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package arp
import (
"os/exec"
"regexp"
"strings"
"penguins.lan/utils"
)
type ArpTable struct {
AddrToMac map[utils.INet4]utils.Mac
}
// Lookup returns the canonical MAC for an IPv4 string, false if it isn't in the
// table or isn't parseable IPv4 (e.g. an IPv6 peer).
func (t *ArpTable) Lookup(ip string) (string, bool) {
addr, err := utils.ParseINet4(ip)
if err != nil {
return "", false
}
mac, ok := t.AddrToMac[*addr]
if !ok {
return "", false
}
return mac.Format(), true
}
type TableProvider interface {
Fetch() (*ArpTable, error)
}
var arpLine = regexp.MustCompile(`\((\d{1,3}(?:\.\d{1,3}){3})\) at ([0-9a-fA-F]{1,2}(?::[0-9a-fA-F]{1,2}){5})`)
type SystemProvider struct{}
func (SystemProvider) Fetch() (*ArpTable, error) {
out, err := exec.Command("arp", "-an").Output()
if err != nil {
return nil, err
}
return parseTable(string(out)), nil
}
func parseTable(out string) *ArpTable {
table := &ArpTable{AddrToMac: make(map[utils.INet4]utils.Mac)}
for _, line := range strings.Split(out, "\n") {
m := arpLine.FindStringSubmatch(line)
if m == nil {
continue
}
addr, err := utils.ParseINet4(m[1])
if err != nil {
continue
}
mac, err := utils.ParseMac(m[2])
if err != nil {
continue
}
table.AddrToMac[*addr] = *mac
}
return table
}
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