set_data_from_slice (#15854)

* data_ensure_equal_to_slice

* rename and change to copy

sdk/src/account.rs

@@ -394,6 +394,20 @@ impl Account {
 }
 
 impl AccountSharedData {
+    /// make account's data equal to 'data'. This may require resizing and copying data.
+    pub fn set_data_from_slice(&mut self, data: &[u8]) {
+        let len = self.data.len();
+        let len_different = len != data.len();
+        if len_different {
+            // if the resize causes a reallocation and copy, it would be better to create a new copy of the final data
+            //  rather than resize (+ copy current) and then copy over below.
+            // however, the implementation of account's data is soon to be copy on write, so the tradeoffs will soon be different.
+            self.data.resize(data.len(), 0);
+        }
+        // we could compare here to determine whether we need to modify the original data or not. In the current implementation, that would
+        //  not make a positive difference.
+        self.data.copy_from_slice(data);
+    }
     pub fn set_data(&mut self, data: Vec<u8>) {
         self.data = data;
     }
@@ -533,6 +547,27 @@ pub mod tests {
         (account1, account2)
     }
 
+    #[test]
+    fn test_account_set_data_from_slice() {
+        let key = Pubkey::new_unique();
+        let (_, mut account) = make_two_accounts(&key);
+        assert_eq!(account.data(), &vec![0, 0]);
+        account.set_data_from_slice(&[1, 2]);
+        assert_eq!(account.data(), &vec![1, 2]);
+        account.set_data_from_slice(&[1, 2, 3]);
+        assert_eq!(account.data(), &vec![1, 2, 3]);
+        account.set_data_from_slice(&[4, 5, 6]);
+        assert_eq!(account.data(), &vec![4, 5, 6]);
+        account.set_data_from_slice(&[4, 5, 6, 0]);
+        assert_eq!(account.data(), &vec![4, 5, 6, 0]);
+        account.set_data_from_slice(&[]);
+        assert_eq!(account.data().len(), 0);
+        account.set_data_from_slice(&[44]);
+        assert_eq!(account.data(), &vec![44]);
+        account.set_data_from_slice(&[44]);
+        assert_eq!(account.data(), &vec![44]);
+    }
+
     #[test]
     fn test_account_data_set_data() {
         let key = Pubkey::new_unique();