Don't return 1.0 feerate if none is found by convert_fee_rate

src/lib.rs

@@ -88,17 +88,14 @@ pub use r#async::AsyncClient;
 
 /// Get a fee value in sats/vbytes from the estimates
 /// that matches the confirmation target set as parameter.
-pub fn convert_fee_rate(target: usize, estimates: HashMap<u16, f64>) -> Result<f32, Error> {
-    let fee_val = {
-        let mut pairs = estimates.into_iter().collect::<Vec<(u16, f64)>>();
-        pairs.sort_unstable_by_key(|(k, _)| std::cmp::Reverse(*k));
-        pairs
-            .into_iter()
-            .find(|(k, _)| *k as usize <= target)
-            .map(|(_, v)| v)
-            .unwrap_or(1.0)
-    };
-    Ok(fee_val as f32)
+///
+/// Returns `None` if no feerate estimate is found at or below `target` confirmations.
+pub fn convert_fee_rate(target: usize, estimates: HashMap<u16, f64>) -> Option<f32> {
+    estimates
+        .into_iter()
+        .filter(|(k, _)| *k as usize <= target)
+        .max_by_key(|(k, _)| *k)
+        .map(|(_, v)| v as f32)
 }
 
 #[derive(Debug, Clone)]
@@ -391,12 +388,17 @@ mod test {
 "#,
         )
         .unwrap();
+        assert!(convert_fee_rate(1, HashMap::new()).is_none());
         assert_eq!(convert_fee_rate(6, esplora_fees.clone()).unwrap(), 2.236);
         assert_eq!(
-            convert_fee_rate(26, esplora_fees).unwrap(),
+            convert_fee_rate(26, esplora_fees.clone()).unwrap(),
             1.015,
             "should inherit from value for 25"
         );
+        assert!(
+            convert_fee_rate(0, esplora_fees).is_none(),
+            "should not return feerate for 0 target"
+        );
     }
 
     #[cfg(all(feature = "blocking", feature = "async"))]