opts: Add the max_fee_multiplier to specify acceptable fee ranges

Signed-off-by: Christian Decker <decker.christian@gmail.com>

lightningd/lightningd.h

@@ -60,6 +60,10 @@ struct config {
 
 	/* ipv6 bind disable */
 	bool no_ipv6_bind;
+
+	/* Accept fee changes only if they are in the range our_fee -
+	 * our_fee*multiplier */
+	u32 max_fee_multiplier;
 };
 
 struct lightningd {

lightningd/options.c

@@ -462,6 +462,13 @@ static void dev_register_opts(struct lightningd *ld)
 	opt_register_arg("--dev-bitcoind-poll", opt_set_u32, opt_show_u32,
 			 &ld->topology->poll_seconds,
 			 "Time between polling for new transactions");
+	opt_register_arg("--dev-max-fee-multiplier", opt_set_u32, opt_show_u32,
+			 &ld->config.max_fee_multiplier,
+			 "Allow the fee proposed by the remote end to be up to "
+			 "multiplier times higher than our own. Small values "
+			 "will cause channels to be closed more often due to "
+			 "fee fluctuations, large values may result in large "
+			 "fees.");
 	opt_register_arg("--dev-override-fee-rates", opt_set_fee_rates, NULL,
 			 ld->topology,
 			 "Force a specific rates (immediate/normal/slow) in satoshis per kw regardless of estimated fees");
@@ -515,6 +522,9 @@ static const struct config testnet_config = {
 
 	/* Rescan 5 hours of blocks on testnet, it's reorg happy */
 	.rescan = 30,
+
+	/* Fees may be in the range our_fee - 10*our_fee */
+	.max_fee_multiplier = 5,
 };
 
 /* aka. "Dude, where's my coins?" */
@@ -568,6 +578,9 @@ static const struct config mainnet_config = {
 
 	/* Rescan 2.5 hours of blocks on startup, it's not so reorg happy */
 	.rescan = 15,
+
+	/* Fees may be in the range our_fee - 10*our_fee */
+	.max_fee_multiplier = 5,
 };
 
 static void check_config(struct lightningd *ld)

lightningd/peer_control.c

@@ -182,13 +182,14 @@ u32 feerate_min(struct lightningd *ld)
  *
  * Given the variance in fees, and the fact that the transaction may
  * be spent in the future, it's a good idea for the fee payer to keep
- * a good margin, say 5x the expected fee requirement */
+ * a good margin, say 10x the expected fee requirement */
 u32 feerate_max(struct lightningd *ld)
 {
 	if (ld->config.ignore_fee_limits)
 		return UINT_MAX;
 
-	return get_feerate(ld->topology, FEERATE_IMMEDIATE) * 5;
+	return get_feerate(ld->topology, FEERATE_IMMEDIATE) *
+	       ld->config.max_fee_multiplier;
 }
 
 static void sign_last_tx(struct channel *channel)