Managing Application Files with Core File Kit in HarmonyOS Next

This article aims to deeply explore the technical details of file management in Huawei's HarmonyOS Next system (as of currently API12) and is summarized based on actual development practices.
Mainly as a carrier for technical sharing and exchange, it is inevitable that there are mistakes and omissions. Colleagues are welcome to put forward valuable opinions and questions for common progress.
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In application development, operations such as file creation, reading, writing, and deletion are very common. HarmonyOS Next provides Core File Kit, a service specifically designed for application file management, helping us easily complete basic file operations. Core File Kit also ensures the security of application files through the sandbox isolation mechanism. This article will introduce in detail the usage scenarios of Core File Kit, basic file operation interfaces, and application security mechanisms.

I. Introduction and usage scenarios of Core File Kit

Core File Kit is a file management service provided by HarmonyOS Next, specifically designed for operations such as creating, reading, writing, and deleting application files. Through Core File Kit, developers can flexibly manage files within the application to meet common needs such as configuration file management and cache file access.

1. Usage scenarios

Core File Kit is suitable for the following types of scenarios:

• Application configuration file management: Applications can use Core File Kit to read and write configuration files, facilitating the storage and management of application settings.
• User data storage: Used to store and manage user-generated data files such as notes and pictures.
• Cache data processing: Manage application cache files through Core File Kit to facilitate cleaning up useless data and optimizing storage space.

II. Description of basic file operation interfaces

Core File Kit provides a rich set of file operation interfaces covering common file management needs. The following is a description of several commonly used interfaces:

1. open interface

The open interface is used to open or create a file and returns a file descriptor for subsequent operations. Developers can ensure file security by setting file access permissions.

import { File } from '@kit.CoreFileKit';

// Open a file (create if it doesn't exist)
const filePath = '/data/storage/el2/files/sample.txt';
let fileDescriptor;
try {
    fileDescriptor = File.open(filePath, File.MODE_READ_WRITE | File.MODE_CREATE);
    console.info('File opened successfully');
} catch (error) {
    console.error('Failed to open file:', error);
}

2. write and read interfaces

The write interface is used to write data to a file, and the read interface is used to read data from a file. By combining the use of open, write, and read, developers can complete the entire operation process of files.

III. Sample code: Basic implementation of file operations

The following code shows the complete process of opening, writing, reading, and deleting files using Core File Kit in HarmonyOS Next.

import { File } from '@kit.CoreFileKit';

const filePath = '/data/storage/el2/files/sample.txt';

try {
    // 1. Open a file (create if it doesn't exist)
    const fileDescriptor = File.open(filePath, File.MODE_READ_WRITE | File.MODE_CREATE);
    console.info('File opened successfully with descriptor:', fileDescriptor);

    // 2. Write data
    const data = 'Hello, HarmonyOS!';
    const bytesWritten = File.write(fileDescriptor, data);
    console.info(`Data written successfully, bytes: ${bytesWritten}`);

    // 3. Read data
    const buffer = new ArrayBuffer(bytesWritten); // Create a buffer
    const bytesRead = File.read(fileDescriptor, buffer);
    const result = String.fromCharCode.apply(null, new Uint8Array(buffer)); // Convert to string
    console.info(`Data read successfully, content: ${result}`);

    // 4. Delete file
    const deleted = File.delete(filePath);
    console.info(`File deleted successfully: ${deleted}`);

} catch (error) {
    console.error('Error during file operations:', error);
}

Code description:

1. Open file: Use the File.open interface to create a file if it doesn't exist.
2. Write data: Write string data to a file through File.write.
3. Read data: Use File.read to read file data and convert it to a string.
4. Delete file: Delete a file through File.delete to free up storage space.

IV. Security of application sandbox isolation mechanism

To ensure data security, HarmonyOS Next adopts a sandbox isolation mechanism. The data of each application is stored in an independent sandbox directory to prevent unauthorized access.

1. Principle of sandbox isolation mechanism

The sandbox directory of an application is an independent storage area allocated by the system for each application and is used to store application configuration files, cache files, and user data. Since the sandbox directory of each application is isolated, other applications cannot access the data in this directory, thereby improving data security.

2. Permission control

In HarmonyOS Next, file operations are restricted by permission control. Only the application itself can operate files in its sandbox directory. To strengthen data protection, the system also restricts read and write permissions for sensitive files to prevent the risk of file leakage.

3. Sandbox security example

When using Core File Kit for file operations, the system will automatically limit the file to the application's sandbox directory. Developers don't need to worry about out-of-bounds access to file data. The system will ensure data isolation. The following is an example of a sandbox isolation path:

const safeFilePath = '/data/storage/el2/files/sample.txt';
console.info(`Safe file path in sandbox: ${safeFilePath}`);

The system will automatically isolate application data in the file path and not allow other applications to access the current application's data through the path, achieving high data security.

Summary

The Core File Kit service provided by HarmonyOS Next allows developers to easily manage operations such as creating, reading, writing, and deleting files within applications, and ensure data security through the sandbox isolation mechanism. When using Core File Kit, we can manage files with confidence without worrying about out-of-bounds access to data. At the same time, we should follow the system's permission control strategy to ensure the security and reliability of user data.