Chrome OS如何使用外部USB存储设备？

本示例代码演示了如何在Chrome OS中使用外部USB存储设备的方法，通过挂载路径实现存储设备的读写操作。具体实现方式如下。

const mountPath = '/mnt/usb';  //挂载路径
chrome.fileSystemProvider.onUnmountRequested.addListener((options, successCallback) => {
  chrome.fileSystemProvider.unmount({fileSystemId: options.fileSystemId}, () => {
    successCallback && successCallback();
  });
});

chrome.fileSystemProvider.onMountRequested.addListener((options, successCallback, errorCallback) => {
  if (options.fileSystemId === 'usb') {
    chrome.fileSystemProvider.mount({
      fileSystemId: options.fileSystemId,
      displayName: 'USB',
      writable: true,
      source: {
        type: 'device',
        id: options.deviceId
      }
    }, () => {
      successCallback && successCallback({mountPath: mountPath});
    });
  } else {
    errorCallback && errorCallback('unsupported');
  }
});

chrome.fileSystemProvider.onReadDirectoryRequested.addListener((options, successCallback, errorCallback) => {
  if (options.directoryPath === mountPath) {
    chrome.fileSystemProvider.getDisplayPath({fileSystemId: options.fileSystemId, filePath: options.directoryPath}, (path) => {
      successCallback && successCallback([{name: 'file.txt', isDirectory: false, mimeType: 'text/plain', size: 1024, fullPath: mountPath + '/file.txt'}]);
    });
  } else {
    errorCallback && errorCallback('not found');
  }
});

chrome.fileSystemProvider.onOpenFileRequested.addListener((options, successCallback, errorCallback) => {
  if (options.filePath === mountPath + '/file.txt') {
    successCallback && successCallback({fileHandleId: 12345, data: 'Hello World!'});
  } else {
    errorCallback && errorCallback('not found');
  }
});

chrome.fileSystemProvider.onWriteFileRequested.addListener((options, successCallback, errorCallback) => {
  if (options.filePath === mountPath + '/file.txt') {
    successCallback && successCallback();
  } else {
    errorCallback && errorCallback('not found');
  }
});

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