Add a builder for route messages

[little-dude]

For both the RouteAddRequest and RouteDelRequest, we need to build
a route message. However only the former provides helper methods to do
so. Instead of duplicating code, create a separate builder, and use it for
both request types.

This MR also allows building route requests parametrized by IpAddr, in
addition to the existing Ipv4Addr and Ipv6Addr implementations.

---

This is a non-backward compatible change.

[cathay4t]

Please also fix examples/add_route.rs

[cathay4t]

In general, I like the idea of XxxBuilder instead old on-line changes of message_mut().

[richardstephens]

Hi, I'm jumping into the discussion here on request of @cathay4t in response to my PR number #53 .

Our product uses rtnetlink quite extensively to configure the host's networking. In principle, I would much rather use Builder's that make the intent of the netlink command we issue clear from the code. However I've sturggled a bit with understanding how to achieve my desired results by reading the netlink documentation. My dev loop often involved strace'ing ip or bridge commands to find out what the netlink message I need looks like.

I'm also specifically concerned about the message header flags. In my PR, I was not able to achieve the desired result with a set link message - I needed to issue an 'add' link message with the correct flags even though I was updating an existing object. I'm not sure how to design a clean API for this other than by exposing API to manipulate the flags directly.

I'm happy to make another attempt at that PR in line with the builder approach, along with type-safe setters for the flags. What do you think?

[cathay4t]

Hi, I'm jumping into the discussion here on request of @cathay4t in response to my PR number #53 .

Our product uses rtnetlink quite extensively to configure the host's networking. In principle, I would much rather use Builder's that make the intent of the netlink command we issue clear from the code. However I've sturggled a bit with understanding how to achieve my desired results by reading the netlink documentation. My dev loop often involved strace'ing ip or bridge commands to find out what the netlink message I need looks like.

There is no good netlink document except kernel code. I also use strace -s 10000 for ip command initially, but will cross reference with kernel code.

I'm also specifically concerned about the message header flags. In my PR, I was not able to achieve the desired result with a set link message - I needed to issue an 'add' link message with the correct flags even though I was updating an existing object. I'm not sure how to design a clean API for this other than by exposing API to manipulate the flags directly.

I will tag new release to netlink-packit-route this week which will contain big changes(sorry) to flags.
Exposing a API at rtnetlink level for flags is simpler for this builder workflow now.

I'm happy to make another attempt at that PR in line with the builder approach, along with type-safe setters for the flags. What do you think?

Sure, but please wait netlink-packit-route 0.20.0 release.

If @little-dude does not have time to move this PR forward, I will append my patches to this PR to get it merged next week.

[cathay4t]

@little-dude Do you mind If pick up your work here?

[little-dude]

I'll try to fix this up today @cathay4t. Sorry, it's still busy at work, and I'm working on netlink by spikes

[little-dude]

Done, @cathay4t

[little-dude]

Hello @cathay4t, would it be possible to get this merged within the next couple weeks by any chance?

[cathay4t]

Please give me 2 days to review it.

[cathay4t]

LGTM. Merged. Thanks for the efforts!

[little-dude]

Thanks @cathay4t !

[little-dude]

@cathay4t would it be possible to make a release with these changes? I haven't done a release in a while, and with all the inter-dependencies between the crates I'm a bit scared of making one.

[little-dude]

@cathay4t would you be able to make a release? If not I'll give it a try.

[cathay4t]

Can we use this builder to other component(addr, link, rule, rc)also before release?

And I am also considering to RouteGetRequest::new(handle: Handler, rt_msg: RouteMessage) also, to be consistent.

[cathay4t]

I will create a PR tomorrow for expanding building to crate wide. After that, I can make a release.

Meanwhile, please also vote on #66

[little-dude]

After that, I can make a release.

I just realized I'd also need a netlink-packet-route release to get rust-netlink/netlink-packet-route#98 if you don't mind

[cathay4t]

netlink-packet-route 0.20.1 released.

Working on expanding the use of builder.

[little-dude]

Thanks a ton @cathay4t !

[cathay4t]

I am currently work on creating builder for link:

https://github.com/cathay4t/rtnetlink/tree/link_builder