Merge pull request #162 from 0xPolygonMiden/frisitano-tx-executor

Introduce data access recording capabilities

benches/store.rs

@@ -1,5 +1,5 @@
 use criterion::{black_box, criterion_group, criterion_main, BatchSize, BenchmarkId, Criterion};
-use miden_crypto::merkle::{MerkleStore, MerkleTree, NodeIndex, SimpleSmt};
+use miden_crypto::merkle::{DefaultMerkleStore as MerkleStore, MerkleTree, NodeIndex, SimpleSmt};
 use miden_crypto::Word;
 use miden_crypto::{hash::rpo::RpoDigest, Felt};
 use rand_utils::{rand_array, rand_value};

src/merkle/mmr/full.rs

@@ -28,6 +28,7 @@ use std::error::Error;
 ///
 /// Since this is a full representation of the MMR, elements are never removed and the MMR will
 /// grow roughly `O(2n)` in number of leaf elements.
+#[derive(Debug, Clone)]
 pub struct Mmr {
     /// Refer to the `forest` method documentation for details of the semantics of this value.
     pub(super) forest: usize,

src/merkle/mod.rs

@@ -1,6 +1,6 @@
 use super::{
     hash::rpo::{Rpo256, RpoDigest},
-    utils::collections::{vec, BTreeMap, BTreeSet, Vec},
+    utils::collections::{vec, BTreeMap, BTreeSet, KvMap, RecordingMap, Vec},
     Felt, StarkField, Word, WORD_SIZE, ZERO,
 };
 use core::fmt;
@@ -33,7 +33,7 @@ mod mmr;
 pub use mmr::{Mmr, MmrPeaks, MmrProof};
 
 mod store;
-pub use store::MerkleStore;
+pub use store::{DefaultMerkleStore, MerkleStore, RecordingMerkleStore};
 
 mod node;
 pub use node::InnerNodeInfo;

src/merkle/partial_mt/mod.rs

@@ -154,7 +154,8 @@ impl PartialMerkleTree {
         self.leaves.iter().map(|&leaf| {
             (
                 leaf,
-                self.get_node(leaf).expect(&format!("Leaf with {leaf} is not in the nodes map")),
+                self.get_node(leaf)
+                    .unwrap_or_else(|_| panic!("Leaf with {leaf} is not in the nodes map")),
             )
         })
     }

src/merkle/partial_mt/tests.rs

@@ -1,5 +1,8 @@
 use super::{
-    super::{digests_to_words, int_to_node, MerkleStore, MerkleTree, NodeIndex, PartialMerkleTree},
+    super::{
+        digests_to_words, int_to_node, DefaultMerkleStore as MerkleStore, MerkleTree, NodeIndex,
+        PartialMerkleTree,
+    },
     RpoDigest, ValuePath, Vec,
 };
 

src/merkle/path.rs

@@ -68,6 +68,12 @@ impl MerklePath {
     }
 }
 
+impl From<MerklePath> for Vec<RpoDigest> {
+    fn from(path: MerklePath) -> Self {
+        path.nodes
+    }
+}
+
 impl From<Vec<RpoDigest>> for MerklePath {
     fn from(path: Vec<RpoDigest>) -> Self {
         Self::new(path)

src/merkle/store/mod.rs

@@ -1,6 +1,7 @@
 use super::{
-    mmr::Mmr, BTreeMap, EmptySubtreeRoots, InnerNodeInfo, MerkleError, MerklePath, MerklePathSet,
-    MerkleTree, NodeIndex, RootPath, Rpo256, RpoDigest, SimpleSmt, TieredSmt, ValuePath, Vec,
+    mmr::Mmr, BTreeMap, EmptySubtreeRoots, InnerNodeInfo, KvMap, MerkleError, MerklePath,
+    MerklePathSet, MerkleTree, NodeIndex, RecordingMap, RootPath, Rpo256, RpoDigest, SimpleSmt,
+    TieredSmt, ValuePath, Vec,
 };
 use crate::utils::{ByteReader, ByteWriter, Deserializable, DeserializationError, Serializable};
 use core::borrow::Borrow;
@@ -8,6 +9,15 @@ use core::borrow::Borrow;
 #[cfg(test)]
 mod tests;
 
+// MERKLE STORE
+// ================================================================================================
+
+/// A default [MerkleStore] which uses a simple [BTreeMap] as the backing storage.
+pub type DefaultMerkleStore = MerkleStore<BTreeMap<RpoDigest, Node>>;
+
+/// A [MerkleStore] with recording capabilities which uses [RecordingMap] as the backing storage.
+pub type RecordingMerkleStore = MerkleStore<RecordingMap<RpoDigest, Node>>;
+
 #[derive(Debug, Default, Copy, Clone, Eq, PartialEq)]
 pub struct Node {
     left: RpoDigest,
@@ -42,7 +52,7 @@ pub struct Node {
 /// # let T1 = MerkleTree::new([A, B, C, D, E, F, G, H1].to_vec()).expect("even number of leaves provided");
 /// # let ROOT0 = T0.root();
 /// # let ROOT1 = T1.root();
-/// let mut store = MerkleStore::new();
+/// let mut store: MerkleStore = MerkleStore::new();
 ///
 /// // the store is initialized with the SMT empty nodes
 /// assert_eq!(store.num_internal_nodes(), 255);
@@ -51,9 +61,8 @@ pub struct Node {
 /// let tree2 = MerkleTree::new(vec![A, B, C, D, E, F, G, H1]).unwrap();
 ///
 /// // populates the store with two merkle trees, common nodes are shared
-/// store
-///     .extend(tree1.inner_nodes())
-///     .extend(tree2.inner_nodes());
+/// store.extend(tree1.inner_nodes());
+/// store.extend(tree2.inner_nodes());
 ///
 /// // every leaf except the last are the same
 /// for i in 0..7 {
@@ -78,40 +87,24 @@ pub struct Node {
 /// assert_eq!(store.num_internal_nodes() - 255, 10);
 /// ```
 #[derive(Debug, Clone, Eq, PartialEq)]
-pub struct MerkleStore {
-    nodes: BTreeMap<RpoDigest, Node>,
+pub struct MerkleStore<T: KvMap<RpoDigest, Node> = BTreeMap<RpoDigest, Node>> {
+    nodes: T,
 }
 
-impl Default for MerkleStore {
+impl<T: KvMap<RpoDigest, Node>> Default for MerkleStore<T> {
     fn default() -> Self {
         Self::new()
     }
 }
 
-impl MerkleStore {
+impl<T: KvMap<RpoDigest, Node>> MerkleStore<T> {
     // CONSTRUCTORS
     // --------------------------------------------------------------------------------------------
 
     /// Creates an empty `MerkleStore` instance.
-    pub fn new() -> MerkleStore {
+    pub fn new() -> MerkleStore<T> {
         // pre-populate the store with the empty hashes
-        let subtrees = EmptySubtreeRoots::empty_hashes(255);
-        let nodes = subtrees
-            .iter()
-            .rev()
-            .copied()
-            .zip(subtrees.iter().rev().skip(1).copied())
-            .map(|(child, parent)| {
-                (
-                    parent,
-                    Node {
-                        left: child,
-                        right: child,
-                    },
-                )
-            })
-            .collect();
-
+        let nodes = empty_hashes().into_iter().collect();
         MerkleStore { nodes }
     }
 
@@ -126,10 +119,10 @@ impl MerkleStore {
     /// Returns the node at `index` rooted on the tree `root`.
     ///
     /// # Errors
-    ///
     /// This method can return the following errors:
     /// - `RootNotInStore` if the `root` is not present in the store.
-    /// - `NodeNotInStore` if a node needed to traverse from `root` to `index` is not present in the store.
+    /// - `NodeNotInStore` if a node needed to traverse from `root` to `index` is not present in
+    ///   the store.
     pub fn get_node(&self, root: RpoDigest, index: NodeIndex) -> Result<RpoDigest, MerkleError> {
         let mut hash = root;
 
@@ -153,7 +146,8 @@ impl MerkleStore {
     /// # Errors
     /// This method can return the following errors:
     /// - `RootNotInStore` if the `root` is not present in the store.
-    /// - `NodeNotInStore` if a node needed to traverse from `root` to `index` is not present in the store.
+    /// - `NodeNotInStore` if a node needed to traverse from `root` to `index` is not present in
+    ///   the store.
     pub fn get_path(&self, root: RpoDigest, index: NodeIndex) -> Result<ValuePath, MerkleError> {
         let mut hash = root;
         let mut path = Vec::with_capacity(index.depth().into());
@@ -197,7 +191,7 @@ impl MerkleStore {
     /// - The path from the root continues to a depth greater than `tree_depth`.
     /// - The provided `tree_depth` is greater than `64.
     /// - The provided `index` is not valid for a depth equivalent to `tree_depth`. For more
-    /// information, check [NodeIndex::new].
+    ///   information, check [NodeIndex::new].
     pub fn get_leaf_depth(
         &self,
         root: RpoDigest,
@@ -261,7 +255,7 @@ impl MerkleStore {
     /// nodes which are descendants of the specified roots.
     ///
     /// The roots for which no descendants exist in this Merkle store are ignored.
-    pub fn subset<I, R>(&self, roots: I) -> MerkleStore
+    pub fn subset<I, R>(&self, roots: I) -> MerkleStore<T>
     where
         I: Iterator<Item = R>,
         R: Borrow<RpoDigest>,
@@ -286,23 +280,6 @@ impl MerkleStore {
     // STATE MUTATORS
     // --------------------------------------------------------------------------------------------
 
-    /// Adds a sequence of nodes yielded by the provided iterator into the store.
-    pub fn extend<I>(&mut self, iter: I) -> &mut MerkleStore
-    where
-        I: Iterator<Item = InnerNodeInfo>,
-    {
-        for node in iter {
-            let value: RpoDigest = node.value;
-            let left: RpoDigest = node.left;
-            let right: RpoDigest = node.right;
-
-            debug_assert_eq!(Rpo256::merge(&[left, right]), value);
-            self.nodes.insert(value, Node { left, right });
-        }
-
-        self
-    }
-
     /// Adds all the nodes of a Merkle path represented by `path`, opening to `node`. Returns the
     /// new root.
     ///
@@ -360,10 +337,10 @@ impl MerkleStore {
     /// Sets a node to `value`.
     ///
     /// # Errors
-    ///
     /// This method can return the following errors:
     /// - `RootNotInStore` if the `root` is not present in the store.
-    /// - `NodeNotInStore` if a node needed to traverse from `root` to `index` is not present in the store.
+    /// - `NodeNotInStore` if a node needed to traverse from `root` to `index` is not present in
+    ///   the store.
     pub fn set_node(
         &mut self,
         mut root: RpoDigest,
@@ -401,6 +378,14 @@ impl MerkleStore {
         Ok(parent)
     }
 
+    // DESTRUCTURING
+    // --------------------------------------------------------------------------------------------
+
+    /// Returns the inner storage of this MerkleStore while consuming `self`.
+    pub fn into_inner(self) -> T {
+        self.nodes
+    }
+
     // HELPER METHODS
     // --------------------------------------------------------------------------------------------
 
@@ -423,52 +408,69 @@ impl MerkleStore {
 // CONVERSIONS
 // ================================================================================================
 
-impl From<&MerkleTree> for MerkleStore {
+impl<T: KvMap<RpoDigest, Node>> From<&MerkleTree> for MerkleStore<T> {
     fn from(value: &MerkleTree) -> Self {
-        let mut store = MerkleStore::new();
-        store.extend(value.inner_nodes());
-        store
+        let nodes = combine_nodes_with_empty_hashes(value.inner_nodes()).collect();
+        Self { nodes }
     }
 }
 
-impl From<&SimpleSmt> for MerkleStore {
+impl<T: KvMap<RpoDigest, Node>> From<&SimpleSmt> for MerkleStore<T> {
     fn from(value: &SimpleSmt) -> Self {
-        let mut store = MerkleStore::new();
-        store.extend(value.inner_nodes());
-        store
+        let nodes = combine_nodes_with_empty_hashes(value.inner_nodes()).collect();
+        Self { nodes }
     }
 }
 
-impl From<&Mmr> for MerkleStore {
+impl<T: KvMap<RpoDigest, Node>> From<&Mmr> for MerkleStore<T> {
     fn from(value: &Mmr) -> Self {
-        let mut store = MerkleStore::new();
-        store.extend(value.inner_nodes());
-        store
+        let nodes = combine_nodes_with_empty_hashes(value.inner_nodes()).collect();
+        Self { nodes }
     }
 }
 
-impl From<&TieredSmt> for MerkleStore {
+impl<T: KvMap<RpoDigest, Node>> From<&TieredSmt> for MerkleStore<T> {
     fn from(value: &TieredSmt) -> Self {
-        let mut store = MerkleStore::new();
-        store.extend(value.inner_nodes());
-        store
+        let nodes = combine_nodes_with_empty_hashes(value.inner_nodes()).collect();
+        Self { nodes }
     }
 }
 
-impl FromIterator<InnerNodeInfo> for MerkleStore {
-    fn from_iter<T: IntoIterator<Item = InnerNodeInfo>>(iter: T) -> Self {
-        let mut store = MerkleStore::new();
-        store.extend(iter.into_iter());
-        store
+impl<T: KvMap<RpoDigest, Node>> From<T> for MerkleStore<T> {
+    fn from(values: T) -> Self {
+        let nodes = values.into_iter().chain(empty_hashes().into_iter()).collect();
+        Self { nodes }
+    }
+}
+
+impl<T: KvMap<RpoDigest, Node>> FromIterator<InnerNodeInfo> for MerkleStore<T> {
+    fn from_iter<I: IntoIterator<Item = InnerNodeInfo>>(iter: I) -> Self {
+        let nodes = combine_nodes_with_empty_hashes(iter.into_iter()).collect();
+        Self { nodes }
+    }
+}
+
+impl<T: KvMap<RpoDigest, Node>> FromIterator<(RpoDigest, Node)> for MerkleStore<T> {
+    fn from_iter<I: IntoIterator<Item = (RpoDigest, Node)>>(iter: I) -> Self {
+        let nodes = iter.into_iter().chain(empty_hashes().into_iter()).collect();
+        Self { nodes }
     }
 }
 
 // ITERATORS
 // ================================================================================================
 
-impl Extend<InnerNodeInfo> for MerkleStore {
-    fn extend<T: IntoIterator<Item = InnerNodeInfo>>(&mut self, iter: T) {
-        self.extend(iter.into_iter());
+impl<T: KvMap<RpoDigest, Node>> Extend<InnerNodeInfo> for MerkleStore<T> {
+    fn extend<I: IntoIterator<Item = InnerNodeInfo>>(&mut self, iter: I) {
+        self.nodes.extend(iter.into_iter().map(|info| {
+            (
+                info.value,
+                Node {
+                    left: info.left,
+                    right: info.right,
+                },
+            )
+        }));
     }
 }
 
@@ -490,7 +492,7 @@ impl Deserializable for Node {
     }
 }
 
-impl Serializable for MerkleStore {
+impl<T: KvMap<RpoDigest, Node>> Serializable for MerkleStore<T> {
     fn write_into<W: ByteWriter>(&self, target: &mut W) {
         target.write_u64(self.nodes.len() as u64);
 
@@ -501,17 +503,55 @@ impl Serializable for MerkleStore {
     }
 }
 
-impl Deserializable for MerkleStore {
+impl<T: KvMap<RpoDigest, Node>> Deserializable for MerkleStore<T> {
     fn read_from<R: ByteReader>(source: &mut R) -> Result<Self, DeserializationError> {
         let len = source.read_u64()?;
-        let mut nodes: BTreeMap<RpoDigest, Node> = BTreeMap::new();
+        let mut nodes: Vec<(RpoDigest, Node)> = Vec::with_capacity(len as usize);
 
         for _ in 0..len {
             let key = RpoDigest::read_from(source)?;
             let value = Node::read_from(source)?;
-            nodes.insert(key, value);
+            nodes.push((key, value));
         }
 
-        Ok(MerkleStore { nodes })
+        Ok(nodes.into_iter().collect())
     }
 }
+
+// HELPER FUNCTIONS
+// ================================================================================================
+
+/// Creates empty hashes for all the subtrees of a tree with a max depth of 255.
+fn empty_hashes() -> impl IntoIterator<Item = (RpoDigest, Node)> {
+    let subtrees = EmptySubtreeRoots::empty_hashes(255);
+    subtrees.iter().rev().copied().zip(subtrees.iter().rev().skip(1).copied()).map(
+        |(child, parent)| {
+            (
+                parent,
+                Node {
+                    left: child,
+                    right: child,
+                },
+            )
+        },
+    )
+}
+
+/// Consumes an iterator of [InnerNodeInfo] and returns an iterator of `(value, node)` tuples
+/// which includes the nodes associate with roots of empty subtrees up to a depth of 255.
+fn combine_nodes_with_empty_hashes(
+    nodes: impl IntoIterator<Item = InnerNodeInfo>,
+) -> impl Iterator<Item = (RpoDigest, Node)> {
+    nodes
+        .into_iter()
+        .map(|info| {
+            (
+                info.value,
+                Node {
+                    left: info.left,
+                    right: info.right,
+                },
+            )
+        })
+        .chain(empty_hashes().into_iter())
+}

src/merkle/store/tests.rs

@@ -1,13 +1,16 @@
 use super::{
-    Deserializable, EmptySubtreeRoots, MerkleError, MerklePath, MerkleStore, NodeIndex, RpoDigest,
-    Serializable,
+    DefaultMerkleStore as MerkleStore, EmptySubtreeRoots, MerkleError, MerklePath, NodeIndex,
+    RecordingMerkleStore, RpoDigest,
 };
 use crate::{
     hash::rpo::Rpo256,
     merkle::{digests_to_words, int_to_leaf, int_to_node, MerklePathSet, MerkleTree, SimpleSmt},
-    Felt, Word, WORD_SIZE,
+    Felt, Word, ONE, WORD_SIZE, ZERO,
 };
 
+#[cfg(feature = "std")]
+use super::{Deserializable, Serializable};
+
 #[cfg(feature = "std")]
 use std::error::Error;
 
@@ -17,6 +20,7 @@ use std::error::Error;
 const KEYS4: [u64; 4] = [0, 1, 2, 3];
 const VALUES4: [RpoDigest; 4] = [int_to_node(1), int_to_node(2), int_to_node(3), int_to_node(4)];
 
+const KEYS8: [u64; 8] = [0, 1, 2, 3, 4, 5, 6, 7];
 const VALUES8: [RpoDigest; 8] = [
     int_to_node(1),
     int_to_node(2),
@@ -810,3 +814,54 @@ fn test_serialization() -> Result<(), Box<dyn Error>> {
     assert_eq!(store, decoded);
     Ok(())
 }
+
+// MERKLE RECORDER
+// ================================================================================================
+#[test]
+fn test_recorder() {
+    // instantiate recorder from MerkleTree and SimpleSmt
+    let mtree = MerkleTree::new(digests_to_words(&VALUES4)).unwrap();
+    let smtree = SimpleSmt::with_leaves(
+        64,
+        KEYS8.into_iter().zip(VALUES8.into_iter().map(|x| x.into()).rev()),
+    )
+    .unwrap();
+
+    let mut recorder: RecordingMerkleStore =
+        mtree.inner_nodes().chain(smtree.inner_nodes()).collect();
+
+    // get nodes from both trees and make sure they are correct
+    let index_0 = NodeIndex::new(mtree.depth(), 0).unwrap();
+    let node = recorder.get_node(mtree.root(), index_0).unwrap();
+    assert_eq!(node, mtree.get_node(index_0).unwrap());
+
+    let index_1 = NodeIndex::new(smtree.depth(), 1).unwrap();
+    let node = recorder.get_node(smtree.root(), index_1).unwrap();
+    assert_eq!(node, smtree.get_node(index_1).unwrap());
+
+    // insert a value and assert that when we request it next time it is accurate
+    let new_value = [ZERO, ZERO, ONE, ONE].into();
+    let index_2 = NodeIndex::new(smtree.depth(), 2).unwrap();
+    let root = recorder.set_node(smtree.root(), index_2, new_value).unwrap().root;
+    assert_eq!(recorder.get_node(root, index_2).unwrap(), new_value);
+
+    // construct the proof
+    let rec_map = recorder.into_inner();
+    let proof = rec_map.into_proof();
+    let merkle_store: MerkleStore = proof.into();
+
+    // make sure the proof contains all nodes from both trees
+    let node = merkle_store.get_node(mtree.root(), index_0).unwrap();
+    assert_eq!(node, mtree.get_node(index_0).unwrap());
+
+    let node = merkle_store.get_node(smtree.root(), index_1).unwrap();
+    assert_eq!(node, smtree.get_node(index_1).unwrap());
+
+    let node = merkle_store.get_node(smtree.root(), index_2).unwrap();
+    assert_eq!(node, smtree.get_leaf(index_2.value()).unwrap().into());
+
+    // assert that is doesnt contain nodes that were not recorded
+    let not_recorded_index = NodeIndex::new(smtree.depth(), 4).unwrap();
+    assert!(merkle_store.get_node(smtree.root(), not_recorded_index).is_err());
+    assert!(smtree.get_node(not_recorded_index).is_ok());
+}

src/utils/kv_map.rs

@@ -0,0 +1,324 @@
+use core::cell::RefCell;
+use winter_utils::{
+    collections::{btree_map::IntoIter, BTreeMap, BTreeSet},
+    Box,
+};
+
+// KEY-VALUE MAP TRAIT
+// ================================================================================================
+
+/// A trait that defines the interface for a key-value map.
+pub trait KvMap<K: Ord + Clone, V: Clone>:
+    Extend<(K, V)> + FromIterator<(K, V)> + IntoIterator<Item = (K, V)>
+{
+    fn get(&self, key: &K) -> Option<&V>;
+    fn contains_key(&self, key: &K) -> bool;
+    fn len(&self) -> usize;
+    fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+    fn insert(&mut self, key: K, value: V) -> Option<V>;
+
+    fn iter(&self) -> Box<dyn Iterator<Item = (&K, &V)> + '_>;
+}
+
+// BTREE MAP `KvMap` IMPLEMENTATION
+// ================================================================================================
+
+impl<K: Ord + Clone, V: Clone> KvMap<K, V> for BTreeMap<K, V> {
+    fn get(&self, key: &K) -> Option<&V> {
+        self.get(key)
+    }
+
+    fn contains_key(&self, key: &K) -> bool {
+        self.contains_key(key)
+    }
+
+    fn len(&self) -> usize {
+        self.len()
+    }
+
+    fn insert(&mut self, key: K, value: V) -> Option<V> {
+        self.insert(key, value)
+    }
+
+    fn iter(&self) -> Box<dyn Iterator<Item = (&K, &V)> + '_> {
+        Box::new(self.iter())
+    }
+}
+
+// RECORDING MAP
+// ================================================================================================
+
+/// A [RecordingMap] that records read requests to the underlying key-value map.
+///
+/// The data recorder is used to generate a proof for read requests.
+///
+/// The [RecordingMap] is composed of three parts:
+/// - `data`: which contains the current set of key-value pairs in the map.
+/// - `updates`: which tracks keys for which values have been since the map was instantiated.
+///   updates include both insertions and updates of values under existing keys.
+/// - `trace`: which contains the key-value pairs from the original data which have been accesses
+///   since the map was instantiated.
+#[derive(Debug, Default, Clone, Eq, PartialEq)]
+pub struct RecordingMap<K, V> {
+    data: BTreeMap<K, V>,
+    updates: BTreeSet<K>,
+    trace: RefCell<BTreeMap<K, V>>,
+}
+
+impl<K: Ord + Clone, V: Clone> RecordingMap<K, V> {
+    // CONSTRUCTOR
+    // --------------------------------------------------------------------------------------------
+    /// Returns a new [RecordingMap] instance initialized with the provided key-value pairs.
+    /// ([BTreeMap]).
+    pub fn new(init: impl IntoIterator<Item = (K, V)>) -> Self {
+        RecordingMap {
+            data: init.into_iter().collect(),
+            updates: BTreeSet::new(),
+            trace: RefCell::new(BTreeMap::new()),
+        }
+    }
+
+    // FINALIZER
+    // --------------------------------------------------------------------------------------------
+
+    /// Consumes the [RecordingMap] and returns a [BTreeMap] containing the key-value pairs from
+    /// the initial data set that were read during recording.
+    pub fn into_proof(self) -> BTreeMap<K, V> {
+        self.trace.take()
+    }
+
+    // TEST HELPERS
+    // --------------------------------------------------------------------------------------------
+
+    #[cfg(test)]
+    pub fn trace_len(&self) -> usize {
+        self.trace.borrow().len()
+    }
+
+    #[cfg(test)]
+    pub fn updates_len(&self) -> usize {
+        self.updates.len()
+    }
+}
+
+impl<K: Ord + Clone, V: Clone> KvMap<K, V> for RecordingMap<K, V> {
+    // PUBLIC ACCESSORS
+    // --------------------------------------------------------------------------------------------
+
+    /// Returns a reference to the value associated with the given key if the value exists.
+    ///
+    /// If the key is part of the initial data set, the key access is recorded.
+    fn get(&self, key: &K) -> Option<&V> {
+        self.data.get(key).map(|value| {
+            if !self.updates.contains(key) {
+                self.trace.borrow_mut().insert(key.clone(), value.clone());
+            }
+            value
+        })
+    }
+
+    /// Returns a boolean to indicate whether the given key exists in the data set.
+    ///
+    /// If the key is part of the initial data set, the key access is recorded.
+    fn contains_key(&self, key: &K) -> bool {
+        self.get(key).is_some()
+    }
+
+    /// Returns the number of key-value pairs in the data set.
+    fn len(&self) -> usize {
+        self.data.len()
+    }
+
+    // MUTATORS
+    // --------------------------------------------------------------------------------------------
+
+    /// Inserts a key-value pair into the data set.
+    ///
+    /// If the key already exists in the data set, the value is updated and the old value is
+    /// returned.
+    fn insert(&mut self, key: K, value: V) -> Option<V> {
+        let new_update = self.updates.insert(key.clone());
+        self.data.insert(key.clone(), value).map(|old_value| {
+            if new_update {
+                self.trace.borrow_mut().insert(key, old_value.clone());
+            }
+            old_value
+        })
+    }
+
+    // ITERATION
+    // --------------------------------------------------------------------------------------------
+
+    /// Returns an iterator over the key-value pairs in the data set.
+    fn iter(&self) -> Box<dyn Iterator<Item = (&K, &V)> + '_> {
+        Box::new(self.data.iter())
+    }
+}
+
+impl<K: Clone + Ord, V: Clone> Extend<(K, V)> for RecordingMap<K, V> {
+    fn extend<T: IntoIterator<Item = (K, V)>>(&mut self, iter: T) {
+        iter.into_iter().for_each(move |(k, v)| {
+            self.insert(k, v);
+        });
+    }
+}
+
+impl<K: Clone + Ord, V: Clone> FromIterator<(K, V)> for RecordingMap<K, V> {
+    fn from_iter<T: IntoIterator<Item = (K, V)>>(iter: T) -> Self {
+        Self::new(iter)
+    }
+}
+
+impl<K: Clone + Ord, V: Clone> IntoIterator for RecordingMap<K, V> {
+    type Item = (K, V);
+    type IntoIter = IntoIter<K, V>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.data.into_iter()
+    }
+}
+
+// TESTS
+// ================================================================================================
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const ITEMS: [(u64, u64); 5] = [(0, 0), (1, 1), (2, 2), (3, 3), (4, 4)];
+
+    #[test]
+    fn test_get_item() {
+        // instantiate a recording map
+        let map = RecordingMap::new(ITEMS.to_vec());
+
+        // get a few items
+        let get_items = [0, 1, 2];
+        for key in get_items.iter() {
+            map.get(key);
+        }
+
+        // convert the map into a proof
+        let proof = map.into_proof();
+
+        // check that the proof contains the expected values
+        for (key, value) in ITEMS.iter() {
+            match get_items.contains(key) {
+                true => assert_eq!(proof.get(key), Some(value)),
+                false => assert_eq!(proof.get(key), None),
+            }
+        }
+    }
+
+    #[test]
+    fn test_contains_key() {
+        // instantiate a recording map
+        let map = RecordingMap::new(ITEMS.to_vec());
+
+        // check if the map contains a few items
+        let get_items = [0, 1, 2];
+        for key in get_items.iter() {
+            map.contains_key(key);
+        }
+
+        // convert the map into a proof
+        let proof = map.into_proof();
+
+        // check that the proof contains the expected values
+        for (key, _) in ITEMS.iter() {
+            match get_items.contains(key) {
+                true => assert_eq!(proof.contains_key(key), true),
+                false => assert_eq!(proof.contains_key(key), false),
+            }
+        }
+    }
+
+    #[test]
+    fn test_len() {
+        // instantiate a recording map
+        let mut map = RecordingMap::new(ITEMS.to_vec());
+        // length of the map should be equal to the number of items
+        assert_eq!(map.len(), ITEMS.len());
+
+        // inserting entry with key that already exists should not change the length, but it does
+        // add entries to the trace and update sets
+        map.insert(4, 5);
+        assert_eq!(map.len(), ITEMS.len());
+        assert_eq!(map.trace_len(), 1);
+        assert_eq!(map.updates_len(), 1);
+
+        // inserting entry with new key should increase the length; it should also record the key
+        // as an updated key, but the trace length does not change since old values were not touched
+        map.insert(5, 5);
+        assert_eq!(map.len(), ITEMS.len() + 1);
+        assert_eq!(map.trace_len(), 1);
+        assert_eq!(map.updates_len(), 2);
+
+        // get some items so that they are saved in the trace; this should record original items
+        // in the trace, but should not affect the set of updates
+        let get_items = [0, 1, 2];
+        for key in get_items.iter() {
+            map.contains_key(key);
+        }
+        assert_eq!(map.trace_len(), 4);
+        assert_eq!(map.updates_len(), 2);
+
+        // read the same items again, this should not have any effect on either length, trace, or
+        // the set of updates
+        let get_items = [0, 1, 2];
+        for key in get_items.iter() {
+            map.contains_key(key);
+        }
+        assert_eq!(map.trace_len(), 4);
+        assert_eq!(map.updates_len(), 2);
+
+        // read a newly inserted item; this should not affect either length, trace, or the set of
+        // updates
+        let _val = map.get(&5).unwrap();
+        assert_eq!(map.trace_len(), 4);
+        assert_eq!(map.updates_len(), 2);
+
+        // update a newly inserted item; this should not affect either length, trace, or the set
+        // of updates
+        map.insert(5, 11);
+        assert_eq!(map.trace_len(), 4);
+        assert_eq!(map.updates_len(), 2);
+
+        // Note: The length reported by the proof will be different to the length originally
+        // reported by the map.
+        let proof = map.into_proof();
+
+        // length of the proof should be equal to get_items + 1. The extra item is the original
+        // value at key = 4u64
+        assert_eq!(proof.len(), get_items.len() + 1);
+    }
+
+    #[test]
+    fn test_iter() {
+        let mut map = RecordingMap::new(ITEMS.to_vec());
+        assert!(map.iter().all(|(x, y)| ITEMS.contains(&(*x, *y))));
+
+        // when inserting entry with key that already exists the iterator should return the new value
+        let new_value = 5;
+        map.insert(4, new_value);
+        assert_eq!(map.iter().count(), ITEMS.len());
+        assert!(map.iter().all(|(x, y)| if x == &4 {
+            y == &new_value
+        } else {
+            ITEMS.contains(&(*x, *y))
+        }));
+    }
+
+    #[test]
+    fn test_is_empty() {
+        // instantiate an empty recording map
+        let empty_map: RecordingMap<u64, u64> = RecordingMap::default();
+        assert!(empty_map.is_empty());
+
+        // instantiate a non-empty recording map
+        let map = RecordingMap::new(ITEMS.to_vec());
+        assert!(!map.is_empty());
+    }
+}

src/utils/mod.rs

@@ -1,5 +1,4 @@
-use super::Word;
-use crate::utils::string::String;
+use super::{utils::string::String, Word};
 use core::fmt::{self, Write};
 
 #[cfg(not(feature = "std"))]
@@ -8,13 +7,23 @@ pub use alloc::format;
 #[cfg(feature = "std")]
 pub use std::format;
 
+mod kv_map;
+
 // RE-EXPORTS
 // ================================================================================================
 pub use winter_utils::{
-    collections, string, uninit_vector, ByteReader, ByteWriter, Deserializable,
-    DeserializationError, Serializable, SliceReader,
+    string, uninit_vector, Box, ByteReader, ByteWriter, Deserializable, DeserializationError,
+    Serializable, SliceReader,
 };
 
+pub mod collections {
+    pub use super::kv_map::*;
+    pub use winter_utils::collections::*;
+}
+
+// UTILITY FUNCTIONS
+// ================================================================================================
+
 /// Converts a [Word] into hex.
 pub fn word_to_hex(w: &Word) -> Result<String, fmt::Error> {
     let mut s = String::new();