configstore: add utility library functions for configstore

this change adds a set of library functions to facilitate
accessing(retrieving) configuration items.

Specifically, added template functions for accessing configuration
items for following types:

OptionalBool, OptionalInt32, OptionalUInt32, OptionalInt64,
OptionalUInt64, OptionalString

Design doc: go/design-confighal
Bug: 34724435
Test: build, run

Change-Id: Icca56d0d9e086b9d94c9b1168df041bf7d418698

configstore/Android.bp

@@ -1,4 +1,5 @@
 // This is an autogenerated file, do not edit.
 subdirs = [
     "1.0",
+    "utils",
 ]

configstore/utils/Android.bp

@@ -0,0 +1,28 @@
+//
+// Copyright (C) 2017 The Android Open Source Project
+//
+// 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.
+//
+
+cc_library_static {
+    name: "android.hardware.configstore-utils",
+    export_include_dirs: ["include"],
+    srcs: [],
+    shared_libs: [
+        "android.hardware.configstore@1.0",
+    ],
+    export_shared_lib_headers: [
+        "android.hardware.configstore@1.0",
+    ],
+}
+

configstore/utils/include/configstore/Utils.h

@@ -0,0 +1,94 @@
+//
+// Copyright (C) 2017 The Android Open Source Project
+//
+// 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.
+//
+
+#ifndef ANDROID_HARDWARE_CONFIGSTORE_UTILS_H
+#define ANDROID_HARDWARE_CONFIGSTORE_UTILS_H
+
+#include <hidl/Status.h>
+#include <stdatomic.h>
+
+namespace android {
+namespace hardware {
+namespace configstore {
+// arguments V: type for the value (i.e., OptionalXXX)
+//           I: interface class name
+//           func: member function pointer
+using namespace V1_0;
+
+template<typename V, typename I, android::hardware::Return<void> (I::* func)
+        (std::function<void(const V&)>)>
+decltype(V::value) get(const decltype(V::value) &defValue) {
+    auto getHelper = []()->V {
+        V ret;
+        sp<I> configs = I::getService();
+
+        if (!configs.get()) {
+            // fallback to the default value
+            ret.specified = false;
+        } else {
+            (*configs.*func)([&ret](V v) {
+                ret = v;
+            });
+        }
+
+        return ret;
+    };
+    static V cachedValue = getHelper();
+
+    return cachedValue.specified ? cachedValue.value : defValue;
+}
+
+template<typename I, android::hardware::Return<void> (I::* func)
+        (std::function<void(const OptionalBool&)>)>
+bool getBool(const bool defValue) {
+    return get<OptionalBool, I, func>(defValue);
+}
+
+template<typename I, android::hardware::Return<void> (I::* func)
+        (std::function<void(const OptionalInt32&)>)>
+int32_t getInt32(const int32_t defValue) {
+    return get<OptionalInt32, I, func>(defValue);
+}
+
+template<typename I, android::hardware::Return<void> (I::* func)
+        (std::function<void(const OptionalUInt32&)>)>
+uint32_t getUInt32(const uint32_t defValue) {
+    return get<OptionalUInt32, I, func>(defValue);
+}
+
+template<typename I, android::hardware::Return<void> (I::* func)
+        (std::function<void(const OptionalInt64&)>)>
+int64_t getInt64(const int64_t defValue) {
+    return get<OptionalInt64, I, func>(defValue);
+}
+
+template<typename I, android::hardware::Return<void> (I::* func)
+        (std::function<void(const OptionalUInt64&)>)>
+uint64_t getUInt64(const uint64_t defValue) {
+    return get<OptionalUInt64, I, func>(defValue);
+}
+
+template<typename I, android::hardware::Return<void> (I::* func)
+        (std::function<void(const OptionalString&)>)>
+std::string getString(const std::string &defValue) {
+    return get<OptionalString, I, func>(defValue);
+}
+
+}  // namespace configstore
+}  // namespace hardware
+}  // namespace android
+
+#endif  // ANDROID_HARDWARE_CONFIGSTORE_UTILS_H