Add RuntimeVariableList and RuntimeFixedVector (#67)

* Add runtime_types

* Feature gate context_deserialize impl

* Fix feature deps

---------

Co-authored-by: Michael Sproul <michaelsproul@users.noreply.github.com>

Author: macladson

Cargo.toml

@@ -13,6 +13,7 @@ categories = ["cryptography::cryptocurrencies"]
 [features]
 default = ["ring"]
 ring = ["tree_hash/ring"]
+runtime_types = ["dep:educe"]
 context_deserialize = ["dep:context_deserialize"]
 
 [dependencies]
@@ -23,9 +24,12 @@ serde = "1.0.0"
 serde_derive = "1.0.0"
 typenum = "1.12.0"
 smallvec = "1.8.0"
-arbitrary = { version = "1.0", features = ["derive"], optional = true }
 itertools = "0.14.0"
+
+# Optional dependencies
+arbitrary = { version = "1.0", features = ["derive"], optional = true }
 context_deserialize = { version = "0.2", optional = true }
+educe = { version = "0.6", optional = true }
 
 [dev-dependencies]
 criterion = "0.7.0"

src/lib.rs

@@ -37,9 +37,13 @@
 //!
 //! ```
 
+pub mod serde_utils;
+pub mod length {
+    pub use ssz::{Fixed, Variable};
+}
+
 #[macro_use]
 mod fixed_vector;
-pub mod serde_utils;
 mod tree_hash;
 mod variable_list;
 
@@ -51,9 +55,11 @@ pub use ssz::{BitList, BitVector, Bitfield};
 pub use typenum;
 pub use variable_list::VariableList;
 
-pub mod length {
-    pub use ssz::{Fixed, Variable};
-}
+#[cfg(feature = "runtime_types")]
+mod runtime_types;
+
+#[cfg(feature = "runtime_types")]
+pub use runtime_types::{RuntimeFixedVector, RuntimeVariableList};
 
 /// Returned when an item encounters an error.
 #[derive(PartialEq, Debug, Clone)]

src/runtime_types/context_deserialize.rs

@@ -0,0 +1,24 @@
+use crate::RuntimeVariableList;
+use context_deserialize::ContextDeserialize;
+use serde::{de::Error as DeError, Deserializer};
+
+impl<'de, C, T> ContextDeserialize<'de, (C, usize)> for RuntimeVariableList<T>
+where
+    T: ContextDeserialize<'de, C>,
+    C: Clone,
+{
+    fn context_deserialize<D>(deserializer: D, context: (C, usize)) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        // First parse out a Vec<C> using the Vec<C> impl you already have.
+        let vec: Vec<T> = Vec::context_deserialize(deserializer, context.0)?;
+        let vec_len = vec.len();
+        RuntimeVariableList::new(vec, context.1).map_err(|e| {
+            DeError::custom(format!(
+                "RuntimeVariableList length {} exceeds max_len {}: {e:?}",
+                vec_len, context.1,
+            ))
+        })
+    }
+}

src/runtime_types/mod.rs

@@ -0,0 +1,7 @@
+#[cfg(feature = "context_deserialize")]
+mod context_deserialize;
+mod runtime_fixed_vector;
+mod runtime_variable_list;
+
+pub use runtime_fixed_vector::RuntimeFixedVector;
+pub use runtime_variable_list::RuntimeVariableList;

src/runtime_types/runtime_fixed_vector.rs

@@ -0,0 +1,90 @@
+//! Emulates a fixed size array but with the length set at runtime.
+//!
+//! The length of the list cannot be changed once it is set.
+
+use std::fmt;
+use std::fmt::Debug;
+
+#[derive(Clone)]
+pub struct RuntimeFixedVector<T> {
+    vec: Vec<T>,
+    len: usize,
+}
+
+impl<T: Debug> Debug for RuntimeFixedVector<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{:?} (len={})", self.vec, self.len)
+    }
+}
+
+impl<T: Clone + Default> RuntimeFixedVector<T> {
+    pub fn new(vec: Vec<T>) -> Self {
+        let len = vec.len();
+        Self { vec, len }
+    }
+
+    pub fn to_vec(&self) -> Vec<T> {
+        self.vec.clone()
+    }
+
+    pub fn as_slice(&self) -> &[T] {
+        self.vec.as_slice()
+    }
+
+    #[allow(clippy::len_without_is_empty)]
+    pub fn len(&self) -> usize {
+        self.len
+    }
+
+    pub fn into_vec(self) -> Vec<T> {
+        self.vec
+    }
+
+    pub fn default(max_len: usize) -> Self {
+        Self {
+            vec: vec![T::default(); max_len],
+            len: max_len,
+        }
+    }
+
+    pub fn take(&mut self) -> Self {
+        let new = std::mem::take(&mut self.vec);
+        *self = Self::new(vec![T::default(); self.len]);
+        Self {
+            vec: new,
+            len: self.len,
+        }
+    }
+}
+
+impl<T> std::ops::Deref for RuntimeFixedVector<T> {
+    type Target = [T];
+
+    fn deref(&self) -> &[T] {
+        &self.vec[..]
+    }
+}
+
+impl<T> std::ops::DerefMut for RuntimeFixedVector<T> {
+    fn deref_mut(&mut self) -> &mut [T] {
+        &mut self.vec[..]
+    }
+}
+
+impl<T> IntoIterator for RuntimeFixedVector<T> {
+    type Item = T;
+    type IntoIter = std::vec::IntoIter<T>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.vec.into_iter()
+    }
+}
+
+impl<'a, T> IntoIterator for &'a RuntimeFixedVector<T> {
+    type Item = &'a T;
+    type IntoIter = std::slice::Iter<'a, T>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.vec.iter()
+    }
+}