Allow to read current connection limits

[dignifiedquire]

Currently it is possible to get to the ConnectionLimits struct for the current swarm, but it is not possible to read the actual limits, which would be useful to for components that want to check how close to the limit the current state is.

Bonus: It might be nice if there were some methods like has_reached_outgoing_connection_limit for more explicit checks.

[thomaseizinger]

Perhaps we should report the limit with each new connection?

[mxinden]

I would welcome any patches for this.

In case anyone is looking into it, I am currently working on a proposal for generic connection management, i.e. the ability for users to implement their own connection management (e.g. limiting) mechanism. I have not yet published this work.

See also #2118 (comment)

[mxinden]

Tracking issue for the above mentioned effort: #2824

First draft: #2828

[thomaseizinger]

Connection limits are now a completely standalone component implemented as NetworkBehaviour. It does currently not expose this functionality but that could easily be added. If really necessary, the behaviour can be forked. Thus closing this issue.

If desired, patches to expose ConnectionLimits are welcome.