Add bitfield helpers for new store

libraries/persistent_store/src/store.rs

@@ -0,0 +1,63 @@
+// Copyright 2019-2020 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use crate::StorageError;
+
+#[derive(Debug, PartialEq, Eq)]
+pub enum StoreError {
+    /// Invalid argument.
+    ///
+    /// The store is left unchanged. The operation will repeatedly fail until the argument is fixed.
+    InvalidArgument,
+
+    /// Not enough capacity.
+    ///
+    /// The store is left unchanged. The operation will repeatedly fail until capacity is freed.
+    NoCapacity,
+
+    /// Reached end of lifetime.
+    ///
+    /// The store is left unchanged. The operation will repeatedly fail until emergency lifetime is
+    /// added.
+    NoLifetime,
+
+    /// A storage operation failed.
+    ///
+    /// The consequences depend on the storage failure. In particular, the operation may or may not
+    /// have succeeded, and the storage may have become invalid. Before doing any other operation,
+    /// the store should be [recovered]. The operation may then be retried if idempotent.
+    ///
+    /// [recovered]: struct.Store.html#method.recover
+    StorageError,
+
+    /// Storage is invalid.
+    ///
+    /// The storage should be erased and the store [recovered]. The store would be empty and have
+    /// lost track of lifetime.
+    ///
+    /// [recovered]: struct.Store.html#method.recover
+    InvalidStorage,
+}
+
+impl From<StorageError> for StoreError {
+    fn from(error: StorageError) -> StoreError {
+        match error {
+            StorageError::CustomError => StoreError::StorageError,
+            // The store always calls the storage correctly.
+            StorageError::NotAligned | StorageError::OutOfBounds => unreachable!(),
+        }
+    }
+}
+
+pub type StoreResult<T> = Result<T, StoreError>;