Support for adding desired capability when registering agent

[hvardhanx]

This pull request adds support to specify desired capability when registering agent through session.register_agent(agent, "KeyboardOnly");

Similar to how it is done here: https://github.com/bluez/bluez/blob/3f03ea4aebcee5166cd057047b5eb511eda90f42/test/simple-agent#L161
manager.RegisterAgent(path, capability);

[surban]

The agent's capability is automatically determined depending on the provided agent methods.

bluer/bluer/src/agent.rs

Lines 258 to 272 in 6bf2b0c

	pub(crate) fn capability(&self) -> &'static str {
	let keyboard = self.request_passkey.is_some() || self.request_pin_code.is_some();
	let display_only = self.display_passkey.is_some() || self.display_pin_code.is_some();
	let yes_no = self.request_confirmation.is_some()
	|| self.request_authorization.is_some()
	|| self.authorize_service.is_some();
	match (keyboard, display_only, yes_no) {
	(true, false, false) => "KeyboardOnly",
	(false, true, false) => "DisplayOnly",
	(false, _, true) => "DisplayYesNo",
	(true, true, _) | (true, _, true) => "KeyboardDisplay",
	(false, false, false) => "NoInputNoOutput",
	}
	}

Could you explain why you would need to override it in another way?

[hvardhanx]

I was overriding the agent's capability because I wanted to set a static pass code which i think only appears in KeyboardOnly or KeyboardDisplay capability.

[surban]

I still don't understand. If you want to set a static pass code you can specify an agent that provides the request_pin_code function. This will set the agent capabilities to KeyboardOnly and call your function to obtain the pass code.

If you override the agent capabilities to KeyboardOnly but do not specify a function handling the request, where is the pass code supposed to come from?

[hvardhanx]

I still don't understand. If you want to set a static pass code you can specify an agent that provides the request_pin_code function. This will set the agent capabilities to KeyboardOnly and call your function to obtain the pass code.

If you override the agent capabilities to KeyboardOnly but do not specify a function handling the request, where is the pass code supposed to come from?

Ahh thanks! I didn't know this 😄