package etchosts import ( "bufio" "bytes" "fmt" "io" "io/ioutil" "os" "regexp" "strings" "sync" ) // Record Structure for a single host record type Record struct { Hosts string IP string } // WriteTo writes record to file and returns bytes written or error func (r Record) WriteTo(w io.Writer) (int64, error) { n, err := fmt.Fprintf(w, "%s\t%s\n", r.IP, r.Hosts) return int64(n), err } var ( // Default hosts config records slice defaultContent = []Record{ {Hosts: "localhost", IP: "127.0.0.1"}, {Hosts: "localhost ip6-localhost ip6-loopback", IP: "::1"}, {Hosts: "ip6-localnet", IP: "fe00::0"}, {Hosts: "ip6-mcastprefix", IP: "ff00::0"}, {Hosts: "ip6-allnodes", IP: "ff02::1"}, {Hosts: "ip6-allrouters", IP: "ff02::2"}, } // A cache of path level locks for synchronizing /etc/hosts // updates on a file level pathMap = make(map[string]*sync.Mutex) // A package level mutex to synchronize the cache itself pathMutex sync.Mutex ) func pathLock(path string) func() { pathMutex.Lock() defer pathMutex.Unlock() pl, ok := pathMap[path] if !ok { pl = &sync.Mutex{} pathMap[path] = pl } pl.Lock() return func() { pl.Unlock() } } // Drop drops the path string from the path cache func Drop(path string) { pathMutex.Lock() defer pathMutex.Unlock() delete(pathMap, path) } // Build function // path is path to host file string required // IP, hostname, and domainname set main record leave empty for no master record // extraContent is an array of extra host records. func Build(path, IP, hostname, domainname string, extraContent []Record) error { defer pathLock(path)() content := bytes.NewBuffer(nil) if IP != "" { //set main record var mainRec Record mainRec.IP = IP // User might have provided a FQDN in hostname or split it across hostname // and domainname. We want the FQDN and the bare hostname. fqdn := hostname if domainname != "" { fqdn = fmt.Sprintf("%s.%s", fqdn, domainname) } parts := strings.SplitN(fqdn, ".", 2) if len(parts) == 2 { mainRec.Hosts = fmt.Sprintf("%s %s", fqdn, parts[0]) } else { mainRec.Hosts = fqdn } if _, err := mainRec.WriteTo(content); err != nil { return err } } // Write defaultContent slice to buffer for _, r := range defaultContent { if _, err := r.WriteTo(content); err != nil { return err } } // Write extra content from function arguments for _, r := range extraContent { if _, err := r.WriteTo(content); err != nil { return err } } return ioutil.WriteFile(path, content.Bytes(), 0644) } // Add adds an arbitrary number of Records to an already existing /etc/hosts file func Add(path string, recs []Record) error { defer pathLock(path)() if len(recs) == 0 { return nil } b, err := mergeRecords(path, recs) if err != nil { return err } return ioutil.WriteFile(path, b, 0644) } func mergeRecords(path string, recs []Record) ([]byte, error) { f, err := os.Open(path) if err != nil { return nil, err } defer f.Close() content := bytes.NewBuffer(nil) if _, err := content.ReadFrom(f); err != nil { return nil, err } for _, r := range recs { if _, err := r.WriteTo(content); err != nil { return nil, err } } return content.Bytes(), nil } // Delete deletes an arbitrary number of Records already existing in /etc/hosts file func Delete(path string, recs []Record) error { defer pathLock(path)() if len(recs) == 0 { return nil } old, err := os.Open(path) if err != nil { return err } var buf bytes.Buffer s := bufio.NewScanner(old) eol := []byte{'\n'} loop: for s.Scan() { b := s.Bytes() if len(b) == 0 { continue } if b[0] == '#' { buf.Write(b) buf.Write(eol) continue } for _, r := range recs { if bytes.HasSuffix(b, []byte("\t"+r.Hosts)) { continue loop } } buf.Write(b) buf.Write(eol) } old.Close() if err := s.Err(); err != nil { return err } return ioutil.WriteFile(path, buf.Bytes(), 0644) } // Update all IP addresses where hostname matches. // path is path to host file // IP is new IP address // hostname is hostname to search for to replace IP func Update(path, IP, hostname string) error { defer pathLock(path)() old, err := ioutil.ReadFile(path) if err != nil { return err } var re = regexp.MustCompile(fmt.Sprintf("(\\S*)(\\t%s)(\\s|\\.)", regexp.QuoteMeta(hostname))) return ioutil.WriteFile(path, re.ReplaceAll(old, []byte(IP+"$2"+"$3")), 0644) }