go-netstat

go-netstat

go-netstat is a Golang library that provides a fast and multi-threaded implementation of the netstat utility on Linux. It is designed to be feature-complete with the net-tools netstat implementation and supports network namespaces for containers. It was written with Talos Linux in mind.

Installation

You can install go-netstat by running the following command:

go get github.com/nberlee/go-netstat/netstat

Usage

Here's an example of how to use go-netstat:

import (
    "context"
    "fmt"

    "github.com/nberlee/go-netstat/netstat"
)

func main() {
    ctx := context.Background()

    features := netstat.EnableFeatures{
        TCP:           true,
        TCP6:          true,
        UDP:           true,
        UDP6:          true,
        UDPLite:       true,
        UDPLite6:      true,
        Raw:           true,
        Raw6:          true,
        PID:           true,
        NoHostNetwork: false,
        AllNetNs:      true,
        NetNsName:     []string{},
        NetNsPids:     []uint32{},
    }

    fn := netstat.NoopFilter

    netstatResp, err := netstat.Netstat(ctx, features, fn)
    if err != nil {
        panic(err)
    }

    for _, entry := range netstatResp {
        fmt.Println(entry)
    }
}

The features struct specifies which types of sockets and connections to include in the result, while the fn function can be used to filter the results further.

Contributing

We welcome contributions to go-netstat! If you have bug fixes, feature requests, or performance improvements, feel free to submit a pull request. We are especially interested in contributions that are close to the core functionality and that benefit Talos Linux netstat.

Credits

The initial version of go-netstat was written by Cihangir Akturk, who contributed the functions ParseAddr, ParseIpv4, and ParseIpv6. Nico Berlee later rewrote and reworked every other function to make it faster by multi-threading and to add features like network namespaces, udplite+raw support and tests.

License

go-netstat is released under the MIT License. See LICENSE for details.

Types

EnableFeatures

The EnableFeatures struct specifies which types of sockets and connections to include in the result.

type EnableFeatures struct {
    TCP           bool
    TCP6          bool
    UDP           bool
    UDP6          bool
    UDPLite       bool
    UDPLite6      bool
    Raw           bool
    Raw6          bool
    PID           bool
    NoHostNetwork bool
    AllNetNs      bool
    NetNsName     []string
    NetNsPids     []uint32
}

SockTabEntry

The SockTabEntry struct represents each line of the /proc/net/[tcp|udp] file.

type SockTabEntry struct {
    Transport      string
    LocalEndpoint  *SockEndpoint
    RemoteEndpoint *SockEndpoint
    State          SkState
    TxQueue        uint64
    RxQueue        uint64
    Tr             TimerActive
    TimerWhen      uint64
    Retrnsmt       uint64
    UID            uint32
    Timeout        uint64
    Inode          uint64
    Ref            uint64
    Process        *common.Process
    NetNS          string
}

SockEndpoint

The SockEndpoint struct represents an IP address and port.

type SockEndpoint struct {
    IP   net.IP
    Port uint16
}

The IP field can be an IPv4 or IPv6 address.

Filter Function

The fn function is used to filter the results of the Netstat function.

type FilterFunc func(*SockTabEntry) bool

Here are some examples of filter functions:

func NoopFilter(s *SockTabEntry) bool {
    return true
}

func ConnectedFilter(s *SockTabEntry) bool {
    return !s.RemoteEndpoint.IP.IsUnspecified() && s.RemoteEndpoint.Port != 0
}

func ListeningFilter(s *SockTabEntry) bool {
    return s.RemoteEndpoint.IP.IsUnspecified() && s.RemoteEndpoint.Port == 0
}

Design decisions

• /proc/net/[tcp|udp|udplite|raw] are chosen over syscalls as accessing directly kernel data structures is can be faster than making syscalls with context switching overhead.
• go-netstat does not enter an network namespace, instead it gets the process id and reads the /proc/processid/net/[tcp|udp|udplite|raw]. This is safer and faster.

Flows

Network namespace

Network Namespace Name -> Find in /var/run/netns -> Follow bindmount to /proc/processid/ns/net, get the symlink which is if for net:[12345678]. Search in /proc/processid/ns/net for the file descriptor with the same symlink.

Process ID + Name

To enrich netstat entries with the process id, the inode is matched against /proc/processid/fd/* symlinks.