bitcoin: expose feerate_floor.

Onchaind will want it.

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

bitcoin/Makefile

@@ -20,6 +20,7 @@ BITCOIN_HEADERS := bitcoin/address.h		\
 	bitcoin/base58.h			\
 	bitcoin/block.h				\
 	bitcoin/chainparams.h			\
+	bitcoin/feerate.h			\
 	bitcoin/locktime.h			\
 	bitcoin/preimage.h			\
 	bitcoin/privkey.h			\

bitcoin/feerate.h

@@ -0,0 +1,50 @@
+#ifndef LIGHTNING_BITCOIN_FEERATE_H
+#define LIGHTNING_BITCOIN_FEERATE_H
+#include "config.h"
+#include <ccan/build_assert/build_assert.h>
+#include <ccan/short_types/short_types.h>
+
+/* bitcoind considers 250 satoshi per kw to be the minimum acceptable fee:
+ * less than this won't even relay.
+ */
+#define BITCOIND_MINRELAYTXFEE_PER_KW 250
+/*
+ * But bitcoind uses vbytes (ie. (weight + 3) / 4) for this
+ * calculation, rather than weight, meaning we can disagree since we do
+ * it sanely (as specified in BOLT #3).
+ */
+#define FEERATE_BITCOIND_SEES(feerate, weight) \
+	(((feerate) * (weight)) / 1000 * 1000 / ((weight) + 3))
+/* ie. fee = (feerate * weight) // 1000
+ * bitcoind needs (worst-case): fee * 1000 / (weight + 3) >= 250
+ *
+ * (feerate * weight) // 1000 * 1000 // (weight + 3) >= 250
+ *
+ * The feerate needs to be higher for lower weight, and our minimum tx weight
+ * is 464 (version (4) + count_tx_in (1) + tx_in (32 + 4 + 1 + 4) +
+ * count_tx_out (1) + amount (8) + P2WSH (1 + 1 + 32) + witness 1 + 1 + <sig>
+ * + 1 + <key>).  Assume it's 400 to give a significant safety margin (it
+ * only makes 1 difference in the result anyway).
+ */
+#define MINIMUM_TX_WEIGHT 400
+
+/*
+ * This formula is satisfied by a feerate of 253 (hand-search).
+ */
+#define FEERATE_FLOOR 253
+
+static inline u32 feerate_floor(void)
+{
+	/* Assert that bitcoind will see this as above minRelayTxFee */
+	BUILD_ASSERT(FEERATE_BITCOIND_SEES(FEERATE_FLOOR, MINIMUM_TX_WEIGHT)
+		     >= BITCOIND_MINRELAYTXFEE_PER_KW);
+	/* And a lesser value won't do */
+	BUILD_ASSERT(FEERATE_BITCOIND_SEES(FEERATE_FLOOR-1, MINIMUM_TX_WEIGHT)
+		     < BITCOIND_MINRELAYTXFEE_PER_KW);
+	/* And I'm right about it being OK for larger txs, too */
+	BUILD_ASSERT(FEERATE_BITCOIND_SEES(FEERATE_FLOOR, (MINIMUM_TX_WEIGHT*2))
+		     >= BITCOIND_MINRELAYTXFEE_PER_KW);
+
+	return FEERATE_FLOOR;
+}
+#endif /* LIGHTNING_BITCOIN_FEERATE_H */

lightningd/chaintopology.c

@@ -1,4 +1,5 @@
 #include "bitcoin/block.h"
+#include "bitcoin/feerate.h"
 #include "bitcoin/script.h"
 #include "bitcoin/tx.h"
 #include "bitcoind.h"
@@ -229,48 +230,6 @@ static const char *feerate_name(enum feerate feerate)
 /* Mutual recursion via timer. */
 static void next_updatefee_timer(struct chain_topology *topo);
 
-/* bitcoind considers 250 satoshi per kw to be the minimum acceptable fee:
- * less than this won't even relay.
- */
-#define BITCOIND_MINRELAYTXFEE_PER_KW 250
-/*
- * But bitcoind uses vbytes (ie. (weight + 3) / 4) for this
- * calculation, rather than weight, meaning we can disagree since we do
- * it sanely (as specified in BOLT #3).
- */
-#define FEERATE_BITCOIND_SEES(feerate, weight) \
-	(((feerate) * (weight)) / 1000 * 1000 / ((weight) + 3))
-/* ie. fee = (feerate * weight) // 1000
- * bitcoind needs (worst-case): fee * 1000 / (weight + 3) >= 4000
- *
- * (feerate * weight) // 1000 * 1000 // (weight + 3) >= 4000
- *
- * The feerate needs to be higher for lower weight, and our minimum tx weight
- * is 464 (version (4) + count_tx_in (1) + tx_in (32 + 4 + 1 + 4) +
- * count_tx_out (1) + amount (8) + P2WSH (1 + 1 + 32) + witness 1 + 1 + <sig>
- * + 1 + <key>).  Assume it's 400 to give a significant safety margin (it
- * only makes 1 difference in the result anyway).
- */
-#define MINIMUM_TX_WEIGHT 400
-/*
- * This formula is satisfied by a feerate of 4030 (hand-search).
- */
-#define FEERATE_FLOOR 253
-u32 feerate_floor(void)
-{
-	/* Assert that bitcoind will see this as above minRelayTxFee */
-	BUILD_ASSERT(FEERATE_BITCOIND_SEES(FEERATE_FLOOR, MINIMUM_TX_WEIGHT)
-		     >= BITCOIND_MINRELAYTXFEE_PER_KW);
-	/* And a lesser value won't do */
-	BUILD_ASSERT(FEERATE_BITCOIND_SEES(FEERATE_FLOOR-1, MINIMUM_TX_WEIGHT)
-		     < BITCOIND_MINRELAYTXFEE_PER_KW);
-	/* And I'm right about it being OK for larger txs, too */
-	BUILD_ASSERT(FEERATE_BITCOIND_SEES(FEERATE_FLOOR, (MINIMUM_TX_WEIGHT*2))
-		     >= BITCOIND_MINRELAYTXFEE_PER_KW);
-
-	return FEERATE_FLOOR;
-}
-
 /* We sanitize feerates if necessary to put them in descending order. */
 static void update_feerates(struct bitcoind *bitcoind,
 			    const u32 *satoshi_per_kw,

lightningd/chaintopology.h

@@ -138,9 +138,6 @@ u32 get_block_height(const struct chain_topology *topo);
 /* Get fee rate in satoshi per kiloweight. */
 u32 get_feerate(const struct chain_topology *topo, enum feerate feerate);
 
-/* Get the minimum possible fee to allow relaying by bitcoind */
-u32 feerate_floor(void);
-
 /* Broadcast a single tx, and rebroadcast as reqd (copies tx).
  * If failed is non-NULL, call that and don't rebroadcast. */
 void broadcast_tx(struct chain_topology *topo,

lightningd/peer_control.c

@@ -2,6 +2,7 @@
 #include "peer_control.h"
 #include "subd.h"
 #include <arpa/inet.h>
+#include <bitcoin/feerate.h>
 #include <bitcoin/script.h>
 #include <bitcoin/tx.h>
 #include <ccan/array_size/array_size.h>

wallet/test/run-wallet.c

@@ -73,9 +73,6 @@ bool extract_channel_id(const u8 *in_pkt UNNEEDED, struct channel_id *channel_id
 /* Generated stub for features_supported */
 bool features_supported(const u8 *gfeatures UNNEEDED, const u8 *lfeatures UNNEEDED)
 { fprintf(stderr, "features_supported called!\n"); abort(); }
-/* Generated stub for feerate_floor */
-u32 feerate_floor(void)
-{ fprintf(stderr, "feerate_floor called!\n"); abort(); }
 /* Generated stub for fromwire_gossipctl_peer_disconnect_reply */
 bool fromwire_gossipctl_peer_disconnect_reply(const void *p UNNEEDED)
 { fprintf(stderr, "fromwire_gossipctl_peer_disconnect_reply called!\n"); abort(); }