Add a NextHop parents yaml parser for use with remap.

[jrushford]

This PR adds a YAML parser for the proposed parents.yaml file in PR #3870 under discussion by the nexhop, working group.

[jrushford]

[approve ci autest]

[jrushford]

[approve ci autest]

[jrushford]

[approve ci autest]

[a-canary]

+1

[SolidWallOfCode]

A key question is whether it's better to do so much of the parsing work in the converters or not. I did as little work as possible there and put most of the parsing logic elsewhere.

[SolidWallOfCode]

Use constexpr, not #define. But better, don't use fixed sized buffers.

[SolidWallOfCode]

This is a bad API design by YAMLCPP IMHO. It means either map access is fraught or you have to do it twice, e.g.

if (!node[NH_strategy]) { ...
} else { // error - missing key
}

I suspect, though, the thrown exception has the data you need and you don't have to catch and rethrow for every access.

[jrushford]

that was my mistake, twice is not necessary.

[SolidWallOfCode]

You can use range for loops on the nodes -

for ( auto const& item : strategy ) {
  if (std::none_of(... item.first.as<std::string>()) ) ...

[SolidWallOfCode]

Look at the Mark method, which gives you access to the line and column location of the node, which is very nice for error messages.

[SolidWallOfCode]

That's a first pass of commentary. One additional note - I don't like the fixed buffer size approach to reading the configuration files. I think it's better to do something like ts::file::load in the IP Allow PR, which loads the entire file in to a std::string at the beginning. Parsing is much easier then and has no arbitrary limits. It's even easier if you use TextView, so that getting the first line is something like

std::string content = ts::file::load(path);
ts::TextView line = ts::TextView{content}.split_prefix_at('\n').trim_if(&isspace);
// line has the first line with white space removed from both ends, so "  #include" is valid

[SolidWallOfCode]

const std::string &

[SolidWallOfCode]

Support there are two "http" ports, say 80 and 3128. How would that be done?

[SolidWallOfCode]

Is this a list of maps, then? It might be better to have either a list of lists, that is a list of pairs effectively, or a map of lists. That is,

protocol:
  - [ http, 80 ]
  - [ http, 3128 ]
  - [ https, 443 ]

or

protocol:
  - http:
    - 80
    - 3128
  - https:
    - 443

[mlibbey]

Of your two, I'd choose the latter -- implied order of an array seems like it will lead to problems. An alternative solution would be to require the admin to list the server twice. I believe the effect of listing multiple ports would be that the server would be in the list twice, and thus get 2x the selections than a server with 1 port. That would be obvious to someone listing the server twice, but, I think not obvious when "just" listing multiple ports.

[jrushford]

I'm +1 on leaving the protocol as is and just listing a server twice as @mlibbey suggests so that it is obvious to the person configuring this.

[jrushford]

[approve ci]