Clear characteristic cccd value when disconnect

[fabik111]

Problem

If the peripheral sketch with a subscribeable characteristic closes the connection with the central calling the BLE.disconnect() all subsequent subscriptions, after the first connection, are not notified and the characteristic stays always as "subscribed".

Solution

In this PR the characteristic CCCD value is cleared when the BLE.disconnect() is called for resetting the characteristic subscription status and allowing new subscriptions.

Sketches for reproducing the problem

Central

#include <ArduinoBLE.h>
void setup() {
  Serial.begin(9600);
  while (!Serial);

  // initialize the Bluetooth® Low Energy hardware
  BLE.begin();
 BLE.scanForUuid("19B10000-E8F2-537E-4F6C-D104768A1214");
}

void loop() {
  // put your main code here, to run repeatedly:
BLEDevice peripheral = BLE.available();

  if (peripheral) {
    // discovered a peripheral, print out address, local name, and advertised service
    Serial.print("Found ");
    Serial.print(peripheral.address());
    Serial.print(" '");
    Serial.print(peripheral.localName());
    Serial.print("' ");
    Serial.print(peripheral.advertisedServiceUuid());
    Serial.println();


    // stop scanning
    BLE.stopScan();

    controlLed(peripheral);
    delay(10000);
    // peripheral disconnected, start scanning again
    BLE.scanForUuid("19b10000-e8f2-537e-4f6c-d104768a1214");
  }
}

void controlLed(BLEDevice peripheral) {
  // connect to the peripheral
  Serial.println("Connecting ...");

  if (peripheral.connect()) {
    Serial.println("Connected");
  } else {
    Serial.println("Failed to connect!");
    return;
  }

  // discover peripheral attributes
  Serial.println("Discovering attributes ...");
  if (peripheral.discoverAttributes()) {
    Serial.println("Attributes discovered");
  } else {
    Serial.println("Attribute discovery failed!");
    peripheral.disconnect();
    return;
  }

  BLECharacteristic byteCharacteristic = peripheral.characteristic("19B10001-E8F2-537E-4F6C-D104768A1214");
  if (!byteCharacteristic) {
    Serial.println("Peripheral does not have LED characteristic!");
    peripheral.disconnect();
    return;
  } else if (!byteCharacteristic.canSubscribe()) {
    Serial.println("Peripheral does not have a writable LED characteristic!");
    peripheral.disconnect();
    return;
  } else if (!byteCharacteristic.subscribe()) {
    Serial.println("subscription failed!");
    peripheral.disconnect();
    return;
  } else {
    Serial.println("Subscribed");
  }
  while (peripheral.connected()) {
    // while the peripheral is connected

    // check if the value of the simple key characteristic has been updated
    if (byteCharacteristic.valueUpdated()) {
      // yes, get the value, characteristic is 1 byte so use byte value
      byte value = 0;
      
      byteCharacteristic.readValue(value);

      Serial.print("received: ");
      Serial.println(value, HEX);
 
    }
  }
  Serial.println("Disconnected");
  
}

Peripheral

#include <ArduinoBLE.h>
BLEService testService("19B10000-E8F2-537E-4F6C-D104768A1214");
BLEByteCharacteristic byteCharacteristic("19B10001-E8F2-537E-4F6C-D104768A1214", BLERead | BLEIndicate | BLEWrite);
volatile bool disconnect = false;
void byteRead(BLEDevice central, BLECharacteristic characteristic){
  Serial.println("Characteristic subscribed, sending data");
  byte c = 0x01; 
  int written = byteCharacteristic.writeValue(c);
  disconnect=true;
}
void setup() {
    Serial.begin(9600);
  while (!Serial);
  // put your setup code here, to run once:
  if (!BLE.begin()) {
    Serial.println("starting Bluetooth® Low Energy module failed!");

    while (1);
  }

  // set advertised local name and service UUID:
  if(!BLE.setLocalName("TEST-LOCAL-NAME")){
    Serial.println("error setting the local name");
  }

  byteCharacteristic.setEventHandler(BLESubscribed, byteRead);
  BLE.setAdvertisedService(testService);

   // add the characteristic to the service
  testService.addCharacteristic(byteCharacteristic);

   // add service
  BLE.addService(testService);

  // start advertising
  BLE.advertise();

  Serial.println("BLE Peripheral");

}

void loop() {
  // put your main code here, to run repeatedly:
  if(disconnect){
    BLE.disconnect();
    disconnect = false;
    Serial.println("disconnected");
  }
 BLE.poll();
 
}

Logs

Here the logs of the current behaviour.
Central

11:18:48.793 -> Found 34:94:54:27:05:66 'TEST-LOCAL-NAME' 19b10000-e8f2-537e-4f6c-d104768a1214
11:18:48.829 -> Connecting ...
11:18:48.897 -> Connected
11:18:48.897 -> Discovering attributes ...
11:18:49.291 -> Attributes discovered
11:18:49.330 -> Subscribed
11:18:49.330 -> received: 1
11:18:49.330 -> Disconnected
//End of the first run
11:18:59.416 -> Found 34:94:54:27:05:66 'TEST-LOCAL-NAME' 19b10000-e8f2-537e-4f6c-d104768a1214
11:18:59.448 -> Connecting ...
11:18:59.527 -> Connected
11:18:59.527 -> Discovering attributes ...
11:18:59.948 -> Attributes discovered
11:18:59.948 -> Subscribed
//Has never received new data since the peripheral never sends it

Peripheral

11:18:27.926 -> BLE Peripheral
11:18:49.291 -> Characteristic subscribed, sending data
11:18:49.330 -> disconnected
// Note that the subscribed event at 11:18:59.948 has never been notified to the sketch

[per1234]

Hi @fabik111. Thanks for your pull request. Please disregard the failed spell check.

This is a spurious failure caused by bit rot in the antiquated infrastructure used for that check, nothing to do with the changes you propose here. The failed check won't block the reviewers from merging your PR and we'll be sure to fix the broken spell check system separately ASAP.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 8 lines in your changes missing coverage. Please review.

Project coverage is 9.60%. Comparing base (c91c02c) to head (80036ba).
Report is 8 commits behind head on master.

Files with missing lines	Patch %	Lines
src/utility/ATT.cpp	0.00%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##           master    #376      +/-   ##
=========================================
- Coverage    9.62%   9.60%   -0.03%     
=========================================
  Files          28      28              
  Lines        3656    3665       +9     
=========================================
  Hits          352     352              
- Misses       3304    3313       +9     

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