node: Implement MemoryState as an extension for state transition validation.

src/node/memorystate.rs

@@ -0,0 +1,62 @@
+use incrementalmerkletree::{bridgetree::BridgeTree, Frontier};
+use log::debug;
+
+use super::state::{ProgramState, State, StateUpdate};
+use crate::crypto::{
+    keypair::PublicKey, merkle_node::MerkleNode, nullifier::Nullifier, proof::VerifyingKey,
+};
+
+/// In-memory state extension for state transition validations
+pub struct MemoryState {
+    /// Canonical state
+    pub canon: State,
+    /// The entire Merkle tree state (copied from `canon`)
+    pub tree: BridgeTree<MerkleNode, 32>,
+    /// List of all previous and the current merkle roots.
+    pub merkle_roots: Vec<MerkleNode>,
+    /// Nullifiers prevent double-spending
+    pub nullifiers: Vec<Nullifier>,
+}
+
+impl ProgramState for MemoryState {
+    fn is_valid_cashier_public_key(&self, public: &PublicKey) -> bool {
+        self.canon.is_valid_cashier_public_key(public)
+    }
+
+    fn is_valid_faucet_public_key(&self, public: &PublicKey) -> bool {
+        self.canon.is_valid_faucet_public_key(public)
+    }
+
+    fn is_valid_merkle(&self, merkle_root: &MerkleNode) -> bool {
+        self.canon.is_valid_merkle(merkle_root) || self.merkle_roots.contains(merkle_root)
+    }
+
+    fn nullifier_exists(&self, nullifier: &Nullifier) -> bool {
+        self.canon.nullifier_exists(nullifier) || self.nullifiers.contains(nullifier)
+    }
+
+    fn mint_vk(&self) -> &VerifyingKey {
+        self.canon.mint_vk()
+    }
+
+    fn burn_vk(&self) -> &VerifyingKey {
+        self.canon.burn_vk()
+    }
+}
+
+impl MemoryState {
+    pub async fn apply(&mut self, update: StateUpdate) {
+        debug!(target: "state_apply", "(in-memory) Extend nullifier set");
+        let mut nfs = update.nullifiers.clone();
+        self.nullifiers.append(&mut nfs);
+
+        debug!(target: "state_apply", "(in-memory) Update Merkle tree and witnesses");
+        for coin in update.coins {
+            let node = MerkleNode(coin.0);
+            self.tree.append(&node);
+            self.merkle_roots.push(self.tree.root());
+        }
+
+        debug!(target: "state_apply", "(in-memory) Finished apply() successfully.");
+    }
+}

src/node/mod.rs

@@ -3,3 +3,6 @@ pub use client::Client;
 
 pub mod state;
 pub use state::State;
+
+pub mod memorystate;
+pub use memorystate::MemoryState;