fix: utxo_digest() must call count_leaves()

utxo_digest() lookup logic was incorrect.

src/rpc_server.rs

@@ -127,8 +127,8 @@ pub trait RPC {
     /// Return the digest for the specified block selector (genesis, tip, or height)
     async fn block_digest(block_selector: BlockSelector) -> Option<Digest>;
 
-    /// Return the digest for the specified UTXO index
-    async fn utxo_digest(index: u64) -> Option<Digest>;
+    /// Return the digest for the specified UTXO leaf index
+    async fn utxo_digest(leaf_index: u64) -> Option<Digest>;
 
     /// Return the block header for the specified block
     async fn header(block_selector: BlockSelector) -> Option<BlockHeader>;
@@ -258,12 +258,12 @@ impl RPC for NeptuneRPCServer {
         self.confirmations_internal().await
     }
 
-    async fn utxo_digest(self, _: context::Context, index: u64) -> Option<Digest> {
+    async fn utxo_digest(self, _: context::Context, leaf_index: u64) -> Option<Digest> {
         let state = self.state.lock_guard().await;
         let aocl = &state.chain.archival_state().archival_mutator_set.ams().aocl;
 
-        match index > 0 && index < aocl.len().await {
-            true => Some(aocl.get_leaf_async(index).await),
+        match leaf_index > 0 && leaf_index < aocl.count_leaves().await {
+            true => Some(aocl.get_leaf_async(leaf_index).await),
             false => None,
         }
     }

src/util_types/mutator_set/archival_mmr.rs

@@ -52,12 +52,6 @@ where
         self.digests.len().await == 1
     }
 
-    /// Returns len of Digests.  Note that elem 0
-    /// is always a dummy digest.
-    pub async fn len(&self) -> u64 {
-        self.digests.len().await
-    }
-
     /// Return the number of leaves in the tree
     pub async fn count_leaves(&self) -> u64 {
         node_index_to_leaf_index(self.digests.len().await).unwrap()