dnsupdater/main.go

package main

import (
	"context"
	"encoding/json"
	"fmt"
	"io/ioutil"
	"net/http"
	"os"
	"path"
	"regexp"
	"time"

	"golang.org/x/xerrors"

	"cdr.dev/slog"

	"cdr.dev/slog/sloggers/sloghuman"
	"github.com/dghubble/sling"
	"github.com/matryer/try"
	"github.com/urfave/cli"
	"gopkg.in/gomail.v2"
)

type Configuration struct {
	Username        string   `json:"name"`
	Email           string   `json:"email"`
	GandiKey        string   `json:"gandikey"`
	Domains         []string `json:"domains"`
	RouterLogin     string   `json:"router_login"`
	RouterPassword  string   `json:"router_password"`
	RouterStatusUrl string   `json:"router_status_url"`
	WanIPRegex      string   `json:"wan_ip_regex"`
	MailSettings    *struct {
		Sender       string   `json:"sender"`
		To           []string `json:"to"`
		SmtpHost     string   `json:"smtp_host"`
		SmtpLogin    string   `json:"smtp_login"`
		SmtpPassword string   `json:"smtp_password"`
		SmtpPort     int      `json:"smtp_port"`
	} `json:"mail_settings"`
}

type DnsResponse struct {
	RecordType string   `json:"rrset_type"`
	Ttl        int      `json:"rrset_ttl"`
	Name       string   `json:"rrset_name"`
	Values     []string `json:"rrset_values"`
}

var (
	configuration Configuration
	configPath    string
	base          *sling.Sling
)

const (
	GandiApiUrl     = "https://dns.api.gandi.net/api/v5/"
	GandiARecordUrl = "domains/%s/records/@/A"
)

var log = sloghuman.Make(os.Stdout)

func main() {

	app := cli.NewApp()
	app.Name = "dnsupdater"
	app.Usage = "Automatically update dns"
	app.Before = before
	app.Action = start
	app.Flags = []cli.Flag{

		cli.StringFlag{
			Name:   "config, C",
			Usage:  "path to config file",
			Value:  "/config",
			EnvVar: "CONFIG_PATH",
		},
	}

	if err := app.Run(os.Args); err != nil {
		log.Fatal(context.Background(), "", slog.Error(err))
	}
}

func before(c *cli.Context) error {
	configPath = path.Join(c.String("config"), "conf.json")
	file, err := os.Open(configPath)
	if err != nil {
		return fmt.Errorf("error while opening config file: %v", err)
	}
	defer file.Close()
	decoder := json.NewDecoder(file)
	configuration = Configuration{}
	err = decoder.Decode(&configuration)
	if err != nil {
		return err
	}

	base = sling.New().Client(&http.Client{
		Timeout: 30 * time.Second,
	}).Base(GandiApiUrl).
		Set("X-Api-Key", configuration.GandiKey)

	return nil
}

func start(*cli.Context) error {
	ctx := context.Background()
	if err := update(ctx); err != nil {
		SendStatusMail(ctx, fmt.Sprintf("Error during update process : %s", err))
		return err
	}
	return nil
}

func update(ctx context.Context) error {
	newIp, err := GetOutboundIP()
	if err != nil {
		return fmt.Errorf("getting outbound ip: %v", err)
	}

	updatedDomains := ""
	for _, domain := range configuration.Domains {
		currentIp, err := GetCurrentIp(ctx, domain)
		if err != nil {
			return fmt.Errorf("getting current ip: %v", err)
		}

		if currentIp == newIp {
			continue
		}
		log.Info(ctx, "ip has changed", slog.F("domain", domain), slog.F("current ip", currentIp), slog.F("new ip", newIp))
		err = SetCurrentIp(newIp, domain)
		if err != nil {
			return fmt.Errorf("setting current ip: %v", err)
		}
		updatedDomains += fmt.Sprintf("\t- %s\n", domain)
	}

	if updatedDomains != "" {
		SendStatusMail(ctx, fmt.Sprintf(`Home IP has changed : %s
Dns updated successfully for domains
%s`, newIp, updatedDomains))
	}

	return nil
}

func SendStatusMail(ctx context.Context, messageText string) {

	settings := configuration.MailSettings
	if settings == nil {
		log.Warn(ctx, "no smtp settings defined > status mail not sent")
		return
	}

	d := gomail.NewDialer(settings.SmtpHost, settings.SmtpPort, settings.SmtpLogin, settings.SmtpPassword)
	s, err := d.Dial()
	if err != nil {
		log.Error(ctx, "dialing smtp server", slog.Error(err))
		return
	}

	m := gomail.NewMessage()
	for _, r := range settings.To {
		m.SetHeader("From", settings.Sender)
		m.SetAddressHeader("To", r, "")
		m.SetHeader("Subject", "DnsUpdater Status")
		m.SetBody("text/plain", messageText)

		if err := gomail.Send(s, m); err != nil {
			log.Warn(ctx, "could not send email", slog.F("recipient", r), slog.Error(err))
		}
		m.Reset()
	}
}

func GetCurrentIp(ctx context.Context, domain string) (string, error) {
	var value string
	err := try.Do(func(attempt int) (bool, error) {
		var err error
		value, err = func(domain string) (string, error) {
			dnsresponse := DnsResponse{}
			resp, err := base.New().Get(fmt.Sprintf(GandiARecordUrl, domain)).
				ReceiveSuccess(&dnsresponse)
			if err != nil {
				return "", fmt.Errorf("requesting gandi dns info: %v", err)
			}
			if resp.StatusCode < 200 || resp.StatusCode > 299 {
				return "", fmt.Errorf("requesting gandi dns info, no 2xx http status code: %d", resp.StatusCode)
			}
			if len(dnsresponse.Values) == 0 {
				return "", fmt.Errorf("no values in dnsresponse")
			}
			return dnsresponse.Values[0], nil
		}(domain)
		if err != nil {
			log.Warn(ctx, "getting current ip from gandi", slog.Error(err))
			time.Sleep(30 * time.Second)
		}
		return attempt < 5, err
	})
	if err != nil {
		return "", xerrors.Errorf("getting current ip from gandi: %w", err)
	}
	return value, nil
}

func SetCurrentIp(newip string, domain string) error {
	resp, err := base.New().Put(fmt.Sprintf(GandiARecordUrl, domain)).
		BodyJSON(struct {
			TTL    int      `json:"rrset_ttl"`
			Values []string `json:"rrset_values"`
		}{
			TTL:    600,
			Values: []string{newip},
		}).ReceiveSuccess(nil)
	if err != nil {
		return xerrors.Errorf("setting gandi dns info: %w", err)
	}
	if resp.StatusCode < 200 || resp.StatusCode > 299 {
		return xerrors.Errorf("setting gandi dns info, no 2xx http status code: %d", resp.StatusCode)
	}
	return nil
}

func GetOutboundIP() (string, error) {
	url := configuration.RouterStatusUrl
	if url == "" {
		url = "http://192.168.1.1/Status_Internet.live.asp"
	}
	req, err := http.NewRequest("GET", url, nil)
	if err != nil {
		return "", fmt.Errorf("creating http request: %v", err)
	}
	if configuration.RouterLogin != "" && configuration.RouterPassword != "" {
		req.SetBasicAuth(configuration.RouterLogin, configuration.RouterPassword)
	}
	res, err := http.DefaultClient.Do(req)
	if err != nil {
		return "", fmt.Errorf("executing http request: %v", err)
	}
	defer res.Body.Close()
	body, err := ioutil.ReadAll(res.Body)
	if err != nil {
		return "", fmt.Errorf("reading response body: %v", err)
	}

	wanipregex := configuration.WanIPRegex
	if wanipregex == "" {
		wanipregex = "wan_ipaddr::([0-9.]*)}"
	}
	r := regexp.MustCompile(wanipregex)
	matches := r.FindStringSubmatch(string(body))
	if len(matches) < 2 {
		return "", fmt.Errorf("unable to find WAN IP with regex %s in %s", wanipregex, string(body))
	}
	return matches[1], nil
}