWN) on success or if unclassified
+msgdata,channeld_offer_htlc_reply,reason,u8,
 
 # Main daemon found out the preimage for an HTLC
 #include <bitcoin/preimage.h>

channeld/full_channel.c

@@ -769,7 +769,7 @@ static enum channel_add_err add_htlc(struct channel *channel,
 	if (enforce_aggregate_limits
 	    && amount_msat_greater(msat_in_htlcs,
 				   channel->config[recipient].max_htlc_value_in_flight)) {
-		return CHANNEL_ERR_MAX_HTLC_VALUE_EXCEEDED;
+		return CHANNEL_ERR_MAX_HTLC_VALUE_IN_FLIGHT_EXCEEDED;
 	}
 
 	/* BOLT #2:

channeld/full_channel_error.h

@@ -12,8 +12,12 @@ enum channel_add_err {
 	CHANNEL_ERR_DUPLICATE,
 	/* Same ID, but otherwise different. */
 	CHANNEL_ERR_DUPLICATE_ID_DIFFERENT,
-	/* Would exceed the specified max_htlc_value_in_flight_msat */
+	/* A single HTLC exceeds the payment amount limit (or an internal
+	 * arithmetic-overflow guard tripped) */
 	CHANNEL_ERR_MAX_HTLC_VALUE_EXCEEDED,
+	/* Aggregate value of committed HTLCs would exceed the specified
+	 * max_htlc_value_in_flight_msat */
+	CHANNEL_ERR_MAX_HTLC_VALUE_IN_FLIGHT_EXCEEDED,
 	/* Can't afford it */
 	CHANNEL_ERR_CHANNEL_CAPACITY_EXCEEDED,
 	/* HTLC is below htlc_minimum_msat */

common/Makefile

@@ -120,6 +120,7 @@ COMMON_HEADERS_NOGEN := $(COMMON_SRC_NOGEN:.c=.h)	\
 	common/crypto_state.h				\
 	common/ecdh.h					\
 	common/errcode.h				\
+	common/forward_failure_reason.h		\
 	common/gossip_constants.h			\
 	common/hash_str.h				\
 	common/hsm_version.h				\