Source: arp.go in package github.com/prometheus/procfs

Copyright 2019 The Prometheus Authors Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.


package procfs

import (
	"fmt"
	"io/ioutil"
	"net"
	"strings"
)

ARPEntry contains a single row of the columnar data represented in /proc/net/arp.

IP address

MAC address

Name of the device

	Device string
}

GatherARPEntries retrieves all the ARP entries, parse the relevant columns, and then return a slice of ARPEntry's.

func (fs FS) GatherARPEntries() ([]ARPEntry, error) {
	data, err := ioutil.ReadFile(fs.proc.Path("net/arp"))
	if err != nil {
		return nil, fmt.Errorf("error reading arp %s: %s", fs.proc.Path("net/arp"), err)
	}

	return parseARPEntries(data)
}

func parseARPEntries(data []byte) ([]ARPEntry, error) {
	lines := strings.Split(string(data), "\n")
	entries := make([]ARPEntry, 0)
	var err error
	const (
		expectedDataWidth   = 6
		expectedHeaderWidth = 9
	)
	for _, line := range lines {
		columns := strings.Fields(line)
		width := len(columns)

		if width == expectedHeaderWidth || width == 0 {
			continue
		} else if width == expectedDataWidth {
			entry, err := parseARPEntry(columns)
			if err != nil {
				return []ARPEntry{}, fmt.Errorf("failed to parse ARP entry: %s", err)
			}
			entries = append(entries, entry)
		} else {
			return []ARPEntry{}, fmt.Errorf("%d columns were detected, but %d were expected", width, expectedDataWidth)
		}

	}

	return entries, err
}

func parseARPEntry(columns []string) (ARPEntry, error) {
	ip := net.ParseIP(columns[0])
	mac := net.HardwareAddr(columns[3])

	entry := ARPEntry{
		IPAddr: ip,
		HWAddr: mac,
		Device: columns[5],
	}

	return entry, nil