Optionally implement Zeroize on ArrayVec/ArrayString

Cargo.toml

@@ -19,6 +19,11 @@ version = "1.0"
 optional = true
 default-features = false
 
+[dependencies.zeroize]
+version = "1.4"
+optional = true
+default-features = false
+
 [dev-dependencies.serde_test]
 version = "1.0"
 

src/array_string.rs

@@ -647,3 +647,27 @@ impl<'a, const CAP: usize> TryFrom<fmt::Arguments<'a>> for ArrayString<CAP>
         Ok(v)
     }
 }
+
+#[cfg(feature = "zeroize")]
+/// "Best efforts" zeroing of the `ArrayString`'s buffer when the `zeroize` feature is enabled.
+///
+/// The length is set to 0, and the buffer is dropped and zeroized.
+/// Cannot ensure that previous moves of the `ArrayString` did not leave values on the stack.
+///
+/// ```
+/// use arrayvec::ArrayString;
+/// use zeroize::Zeroize;
+/// let mut string = ArrayString::<6>::from("foobar").unwrap();
+/// string.zeroize();
+/// assert_eq!(string.len(), 0);
+/// unsafe { string.set_len(string.capacity()) };
+/// assert_eq!(&*string, "\0\0\0\0\0\0");
+/// ```
+impl<const CAP: usize> zeroize::Zeroize for ArrayString<CAP> {
+    fn zeroize(&mut self) {
+        // There are no elements to drop
+        self.clear();
+        // Zeroize the backing array.
+        self.xs.zeroize();
+    }
+}

src/arrayvec.rs

@@ -848,6 +848,32 @@ impl<T, const CAP: usize> IntoIterator for ArrayVec<T, CAP> {
 }
 
 
+#[cfg(feature = "zeroize")]
+/// "Best efforts" zeroing of the `ArrayVec`'s buffer when the `zeroize` feature is enabled.
+///
+/// The length is set to 0, and the buffer is dropped and zeroized.
+/// Cannot ensure that previous moves of the `ArrayVec` did not leave values on the stack.
+///
+/// ```
+/// use arrayvec::ArrayVec;
+/// use zeroize::Zeroize;
+/// let mut array = ArrayVec::from([1, 2, 3]);
+/// array.zeroize();
+/// assert_eq!(array.len(), 0);
+/// let data = unsafe { core::slice::from_raw_parts(array.as_ptr(), array.capacity()) };
+/// assert_eq!(data, [0, 0, 0]);
+/// ```
+impl<Z: zeroize::Zeroize, const CAP: usize> zeroize::Zeroize for ArrayVec<Z, CAP> {
+    fn zeroize(&mut self) {
+        // Zeroize all the contained elements.
+        self.iter_mut().zeroize();
+        // Drop all the elements and set the length to 0.
+        self.clear();
+        // Zeroize the backing array.
+        self.xs.zeroize();
+    }
+}
+
 /// By-value iterator for `ArrayVec`.
 pub struct IntoIter<T, const CAP: usize> {
     index: usize,