add nexthop support #225

nanamicat · 2026-01-10T17:15:54Z

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

gemini-code-assist · 2026-01-10T17:16:14Z

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 enhances the library's Netlink capabilities by adding full support for next-hop management. It introduces new data structures and parsing/emitting logic for next-hop messages and their attributes, as well as integrating these new message types into the existing Netlink message handling framework. This allows for more granular control and querying of next-hop configurations in the Linux kernel.

Highlights

New Nexthop Module: Introduced a dedicated nexthop module to handle Netlink next-hop messages, including structures for messages, headers, and attributes.
Netlink Message Integration: Integrated next-hop message types (RTM_NEWNEXTHOP, RTM_DELNEXTHOP, RTM_GETNEXTHOP) into the main RouteNetlinkMessage enum, enabling parsing and emitting of these messages.
Route Attribute Extension: Added support for RTA_NH_ID (Next-Hop ID) within RouteAttribute, allowing routes to reference specific next-hop objects.

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Code Review

This pull request adds support for nexthop objects, which is a great addition. The implementation is solid and follows the existing patterns in the crate. I've identified a few areas for improvement, mainly around making the parsing logic more robust and idiomatic. These changes will improve code clarity and maintainability.

gemini-code-assist · 2026-01-10T17:19:08Z

src/nexthop/attribute.rs

+                if payload.len() % 8 != 0 {
+                    return Err(DecodeError::from("Invalid NHA_GROUP length"));
+                }
+                let mut entries = Vec::new();
+                for chunk in payload.chunks(8) {
+                    if let Ok(entry) = NexthopGroupEntry::parse(&chunk) {
+                        entries.push(entry);
+                    } else {
+                        return Err(DecodeError::from(
+                            "Failed to parse group entry",
+                        ));
+                    }
+                }
+                NexthopAttribute::Group(entries)


The current implementation for parsing NHA_GROUP contains an unreachable else block. The length check payload.len() % 8 != 0 ensures that payload.chunks(8) only yields 8-byte slices, for which NexthopGroupEntry::parse will not fail. This can be refactored to be more concise and idiomatic using chunks_exact and iterator collect, which also makes the code's intent clearer and removes the dead code.

if payload.len() % 8 != 0 { return Err(DecodeError::from("Invalid NHA_GROUP length")); } NexthopAttribute::Group( payload .chunks_exact(8) .map(NexthopGroupEntry::parse) .collect::<Result<Vec<_, _>>>() .map_err(|_| // This should be unreachable given the length check above. DecodeError::from("Failed to parse group entry"))?, )

gemini-code-assist · 2026-01-10T17:19:08Z

src/nexthop/attribute.rs

+                if payload.len() != 4 {
+                    return Err(DecodeError::from("Invalid NHA_ID length"));
+                }
+                NexthopAttribute::Id(u32::from_ne_bytes(
+                    payload.try_into().map_err(|_| {
+                        DecodeError::from("Invalid NHA_ID length")
+                    })?,
+                ))


The parsing logic for fixed-size attributes like NHA_ID can be simplified. Instead of an explicit length check followed by try_into(), you can rely on try_into() alone to handle the length validation. This makes the code more concise and idiomatic Rust. This same feedback applies to the parsing of NHA_GROUP_TYPE, NHA_OIF, and NHA_ENCAP_TYPE in this file.

NexthopAttribute::Id(u32::from_ne_bytes( payload.try_into().map_err(|_| { DecodeError::from("Invalid NHA_ID length") })?, ))

gemini-code-assist · 2026-01-10T17:19:08Z

src/nexthop/attribute.rs

+                if payload.len() != 2 {
+                    return Err(DecodeError::from(
+                        "Invalid NHA_GROUP_TYPE length",
+                    ));
+                }
+                NexthopAttribute::GroupType(u16::from_ne_bytes(
+                    payload.try_into().map_err(|_| {
+                        DecodeError::from("Invalid NHA_GROUP_TYPE length")
+                    })?,
+                ))


The parsing logic for NHA_GROUP_TYPE can be simplified. By relying on try_into() to validate the payload length, the code becomes more concise and idiomatic.

NexthopAttribute::GroupType(u16::from_ne_bytes( payload.try_into().map_err(|_| { DecodeError::from("Invalid NHA_GROUP_TYPE length") })?, ))

gemini-code-assist · 2026-01-10T17:19:08Z

src/nexthop/attribute.rs

+                if payload.len() != 4 {
+                    return Err(DecodeError::from("Invalid NHA_OIF length"));
+                }
+                NexthopAttribute::Oif(u32::from_ne_bytes(
+                    payload.try_into().map_err(|_| {
+                        DecodeError::from("Invalid NHA_OIF length")
+                    })?,
+                ))


The parsing logic for NHA_OIF can be simplified. By relying on try_into() to validate the payload length, the code becomes more concise and idiomatic.

NexthopAttribute::Oif(u32::from_ne_bytes( payload.try_into().map_err(|_| { DecodeError::from("Invalid NHA_OIF length") })?, ))

gemini-code-assist · 2026-01-10T17:19:08Z

src/nexthop/attribute.rs

+                if payload.len() != 2 {
+                    return Err(DecodeError::from(
+                        "Invalid NHA_ENCAP_TYPE length",
+                    ));
+                }
+                NexthopAttribute::EncapType(u16::from_ne_bytes(
+                    payload.try_into().map_err(|_| {
+                        DecodeError::from("Invalid NHA_ENCAP_TYPE length")
+                    })?,
+                ))


The parsing logic for NHA_ENCAP_TYPE can be simplified. By relying on try_into() to validate the payload length, the code becomes more concise and idiomatic.

NexthopAttribute::EncapType(u16::from_ne_bytes( payload.try_into().map_err(|_| { DecodeError::from("Invalid NHA_ENCAP_TYPE length") })?, ))

gemini-code-assist · 2026-01-10T17:19:08Z

src/nexthop/message.rs

+impl<'a, T: AsRef<[u8]> + 'a> Parseable<NexthopMessageBuffer<&'a T>>
+    for Vec<NexthopAttribute>
+{
+    fn parse(buf: &NexthopMessageBuffer<&'a T>) -> Result<Self, DecodeError> {
+        let mut nlas = vec![];
+        for nla_buf in buf.attributes() {
+            let nla = nla_buf?;
+            nlas.push(NexthopAttribute::parse_with_param(
+                &(nla.value(), nla.kind()),
+                (),
+            )?);
+        }
+        Ok(nlas)
+    }
+}


The parse implementation for Vec<NexthopAttribute> can be written more idiomatically using a functional style with map and collect. This makes the code more concise and easier to read.

Suggested change

impl<'a, T: AsRef<[u8]> + 'a> Parseable<NexthopMessageBuffer<&'a T>>

for Vec<NexthopAttribute>

{

fn parse(buf: &NexthopMessageBuffer<&'a T>) -> Result<Self, DecodeError> {

let mut nlas = vec![];

for nla_buf in buf.attributes() {

let nla = nla_buf?;

nlas.push(NexthopAttribute::parse_with_param(

&(nla.value(), nla.kind()),

(),

)?);

}

Ok(nlas)

}

}

impl<'a, T: AsRef<[u8]> + 'a> Parseable<NexthopMessageBuffer<&'a T>>

for Vec<NexthopAttribute>

{

fn parse(buf: &NexthopMessageBuffer<&'a T>) -> Result<Self, DecodeError> {

buf.attributes()

.map(|nla_buf| {

let nla = nla_buf?;

NexthopAttribute::parse_with_param(

&(nla.value(), nla.kind()),

(),

)

})

.collect()

}

}

nanamicat added 2 commits January 10, 2026 21:41

add nexthop support

545f2db

fix

dfc76d7

gemini-code-assist bot reviewed Jan 10, 2026

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