package util import ( "bufio" "io" "io/ioutil" "net" "os" "runtime" "strings" "sync" "github.com/AdguardTeam/golibs/log" "github.com/fsnotify/fsnotify" "github.com/miekg/dns" ) type onChangedT func() // AutoHosts - automatic DNS records type AutoHosts struct { lock sync.Mutex // serialize access to table table map[string][]net.IP // 'hostname -> IP' table tableReverse map[string]string // "IP -> hostname" table for reverse lookup hostsFn string // path to the main hosts-file hostsDirs []string // paths to OS-specific directories with hosts-files watcher *fsnotify.Watcher // file and directory watcher object updateChan chan bool // signal for 'updateLoop' goroutine onChanged onChangedT // notification to other modules } // SetOnChanged - set callback function that will be called when the data is changed func (a *AutoHosts) SetOnChanged(onChanged onChangedT) { a.onChanged = onChanged } // Notify other modules func (a *AutoHosts) notify() { if a.onChanged == nil { return } a.onChanged() } // Init - initialize // hostsFn: Override default name for the hosts-file (optional) func (a *AutoHosts) Init(hostsFn string) { a.table = make(map[string][]net.IP) a.updateChan = make(chan bool, 2) a.hostsFn = "/etc/hosts" if runtime.GOOS == "windows" { a.hostsFn = os.ExpandEnv("$SystemRoot\\system32\\drivers\\etc\\hosts") } if len(hostsFn) != 0 { a.hostsFn = hostsFn } if IsOpenWrt() { a.hostsDirs = append(a.hostsDirs, "/tmp/hosts") // OpenWRT: "/tmp/hosts/dhcp.cfg01411c" } var err error a.watcher, err = fsnotify.NewWatcher() if err != nil { log.Error("AutoHosts: %s", err) } } // Start - start module func (a *AutoHosts) Start() { log.Debug("Start AutoHosts module") go a.updateLoop() a.updateChan <- true go a.watcherLoop() err := a.watcher.Add(a.hostsFn) if err != nil { log.Error("Error while initializing watcher for a file %s: %s", a.hostsFn, err) } for _, dir := range a.hostsDirs { err = a.watcher.Add(dir) if err != nil { log.Error("Error while initializing watcher for a directory %s: %s", dir, err) } } } // Close - close module func (a *AutoHosts) Close() { a.updateChan <- false close(a.updateChan) _ = a.watcher.Close() } // update table func (a *AutoHosts) updateTable(table map[string][]net.IP, host string, ipAddr net.IP) { ips, ok := table[host] if ok { for _, ip := range ips { if ip.Equal(ipAddr) { // IP already exists: don't add duplicates ok = false break } } if !ok { ips = append(ips, ipAddr) table[host] = ips } } else { table[host] = []net.IP{ipAddr} ok = true } if ok { log.Debug("AutoHosts: added %s -> %s", ipAddr, host) } } // update "reverse" table func (a *AutoHosts) updateTableRev(tableRev map[string]string, host string, ipAddr net.IP) { ipStr := ipAddr.String() _, ok := tableRev[ipStr] if !ok { tableRev[ipStr] = host log.Debug("AutoHosts: added reverse-address %s -> %s", ipStr, host) } } // Read IP-hostname pairs from file // Multiple hostnames per line (per one IP) is supported. func (a *AutoHosts) load(table map[string][]net.IP, tableRev map[string]string, fn string) { f, err := os.Open(fn) if err != nil { log.Error("AutoHosts: %s", err) return } defer f.Close() r := bufio.NewReader(f) log.Debug("AutoHosts: loading hosts from file %s", fn) finish := false for !finish { line, err := r.ReadString('\n') if err == io.EOF { finish = true } else if err != nil { log.Error("AutoHosts: %s", err) return } line = strings.TrimSpace(line) ip := SplitNext(&line, ' ') ipAddr := net.ParseIP(ip) if ipAddr == nil { continue } for { host := SplitNext(&line, ' ') if len(host) == 0 { break } a.updateTable(table, host, ipAddr) a.updateTableRev(tableRev, host, ipAddr) } } } // Receive notifications from fsnotify package func (a *AutoHosts) watcherLoop() { for { select { case event, ok := <-a.watcher.Events: if !ok { return } // skip duplicate events repeat := true for repeat { select { case _ = <-a.watcher.Events: // skip this event default: repeat = false } } if event.Op&fsnotify.Write == fsnotify.Write { log.Debug("AutoHosts: modified: %s", event.Name) select { case a.updateChan <- true: // sent a signal to 'updateLoop' goroutine default: // queue is full } } case err, ok := <-a.watcher.Errors: if !ok { return } log.Error("AutoHosts: %s", err) } } } // updateLoop - read static hosts from system files func (a *AutoHosts) updateLoop() { for { select { case ok := <-a.updateChan: if !ok { log.Debug("Finished AutoHosts update loop") return } a.updateHosts() } } } // updateHosts - loads system hosts func (a *AutoHosts) updateHosts() { table := make(map[string][]net.IP) tableRev := make(map[string]string) a.load(table, tableRev, a.hostsFn) for _, dir := range a.hostsDirs { fis, err := ioutil.ReadDir(dir) if err != nil { if !os.IsNotExist(err) { log.Error("AutoHosts: Opening directory: %s: %s", dir, err) } continue } for _, fi := range fis { a.load(table, tableRev, dir+"/"+fi.Name()) } } a.lock.Lock() a.table = table a.tableReverse = tableRev a.lock.Unlock() a.notify() } // Process - get the list of IP addresses for the hostname // Return nil if not found func (a *AutoHosts) Process(host string, qtype uint16) []net.IP { if qtype == dns.TypePTR { return nil } var ipsCopy []net.IP a.lock.Lock() ips, _ := a.table[host] if len(ips) != 0 { ipsCopy = make([]net.IP, len(ips)) copy(ipsCopy, ips) } a.lock.Unlock() log.Debug("AutoHosts: answer: %s -> %v", host, ipsCopy) return ipsCopy } // convert character to hex number func charToHex(n byte) int8 { if n >= '0' && n <= '9' { return int8(n) - '0' } else if (n|0x20) >= 'a' && (n|0x20) <= 'f' { return (int8(n) | 0x20) - 'a' + 10 } return -1 } // parse IPv6 reverse address func ipParseArpa6(s string) net.IP { if len(s) != 63 { return nil } ip6 := make(net.IP, 16) for i := 0; i != 64; i += 4 { // parse "0.1." n := charToHex(s[i]) n2 := charToHex(s[i+2]) if s[i+1] != '.' || (i != 60 && s[i+3] != '.') || n < 0 || n2 < 0 { return nil } ip6[16-i/4-1] = byte(n2<<4) | byte(n&0x0f) } return ip6 } // ipReverse - reverse IP address: 1.0.0.127 -> 127.0.0.1 func ipReverse(ip net.IP) net.IP { n := len(ip) r := make(net.IP, n) for i := 0; i != n; i++ { r[i] = ip[n-i-1] } return r } // Convert reversed ARPA address to a normal IP address func dnsUnreverseAddr(s string) net.IP { const arpaV4 = ".in-addr.arpa" const arpaV6 = ".ip6.arpa" if strings.HasSuffix(s, arpaV4) { ip := strings.TrimSuffix(s, arpaV4) ip4 := net.ParseIP(ip).To4() if ip4 == nil { return nil } return ipReverse(ip4) } else if strings.HasSuffix(s, arpaV6) { ip := strings.TrimSuffix(s, arpaV6) return ipParseArpa6(ip) } return nil // unknown suffix } // ProcessReverse - process PTR request // Return "" if not found or an error occurred func (a *AutoHosts) ProcessReverse(addr string, qtype uint16) string { if qtype != dns.TypePTR { return "" } ipReal := dnsUnreverseAddr(addr) if ipReal == nil { return "" // invalid IP in question } ipStr := ipReal.String() a.lock.Lock() host := a.tableReverse[ipStr] a.lock.Unlock() if len(host) == 0 { return "" // not found } log.Debug("AutoHosts: reverse-lookup: %s -> %s", addr, host) return host } // List - get the hosts table. Thread-safe. func (a *AutoHosts) List() map[string][]net.IP { table := make(map[string][]net.IP) a.lock.Lock() for k, v := range a.table { table[k] = v } a.lock.Unlock() return table }