fastboot: Introduce network-connected devices storage

Bug: 267507577
Bug: 267505625
Test: tested file lock api works on linux/windows
Test: tested storage api works on linux/windows
Change-Id: I33dda819370900310ae7fc63cbf6b00ba22ad4e8
Signed-off-by: Dmitrii Merkurev <dimorinny@google.com>
diff --git a/fastboot/storage.cpp b/fastboot/storage.cpp
new file mode 100644
index 0000000..db13dd6
--- /dev/null
+++ b/fastboot/storage.cpp
@@ -0,0 +1,67 @@
+/*
+ * Copyright (C) 2023 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.
+ */
+
+#include <android-base/file.h>
+#include <android-base/logging.h>
+
+#include <fstream>
+
+#include "storage.h"
+#include "util.h"
+
+ConnectedDevicesStorage::ConnectedDevicesStorage() {
+    const std::string home_path = GetHomeDirPath();
+    if (home_path.empty()) {
+        return;
+    }
+
+    const std::string home_fastboot_path = home_path + kPathSeparator + ".fastboot";
+
+    if (!EnsureDirectoryExists(home_fastboot_path)) {
+        LOG(FATAL) << "Cannot create directory: " << home_fastboot_path;
+    }
+
+    // We're using a separate file for locking because the Windows LockFileEx does not
+    // permit opening a file stream for the locked file, even within the same process. So,
+    // we have to use fd or handle API to manipulate the storage files, which makes it
+    // nearly impossible to fully rewrite a file content without having to recreate it.
+    // Unfortunately, this is not an option during holding a lock.
+    devices_path_ = home_fastboot_path + kPathSeparator + "devices";
+    devices_lock_path_ = home_fastboot_path + kPathSeparator + "devices.lock";
+}
+
+void ConnectedDevicesStorage::WriteDevices(const std::set<std::string>& devices) {
+    std::ofstream devices_stream(devices_path_);
+    std::copy(devices.begin(), devices.end(),
+              std::ostream_iterator<std::string>(devices_stream, "\n"));
+}
+
+std::set<std::string> ConnectedDevicesStorage::ReadDevices() {
+    std::ifstream devices_stream(devices_path_);
+    std::istream_iterator<std::string> start(devices_stream), end;
+    std::set<std::string> devices(start, end);
+    return devices;
+}
+
+void ConnectedDevicesStorage::Clear() {
+    if (!android::base::RemoveFileIfExists(devices_path_)) {
+        LOG(FATAL) << "Failed to clear connected device list: " << devices_path_;
+    }
+}
+
+FileLock ConnectedDevicesStorage::Lock() const {
+    return FileLock(devices_lock_path_);
+}
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