db.go

// arplogger is a tool for Linux systems that listens for arp packets on
// the specified interface(s) to discover new hosts appearing on the
// local IPv4 network.
//
// Copyright (c) 2021-2022 Johannes Heimansberg
// SPDX-License-Identifier: MIT
package main

import (
	"bufio"
	"fmt"
	"net"
	"os"
	"strings"
	"sync"
)

type DB struct {
	mu           sync.RWMutex
	databasePath string
}

func (db *DB) Init(dbPath string) error {
	db.mu.Lock()
	defer db.mu.Unlock()
	db.databasePath = dbPath
	f, err := os.OpenFile(db.databasePath, os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0644)
	if err == nil {
		f.Close()
	}
	return err
}

func (db *DB) Clear() error {
	return os.Truncate(db.databasePath, 0)
}

// verifyIP checks if the supplied string has the correct format for an IP address
func (db *DB) verifyIP(ip string) error {
	res := net.ParseIP(ip)
	if res == nil {
		return fmt.Errorf("Inavlid IP address")
	}
	return nil
}

// CheckMAC checks if the supplied MAC address is found in the database
func (db *DB) CheckMAC(mac string) (bool, error) {
	macAddr, err := net.ParseMAC(mac)
	if err != nil {
		return false, err
	}
	mac = macAddr.String()
	db.mu.RLock()
	defer db.mu.RUnlock()
	f, err := os.OpenFile(db.databasePath, os.O_RDONLY, 0644)
	defer f.Close()
	if err != nil {
		return false, err
	}
	s := bufio.NewScanner(f)
	s.Split(bufio.ScanLines)
	for s.Scan() {
		entry := strings.Split(s.Text(), " ")
		if entry[0] == mac { // Match found
			return true, nil
		}
	}
	return false, nil
}

// Add adds a new entry to the database
func (db *DB) Add(mac string, ip string) error {
	macAddr, err := net.ParseMAC(mac)
	if err != nil {
		return err
	}
	if err := db.verifyIP(ip); err != nil {
		return err
	}
	db.mu.Lock()
	defer db.mu.Unlock()
	f, err := os.OpenFile(db.databasePath, os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0644)
	defer f.Close()
	if err != nil {
		return err
	}
	fmt.Fprintf(f, "%s %s\n", macAddr.String(), ip)
	return nil
}