Extend NetUtils for network range scanning

[lsiepel]

Multiple bindings scan the network for devices by looping though all ip addresses. When trying to get rid of the apache libs, i also noticed the code is similar and it would be better to deduplicate this.

In future we can discuss if this scanning should be limited to the openHAB network setting or to all interfaces, but that is beyond the scope of this PR. Atleast we then have a central place to control that behaviour.

Reference: #3965

[lsiepel]

Would be nice to have this in the next milestone. Anything I can do to get this forward?

[holgerfriedrich]

Hi @lsiepel, it seems we have some doubts when it comes to the network scanning - we had some trouble with docker VMs during the last release phase. I am still not sure how this scanning should be implemented, restricting to primary interface, etc....

Additionally, it is not clear to me what is the benefit of getting rid of apache commons in this area - especially as we still need it for the telnet based addons.

Maybe you could try to convince us ;-)
Overall, the methods below do not harm in core. But not sure if this will be the basis for all plugins which try some kind of scanning or if we need to elaborate a more complex concept.

Besides that, one technical comment below.

[lsiepel]

You write we, so I suppose there has been a discussion amongst core maintainers?

1. With or without this PR, network scanning is happening. I would rather have a central place to influence this behaviour, then rely on multiple binding implementations.
2. This de-duplicates code
3. It removes/reduces the dependency on apache. In general less dependency is good. There might be other issues that prevent full removal of apache, but I have always learned to make problems smaller and take them one by one. We have already come a long way. Please check Removal of dependency on 'org.apache.commons.*' openhab-addons#7722
4. It does not harm core in a negative way.

If there are still doubts, i’m happy to incorporate suggestions as I really tho k this is a step forward.

[holgerfriedrich]

You write we, so I suppose there has been a discussion amongst core maintainers?

Sorry, you got me wrong. No recent discussion about this, my comment is just based on what I remember from the discussion about IP "scanning" for addon detection.

1. With or without this PR, network scanning is happening.  I would rather have a central place to influence this behaviour, then rely on multiple binding implementations.

2. This de-duplicates code

3. It removes/reduces the dependency on apache. In general less dependency is good. There might be other issues that prevent full removal of apache, but I have always learned to make problems smaller and take them one by one.  We have already come a long way. Please check [Removal of dependency on 'org.apache.commons.*' openhab-addons#7722](https://github.com/openhab/openhab-addons/issues/7722)

4. It does not harm core in a negative way.

If there are still doubts, i’m happy to incorporate suggestions as I really tho k this is a step forward.

Fair enough, lets go forward and get this into core. 👍

[lsiepel]

Thanks for looking into this and sharing your doubts.

[holgerfriedrich]

Thanks @lsiepel for the patience regarding this PR.

I now went through the code and also had a quick look into the PRs in addons - I can now understand why you want this in core.

I have some doubts regarding that gist you added for the helper functions. See my comment below.

[holgerfriedrich]

LGTM.
Thanks for taking all the comments into consideration.
Looks much simpler now 👍