Crate neli

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Expand description

Rationale

This crate aims to be a pure Rust implementation that defines the necessary constants and wraps them in enums to distinguish between various categories of constants in the context of netlink.

The project is broken down into the following modules:

  • attr - This defines a generic interface for netlink attributes (both generic and routing netlink attributes).
  • consts - This is where all of the C-defined constants are wrapped into type safe enums for use in the library.
  • err - This module contains all of the protocol and library-level errors encountered in the code.
  • genl - This code provides parsing for the generic netlink
  • iter - This code handles iterating over received netlink packets.
  • nl - This is the top level netlink header code that handles the header that all netlink messages are encapsulated in.
  • rtnl - This module is for the routing netlink subsystem of the netlink protocol.
  • socket - This provides a socket structure for use in sending and receiving messages and a number of convenience functions for commonly encountered use cases.

Design decisions

This is a fairly low level library that currently does not have a whole lot of higher level handle-type data structures and relies mostly on the NlSocket and NlSocketHandle structs to provide most of the convenience functions.

The goal of this library is completeness for handling netlink and am working to incorporate features that will make this library easier to use in all use cases. If you have a use case you would like to see supported, please open an issue on Github.

Examples

Examples of working code exist in the examples/ subdirectory on Github. They have a separate Cargo.toml file to provide easy testing and use.

Workflows seem to usually follow a pattern of socket creation,and then either sending and receiving messages in request/response formats:

use std::error::Error;

use neli::{
    consts::{genl::*, nl::*, socket::*},
    err::NlError,
    genl::{Genlmsghdr, Nlattr},
    nl::{Nlmsghdr, NlPayload},
    socket::NlSocketHandle,
    types::{Buffer, GenlBuffer},
};

const GENL_VERSION: u8 = 1;

fn request_response() -> Result<(), Box<dyn Error>> {
    let mut socket = NlSocketHandle::connect(
        NlFamily::Generic,
        None,
        &[],
    )?;

    let attrs: GenlBuffer<Index, Buffer> = GenlBuffer::new();
    let genlhdr = Genlmsghdr::new(
        CtrlCmd::Getfamily,
        GENL_VERSION,
        attrs,
    );
    let nlhdr = {
        let len = None;
        let nl_type = GenlId::Ctrl;
        let flags = NlmFFlags::new(&[NlmF::Request, NlmF::Dump]);
        let seq = None;
        let pid = None;
        let payload = NlPayload::Payload(genlhdr);
        Nlmsghdr::new(len, nl_type, flags, seq, pid, payload)
    };
    socket.send(nlhdr)?;
     
    // Do things with multi-message response to request...
    let mut iter = socket.iter::<NlTypeWrapper, Genlmsghdr<CtrlCmd, CtrlAttr>>(false);
    while let Some(Ok(response)) = iter.next() {
        // Do things with response here...
    }
     
    // Or get single message back...
    let msg = socket.recv::<Nlmsg, Genlmsghdr<CtrlCmd, CtrlAttr>>()?;

    Ok(())
}

or a subscriptions to a stream of event notifications from netlink:

use std::error::Error;

use neli::{
    consts::{genl::*, nl::*, socket::*},
    err::NlError,
    genl::Genlmsghdr,
    socket,
};

fn subscribe_to_mcast() -> Result<(), Box<dyn Error>> {
    let mut s = socket::NlSocketHandle::connect(
        NlFamily::Generic,
        None,
        &[],
    )?;
    let id = s.resolve_nl_mcast_group(
        "my_family_name",
        "my_multicast_group_name",
    )?;
    s.add_mcast_membership(&[id])?;
    for next in s.iter::<NlTypeWrapper, Genlmsghdr<u8, u16>>(true) {
        // Do stuff here with parsed packets...
     
        // like printing a debug representation of them:
        println!("{:?}", next?);
    }

    Ok(())
}

Documentation

Each module has been documented extensively to provide information on how to use the code contained in the module. Pull requests for documentation mistakes, updates, and rewording for clarity is a valuable contribution as this project aims to be as simple to use as possible.

Modules

attr

Shared attribute code for all types of netlink attributes.

consts

High level notes

err

This is the module that contains the error types used in neli

genl

This module contains generic netlink parsing data structures. This is all handled by the Genlmsghdr header struct which contains all of the information needed for the generic netlink layer.

iter

Module for iteration over netlink responses

nl

This module contains the top level netlink header code. Every netlink message will be encapsulated in a top level Nlmsghdr.

rtnl

This module provides an implementation of routing netlink structures and the routing attributes that are at the end of most routing netlink responses.

socket

This module provides code that glues all of the other modules together and allows message send and receive operations.

types

Module containing various types used across the various netlink structures used in neli.

utils

A module containing utilities for working with constructs like bitflags and other low level operations.

Macros

impl_flags

Implement a container for bit flag enums where the set of flags will be condensed into a single value.

impl_trait

For generating a marker trait that flags a new enum as usable in a field that accepts a generic type. This way, the type parameter can be constrained by a trait bound to only accept enums that implement the marker trait.

Structs

BeU64

A u64 data type that will always be serialized as big endian

Traits

FromBytes

A trait defining how to convert from a byte buffer to a netlink data structure.

FromBytesWithInput

Takes an arbitrary input which serves as additional information for guiding the conversion from a byte buffer to a data structure. A common workflow is a data structure that has a size to determine how much more of the data in the byte buffer is part of a given data structure.

Header

Defined for data structures that contain a header.

Size

A trait defining methods that apply to all netlink data structures related to sizing of data types.

ToBytes

A trait defining a netlink data structure’s conversion to a byte buffer.

TypeSize

A trait defining methods that apply to constant-sized data types related to size.

Attribute Macros

neli_enum

This method converts a method from the form:

Derive Macros

FromBytes

Derives the neli FromBytes trait for a struct.

FromBytesWithInput

Derives the neli FromBytesWithInput trait for a struct.

Header

Derives the neli Header trait for a struct or enum. Unlike other derive macros in this crate, the Header derive macro does not impose type parameter bounds on type parameters. See the accepted attribute for more information. The reason for this is that the last field is considered to be the payload. Because the payload may be represented by a type parameter, we cannot blindly restrict type parameters or else we impose an artificial restriction of TypeSize on the payload type parameter. This is a problem for the Header trait as the payload may be unsized even if the rest of the header is composed exclusively of statically sized types and are therefore compatible with the TypeSize trait.

Size

Derives the neli Size trait for a struct or enum.

ToBytes

Derives the neli ToBytes trait for a struct or enum.