NVS: expose C++ API

Closes https://github.com/espressif/esp-idf/issues/3540

components/nvs_flash/src/nvs_cxx_api.cpp

@@ -0,0 +1,68 @@
+// Copyright 2015-2016 Espressif Systems (Shanghai) PTE LTD
+//
+// 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.
+#include "nvs_partition_manager.hpp"
+#include "nvs_handle.hpp"
+#include "nvs_handle_simple.hpp"
+#include "nvs_handle_locked.hpp"
+#include "nvs_platform.hpp"
+
+namespace nvs {
+
+std::unique_ptr<NVSHandle> open_nvs_handle_from_partition(const char *partition_name,
+        const char *ns_name,
+        nvs_open_mode_t open_mode,
+        esp_err_t *err)
+{
+    if (partition_name == nullptr || ns_name == nullptr) {
+        if (err) {
+            *err = ESP_ERR_INVALID_ARG;
+        }
+        return nullptr;
+    }
+
+    Lock lock;
+
+    NVSHandleSimple *handle_simple;
+    esp_err_t result = nvs::NVSPartitionManager::get_instance()->
+            open_handle(partition_name, ns_name, open_mode, &handle_simple);
+
+    if (err) {
+        *err = result;
+    }
+
+    if (result != ESP_OK) {
+        return nullptr;
+    }
+
+    NVSHandleLocked *locked_handle = new (nothrow) NVSHandleLocked(handle_simple);
+
+    if (!locked_handle) {
+        if (err) {
+            *err = ESP_ERR_NO_MEM;
+        }
+        delete handle_simple;
+        return nullptr;
+    }
+
+    return std::unique_ptr<NVSHandleLocked>(locked_handle);
+}
+
+std::unique_ptr<NVSHandle> open_nvs_handle(const char *ns_name,
+        nvs_open_mode_t open_mode,
+        esp_err_t *err)
+{
+    return open_nvs_handle_from_partition(NVS_DEFAULT_PART_NAME, ns_name, open_mode, err);
+}
+
+} // namespace nvs