add nexthop support

[nanamicat]

https://www.man7.org/linux/man-pages/man8/ip-nexthop.8.html

[gemini-code-assist]

Summary of Changes

Hello @nanamicat, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly expands the library's networking capabilities by introducing full support for nexthop management. It provides a structured and type-safe way to interact with nexthop entries, enabling programmatic control over how packets are forwarded. This enhancement is crucial for applications requiring fine-grained control over routing decisions and network topology.

Highlights

• Nexthop Management API: Introduced a comprehensive API for managing nexthop entries, mirroring ip nexthop commands. This includes functionalities to add, delete, and retrieve nexthops.
• New NexthopHandle: Added a nexthop() method to the main Handle struct, providing a dedicated entry point for nexthop-related operations.
• Nexthop Message Builder: Implemented NexthopMessageBuilder to facilitate the construction of nexthop messages, supporting various attributes like ID, output interface, blackhole status, groups, flags, protocol, scope, and gateway IP addresses (IPv4, IPv6, and generic).
• Route Builder Enhancement: The RouteMessageBuilder now includes a nexthop_id method, allowing routes to be associated with specific nexthop IDs.
• Minor Fixes and Refinements: Corrected a typo in src/link/bridge_port.rs (NeighVlanSupress to NeighVlanSuppress) and updated the ad_select attribute handling in src/link/bond.rs for better type safety.

Using Gemini Code Assist

The full guide for Gemini Code Assist can be found on our documentation page, here are some quick tips.

Invoking Gemini

You can request assistance from Gemini at any point by creating a comment using either /gemini <command> or @gemini-code-assist <command>. Below is a summary of the supported commands on the current page.

Feature	Command	Description
Code Review	/gemini review	Performs a code review for the current pull request in its current state.
Pull Request Summary	/gemini summary	Provides a summary of the current pull request in its current state.
Comment	@gemini-code-assist	Responds in comments when explicitly tagged, both in pull request comments and review comments.
Help	/gemini help	Displays a list of available commands.

Customization

To customize Gemini Code Assist for GitHub experience, repository maintainers can create a configuration file and/or provide a custom code review style guide (such as PEP-8 for Python) by creating and adding files to a .gemini/ folder in the base of the repository. Detailed instructions can be found here.

Limitations & Feedback

Gemini Code Assist may make mistakes. Please leave feedback on any instances where its feedback is incorrect or counter productive. You can react with 👍 and 👎 on @gemini-code-assist comments. If you're interested in giving your feedback about your experience with Gemini Code Assist for Github and other Google products, sign up here.

You can also get AI-powered code generation, chat, as well as code reviews directly in the IDE at no cost with the Gemini Code Assist IDE Extension.

Footnotes

1. Review the Privacy Notices, Generative AI Prohibited Use Policy, Terms of Service, and learn how to configure Gemini Code Assist in GitHub here. Gemini can make mistakes, so double check it and use code with caution. ↩

[gemini-code-assist]

Code Review

This pull request adds support for managing nexthop objects, equivalent to ip nexthop commands. It introduces a new nexthop module with handles, requests, and a message builder, following the existing patterns in the crate. The changes also include adding nexthop_id to the route builder to allow routes to use nexthop objects. The implementation is comprehensive and well-integrated. I have one suggestion to improve the robustness of the NexthopMessageBuilder by adding validation for consistent IP address families when setting the gateway.

[gemini-code-assist]

The current implementation of gateway() can lead to an inconsistent NexthopMessage if it's called multiple times with IP addresses of different families. The address family is set based on the first call, but this is not validated on subsequent calls. This could result in a message with family = Inet but a gateway with an IPv6 address, which the kernel would likely reject.

To ensure correctness, the method should validate that any subsequent calls use an IP address of the same family. Panicking on misuse is an acceptable and common approach for builders to enforce correct usage.

The comment on line 157 is also a bit confusing and can be removed as part of this change.

    pub fn gateway(mut self, addr: IpAddr) -> Self {
        let (family, bytes) = match addr {
            IpAddr::V4(addr) => (AddressFamily::Inet, addr.octets().to_vec()),
            IpAddr::V6(addr) => (AddressFamily::Inet6, addr.octets().to_vec()),
        };
        if self.message.header.family == AddressFamily::Unspec {
            self.message.header.family = family;
        } else if self.message.header.family != family {
            panic!("Attempted to set gateway with an inconsistent IP address family");
        }
        self.message.nlas.push(NexthopAttribute::Gateway(bytes));
        self
    }