Introduce private helper method in_network for Ipv{4,6}Addr

[CDirkx]

As I proposed in #86634 (comment), this PR introduces a private helper method in_network to check if an IP address is in a network. Checking if address is in 224.0.0.0/4 would be written as:

address.in_network(&Ipv4Addr::new(224, 0, 0, 0), 4)

This improves readability and possibly performance (based on https://rust.godbolt.org/z/6KEGWcd5a) over the various other ways this is implemented right now:

self.octets()[0] == 192 && self.octets()[1] == 0 && self.octets()[2] == 0

self.octets()[0] == 198 && (self.octets()[1] & 0xfe) == 18

self.octets()[0] >= 224 && self.octets()[0] <= 239

matches!(self.octets(), [169, 254, ..])

I think it would be a good idea to eventually offer this kind of functionality publically, although with a different API. Maybe Rust could get dedicated Ipv{4,6}Network types like Python?

[rust-highfive]

r? @joshtriplett

(rust-highfive has picked a reviewer for you, use r? to override)

[the8472]

Wouldn't a full mask be more efficient? if (addr & mask) == reference that way some of the more unusual ranges which aren't prefix-based could also be expressed. There are plans to change the IPv4 storage to u32 so this could boil down to two instructions, same for ipv6 but as a u128 so that shouldn't be more than a handful either, especially with simd operations.

By that I mean the ability to specify a mask, not just a prefix.

[CDirkx]

What would be non-prefix based ranges? Currently the method is only intended to be used as a helper for the implementation of the other methods (is_multicast etc. which are all prefix based). An eventually public API could indeed be more flexible.

[the8472]

I think this check from another PR of yours could be expressed as a mask with a gap

(matches!(self.segments(), [0x2001, b, 0, 0, _, _, _, _] if b < 0x200)

[CDirkx]

Ah from #86634. That code should check if the address is in 2001::/23 however, so still a prefix (I'll double check to make sure it is correct). Code like that is exactly why I want to introduce this helper method, since it is hard to see the mapping.

Edit: the code is incorrect, as written it would indeed be a mask with a gap. It should be (matches!(self.segments(), [0x2001, b, _, _, _, _, _, _] if b < 0x200) instead. I fixed it in the other PR, thanks!

[joshtriplett]

I like the concept of this, but if we're going to have functionality like this, I think we should have a dedicated type for a network, with ways to construct a network with either address and mask or address and number of bits.

[CDirkx]

I can additionally work on a public API version of this functionality. However I see this PR more as a refactoring of all the is_ methods to improve the readability and correctness (as shown by the mistake in #86969 (comment)) and think the private helper is still valuable on its own for now.

[CDirkx]

I opened #86992 to introduce public types representing IP prefixes.

[faern]

address.in_network(&Ipv4Addr::new(224, 0, 0, 0), 4)

You can do exactly this with Ipv4Network::contains. Why does it need to be in std? If any functionality on IP network computation is missing we can probably add it to ipnetwork.

[bors]

☔ The latest upstream changes (presumably #87535) made this pull request unmergeable. Please resolve the merge conflicts.

[JohnCSimon]

Ping from triage:
@CDirkx can you please address the merge conflict?

[JohnCSimon]

Ping again from triage:
@CDirkx can you please address the merge conflict?

@rustbot label: +S-waiting-on-author -S-waiting-on-review

[JohnCSimon]

Ping from triage:
@CDirkx I'm closing this as inactive, please feel free to reopen when you're ready to continue.

@rustbot label: S-inactive