add MastNodeId::TryFrom<u32>

core/src/mast/mod.rs

@@ -24,9 +24,22 @@ pub trait MerkleTreeNode {
 /// Note that the [`MastForest`] does *not* ensure that equal [`MastNode`]s have equal
 /// [`MastNodeId`] handles. Hence, [`MastNodeId`] equality must not be used to test for equality of
 /// the underlying [`MastNode`].
+///
+/// [`MastNodeId`] u32 value must be less than 2^30.
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct MastNodeId(u32);
 
+impl TryFrom<u32> for MastNodeId {
+    type Error = &'static str;
+
+    fn try_from(id: u32) -> Result<Self, Self::Error> {
+        if id > u32::MAX >> 2 {
+            return Err("MastNodeId must be less than 2^30");
+        }
+        Ok(Self(id))
+    }
+}
+
 impl fmt::Display for MastNodeId {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(f, "MastNodeId({})", self.0)
@@ -62,13 +75,13 @@ impl MastForest {
     /// Adds a node to the forest, and returns the associated [`MastNodeId`].
     ///
     /// Adding two duplicate nodes will result in two distinct returned [`MastNodeId`]s.
+    ///
+    /// # Panics
+    ///
+    /// This function will panic if the length of the provided node is greater than 2^30.
     pub fn add_node(&mut self, node: MastNode) -> MastNodeId {
-        let new_node_id = MastNodeId(
-            self.nodes
-                .len()
-                .try_into()
-                .expect("invalid node id: exceeded maximum number of nodes in a single forest"),
-        );
+        let new_node_id = MastNodeId::try_from(self.nodes.len() as u32)
+            .expect("invalid node id: exceeded maximum number of nodes in a single forest");
 
         self.nodes.push(node);
 
@@ -132,3 +145,26 @@ impl Index<MastNodeId> for MastForest {
         &self.nodes[idx]
     }
 }
+
+#[cfg(test)]
+mod test {
+    #[test]
+    fn test_mast_node_id_try_from_u32() {
+        use super::MastNodeId;
+        use std::convert::TryFrom;
+
+        let tests = vec![
+            (u32::MAX, false),
+            (u32::MAX >> 1, false),
+            ((u32::MAX >> 2) + 1, false),
+            (u32::MAX >> 2, true),
+            (1_073_741_824, false),
+            (1_073_741_823, true),
+            (0, true),
+        ];
+        for (id, expected) in tests {
+            let result = MastNodeId::try_from(id).is_ok();
+            assert_eq!(result, expected, "id: {}", id);
+        }
+    }
+}