DNS resolution might yield multiple IP-addresses

[IvanKuchin]

If DNS resolves to multiple IP-addresses, all of them must be taken into consideration. Current implementation take only first A-record, all other are dropped. See hostname/mod.rs from-trait

[IvanKuchin]

Potential solution

Instead of modifying optimize_prefixes to handle Hostname explicitly, we introduce a method in PrefixListItem that ensures it always returns a collection of contiguous PrefixListItem instances. This method will be called before passing the items to optimize_prefixes.

Implementation

1. Hostname struct must hold multiple IP-addresses

pub struct Hostname {
    name: String,
    ips: Vec<IPv4>,
}

impl Hostname {
    pub fn start_ip(&self) -> &IPv4 {
        expect("not suppose to call")
    }

    pub fn end_ip(&self) -> &IPv4 {
        expect("not suppose to call")
    }
}

2. Add a to_contiguous_items Method to PrefixListItem
   This method will handle the expansion of Hostname into multiple PrefixListItem::IPRange instances while leaving other variants unchanged.

impl PrefixListItem {
    /// Converts the `PrefixListItem` into a collection of contiguous items.
    pub fn to_contiguous_items(&self) -> Vec<PrefixListItem> {
        match self {
            PrefixListItem::Hostname(hostname) => {
                hostname
                    .resolve_to_ip_ranges()
                    .unwrap_or_default()
                    .into_iter()
                    .map(PrefixListItem::IPRange)
                    .collect()
            }
            _ => vec![self.clone()],
        }
    }
}

3. prefix_list/mod.rs from_str(____) call to_contiguous_items before returning