Implement string comparison

src/lib.rs

@@ -341,6 +341,20 @@ impl<T: ConstantTimeEq> ConstantTimeEq for [T] {
     }
 }
 
+impl ConstantTimeEq for str {
+    /// Check whether two strings are equal.
+    ///
+    /// # Note
+    ///
+    /// This function short-circuits if the lengths of the input strings
+    /// are different.  Otherwise, it should execute in time independent
+    /// of the values.
+    #[inline]
+    fn ct_eq(&self, rhs: &Self) -> Choice {
+        self.as_bytes().ct_eq(rhs.as_bytes())
+    }
+}
+
 impl ConstantTimeEq for Choice {
     #[inline]
     fn ct_eq(&self, rhs: &Choice) -> Choice {

tests/mod.rs

@@ -31,6 +31,13 @@ fn slices_equal() {
     assert_eq!(a_eq_c.unwrap_u8(), 0);
 }
 
+#[test]
+fn str_equal() {
+    assert_eq!("".ct_eq("").unwrap_u8(), 1);
+    assert_eq!("xxx".ct_eq("xxxx").unwrap_u8(), 0);
+    assert_eq!("abcd".ct_eq("abcd").unwrap_u8(), 1);
+}
+
 #[test]
 fn conditional_assign_i32() {
     let mut a: i32 = 5;