refactor: simple code cleanups in mst implementation

.github/workflows/rust.yml

@@ -15,6 +15,7 @@ env:
 
 jobs:
   wakeup:
+    if: github.event.pull_request.head.repo.full_name == 'summa-dev/summa-solvency'
     runs-on: ubuntu-latest
     permissions:
       id-token: write
@@ -31,9 +32,10 @@ jobs:
           aws-region: us-west-2
 
       - name: Wakeup runner
-        run: .github/scripts/wakeup.sh 
+        run: .github/scripts/wakeup.sh
 
   build:
+    if: github.event.pull_request.head.repo.full_name == 'summa-dev/summa-solvency'
     runs-on: [summa-solvency-runner]
     needs: [wakeup]
 
@@ -71,4 +73,56 @@ jobs:
         run: |
           cd backend
           cargo run --release --example summa_solvency_flow
-
+
+  test-zk-prover:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Test Zk Prover
+        run: |
+          cd zk_prover
+          cargo test --release --features dev-graph -- --nocapture
+
+  test-zk-prover-examples:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Install solc
+        run: (hash svm 2>/dev/null || cargo install --version 0.2.23 svm-rs) && svm install 0.8.20 && solc --version
+      - name: Test Zk Prover examples
+        run: |
+          cd zk_prover
+          cargo run --release --example gen_inclusion_verifier
+          cargo run --release --example gen_commitment
+          cargo run --release --example gen_inclusion_proof
+
+  test-zk-prover-examples-nova:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Test Zk Prover examples
+        run: |
+          cd zk_prover
+          cargo run --release --example nova_incremental_verifier
+
+  test-backend:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Install Foundry
+        uses: foundry-rs/foundry-toolchain@v1
+      - name: Test backend
+        run: |
+          cd backend
+          cargo test --release -- --nocapture
+
+  test-backend-examples:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Install Foundry
+        uses: foundry-rs/foundry-toolchain@v1
+      - name: Test backend example
+        run: |
+          cd backend
+          cargo run --release --example summa_solvency_flow

backend/src/apis/mod.rs

@@ -20,7 +20,7 @@ where
         .map(|balance| BigUint::from_str_radix(balance, 10).unwrap())
         .collect();
 
-    let entry: Entry<N_CURRENCIES> = Entry::new(username, balances.try_into().unwrap()).unwrap();
+    let entry: Entry<N_CURRENCIES> = Entry::new(username, balances.try_into().unwrap());
 
     // Convert Fp to U256
     let hash_str = format!("{:?}", entry.compute_leaf().hash);

zk_prover/src/circuits/merkle_sum_tree.rs

@@ -249,7 +249,7 @@ where
         // Assign the entry username to the witness
         let username = self.assign_value_to_witness(
             layouter.namespace(|| "assign entry username"),
-            big_uint_to_fp(self.entry.username_as_big_uint()),
+            big_uint_to_fp(&self.entry.username_as_big_uint()),
             "entry username",
             config.advices[0],
         )?;

zk_prover/src/circuits/tests.rs

@@ -172,8 +172,7 @@ mod test {
         let invalid_leaf_balances = [1000.to_biguint().unwrap(), 1000.to_biguint().unwrap()];
 
         // invalidate user entry
-        let invalid_entry =
-            Entry::new(circuit.entry.username().to_string(), invalid_leaf_balances).unwrap();
+        let invalid_entry = Entry::new(circuit.entry.username().to_string(), invalid_leaf_balances);
 
         circuit.entry = invalid_entry;
 

zk_prover/src/merkle_sum_tree/entry.rs

@@ -12,18 +12,18 @@ pub struct Entry<const N_CURRENCIES: usize> {
 }
 
 impl<const N_CURRENCIES: usize> Entry<N_CURRENCIES> {
-    pub fn new(username: String, balances: [BigUint; N_CURRENCIES]) -> Result<Self, &'static str> {
+    pub fn new(username: String, balances: [BigUint; N_CURRENCIES]) -> Self {
         // Security Assumptions:
         // Using `keccak256` for `hashed_username` ensures high collision resistance,
         // appropriate for the assumed userbase of $2^{30}$.
         // The `hashed_username` utilizes the full 256 bits produced by `keccak256`,
         // but is adjusted to the field size through the Poseidon hash function's modulo operation.
         let hashed_username: BigUint = BigUint::from_bytes_be(&keccak256(username.as_bytes()));
-        Ok(Entry {
+        Entry {
             hashed_username,
             balances,
             username,
-        })
+        }
     }
 
     /// Returns a zero entry where the username is 0 and the balances are all 0

zk_prover/src/merkle_sum_tree/mst.rs

@@ -111,8 +111,6 @@ impl<const N_CURRENCIES: usize, const N_BYTES: usize> MerkleSumTree<N_CURRENCIES
     {
         let depth = (entries.len() as f64).log2().ceil() as usize;
 
-        let mut nodes = vec![];
-
         // Pad the entries with empty entries to make the number of entries equal to 2^depth
         if entries.len() < 2usize.pow(depth as u32) {
             entries.extend(vec![
@@ -123,7 +121,7 @@ impl<const N_CURRENCIES: usize, const N_BYTES: usize> MerkleSumTree<N_CURRENCIES
 
         let leaves = build_leaves_from_entries(&entries);
 
-        let root = build_merkle_tree_from_leaves(&leaves, depth, &mut nodes)?;
+        let (root, nodes) = build_merkle_tree_from_leaves(&leaves, depth)?;
 
         Ok(MerkleSumTree {
             root,
@@ -202,7 +200,6 @@ impl<const N_CURRENCIES: usize, const N_BYTES: usize> MerkleSumTree<N_CURRENCIES
         }
 
         let root = self.nodes[self.depth][0].clone();
-
         Ok(root)
     }
 

zk_prover/src/merkle_sum_tree/node.rs

@@ -58,8 +58,11 @@ impl<const N_CURRENCIES: usize> Node<N_CURRENCIES> {
     where
         [usize; N_CURRENCIES + 1]: Sized,
     {
+        let hash =
+            poseidon::Hash::<Fp, PoseidonSpec, ConstantLength<{ N_CURRENCIES + 1 }>, 2, 1>::init()
+                .hash(preimage.clone());
         Node {
-            hash: Self::poseidon_hash_leaf(preimage[0], preimage[1..].try_into().unwrap()),
+            hash,
             balances: preimage[1..].try_into().unwrap(),
         }
     }
@@ -71,44 +74,12 @@ impl<const N_CURRENCIES: usize> Node<N_CURRENCIES> {
     where
         [usize; N_CURRENCIES + 2]: Sized,
     {
+        let hash =
+            poseidon::Hash::<Fp, PoseidonSpec, ConstantLength<{ N_CURRENCIES + 2 }>, 2, 1>::init()
+                .hash(preimage.clone());
         Node {
-            hash: Self::poseidon_hash_middle(
-                preimage[0..N_CURRENCIES].try_into().unwrap(),
-                preimage[N_CURRENCIES],
-                preimage[N_CURRENCIES + 1],
-            ),
+            hash,
             balances: preimage[0..N_CURRENCIES].try_into().unwrap(),
         }
     }
-
-    fn poseidon_hash_middle(
-        balances_sum: [Fp; N_CURRENCIES],
-        hash_child_left: Fp,
-        hash_child_right: Fp,
-    ) -> Fp
-    where
-        [usize; N_CURRENCIES + 2]: Sized,
-    {
-        let mut hash_inputs: [Fp; N_CURRENCIES + 2] = [Fp::zero(); N_CURRENCIES + 2];
-
-        hash_inputs[0..N_CURRENCIES].copy_from_slice(&balances_sum);
-        hash_inputs[N_CURRENCIES] = hash_child_left;
-        hash_inputs[N_CURRENCIES + 1] = hash_child_right;
-
-        poseidon::Hash::<Fp, PoseidonSpec, ConstantLength<{ N_CURRENCIES + 2 }>, 2, 1>::init()
-            .hash(hash_inputs)
-    }
-
-    fn poseidon_hash_leaf(username: Fp, balances: [Fp; N_CURRENCIES]) -> Fp
-    where
-        [usize; N_CURRENCIES + 1]: Sized,
-    {
-        let mut hash_inputs: [Fp; N_CURRENCIES + 1] = [Fp::zero(); N_CURRENCIES + 1];
-
-        hash_inputs[0] = username;
-        hash_inputs[1..N_CURRENCIES + 1].copy_from_slice(&balances);
-
-        poseidon::Hash::<Fp, PoseidonSpec, ConstantLength<{ N_CURRENCIES + 1 }>, 2, 1>::init()
-            .hash(hash_inputs)
-    }
 }

zk_prover/src/merkle_sum_tree/tests.rs

@@ -53,8 +53,7 @@ mod test {
         let invalid_entry = Entry::new(
             "AtwIxZHo".to_string(),
             [35479.to_biguint().unwrap(), 35479.to_biguint().unwrap()],
-        )
-        .unwrap();
+        );
         let invalid_entry = invalid_entry;
         let mut proof_invalid_1 = proof.clone();
         proof_invalid_1.entry = invalid_entry;

zk_prover/src/merkle_sum_tree/tree.rs

@@ -71,7 +71,7 @@ pub trait Tree<const N_CURRENCIES: usize> {
         let mut preimage = [Fp::zero(); N_CURRENCIES + 1];
 
         // Add username to preimage
-        preimage[0] = big_uint_to_fp(entry.username_as_big_uint());
+        preimage[0] = big_uint_to_fp(&entry.username_as_big_uint());
 
         // Add balances to preimage
         for (i, balance) in preimage.iter_mut().enumerate().skip(1).take(N_CURRENCIES) {
@@ -97,6 +97,7 @@ pub trait Tree<const N_CURRENCIES: usize> {
         if index >= nodes[0].len() {
             return Err(Box::from("Index out of bounds"));
         }
+        assert_eq!(nodes[0].len(), 2usize.pow(depth as u32));
 
         let mut sibling_middle_node_hash_preimages = Vec::with_capacity(depth - 1);
 
@@ -111,7 +112,9 @@ pub trait Tree<const N_CURRENCIES: usize> {
             let position = current_index % 2;
             let sibling_index = current_index - position + (1 - position);
 
-            if sibling_index < nodes[level].len() && level != 0 {
+            // we asserted that the leaves vec length is a power of 2
+            // so the index shouldn't overflow the level's length
+            if level > 0 {
                 // Fetch hash preimage for sibling middle nodes
                 let sibling_node_preimage =
                     self.get_middle_node_hash_preimage(level, sibling_index)?;
@@ -152,14 +155,13 @@ pub trait Tree<const N_CURRENCIES: usize> {
         if proof.path_indices[0] == 0.into() {
             hash_preimage[N_CURRENCIES] = node.hash;
             hash_preimage[N_CURRENCIES + 1] = sibling_leaf_node.hash;
-            node = Node::middle_node_from_preimage(&hash_preimage);
         } else {
             hash_preimage[N_CURRENCIES] = sibling_leaf_node.hash;
             hash_preimage[N_CURRENCIES + 1] = node.hash;
-            node = Node::middle_node_from_preimage(&hash_preimage);
         }
+        node = Node::middle_node_from_preimage(&hash_preimage);
 
-        for i in 1..proof.path_indices.len() {
+        for (i, path_index) in proof.path_indices.iter().enumerate().skip(1) {
             let sibling_node = Node::<N_CURRENCIES>::middle_node_from_preimage(
                 &proof.sibling_middle_node_hash_preimages[i - 1],
             );
@@ -169,15 +171,14 @@ pub trait Tree<const N_CURRENCIES: usize> {
                 *balance = node.balances[i] + sibling_node.balances[i];
             }
 
-            if proof.path_indices[i] == 0.into() {
+            if *path_index == 0.into() {
                 hash_preimage[N_CURRENCIES] = node.hash;
                 hash_preimage[N_CURRENCIES + 1] = sibling_node.hash;
-                node = Node::middle_node_from_preimage(&hash_preimage);
             } else {
                 hash_preimage[N_CURRENCIES] = sibling_node.hash;
                 hash_preimage[N_CURRENCIES + 1] = node.hash;
-                node = Node::middle_node_from_preimage(&hash_preimage);
             }
+            node = Node::middle_node_from_preimage(&hash_preimage);
         }
 
         proof.root.hash == node.hash && proof.root.balances == node.balances

zk_prover/src/merkle_sum_tree/utils/build_tree.rs

@@ -5,48 +5,25 @@ use rayon::prelude::*;
 pub fn build_merkle_tree_from_leaves<const N_CURRENCIES: usize>(
     leaves: &[Node<N_CURRENCIES>],
     depth: usize,
-    nodes: &mut Vec<Vec<Node<N_CURRENCIES>>>,
-) -> Result<Node<N_CURRENCIES>, Box<dyn std::error::Error>>
+) -> Result<(Node<N_CURRENCIES>, Vec<Vec<Node<N_CURRENCIES>>>), Box<dyn std::error::Error>>
 where
     [usize; N_CURRENCIES + 1]: Sized,
     [usize; N_CURRENCIES + 2]: Sized,
 {
-    let n = leaves.len();
-
     let mut tree: Vec<Vec<Node<N_CURRENCIES>>> = Vec::with_capacity(depth + 1);
 
-    tree.push(vec![
-        Node {
-            hash: Fp::from(0),
-            balances: [Fp::from(0); N_CURRENCIES]
-        };
-        n
-    ]);
-
-    for _ in 1..=depth {
-        let previous_level = tree.last().unwrap();
-        let nodes_in_level = (previous_level.len() + 1) / 2;
+    // the size of a leaf layer must be a power of 2
+    // if not, the `leaves` Vec should be completed with "zero entries" until a power of 2
+    assert_eq!(leaves.len(), 2usize.pow(depth as u32));
 
-        tree.push(vec![
-            Node {
-                hash: Fp::from(0),
-                balances: [Fp::from(0); N_CURRENCIES]
-            };
-            nodes_in_level
-        ]);
-    }
-
-    for (index, leaf) in leaves.iter().enumerate() {
-        tree[0][index] = leaf.clone();
-    }
+    tree.push(leaves.to_vec());
 
     for level in 1..=depth {
         build_middle_level(level, &mut tree)
     }
 
     let root = tree[depth][0].clone();
-    *nodes = tree;
-    Ok(root)
+    Ok((root, tree))
 }
 
 pub fn build_leaves_from_entries<const N_CURRENCIES: usize>(
@@ -74,8 +51,10 @@ where
     leaves
 }
 
-fn build_middle_level<const N_CURRENCIES: usize>(level: usize, tree: &mut [Vec<Node<N_CURRENCIES>>])
-where
+fn build_middle_level<const N_CURRENCIES: usize>(
+    level: usize,
+    tree: &mut Vec<Vec<Node<N_CURRENCIES>>>,
+) where
     [usize; N_CURRENCIES + 2]: Sized,
 {
     let results: Vec<Node<N_CURRENCIES>> = (0..tree[level - 1].len())
@@ -95,7 +74,5 @@ where
         })
         .collect();
 
-    for (index, new_node) in results.into_iter().enumerate() {
-        tree[level][index] = new_node;
-    }
+    tree.push(results);
 }

zk_prover/src/merkle_sum_tree/utils/csv_parser.rs

@@ -50,7 +50,8 @@ pub fn parse_csv_to_entries<P: AsRef<Path>, const N_CURRENCIES: usize, const N_B
             balances_big_int.push(balance);
         }
 
-        let entry = Entry::new(username, balances_big_int.try_into().unwrap())?;
+        let entry = Entry::new(username, balances_big_int.try_into().unwrap());
+
         entries.push(entry);
     }