text: // 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.
  type ARPEntry struct {
  	// IP address
  	IPAddr net.IP
  	// MAC address
  	HWAddr net.HardwareAddr
  	// 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
  }
  