How to determine the length of string received through characteristic

[Muhammad Akram Karimi]

Hello everyone,

It seems like a very basic issue but somehow I am unable to resolve it.

I have a characteristic of length 20 bytes. This characteristic is supposed to receive a string of max 20 bytes. When I receive the string in this characteristic and my string is of less than 20 characters (which will be in most of the cases); the received string is appended by the remaining bytes which were already part of the characteristic previously.

Here is the code I am using to receive string:

uint8_t	msg_value;
uint16_t msg_handle1=m_our_service.msg_handle.value_handle;	
GATT_MSG.p_value = &msg_value;						
GATT_MSG.len=MSG_LEN;
GATT_MSG.offset=0;
err_code = sd_ble_gatts_value_get(0xFFFF, msg_handle1, &GATT_MSG);

Now,

GATT_MSG.p_value is where I have the string (appended by the previously written characters)

What I wish GATT_MSG.len should have is the LENGTH of the received string BUT GATT_MSG.len is ALWAYS=20 which is the total length of this particular characteristic.

Can anyone help me figuring out how can I determine the length of characteristic received?

Thanks

[Susheel Nuguru]

Most likely the problem is at the sending side where you might be setting the default size of the message to 20, instead of adjusting it based on your string size. Just guessing.