From fd1d154b15051a6b9491fc8d4346bf178aaf24a9 Mon Sep 17 00:00:00 2001
From: zero <zero@zero>
Date: Tue, 19 Mar 2024 10:26:01 +0100
Subject: [PATCH] runtime/smt: return early with SUCCESS (but give a warning)
 if the nullifiers list for changing the tree is empty.

---
 src/runtime/import/smt.rs | 11 ++++++++++-
 tests/smt.rs              |  2 +-
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/src/runtime/import/smt.rs b/src/runtime/import/smt.rs
index 85a2fbee1..a993a21f1 100644
--- a/src/runtime/import/smt.rs
+++ b/src/runtime/import/smt.rs
@@ -24,7 +24,7 @@ use darkfi_sdk::crypto::{
 };
 use darkfi_serial::Decodable;
 use halo2_proofs::pasta::pallas;
-use log::error;
+use log::{error, warn};
 use num_bigint::BigUint;
 use wasmer::{FunctionEnvMut, WasmPtr};
 
@@ -158,6 +158,15 @@ pub(crate) fn sparse_merkle_insert_batch(
         }
     };
 
+    // Nothing to do so just return here
+    if nullifiers.is_empty() {
+        warn!(
+            target: "runtime::smt::sparse_merkle_insert_batch",
+            "[WASM] [{}] sparse_merkle_insert_batch(): Nothing to add! Returning.", cid
+        );
+        return darkfi_sdk::entrypoint::SUCCESS
+    }
+
     // Make sure we've read the entire buffer
     if buf_reader.position() != (len as u64) {
         error!(
diff --git a/tests/smt.rs b/tests/smt.rs
index f10803e95..3c4c83240 100644
--- a/tests/smt.rs
+++ b/tests/smt.rs
@@ -44,7 +44,7 @@ fn zkvm_smt() -> Result<()> {
     // Use the leaf value as its position in the SMT
     // Therefore we need an additional constraint that leaf == pos
     let leaves: Vec<_> = leaves.into_iter().map(|l| (l, l)).collect();
-    smt.insert_batch(leaves.clone());
+    smt.insert_batch(leaves.clone()).unwrap();
 
     let (pos, leaf) = leaves[2];
     assert_eq!(pos, leaf);