Changing characteristic's length after initial declaration

[José Villanueva]

Hi everyone,

I wanted to know if it's possible to change the length of a characteristic's value after it has been put in the attribute table. Reading some other answers in this zone, I found it was possible to change a characteristic's value after its creation (I already did it using sd_ble_gatts_value_set(...)).

To give you more context, I have a characteristic with these values (in a server device):

attr_char_value.max_len     = 8;
attr_char_value.init_len    = 8;
uint8_t value[8]            = {0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00};
attr_char_value.p_value     = value;

Then, with a client device, I perform a Write Command, which generates a write event that allows me to use sd_ble_gatts_value_set(...), which changes the value of my characteristic. So, instead of changing the value, I would like to change the length from 8 to 1 byte, so that, after that first Write Command I can only write or read 1 smooth byte of information, is that possible?

Best regards!

[RK]

well yes - that's why there's a max_len and an initial len. The first is how much space to reserve, the second is how long the characteristic value currently is. You can't change the first, you can change the second on any and every update.

[José Villanueva]

Hi RK, at first I noticed the same but I didn't know how to do that. I was searching for a specific function to do that for me because I could not access to this attribute but I didn't find one in any of the library files. Then I realized the way to do that was setting vlen = 1, which allowed me to have a variable length value for my characteristic so I could write as most the number of bytes defined in max_len and read just the bytes desired in my application. Thanks!!