gossmap: add gossmap_chan_get_capacity() helper.

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

common/gossmap.c

@@ -577,9 +577,7 @@ static bool map_catchup(struct gossmap *map)
 		u16 type;
 
 		map_copy(map, map->map_end, &ghdr, sizeof(ghdr));
-		reclen = (be32_to_cpu(ghdr.len)
+		reclen = (be32_to_cpu(ghdr.len) & GOSSIP_STORE_LEN_MASK)
-			  & ~(GOSSIP_STORE_LEN_DELETED_BIT|
-			      GOSSIP_STORE_LEN_PUSH_BIT))
 			+ sizeof(ghdr);
 
 		if (be32_to_cpu(ghdr.len) & GOSSIP_STORE_LEN_DELETED_BIT)
@@ -947,6 +945,39 @@ void gossmap_node_get_id(const struct gossmap *map,
 		   + 8 + PUBKEY_CMPR_LEN*dir, id);
 }
 
+bool gossmap_chan_get_capacity(const struct gossmap *map,
+			       const struct gossmap_chan *c,
+			       struct amount_sat *amount)
+{
+	struct gossip_hdr ghdr;
+	size_t off;
+	u16 type;
+
+	/* For private, we need to go back WIRE_GOSSIP_STORE_PRIVATE_CHANNEL,
+	 * which is 8 (satoshis) + 2 (len) */
+	if (c->private) {
+		*amount = amount_sat(map_be64(map, c->cann_off - 8 - 2));
+		return true;
+	}
+
+	/* Skip over this record to next; expect a gossip_store_channel_amount */
+	off = c->cann_off - sizeof(ghdr);
+	map_copy(map, off, &ghdr, sizeof(ghdr));
+	off += sizeof(ghdr) + (be32_to_cpu(ghdr.len) & GOSSIP_STORE_LEN_MASK);
+
+	/* Partial write, this can happen. */
+	if (off + sizeof(ghdr) + 2 > map->map_size)
+		return false;
+
+	/* Get type of next field. */
+	type = map_be16(map, off + sizeof(ghdr));
+	if (type != WIRE_GOSSIP_STORE_CHANNEL_AMOUNT)
+		return false;
+
+	*amount = amount_sat(map_be64(map, off + sizeof(ghdr) + sizeof(be16)));
+	return true;
+}
+
 struct gossmap_chan *gossmap_nth_chan(const struct gossmap *map,
 				      const struct gossmap_node *node,
 				      u32 n,

common/gossmap.h

@@ -111,6 +111,11 @@ static inline bool gossmap_chan_set(const struct gossmap_chan *chan, int dir)
 	return chan->half[dir].htlc_max != 0;
 }
 
+/* Return capacity if it's known (fails only on race condition) */
+bool gossmap_chan_get_capacity(const struct gossmap *map,
+			       const struct gossmap_chan *c,
+			       struct amount_sat *amount);
+
 /* Get the announcement msg which created this chan */
 u8 *gossmap_chan_get_announce(const tal_t *ctx,
 			      const struct gossmap *map,

common/test/run-gossmap_local.c

@@ -1,4 +1,5 @@
 /* Test local modifications to gossmap */
+#include "../amount.c"
 #include "../fp16.c"
 #include "../gossmap.c"
 #include "../node_id.c"
@@ -10,43 +11,9 @@
 #include <stdio.h>
 
 /* AUTOGENERATED MOCKS START */
-/* Generated stub for amount_asset_is_main */
-bool amount_asset_is_main(struct amount_asset *asset UNNEEDED)
-{ fprintf(stderr, "amount_asset_is_main called!\n"); abort(); }
-/* Generated stub for amount_asset_to_sat */
-struct amount_sat amount_asset_to_sat(struct amount_asset *asset UNNEEDED)
-{ fprintf(stderr, "amount_asset_to_sat called!\n"); abort(); }
-/* Generated stub for amount_sat */
-struct amount_sat amount_sat(u64 satoshis UNNEEDED)
-{ fprintf(stderr, "amount_sat called!\n"); abort(); }
-/* Generated stub for amount_sat_add */
- bool amount_sat_add(struct amount_sat *val UNNEEDED,
-				       struct amount_sat a UNNEEDED,
-				       struct amount_sat b UNNEEDED)
-{ fprintf(stderr, "amount_sat_add called!\n"); abort(); }
-/* Generated stub for amount_sat_eq */
-bool amount_sat_eq(struct amount_sat a UNNEEDED, struct amount_sat b UNNEEDED)
-{ fprintf(stderr, "amount_sat_eq called!\n"); abort(); }
-/* Generated stub for amount_sat_greater_eq */
-bool amount_sat_greater_eq(struct amount_sat a UNNEEDED, struct amount_sat b UNNEEDED)
-{ fprintf(stderr, "amount_sat_greater_eq called!\n"); abort(); }
-/* Generated stub for amount_sat_sub */
- bool amount_sat_sub(struct amount_sat *val UNNEEDED,
-				       struct amount_sat a UNNEEDED,
-				       struct amount_sat b UNNEEDED)
-{ fprintf(stderr, "amount_sat_sub called!\n"); abort(); }
-/* Generated stub for amount_sat_to_asset */
-struct amount_asset amount_sat_to_asset(struct amount_sat *sat UNNEEDED, const u8 *asset UNNEEDED)
-{ fprintf(stderr, "amount_sat_to_asset called!\n"); abort(); }
-/* Generated stub for amount_tx_fee */
-struct amount_sat amount_tx_fee(u32 fee_per_kw UNNEEDED, size_t weight UNNEEDED)
-{ fprintf(stderr, "amount_tx_fee called!\n"); abort(); }
 /* Generated stub for fromwire */
 const u8 *fromwire(const u8 **cursor UNNEEDED, size_t *max UNNEEDED, void *copy UNNEEDED, size_t n UNNEEDED)
 { fprintf(stderr, "fromwire called!\n"); abort(); }
-/* Generated stub for fromwire_amount_sat */
-struct amount_sat fromwire_amount_sat(const u8 **cursor UNNEEDED, size_t *max UNNEEDED)
-{ fprintf(stderr, "fromwire_amount_sat called!\n"); abort(); }
 /* Generated stub for fromwire_bool */
 bool fromwire_bool(const u8 **cursor UNNEEDED, size_t *max UNNEEDED)
 { fprintf(stderr, "fromwire_bool called!\n"); abort(); }
@@ -82,9 +49,6 @@ void fromwire_u8_array(const u8 **cursor UNNEEDED, size_t *max UNNEEDED, u8 *arr
 /* Generated stub for towire */
 void towire(u8 **pptr UNNEEDED, const void *data UNNEEDED, size_t len UNNEEDED)
 { fprintf(stderr, "towire called!\n"); abort(); }
-/* Generated stub for towire_amount_sat */
-void towire_amount_sat(u8 **pptr UNNEEDED, const struct amount_sat sat UNNEEDED)
-{ fprintf(stderr, "towire_amount_sat called!\n"); abort(); }
 /* Generated stub for towire_bool */
 void towire_bool(u8 **pptr UNNEEDED, bool v UNNEEDED)
 { fprintf(stderr, "towire_bool called!\n"); abort(); }
@@ -335,6 +299,7 @@ int main(int argc, char *argv[])
 	struct short_channel_id scid23, scid12, scid_local;
 	struct gossmap_chan *chan;
 	struct gossmap_localmods *mods;
+	struct amount_sat capacity;
 
 	common_setup(argv[0]);
 
@@ -359,6 +324,12 @@ int main(int argc, char *argv[])
 	assert(!gossmap_find_chan(map, &scid23)->private);
 	assert(gossmap_find_chan(map, &scid12));
 	assert(gossmap_find_chan(map, &scid12)->private);
+	assert(gossmap_chan_get_capacity(map, gossmap_find_chan(map, &scid23),
+					 &capacity));
+	assert(amount_sat_eq(capacity, AMOUNT_SAT(1000000)));
+	assert(gossmap_chan_get_capacity(map, gossmap_find_chan(map, &scid12),
+					 &capacity));
+	assert(amount_sat_eq(capacity, AMOUNT_SAT(1000000)));
 
 	/* Now, let's add a new channel l1 -> l4. */
 	mods = gossmap_localmods_new(tmpctx);