channeld: get htlc_maximum_msat from lightningd.

We used to calculate it ourselves.  Unfortunately this needs to
be done in several places, since new_channel() isn't used to fully
create a channel in the case of dual funding :(

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

channeld/channeld.c

@@ -119,8 +119,12 @@ struct peer {
 
 	/* CLTV delta to announce to peers */
 	u16 cltv_delta;
+
+	/* We only really know these because we're the ones who create
+	 * the channel_updates. */
 	u32 fee_base;
 	u32 fee_per_satoshi;
+	struct amount_msat htlc_maximum_msat;
 
 	/* The scriptpubkey to use for shutting down. */
 	u32 *final_index;
@@ -212,42 +216,6 @@ const u8 *hsm_req(const tal_t *ctx, const u8 *req TAKES)
 	return msg;
 }
 
-/*
- * The maximum msat that this node will accept for an htlc.
- * It's flagged as an optional field in `channel_update`.
- *
- * We advertize the maximum value possible, defined as the smaller
- * of the remote's maximum in-flight HTLC or the total channel
- * capacity the reserve we have to keep.
- * FIXME: does this need fuzz?
- */
-static struct amount_msat advertized_htlc_max(const struct channel *channel)
-{
-	struct amount_sat lower_bound;
-	struct amount_msat lower_bound_msat;
-
-	/* This shouldn't fail */
-	if (!amount_sat_sub(&lower_bound, channel->funding_sats,
-			    channel->config[REMOTE].channel_reserve)) {
-		status_failed(STATUS_FAIL_INTERNAL_ERROR,
-			      "funding %s - remote reserve %s?",
-			      type_to_string(tmpctx, struct amount_sat,
-					     &channel->funding_sats),
-			      type_to_string(tmpctx, struct amount_sat,
-					     &channel->config[REMOTE]
-					     .channel_reserve));
-	}
-
-	if (!amount_sat_to_msat(&lower_bound_msat, lower_bound)) {
-		status_failed(STATUS_FAIL_INTERNAL_ERROR,
-			      "lower_bound %s invalid?",
-			      type_to_string(tmpctx, struct amount_sat,
-					     &lower_bound));
-	}
-
-	return lower_bound_msat;
-}
-
 #if EXPERIMENTAL_FEATURES
 static void maybe_send_stfu(struct peer *peer)
 {
@@ -396,7 +364,7 @@ static void send_channel_update(struct peer *peer, int disable_flag)
 						  peer->channel->config[REMOTE].htlc_minimum,
 						  peer->fee_base,
 						  peer->fee_per_satoshi,
-						  advertized_htlc_max(peer->channel));
+						  peer->htlc_maximum_msat);
 	wire_sync_write(MASTER_FD, take(msg));
 }
 
@@ -3774,6 +3742,7 @@ static void init_channel(struct peer *peer)
 				    &opener,
 				    &peer->fee_base,
 				    &peer->fee_per_satoshi,
+				    &peer->htlc_maximum_msat,
 				    &local_msat,
 				    &points[LOCAL],
 				    &funding_pubkey[LOCAL],

channeld/channeld_wire.csv

@@ -35,6 +35,7 @@ msgdata,channeld_init,old_remote_per_commit,pubkey,
 msgdata,channeld_init,opener,enum side,
 msgdata,channeld_init,fee_base,u32,
 msgdata,channeld_init,fee_proportional,u32,
+msgdata,channeld_init,htlc_maximum_msat,amount_msat,
 msgdata,channeld_init,local_msatoshi,amount_msat,
 msgdata,channeld_init,our_basepoints,basepoints,
 msgdata,channeld_init,our_funding_pubkey,pubkey,

lightningd/channel.c

@@ -317,7 +317,7 @@ struct channel *new_unsaved_channel(struct peer *peer,
  * capacity the reserve we have to keep.
  * FIXME: does this need fuzz?
  */
-static struct amount_msat htlc_max_possible_send(const struct channel *channel)
+struct amount_msat htlc_max_possible_send(const struct channel *channel)
 {
 	struct amount_sat lower_bound;
 	struct amount_msat lower_bound_msat;

lightningd/channel.h

@@ -481,4 +481,5 @@ struct htlc_out *channel_has_htlc_out(struct channel *channel);
 
 const u8 *get_channel_update(struct channel *channel);
 
+struct amount_msat htlc_max_possible_send(const struct channel *channel);
 #endif /* LIGHTNING_LIGHTNINGD_CHANNEL_H */

lightningd/channel_control.c

@@ -702,6 +702,7 @@ void peer_start_channeld(struct channel *channel,
 				       channel->opener,
 				       channel->feerate_base,
 				       channel->feerate_ppm,
+				       channel->htlc_maximum_msat,
 				       channel->our_msat,
 				       &channel->local_basepoints,
 				       &channel->local_funding_pubkey,

lightningd/dual_open_control.c

@@ -1110,6 +1110,7 @@ wallet_update_channel(struct lightningd *ld,
 	channel->msat_to_us_min = our_msat;
 	channel->msat_to_us_max = our_msat;
 	channel->lease_expiry = lease_expiry;
+	channel->htlc_maximum_msat = htlc_max_possible_send(channel);
 
 	tal_free(channel->lease_commit_sig);
 	channel->lease_commit_sig = tal_steal(channel, lease_commit_sig);
@@ -1252,6 +1253,7 @@ wallet_commit_channel(struct lightningd *ld,
 
 	channel->lease_chan_max_msat = lease_chan_max_msat;
 	channel->lease_chan_max_ppt = lease_chan_max_ppt;
+	channel->htlc_maximum_msat = htlc_max_possible_send(channel);
 
 	/* Now we finally put it in the database. */
 	wallet_channel_insert(ld->wallet, channel);