rust: make sure the relay fee isn't lower than the minimum

Fixes the case where fees are returned below the minimum AND the relay
fee is also below the minimum, while respecting the relay fee if it
rises.

subprojects/gdk_rust/gdk_electrum/src/lib.rs

@@ -228,17 +228,18 @@ fn socksify(proxy: Option<&str>) -> Option<String> {
     }
 }
 
-fn try_get_fee_estimates(client: &Client) -> Result<Vec<FeeEstimate>, Error> {
+fn try_get_fee_estimates(client: &Client, min_rate: u64) -> Result<Vec<FeeEstimate>, Error> {
     let relay_fee = (client.relay_fee()? * 100_000_000.0) as u64;
+    let min_rate = min_rate.max(relay_fee);
     let blocks: Vec<usize> = (1..25).collect();
     // max is covering a rounding errors in production electrs which sometimes cause a fee
     // estimates lower than relay fee
     let mut estimates: Vec<FeeEstimate> = client
         .batch_estimate_fee(blocks)?
         .iter()
-        .map(|e| FeeEstimate(relay_fee.max((*e * 100_000_000.0) as u64)))
+        .map(|e| FeeEstimate(min_rate.max((*e * 100_000_000.0) as u64)))
         .collect();
-    estimates.insert(0, FeeEstimate(relay_fee));
+    estimates.insert(0, FeeEstimate(min_rate));
     Ok(estimates)
 }
 
@@ -566,8 +567,9 @@ impl ElectrumSession {
             info!("building built end");
             let fee_store = self.store()?;
             let fee_fetched_at = self.fee_fetched_at.clone();
+            let min_rate = self.network.id().default_min_fee_rate();
             thread::spawn(move || {
-                match try_get_fee_estimates(&fee_client) {
+                match try_get_fee_estimates(&fee_client, min_rate) {
                     Ok(fee_estimates) => {
                         fee_store.write().unwrap().cache.fee_estimates = fee_estimates;
                         let mut fee_fetched_at = fee_fetched_at.lock().unwrap();
@@ -1113,10 +1115,12 @@ impl ElectrumSession {
             // Skip network call
             Ok(self.store()?.read()?.fee_estimates())
         } else {
-            let default_min_rate = self.network.id().default_min_fee_rate();
-            let fee_estimates =
-                try_get_fee_estimates(&self.url.build_client(self.proxy.as_deref(), None)?)
-                    .unwrap_or_else(|_| vec![FeeEstimate(default_min_rate); 25]);
+            let min_rate = self.network.id().default_min_fee_rate();
+            let fee_estimates = try_get_fee_estimates(
+                &self.url.build_client(self.proxy.as_deref(), None)?,
+                min_rate,
+            )
+            .unwrap_or_else(|_| vec![FeeEstimate(min_rate); 25]);
             self.store()?.write()?.cache.fee_estimates = fee_estimates.clone();
             *fee_fetched_at = SystemTime::now();
             Ok(fee_estimates)