From: Matt Corallo <git@bluematt.me>
Date: Sat, 26 Jun 2021 17:19:34 +0000 (+0000)
Subject: Correct feerate units
X-Git-Url: http://git.bitcoin.ninja/index.cgi?a=commitdiff_plain;h=2dbe461743604d8ce8219e99ea337dd7b8b498df;p=ldk-sample

Correct feerate units

Lightning, unlike every other Bitcoin-related protocol or API, uses
satoshis-per-1000-weight, instead of
satoshis-per-1000-virtual-bytes. This requires a division by 4 to
calculate the correct fees when passing Bitcoin Core fees into LDK.
---

diff --git a/src/bitcoind_client.rs b/src/bitcoind_client.rs
index 56b7f1a..90552d9 100644
--- a/src/bitcoind_client.rs
+++ b/src/bitcoind_client.rs
@@ -60,6 +60,9 @@ impl BlockSource for &BitcoindClient {
 	}
 }
 
+/// The minimum feerate we are allowed to send, as specify by LDK.
+const MIN_FEERATE: u32 = 253;
+
 impl BitcoindClient {
 	pub async fn new(
 		host: String, port: u16, rpc_user: String, rpc_password: String,
@@ -76,7 +79,7 @@ impl BitcoindClient {
 				"Failed to make initial call to bitcoind - please check your RPC user/password and access settings")
 			})?;
 		let mut fees: HashMap<Target, AtomicU32> = HashMap::new();
-		fees.insert(Target::Background, AtomicU32::new(253));
+		fees.insert(Target::Background, AtomicU32::new(MIN_FEERATE));
 		fees.insert(Target::Normal, AtomicU32::new(2000));
 		fees.insert(Target::HighPriority, AtomicU32::new(5000));
 		let client = Self {
@@ -111,12 +114,11 @@ impl BitcoindClient {
 						)
 						.await
 						.unwrap();
-					match resp.feerate {
-						Some(fee) => fee,
-						None => 253,
+					match resp.feerate_sat_per_kw {
+						Some(feerate) => std::cmp::max(feerate, MIN_FEERATE),
+						None => MIN_FEERATE,
 					}
 				};
-				// if background_estimate.
 
 				let normal_estimate = {
 					let mut rpc = rpc_client.lock().await;
@@ -129,8 +131,8 @@ impl BitcoindClient {
 						)
 						.await
 						.unwrap();
-					match resp.feerate {
-						Some(fee) => fee,
+					match resp.feerate_sat_per_kw {
+						Some(feerate) => std::cmp::max(feerate, MIN_FEERATE),
 						None => 2000,
 					}
 				};
@@ -147,8 +149,8 @@ impl BitcoindClient {
 						.await
 						.unwrap();
 
-					match resp.feerate {
-						Some(fee) => fee,
+					match resp.feerate_sat_per_kw {
+						Some(feerate) => std::cmp::max(feerate, MIN_FEERATE),
 						None => 5000,
 					}
 				};
diff --git a/src/convert.rs b/src/convert.rs
index a652980..6403923 100644
--- a/src/convert.rs
+++ b/src/convert.rs
@@ -51,7 +51,7 @@ impl TryInto<NewAddress> for JsonResponse {
 }
 
 pub struct FeeResponse {
-	pub feerate: Option<u32>,
+	pub feerate_sat_per_kw: Option<u32>,
 	pub errored: bool,
 }
 
@@ -61,8 +61,13 @@ impl TryInto<FeeResponse> for JsonResponse {
 		let errored = !self.0["errors"].is_null();
 		Ok(FeeResponse {
 			errored,
-			feerate: match self.0["feerate"].as_f64() {
-				Some(fee) => Some((fee * 100_000_000.0).round() as u32),
+			feerate_sat_per_kw: match self.0["feerate"].as_f64() {
+				// Bitcoin Core gives us a feerate in BTC/KvB, which we need to convert to
+				// satoshis/KW. Thus, we first multiply by 10^8 to get satoshis, then divide by 4
+				// to convert virtual-bytes into weight units.
+				Some(feerate_btc_per_kvbyte) => {
+					Some((feerate_btc_per_kvbyte * 100_000_000.0 / 4.0).round() as u32)
+				}
 				None => None,
 			},
 		})