Terrible handling of initLen / minLen and variable length characteristics.

[Timmmm]

See: https://devzone.nordicsemi.com/question/34390/no-ble_gatt_hvx_notification-under-20-bytes/?answer=55637#post-id-55637

Basically there are two problems:

1. The GattCharacteristic initLen parameter is randomly named minLen too. If you follow the code all the way through it actually does two things - it is the initial length (not minimum), and it determines whether the characteristic is variable length or not.
2. The characteristic for nRF51822 code is only variable length if initLen != maxLen. This is really stupid because you might want the initial length to equal the maximum length but still have variable length. It also isn't documented anywhere.

I suggest the following solution:

1. Add extra constructors with an extra parameter: bool variableLength.
2. Name initLen to be initLen everywhere consistently (and not minLen).
3. Deprecate the old constructors.

[rainierwolfcastle]

ARM Internal Ref: IOTSFW-1159

[rgrover]

@Timmmm I agree that initLen should not have been renamed as minLen. I also agree that initlen != minLen should not be a criteria for variable-length characteristics.

[andresag01]

@Timmmm Apologies on the delay for a fix. I have just submitted two pull requests to address the issue (to ble and ble-nrf51822). The GattAttribute.initialLen was removed and we are now using len as the current length of *valuePtr and maxLen as the maximum value of *valuePtr. Therefore, we have removed the accessor getInitialLen() and replaced this with getLength() where required in ble-nrf51822 module.

Notice that currently all attributes are marked as 'variable'. We will be submitting pull requests to deal with this shortly, but it was decided that we would do this separately because it requires changing the constructors of the GattCharacteristic and GattAttribute.

[Timmmm]

Awesome, no need to apologise!

[andresag01]

@Timmmm I have made the latest changes to allow variable length characteristics by passing a boolean to the constructor. Please see: d71c316.

[Timmmm]

Excellent, thanks!