Add optional length limit to ProgressiveVariableList

src/context_deserialize.rs

@@ -17,16 +17,45 @@ where
     }
 }
 
-impl<'de, C, T> ContextDeserialize<'de, C> for ProgressiveVariableList<T>
+impl<'de, C, T, N> ContextDeserialize<'de, C> for ProgressiveVariableList<T, N>
 where
     T: ContextDeserialize<'de, C>,
+    N: Unsigned,
     C: Clone,
 {
     fn context_deserialize<D>(deserializer: D, context: C) -> Result<Self, D::Error>
     where
         D: Deserializer<'de>,
     {
         let vec = Vec::<T>::context_deserialize(deserializer, context)?;
-        Ok(ProgressiveVariableList::new(vec))
+        ProgressiveVariableList::new(vec).map_err(D::Error::custom)
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use crate::ProgressiveVariableList;
+    use context_deserialize::ContextDeserialize;
+    use typenum::U4;
+
+    fn context_deserialize_u64s(json: &str) -> Result<ProgressiveVariableList<u64, U4>, String> {
+        let mut deserializer = serde_json::Deserializer::from_str(json);
+        ProgressiveVariableList::context_deserialize(&mut deserializer, ())
+            .map_err(|e| e.to_string())
+    }
+
+    #[test]
+    fn context_deserialize_accepts_list_at_limit() {
+        let list = context_deserialize_u64s("[1,2,3,4]").unwrap();
+        assert_eq!(&list[..], &[1, 2, 3, 4]);
+    }
+
+    #[test]
+    fn context_deserialize_rejects_list_past_limit() {
+        let err = context_deserialize_u64s("[1,2,3,4,5]").unwrap_err();
+        assert!(
+            err.contains("Index out of bounds: index 5, length 4"),
+            "{err}"
+        );
     }
 }