Need to check that disconnected BLEClient doesn't try and use connection

[nkolban]

Imagine the ESP32 is running as a BLE Client. It connects to the target BLE Server and reads and writes characteristics. All is well. Now imagine that the client is "disconnected" from the BLE Server. We will be notified that we have been disconnected. All good. However, what if the programmer then attempts to continue to read/write to the BLE Server now the connection is gone? We don't handle that at all.

Today, we interact with a BLE Server by getting a BLERemoteCharacteristic object and then calling its readValue() and writeValue() methods. Since we can't get a BLERemoteCharacteristic object without first connecting to the server, we don't have to worry about attempting to interact with the server without first having formed a connection. What we failed to appreciate is that having a BLERemoteCharacteristic NOW doesn't mean that this object will be good into the future. Specifically, it is no longer good once we have lost the connection. We need to maintain state in the client such that if the connection is lost, an attempt (mistakenly) by the programmer to use the connection is rejected.

[nkolban]

One immediate workaround without code changes in the library appears to be to invoke the:

BLEClient::isConnected()

and only if we are connected, then perform the read or write.

We also need to add an onDisconnect() method to the BLEClientCallbacks class.

[skyng22003]

I see, thank you very much for your help!

[nkolban]

Studying the traces when a server disappears from a connected ESP32 BLE Client, I seem to see two events. These are ESP_GATTC_DISCONNECT_EVT and ESP_GATTC_CLOSE_EVT. Now I need to study to determine the distinction between these.

[nkolban]

Some non trivial changes have now been made.

• We now detect a disconnect
• A callback function called onDisconnect() which is part of the BLEClientCallbacks class is now available and will be called when a disconnection is discovered.
• When we attempt to re-connect or when we attempt to perform a subsequent getServices(), the cache of existing services (and their chains of characteristics and descriptors) are released.
• If we attempt to perform a read or write on a characteristic or descriptor where we have no connection results in a BLEDisconnectedException being thrown which can be caught.

[reaper7]

I tried to use this callback on esp32 arduino but I got:

C:\PROGRAMY\arduino\hardware\espressif\esp32\libraries\BLE\src/BLEExceptions.h:13:2: error: #error "C++ exception handling must be enabled within make menuconfig. See Compiler Options > Enable C++ Exceptions."

 #error "C++ exception handling must be enabled within make menuconfig. See Compiler Options > Enable C++ Exceptions."

[chegewara]

You have to edit sdkconfig.h file and set this option:
CXX_EXCEPTIONS=y

[reaper7]

ok :) thank you for the tips.
This change will be introduced in arduino-esp? Is anyone working on it?
I use daily sync with master repo and I do not want to change files locally.

[chegewara]

This is option you have to change locally, sorry but we cant change it