Make update drop-able

src/lib.rs

@@ -68,7 +68,7 @@ pub use kyoto::{
 
 use kyoto::Receiver;
 use kyoto::UnboundedReceiver;
-use kyoto::{Event, IndexedBlock};
+use kyoto::{BlockHash, Event, IndexedBlock};
 
 pub mod builder;
 
@@ -97,6 +97,8 @@ pub struct UpdateSubscriber {
     chain: local_chain::LocalChain,
     // receive graph
     graph: IndexedTxGraph<ConfirmationBlockTime, KeychainTxOutIndex<KeychainKind>>,
+    // staged changes for the chain
+    chain_changeset: BTreeMap<u32, Option<BlockHash>>,
 }
 
 impl UpdateSubscriber {
@@ -110,6 +112,7 @@ impl UpdateSubscriber {
             receiver,
             chain: LocalChain::from_tip(cp)?,
             graph: IndexedTxGraph::new(index.clone()),
+            chain_changeset: BTreeMap::new(),
         })
     }
 
@@ -121,47 +124,48 @@ impl UpdateSubscriber {
     /// running node. Production applications should define how the application handles
     /// these events and displays them to end users.
     pub async fn update(&mut self) -> Option<Update> {
-        let mut chain_changeset = BTreeMap::new();
         while let Some(message) = self.receiver.recv().await {
             match message {
                 Event::Block(IndexedBlock { height, block }) => {
                     let hash = block.header.block_hash();
-                    chain_changeset.insert(height, Some(hash));
+                    self.chain_changeset.insert(height, Some(hash));
                     let _ = self.graph.apply_block_relevant(&block, height);
                 }
                 Event::BlocksDisconnected(headers) => {
                     for header in headers {
                         let height = header.height;
-                        chain_changeset.insert(height, None);
+                        self.chain_changeset.insert(height, None);
                     }
                 }
                 Event::Synced(SyncUpdate {
                     tip,
                     recent_history,
                 }) => {
-                    if chain_changeset.is_empty()
+                    if self.chain_changeset.is_empty()
                         && self.chain.tip().height() == tip.height
                         && self.chain.tip().hash() == tip.hash
                     {
                         // return early if we're already synced
                         return None;
                     }
                     recent_history.into_iter().for_each(|(height, header)| {
-                        chain_changeset.insert(height, Some(header.block_hash()));
+                        self.chain_changeset
+                            .insert(height, Some(header.block_hash()));
                     });
                     break;
                 }
             }
         }
-        self.chain
-            .apply_changeset(&local_chain::ChangeSet::from(chain_changeset))
-            .expect("chain was initialized with genesis");
         Some(self.get_scan_response())
     }
 
     // When the client is believed to have synced to the chain tip of most work,
     // we can return a wallet update.
     fn get_scan_response(&mut self) -> Update {
+        let chain_changeset = core::mem::take(&mut self.chain_changeset);
+        self.chain
+            .apply_changeset(&local_chain::ChangeSet::from(chain_changeset))
+            .expect("chain was initialized with genesis");
         let tx_update = TxUpdate::from(self.graph.graph().clone());
         let graph = core::mem::take(&mut self.graph);
         let last_active_indices = graph.index.last_used_indices();