feat(anvil): add ability to listen on multiple IP addresses

[0xZerohero]

Motivation

In complex setups, there is sometimes a need to listen on multiple internal network addresses or both IPv4 and IPv6 simultaneously.

Resolves #4941

Solution

I updated the NodeHandle to store Vecs of server handles and addresses.
The following commands work the same way they worked before:
anvil - makes it listen on 127.0.0.1:8545
env ANVIL_IP_ADDR="1.1.1.1" anvil - makes it listen on 1.1.1.1:8545
anvil --host 1.1.1.1 - makes it listen on 1.1.1.1:8545
etc.
but now you can also add additional hosts if needed
anvil --host :: --host 127.0.0.1 --host 1.1.1.1 - makes it listen on [::]:8545, 127.0.0.1:8545, 1.1.1.1:8545
env ANVIL_IP_ADDR="::1,1.1.1.1" anvil - makes it listen on [::1]:8545, 1.1.1.1:8545

The limitations in the current implementation are:

• all hosts will listen on the same port. This can be fixed in a clean way only by introducing a breaking change

TBD:

• The "host" option can be in format "ip:port" - which provides the most flexibility. However this change is not backward compatible with the current ANVIL_IP_ADDR format.
• I noticed an odd arrangement: the "host" command option is located in the "Server options" section, while the "port" option is placed within the "EVM options" section. In my opinion, it would be more logical to have the "port" option in the "Server options" section.
• NodeHandle::socket_address now returns the first listening address, making sure all other methods that depend on it play nicely. Based on my observations, these methods are primarily used for testing, but in any case, they should work. So I reckon this should be good to go, right?

I'm opening a Draft Pull Request to get your feedback on this :)

[Evalir]

Will review and QA later to ensure this is not a breaking change

[0xZerohero]

- you can't add more than one host when using the environment variable ANVIL_IP_ADDR
This was actually easier to fix than I thought. Description is updated.

[0xZerohero]

Is there anything else that needs to be done here ?
@Evalir

[Evalir]

Will review soon! sorry for the wait

[mattsse]

I can see how this could be useful,

supportive, since this only adds functionality and doesn't break anything

[mattsse]

lgtm

[Evalir]

looks good now!

[llllvvuu]

Nice! Minor point since my issue is already solved (becomes even more minor if Node.js 20+ keeps Happy Eyeballs on by default - but they may revert 🥴), but one way to make localhost "just work" could be to introduce (if it's not too breaking?):

- default_value = "127.0.0.1",
+ default_value = "::1,127.0.0.1",

- host: vec![IpAddr::V4(Ipv4Addr::LOCALHOST)],
+ host: vec![IpAddr::V4(Ipv4Addr::LOCALHOST), IpAddr::V6(Ipv6Addr::LOCALHOST)],

- self.host = if host.is_empty() { vec![IpAddr::V4(Ipv4Addr::LOCALHOST)] } else { host };
+ self.host = if host.is_empty() { vec![IpAddr::V4(Ipv4Addr::LOCALHOST), IpAddr::V6(Ipv6Addr::LOCALHOST)] } else { host };

Or support hostnames and default to localhost (could be even more breaking?):

; evcxr
>> use std::net::ToSocketAddrs;
>> let addrs_iter = "localhost:8545".to_socket_addrs().unwrap();
>> addrs_iter
IntoIter([[::1]:8545, 127.0.0.1:8545])

For reference, geth serves on localhost by default (although this is still wonky in Go).

the tl;dr of the rabbit hole is that:

• Most of the non-Rust world resolves localhost and serves on the first matching interface. It would have been a fair assumption a few years ago that localhost resolves to only one interface.
• Much of the Rust world doesn't bother resolving localhost and just uses 127.0.0.1 (except for Iron, which does resolve localhost to the first interface). It would have been a fair assumption a few years ago that these are the same thing.
• None of 127.0.0.1, ::1, or localhost are guaranteed to be substitutable for each other. Mixing conventions causes mildly confusing issues.

Given how all over the place the networking standards/conventions are (to the point where even language stdlibs don't have it together), perhaps the sanest thing may be to ignore all of my above ideas and just put something in the docs to the effect of "anvil serves on only 127.0.0.1 by default, don't try to connect to it via localhost" and call it a day. hardhat switched to 127.0.0.1 a while back so we'd be in good company.