aioble on PICO_W: getting notified of pairing failures.

[brianreinhold]

Note: the PICO-W micropython uses the btstack.
I don't know what I am doing wrong, but when I invoke the pair method on the DeviceConnection object in aioble, the await returns successfully when the pairing succeeds, but if it fails, it does not return and I get no indication of the failure. I am not sure what I need to do to catch the error. Looking at the code I do not see any note about exceptions raised or a way to get a status field. It might be there, but I don't know how to access it.

The aioble code that invokes the pairing is

async def pair(
    connection,
    bond=True,
    le_secure=True,
    mitm=True,
    io=_IO_CAPABILITY_NO_INPUT_OUTPUT,
    timeout_ms=20000,
):
    ble.config(bond=bond, le_secure=le_secure, mitm=mitm, io=io)

    with connection.timeout(timeout_ms):
        connection._pair_event = asyncio.ThreadSafeFlag()
        ble.gap_pair(connection._conn_handle)
        await connection._pair_event.wait()
        # TODO: Allow the passkey action to return to here and
        # invoke a callback or task to process the action.

My application code simply does

    try:
        await deviceConnection.pair(
            True,         # bond=True,
            le_secure,         # le_secure=True,
            True,         # mitm=True
            Btle.IO_CAPABILITY_KEYBOARD_DISPLAY,
            60000)        # timeout
    except Exception as e:
        logger.error('LNI: Pairing/Encryption failed')
        return

The event being handled is the Encryption changed event. How do I trap the error? I do not catch it in the exception but here is the log from the btstack and support code:

[00:00:33.294] LOG -- sm.c.636: SM pairing started called
Pairing started
[00:00:33.304] LOG -- sm.c.2807: sm_run: state 43
  --> enc/auth/pair/bond change
    --> SM_EVENT_PAIRING_COMPLETE
Pairing failed, authentication failure with reason = 5
[00:00:33.334] LOG -- sm.c.1099: sm: connection 0x40 released setup context

This situation comes from a pulse oximeter that is paired with another client and the device sends a 'pairing not supported' message (misleading error message but that's what the spec says) and it clears its LTKs and it is then ready to connect again and repair. The problem is my client does not know the error occurs and the patient doesnt either and the device remains connected until it is detached from the patient. I need to trap that error and disconnect. This will cause the pulse oximeter to re-advertise and my client can reconnect, repair and do so successfully. The patient would have no idea that happened.

Outside of my particular use case, it is generally important for a client to know when a (bt) transaction fails.

[brianreinhold]

@jimmo I am trying to get the status of a pairing attempt. I can get the status in the modbluetooth_btstack.c by doing this:

        mp_bluetooth_gatts_on_encryption_update(conn_handle,
            desc->sm_connection_encrypted,
            desc->sm_connection_authenticated,
            desc->sm_le_db_index != -1,
            desc->sm_actual_encryption_key_size,
            sm_event_pairing_complete_get_status(packet));

I add the extra parameter at the end of the call. The method then looks as follows (also in modbluetooth_btstack.c)

#if MICROPY_PY_BLUETOOTH_ENABLE_PAIRING_BONDING
void mp_bluetooth_gatts_on_encryption_update(uint16_t conn_handle, bool encrypted, bool authenticated, bool bonded, uint8_t key_size, uint8_t status) {
    mp_int_t args[] = {conn_handle, encrypted, authenticated, bonded, key_size, status};
    invoke_irq_handler(MP_BLUETOOTH_IRQ_ENCRYPTION_UPDATE, args, 6, 0, NULL_ADDR, NULL_UUID, NULL_DATA, NULL_DATA_LEN, 0);
}

Note that I changed the size of args to be 6 instead of 5.
I update the declaration in the corresponding h file:

#if MICROPY_PY_BLUETOOTH_ENABLE_PAIRING_BONDING
// Call this when any connection encryption has been changed (e.g. during pairing).
void mp_bluetooth_gatts_on_encryption_update(uint16_t conn_handle, bool encrypted, bool authenticated, bool bonded, uint8_t key_size, uint8_t status);

I don't think I need to do anything else in the C code. However I am not sure how to handle the python code in aioble security.py here:

def _security_irq(event, data):
    global _modified

    if event == _IRQ_ENCRYPTION_UPDATE:
        # Connection has updated (usually due to pairing).
        conn_handle, encrypted, authenticated, bonded, key_size, status = data
        log_info("encryption update", conn_handle, encrypted, authenticated, bonded, key_size)
        if connection := DeviceConnection._connected.get(conn_handle, None):
            connection.encrypted = encrypted
            connection.authenticated = authenticated
            connection.bonded = bonded
            connection.key_size = key_size
            # TODO: Handle failure.
            if encrypted and connection._pair_event:
                connection._pair_event.set()

Of course I tried just adding the status field but I get an error that it is undefined. If I do nothing I get an error that it is expecting 5 fields but it is getting more. Well that is a start. I am not sure why it is expecting 5 fields when I changed the underlying event to deliver 6.

What steps am I missing?

Cant get any logging either in spite of setting log level = 2

Thanks

[brianreinhold]

@jimmo The status value IS getting passed up to aioble security event handler. What I cant figure out is how to raise the exception so the application gets it. I tried this:

# Use device.pair() rather than calling this directly.
async def pair(
    connection: DeviceConnection,
    bond: bool=True,
    le_secure: bool=True,
    mitm: bool=True,
    io: int=_IO_CAPABILITY_NO_INPUT_OUTPUT,
    timeout_ms: int=20000,
):
    global pair_status
    ble.config(bond=bond, le_secure=le_secure, mitm=mitm, io=io)

    with connection.timeout(timeout_ms):
        connection._pair_event = asyncio.ThreadSafeFlag()

        ble.gap_pair(connection._conn_handle)
        await connection._pair_event.wait()
        # TODO: Allow the passkey action to return to here and
        # invoke a callback or task to process the action.
        if pair_status > 0:
            raise GattError(pair_status)

by making a global variable pair_status, setting it in the irq handler and then trying to raise the exception. I catch the exception in the application code where I call the pairing method. But I do not get the exception. What am I doing wrong?

DO I need to raise the exception in the DeviceConnection pair method? Perhaps it is simpler to call the pair method directly?

[brianreinhold]

I figured it out

I didnt catch this line in the event handler

            if encrypted and connection._pair_event:
                connection._pair_event.set()

Just needed to remove the conditional then raise the exception in the pairing method call. The event wasn't getting triggered of course.