Android蓝牙低功耗：characteristic.getPermissions（）返回0？

Question

I am writing an Android BLE application, and I am trying to get the permissions of a certain characteristic. I have already managed to get the characteristic properties with characteristic.getProperties(), and it returns a non-zero value, however, when I use the getPermission() method it returns 0 even though I am sure that the characteristic has PERMISSION_WRITE_ENCRYPTED_MITM (0x00000040).

Here is a code snippet

    // properties
    int properties = ch.getProperties();
    DebugWrapper.infoMsg("properties: " + properties, TAG); //returns non-zero value

    // permissions      
    int permissions = ch.getPermissions();  
    DebugWrapper.infoMsg("permissions: " + permissions, TAG); //returns zero value

Am I doing something wrong? Is there a specific way to get the permissions of the characteristic or is this a problem with the android api?

I am using API 19 and testing my program on a Samsung Galaxy Note 3.

I appreciate any help.

Answer 1

This looks like an issue with the underlying framework. This link shows the block of code that the framework executes when discovering services/characteristics on the remote device. You can see when the new BluetoothGattCharacteristic is created, the permissions parameter is always passed in as 0 .

Additionally, even when the characteristic is later read, only the characteristic's value is updated, no other parameters are reset on the object.

Instead, it seems Android attempts to handle authentication/permission issues on a trial and error basis. In other words, the framework always attempts a basic read/write, and if it fails for authentication reasons, it automatically tries again with MITM authentication requested.