update-dns/main.go

package main

import (
	"encoding/json"
	"fmt"
	"net/http"
	"os"
	"strconv"
	"strings"
	"sync"

	"github.com/dnsimple/dnsimple-go/dnsimple"
	"github.com/pkg/errors"
	"github.com/urfave/cli"
)

func main() {
	app := cli.NewApp()
	app.Name = "update-dns"
	app.Usage = "update dnsimple with public ip address"
	app.Action = action

	app.Flags = []cli.Flag{
		cli.StringFlag{
			Name:  "url",
			Value: "https://whatismyipv6.buddy.wtf/json",
			Usage: "url to use to get public ip address",
		},

		cli.StringFlag{
			EnvVar: "DNSIMPLE_TOKEN",
			Name:   "dnsimple-token",
			Usage:  "dnsimple token",
		},
	}

	app.Run(os.Args)
}

type runtimeError string

func (e runtimeError) Error() string {
	return string(e)
}

func action(context *cli.Context) error {
	var wg sync.WaitGroup
	if context.NArg() < 1 {
		return runtimeError("requires host argument")
	}

	host := context.Args().Get(0)

	wg.Add(1)
	var getIPError error
	var ip string
	go func() {
		defer wg.Done()
		result, err := getIP(context.String("url"))
		if err != nil {
			getIPError = errors.Wrap(err, "could not get IP address")
			return
		}
		ip = result.IP
	}()

	var dnSimpleAccountID string
	var getRecordError error
	var record *dnsimple.ZoneRecord
	credentials := dnsimple.NewOauthTokenCredentials(context.String("dnsimple-token"))
	dnSimpleClient := dnsimple.NewClient(credentials)
	wg.Add(1)
	go func() {
		defer wg.Done()

		accountID, result, err := getRecord(dnSimpleClient, host, "AAAA")
		dnSimpleAccountID = accountID
		if err != nil {
			getRecordError = errors.Wrap(err, "could not get ip for host")
			return
		}
		record = result
	}()

	wg.Wait()

	if getIPError != nil {
		return errors.Wrap(getIPError, "could no get ip address")
	}
	if getRecordError != nil {
		switch errors.Cause(getRecordError).(type) {
		case notFoundError:
			break
		default:
			return errors.Wrap(getRecordError, "could no get record")
		}
	}

	subdomain, domain, _ := splitHost(host)
	if record == nil {
		_, err := dnSimpleClient.Zones.CreateRecord(dnSimpleAccountID, domain, dnsimple.ZoneRecord{
			Name:    subdomain,
			Type:    "AAAA",
			Content: ip,
		})
		if err != nil {
			return errors.Wrap(err, "could not create record")
		}
		fmt.Printf("%s record created for %s as %s\n", "AAAA", host, ip)
	} else if ip != record.Content {
		record.Content = ip
		_, err := dnSimpleClient.Zones.UpdateRecord(dnSimpleAccountID, domain, record.ID, *record)
		if err != nil {
			return errors.Wrap(err, "could not update record")
		}
		fmt.Printf("%s record for %s updated to %s\n", "AAAA", host, ip)
	} else {
		fmt.Printf("%s record for %s already set as %s\n", "AAAA", host, ip)
	}
	return nil
}

type whatIsMyIPResult struct {
	IP      string `json:ip`
	Version string `json:version`
}

type notFoundError error

func getRecord(client *dnsimple.Client, host string, kind string) (string, *dnsimple.ZoneRecord, error) {
	subdomain, domain, err := splitHost(host)
	if err != nil {
		return "", nil, errors.Wrap(err, "unable to parse host")
	}
	accountID, err := getAccountID(client)
	if err != nil {
		return "", nil, errors.Wrap(err, "could not get account id")
	}

	records, err := client.Zones.ListRecords(accountID, domain, &dnsimple.ZoneRecordListOptions{})
	if err != nil {
		return "", nil, errors.Wrap(err, "could not get list of records")
	}

	for _, record := range records.Data {
		if record.ZoneID == domain && record.Name == subdomain && record.Type == kind {
			return accountID, &record, nil
		}
	}

	return accountID, nil, notFoundError(errors.New("could not find record"))
}

func getAccountID(client *dnsimple.Client) (string, error) {
	whoamiResponse, err := client.Identity.Whoami()
	if err != nil {
		return "", errors.Wrap(err, "could not get account information from dnsimple")
	}
	if whoamiResponse.Data.Account == nil {
		return "", errors.New("could not get account information")
	}
	return strconv.Itoa(whoamiResponse.Data.Account.ID), nil
}

func splitHost(host string) (subdomain string, domain string, err error) {
	subdomains := strings.Split(host, ".")

	if len(subdomains) >= 3 {
		domain = strings.Join(subdomains[len(subdomains)-2:], ".")
		subdomain = strings.Join(subdomains[:len(subdomains)-2], ".")
	} else if len(subdomains) == 2 {
		domain = strings.Join(subdomains, ".")
	} else {
		err = errors.New("invalid domain")
	}
	return subdomain, domain, err
}

func getIP(url string) (*whatIsMyIPResult, error) {
	result, err := http.Get(url)
	if err != nil {
		return nil, errors.Wrap(err, "could not get url "+url)
	}
	defer result.Body.Close()
	ipResult := &whatIsMyIPResult{}
	if err := json.NewDecoder(result.Body).Decode(ipResult); err != nil {
		return nil, errors.Wrap(err, "could parse json from url "+url)
	}
	return ipResult, nil
}