feat(kyoto): add avg feerate and connect

Users may want to add a `Peer` while the node is running, perhaps after
the user updates a list. This is easily done.

Developers that are working on desktop or even server platforms may have
less strict bandwidth requirements than in the mobile case. These users
could make use of fetching the average fee rate for a block, which could
be used in some cases to fall-back or roughly estimate fee rates with.

Author: rustaceanrob

bdk-ffi/src/kyoto.rs

@@ -23,6 +23,7 @@ use std::time::Duration;
 
 use tokio::sync::Mutex;
 
+use crate::bitcoin::BlockHash;
 use crate::bitcoin::Transaction;
 use crate::error::{CbfBuilderError, CbfError};
 use crate::types::Update;
@@ -340,6 +341,27 @@ impl CbfClient {
             .map(|fee| Arc::new(FeeRate(fee)))
     }
 
+    /// Fetch the average fee rate for a block by requesting it from a peer. Not recommend for
+    /// resource-limited devices.
+    pub async fn average_fee_rate(
+        &self,
+        blockhash: Arc<BlockHash>,
+    ) -> Result<Arc<FeeRate>, CbfError> {
+        let fee_rate = self
+            .sender
+            .average_fee_rate(blockhash.0)
+            .await
+            .map_err(|_| CbfError::NodeStopped)?;
+        Ok(Arc::new(fee_rate.into()))
+    }
+
+    /// Add another [`Peer`] to attempt a connection with.
+    pub fn connect(&self, peer: Peer) -> Result<(), CbfError> {
+        self.sender
+            .add_peer(peer)
+            .map_err(|_| CbfError::NodeStopped)
+    }
+
     /// Query a Bitcoin DNS seeder using the configured resolver.
     ///
     /// This is **not** a generic DNS implementation. Host names are prefixed with a `x849` to filter