headscale/integration/tsic/tsic.go

package tsic

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log"
	"net/netip"
	"net/url"
	"strconv"
	"strings"
	"time"

	"github.com/juanfont/headscale/hscontrol/util"
	"github.com/juanfont/headscale/integration/dockertestutil"
	"github.com/juanfont/headscale/integration/integrationutil"
	"github.com/ory/dockertest/v3"
	"github.com/ory/dockertest/v3/docker"
	"tailscale.com/ipn"
	"tailscale.com/ipn/ipnstate"
	"tailscale.com/net/netcheck"
	"tailscale.com/types/netmap"
)

const (
	tsicHashLength       = 6
	defaultPingTimeout   = 300 * time.Millisecond
	defaultPingCount     = 10
	dockerContextPath    = "../."
	headscaleCertPath    = "/usr/local/share/ca-certificates/headscale.crt"
	dockerExecuteTimeout = 60 * time.Second
)

var (
	errTailscalePingFailed             = errors.New("ping failed")
	errTailscalePingNotDERP            = errors.New("ping not via DERP")
	errTailscaleNotLoggedIn            = errors.New("tailscale not logged in")
	errTailscaleWrongPeerCount         = errors.New("wrong peer count")
	errTailscaleCannotUpWithoutAuthkey = errors.New("cannot up without authkey")
	errTailscaleNotConnected           = errors.New("tailscale not connected")
	errTailscaledNotReadyForLogin      = errors.New("tailscaled not ready for login")
)

func errTailscaleStatus(hostname string, err error) error {
	return fmt.Errorf("%s failed to fetch tailscale status: %w", hostname, err)
}

// TailscaleInContainer is an implementation of TailscaleClient which
// sets up a Tailscale instance inside a container.
type TailscaleInContainer struct {
	version  string
	hostname string

	pool      *dockertest.Pool
	container *dockertest.Resource
	network   *dockertest.Network

	// "cache"
	ips  []netip.Addr
	fqdn string

	// optional config
	headscaleCert     []byte
	headscaleHostname string
	withSSH           bool
	withTags          []string
	withEntrypoint    []string
	withExtraHosts    []string
	workdir           string
	netfilter         string
}

// Option represent optional settings that can be given to a
// Tailscale instance.
type Option = func(c *TailscaleInContainer)

// WithHeadscaleTLS takes the certificate of the Headscale instance
// and adds it to the trusted surtificate of the Tailscale container.
func WithHeadscaleTLS(cert []byte) Option {
	return func(tsic *TailscaleInContainer) {
		tsic.headscaleCert = cert
	}
}

// WithOrCreateNetwork sets the Docker container network to use with
// the Tailscale instance, if the parameter is nil, a new network,
// isolating the TailscaleClient, will be created. If a network is
// passed, the Tailscale instance will join the given network.
func WithOrCreateNetwork(network *dockertest.Network) Option {
	return func(tsic *TailscaleInContainer) {
		if network != nil {
			tsic.network = network

			return
		}

		network, err := dockertestutil.GetFirstOrCreateNetwork(
			tsic.pool,
			fmt.Sprintf("%s-network", tsic.hostname),
		)
		if err != nil {
			log.Fatalf("failed to create network: %s", err)
		}

		tsic.network = network
	}
}

// WithHeadscaleName set the name of the headscale instance,
// mostly useful in combination with TLS and WithHeadscaleTLS.
func WithHeadscaleName(hsName string) Option {
	return func(tsic *TailscaleInContainer) {
		tsic.headscaleHostname = hsName
	}
}

// WithTags associates the given tags to the Tailscale instance.
func WithTags(tags []string) Option {
	return func(tsic *TailscaleInContainer) {
		tsic.withTags = tags
	}
}

// WithSSH enables SSH for the Tailscale instance.
func WithSSH() Option {
	return func(tsic *TailscaleInContainer) {
		tsic.withSSH = true
	}
}

// WithDockerWorkdir allows the docker working directory to be set.
func WithDockerWorkdir(dir string) Option {
	return func(tsic *TailscaleInContainer) {
		tsic.workdir = dir
	}
}

func WithExtraHosts(hosts []string) Option {
	return func(tsic *TailscaleInContainer) {
		tsic.withExtraHosts = hosts
	}
}

// WithDockerEntrypoint allows the docker entrypoint of the container
// to be overridden. This is a dangerous option which can make
// the container not work as intended as a typo might prevent
// tailscaled and other processes from starting.
// Use with caution.
func WithDockerEntrypoint(args []string) Option {
	return func(tsic *TailscaleInContainer) {
		tsic.withEntrypoint = args
	}
}

// WithNetfilter configures Tailscales parameter --netfilter-mode
// allowing us to turn of modifying ip[6]tables/nftables.
// It takes: "on", "off", "nodivert".
func WithNetfilter(state string) Option {
	return func(tsic *TailscaleInContainer) {
		tsic.netfilter = state
	}
}

// New returns a new TailscaleInContainer instance.
func New(
	pool *dockertest.Pool,
	version string,
	network *dockertest.Network,
	opts ...Option,
) (*TailscaleInContainer, error) {
	hash, err := util.GenerateRandomStringDNSSafe(tsicHashLength)
	if err != nil {
		return nil, err
	}

	hostname := fmt.Sprintf("ts-%s-%s", strings.ReplaceAll(version, ".", "-"), hash)

	tsic := &TailscaleInContainer{
		version:  version,
		hostname: hostname,

		pool:    pool,
		network: network,

		withEntrypoint: []string{
			"/bin/sh",
			"-c",
			"/bin/sleep 3 ; update-ca-certificates ; tailscaled --tun=tsdev --verbose=10",
		},
	}

	for _, opt := range opts {
		opt(tsic)
	}

	tailscaleOptions := &dockertest.RunOptions{
		Name:     hostname,
		Networks: []*dockertest.Network{tsic.network},
		// Cmd: []string{
		// 	"tailscaled", "--tun=tsdev",
		// },
		Entrypoint: tsic.withEntrypoint,
		ExtraHosts: tsic.withExtraHosts,
	}

	if tsic.headscaleHostname != "" {
		tailscaleOptions.ExtraHosts = []string{
			"host.docker.internal:host-gateway",
			fmt.Sprintf("%s:host-gateway", tsic.headscaleHostname),
		}
	}

	if tsic.workdir != "" {
		tailscaleOptions.WorkingDir = tsic.workdir
	}

	// dockertest isnt very good at handling containers that has already
	// been created, this is an attempt to make sure this container isnt
	// present.
	err = pool.RemoveContainerByName(hostname)
	if err != nil {
		return nil, err
	}

	var container *dockertest.Resource
	switch version {
	case "head":
		buildOptions := &dockertest.BuildOptions{
			Dockerfile: "Dockerfile.tailscale-HEAD",
			ContextDir: dockerContextPath,
			BuildArgs:  []docker.BuildArg{},
		}

		container, err = pool.BuildAndRunWithBuildOptions(
			buildOptions,
			tailscaleOptions,
			dockertestutil.DockerRestartPolicy,
			dockertestutil.DockerAllowLocalIPv6,
			dockertestutil.DockerAllowNetworkAdministration,
		)
	case "unstable":
		tailscaleOptions.Repository = "tailscale/tailscale"
		tailscaleOptions.Tag = version

		container, err = pool.RunWithOptions(
			tailscaleOptions,
			dockertestutil.DockerRestartPolicy,
			dockertestutil.DockerAllowLocalIPv6,
			dockertestutil.DockerAllowNetworkAdministration,
		)
	default:
		tailscaleOptions.Repository = "tailscale/tailscale"
		tailscaleOptions.Tag = "v" + version

		container, err = pool.RunWithOptions(
			tailscaleOptions,
			dockertestutil.DockerRestartPolicy,
			dockertestutil.DockerAllowLocalIPv6,
			dockertestutil.DockerAllowNetworkAdministration,
		)
	}

	if err != nil {
		return nil, fmt.Errorf(
			"%s could not start tailscale container (version: %s): %w",
			hostname,
			version,
			err,
		)
	}
	log.Printf("Created %s container\n", hostname)

	tsic.container = container

	if tsic.hasTLS() {
		err = tsic.WriteFile(headscaleCertPath, tsic.headscaleCert)
		if err != nil {
			return nil, fmt.Errorf("failed to write TLS certificate to container: %w", err)
		}
	}

	return tsic, nil
}

func (t *TailscaleInContainer) hasTLS() bool {
	return len(t.headscaleCert) != 0
}

// Shutdown stops and cleans up the Tailscale container.
func (t *TailscaleInContainer) Shutdown() error {
	err := t.SaveLog("/tmp/control")
	if err != nil {
		log.Printf(
			"Failed to save log from %s: %s",
			t.hostname,
			fmt.Errorf("failed to save log: %w", err),
		)
	}

	return t.pool.Purge(t.container)
}

// Hostname returns the hostname of the Tailscale instance.
func (t *TailscaleInContainer) Hostname() string {
	return t.hostname
}

// Version returns the running Tailscale version of the instance.
func (t *TailscaleInContainer) Version() string {
	return t.version
}

// ID returns the Docker container ID of the TailscaleInContainer
// instance.
func (t *TailscaleInContainer) ID() string {
	return t.container.Container.ID
}

// Execute runs a command inside the Tailscale container and returns the
// result of stdout as a string.
func (t *TailscaleInContainer) Execute(
	command []string,
	options ...dockertestutil.ExecuteCommandOption,
) (string, string, error) {
	stdout, stderr, err := dockertestutil.ExecuteCommand(
		t.container,
		command,
		[]string{},
		options...,
	)
	if err != nil {
		// log.Printf("command issued: %s", strings.Join(command, " "))
		// log.Printf("command stderr: %s\n", stderr)

		if stdout != "" {
			log.Printf("command stdout: %s\n", stdout)
		}

		if strings.Contains(stderr, "NeedsLogin") {
			return stdout, stderr, errTailscaleNotLoggedIn
		}

		return stdout, stderr, err
	}

	return stdout, stderr, nil
}

// Up runs the login routine on the given Tailscale instance.
// This login mechanism uses the authorised key for authentication.
func (t *TailscaleInContainer) Login(
	loginServer, authKey string,
) error {
	command := []string{
		"tailscale",
		"up",
		"--login-server=" + loginServer,
		"--authkey=" + authKey,
		"--hostname=" + t.hostname,
		"--accept-routes=false",
	}

	if t.withSSH {
		command = append(command, "--ssh")
	}

	if t.netfilter != "" {
		command = append(command, "--netfilter-mode="+t.netfilter)
	}

	if len(t.withTags) > 0 {
		command = append(command,
			fmt.Sprintf(`--advertise-tags=%s`, strings.Join(t.withTags, ",")),
		)
	}

	if _, _, err := t.Execute(command, dockertestutil.ExecuteCommandTimeout(dockerExecuteTimeout)); err != nil {
		return fmt.Errorf(
			"%s failed to join tailscale client (%s): %w",
			t.hostname,
			strings.Join(command, " "),
			err,
		)
	}

	return nil
}

// Up runs the login routine on the given Tailscale instance.
// This login mechanism uses web + command line flow for authentication.
func (t *TailscaleInContainer) LoginWithURL(
	loginServer string,
) (*url.URL, error) {
	command := []string{
		"tailscale",
		"up",
		"--login-server=" + loginServer,
		"--hostname=" + t.hostname,
		"--accept-routes=false",
	}

	_, stderr, err := t.Execute(command)
	if errors.Is(err, errTailscaleNotLoggedIn) {
		return nil, errTailscaleCannotUpWithoutAuthkey
	}

	urlStr := strings.ReplaceAll(stderr, "\nTo authenticate, visit:\n\n\t", "")
	urlStr = strings.TrimSpace(urlStr)

	// parse URL
	loginURL, err := url.Parse(urlStr)
	if err != nil {
		log.Printf("Could not parse login URL: %s", err)
		log.Printf("Original join command result: %s", stderr)

		return nil, err
	}

	return loginURL, nil
}

// Logout runs the logout routine on the given Tailscale instance.
func (t *TailscaleInContainer) Logout() error {
	_, _, err := t.Execute([]string{"tailscale", "logout"})
	if err != nil {
		return err
	}

	return nil
}

// Helper that runs `tailscale up` with no arguments.
func (t *TailscaleInContainer) Up() error {
	command := []string{
		"tailscale",
		"up",
	}

	if _, _, err := t.Execute(command, dockertestutil.ExecuteCommandTimeout(dockerExecuteTimeout)); err != nil {
		return fmt.Errorf(
			"%s failed to bring tailscale client up (%s): %w",
			t.hostname,
			strings.Join(command, " "),
			err,
		)
	}

	return nil
}

// Helper that runs `tailscale down` with no arguments.
func (t *TailscaleInContainer) Down() error {
	command := []string{
		"tailscale",
		"down",
	}

	if _, _, err := t.Execute(command, dockertestutil.ExecuteCommandTimeout(dockerExecuteTimeout)); err != nil {
		return fmt.Errorf(
			"%s failed to bring tailscale client down (%s): %w",
			t.hostname,
			strings.Join(command, " "),
			err,
		)
	}

	return nil
}

// IPs returns the netip.Addr of the Tailscale instance.
func (t *TailscaleInContainer) IPs() ([]netip.Addr, error) {
	if t.ips != nil && len(t.ips) != 0 {
		return t.ips, nil
	}

	ips := make([]netip.Addr, 0)

	command := []string{
		"tailscale",
		"ip",
	}

	result, _, err := t.Execute(command)
	if err != nil {
		return []netip.Addr{}, fmt.Errorf("%s failed to join tailscale client: %w", t.hostname, err)
	}

	for _, address := range strings.Split(result, "\n") {
		address = strings.TrimSuffix(address, "\n")
		if len(address) < 1 {
			continue
		}
		ip, err := netip.ParseAddr(address)
		if err != nil {
			return nil, err
		}
		ips = append(ips, ip)
	}

	return ips, nil
}

// Status returns the ipnstate.Status of the Tailscale instance.
func (t *TailscaleInContainer) Status() (*ipnstate.Status, error) {
	command := []string{
		"tailscale",
		"status",
		"--json",
	}

	result, _, err := t.Execute(command)
	if err != nil {
		return nil, fmt.Errorf("failed to execute tailscale status command: %w", err)
	}

	var status ipnstate.Status
	err = json.Unmarshal([]byte(result), &status)
	if err != nil {
		return nil, fmt.Errorf("failed to unmarshal tailscale status: %w", err)
	}

	return &status, err
}

// Netmap returns the current Netmap (netmap.NetworkMap) of the Tailscale instance.
// Only works with Tailscale 1.56 and newer.
// Panics if version is lower then minimum.
// func (t *TailscaleInContainer) Netmap() (*netmap.NetworkMap, error) {
// 	if !util.TailscaleVersionNewerOrEqual("1.56", t.version) {
// 		panic(fmt.Sprintf("tsic.Netmap() called with unsupported version: %s", t.version))
// 	}

// 	command := []string{
// 		"tailscale",
// 		"debug",
// 		"netmap",
// 	}

// 	result, stderr, err := t.Execute(command)
// 	if err != nil {
// 		fmt.Printf("stderr: %s\n", stderr)
// 		return nil, fmt.Errorf("failed to execute tailscale debug netmap command: %w", err)
// 	}

// 	var nm netmap.NetworkMap
// 	err = json.Unmarshal([]byte(result), &nm)
// 	if err != nil {
// 		return nil, fmt.Errorf("failed to unmarshal tailscale netmap: %w", err)
// 	}

// 	return &nm, err
// }

// Netmap returns the current Netmap (netmap.NetworkMap) of the Tailscale instance.
// This implementation is based on getting the netmap from `tailscale debug watch-ipn`
// as there seem to be some weirdness omitting endpoint and DERP info if we use
// Patch updates.
// This implementation works on all supported versions.
func (t *TailscaleInContainer) Netmap() (*netmap.NetworkMap, error) {
	// watch-ipn will only give an update if something is happening,
	// since we send keep alives, the worst case for this should be
	// 1 minute, but set a slightly more conservative time.
	ctx, _ := context.WithTimeout(context.Background(), 3*time.Minute)

	notify, err := t.watchIPN(ctx)
	if err != nil {
		return nil, err
	}

	if notify.NetMap == nil {
		return nil, fmt.Errorf("no netmap present in ipn.Notify")
	}

	return notify.NetMap, nil
}

// watchIPN watches `tailscale debug watch-ipn` for a ipn.Notify object until
// it gets one that has a netmap.NetworkMap.
func (t *TailscaleInContainer) watchIPN(ctx context.Context) (*ipn.Notify, error) {
	pr, pw := io.Pipe()

	type result struct {
		notify *ipn.Notify
		err    error
	}
	resultChan := make(chan result, 1)

	// There is no good way to kill the goroutine with watch-ipn,
	// so make a nice func to send a kill command to issue when
	// we are done.
	killWatcher := func() {
		stdout, stderr, err := t.Execute([]string{
			"/bin/sh", "-c", `kill $(ps aux | grep "tailscale debug watch-ipn" | grep -v grep | awk '{print $1}') || true`,
		})
		if err != nil {
			log.Printf("failed to kill tailscale watcher, \nstdout: %s\nstderr: %s\nerr: %s", stdout, stderr, err)
		}
	}

	go func() {
		_, _ = t.container.Exec(
			// Prior to 1.56, the initial "Connected." message was printed to stdout,
			// filter out with grep.
			[]string{"/bin/sh", "-c", `tailscale debug watch-ipn | grep -v "Connected."`},
			dockertest.ExecOptions{
				// The interesting output is sent to stdout, so ignore stderr.
				StdOut: pw,
				// StdErr: pw,
			},
		)
	}()

	go func() {
		decoder := json.NewDecoder(pr)
		for decoder.More() {
			var notify ipn.Notify
			if err := decoder.Decode(&notify); err != nil {
				resultChan <- result{nil, fmt.Errorf("parse notify: %w", err)}
			}

			if notify.NetMap != nil {
				resultChan <- result{&notify, nil}
			}
		}
	}()

	select {
	case <-ctx.Done():
		killWatcher()

		return nil, ctx.Err()

	case result := <-resultChan:
		killWatcher()

		if result.err != nil {
			return nil, result.err
		}

		return result.notify, nil
	}
}

// Netcheck returns the current Netcheck Report (netcheck.Report) of the Tailscale instance.
func (t *TailscaleInContainer) Netcheck() (*netcheck.Report, error) {
	command := []string{
		"tailscale",
		"netcheck",
		"--format=json",
	}

	result, stderr, err := t.Execute(command)
	if err != nil {
		fmt.Printf("stderr: %s\n", stderr)
		return nil, fmt.Errorf("failed to execute tailscale debug netcheck command: %w", err)
	}

	var nm netcheck.Report
	err = json.Unmarshal([]byte(result), &nm)
	if err != nil {
		return nil, fmt.Errorf("failed to unmarshal tailscale netcheck: %w", err)
	}

	return &nm, err
}

// FQDN returns the FQDN as a string of the Tailscale instance.
func (t *TailscaleInContainer) FQDN() (string, error) {
	if t.fqdn != "" {
		return t.fqdn, nil
	}

	status, err := t.Status()
	if err != nil {
		return "", fmt.Errorf("failed to get FQDN: %w", err)
	}

	return status.Self.DNSName, nil
}

// PrettyPeers returns a formatted-ish table of peers in the client.
func (t *TailscaleInContainer) PrettyPeers() (string, error) {
	status, err := t.Status()
	if err != nil {
		return "", fmt.Errorf("failed to get FQDN: %w", err)
	}

	str := fmt.Sprintf("Peers of %s\n", t.hostname)
	str += "Hostname\tOnline\tLastSeen\n"

	peerCount := len(status.Peers())
	onlineCount := 0

	for _, peerKey := range status.Peers() {
		peer := status.Peer[peerKey]

		if peer.Online {
			onlineCount++
		}

		str += fmt.Sprintf("%s\t%t\t%s\n", peer.HostName, peer.Online, peer.LastSeen)
	}

	str += fmt.Sprintf("Peer Count: %d, Online Count: %d\n\n", peerCount, onlineCount)

	return str, nil
}

// WaitForNeedsLogin blocks until the Tailscale (tailscaled) instance has
// started and needs to be logged into.
func (t *TailscaleInContainer) WaitForNeedsLogin() error {
	return t.pool.Retry(func() error {
		status, err := t.Status()
		if err != nil {
			return errTailscaleStatus(t.hostname, err)
		}

		// ipnstate.Status.CurrentTailnet was added in Tailscale 1.22.0
		// https://github.com/tailscale/tailscale/pull/3865
		//
		// Before that, we can check the BackendState to see if the
		// tailscaled daemon is connected to the control system.
		if status.BackendState == "NeedsLogin" {
			return nil
		}

		return errTailscaledNotReadyForLogin
	})
}

// WaitForRunning blocks until the Tailscale (tailscaled) instance is logged in
// and ready to be used.
func (t *TailscaleInContainer) WaitForRunning() error {
	return t.pool.Retry(func() error {
		status, err := t.Status()
		if err != nil {
			return errTailscaleStatus(t.hostname, err)
		}

		// ipnstate.Status.CurrentTailnet was added in Tailscale 1.22.0
		// https://github.com/tailscale/tailscale/pull/3865
		//
		// Before that, we can check the BackendState to see if the
		// tailscaled daemon is connected to the control system.
		if status.BackendState == "Running" {
			return nil
		}

		return errTailscaleNotConnected
	})
}

// WaitForPeers blocks until N number of peers is present in the
// Peer list of the Tailscale instance and is reporting Online.
func (t *TailscaleInContainer) WaitForPeers(expected int) error {
	return t.pool.Retry(func() error {
		status, err := t.Status()
		if err != nil {
			return errTailscaleStatus(t.hostname, err)
		}

		if peers := status.Peers(); len(peers) != expected {
			return fmt.Errorf(
				"%s err: %w expected %d, got %d",
				t.hostname,
				errTailscaleWrongPeerCount,
				expected,
				len(peers),
			)
		} else {
			// Verify that the peers of a given node is Online
			// has a hostname and a DERP relay.
			for _, peerKey := range peers {
				peer := status.Peer[peerKey]

				if !peer.Online {
					return fmt.Errorf("[%s] peer count correct, but %s is not online", t.hostname, peer.HostName)
				}

				if peer.HostName == "" {
					return fmt.Errorf("[%s] peer count correct, but %s does not have a Hostname", t.hostname, peer.HostName)
				}

				if peer.Relay == "" {
					return fmt.Errorf("[%s] peer count correct, but %s does not have a DERP", t.hostname, peer.HostName)
				}
			}
		}

		return nil
	})
}

type (
	// PingOption represent optional settings that can be given
	// to ping another host.
	PingOption = func(args *pingArgs)

	pingArgs struct {
		timeout time.Duration
		count   int
		direct  bool
	}
)

// WithPingTimeout sets the timeout for the ping command.
func WithPingTimeout(timeout time.Duration) PingOption {
	return func(args *pingArgs) {
		args.timeout = timeout
	}
}

// WithPingCount sets the count of pings to attempt.
func WithPingCount(count int) PingOption {
	return func(args *pingArgs) {
		args.count = count
	}
}

// WithPingUntilDirect decides if the ping should only succeed
// if a direct connection is established or if successful
// DERP ping is sufficient.
func WithPingUntilDirect(direct bool) PingOption {
	return func(args *pingArgs) {
		args.direct = direct
	}
}

// Ping executes the Tailscale ping command and pings a hostname
// or IP. It accepts a series of PingOption.
// TODO(kradalby): Make multiping, go routine magic.
func (t *TailscaleInContainer) Ping(hostnameOrIP string, opts ...PingOption) error {
	args := pingArgs{
		timeout: defaultPingTimeout,
		count:   defaultPingCount,
		direct:  true,
	}

	for _, opt := range opts {
		opt(&args)
	}

	command := []string{
		"tailscale", "ping",
		fmt.Sprintf("--timeout=%s", args.timeout),
		fmt.Sprintf("--c=%d", args.count),
		fmt.Sprintf("--until-direct=%s", strconv.FormatBool(args.direct)),
	}

	command = append(command, hostnameOrIP)

	result, _, err := t.Execute(
		command,
		dockertestutil.ExecuteCommandTimeout(
			time.Duration(int64(args.timeout)*int64(args.count)),
		),
	)
	if err != nil {
		log.Printf(
			"failed to run ping command from %s to %s, err: %s",
			t.Hostname(),
			hostnameOrIP,
			err,
		)

		return err
	}

	if strings.Contains(result, "is local") {
		return nil
	}

	if !strings.Contains(result, "pong") {
		return errTailscalePingFailed
	}

	if !args.direct {
		if strings.Contains(result, "via DERP") {
			return nil
		} else {
			return errTailscalePingNotDERP
		}
	}

	return nil
}

type (
	// CurlOption repreent optional settings that can be given
	// to curl another host.
	CurlOption = func(args *curlArgs)

	curlArgs struct {
		connectionTimeout time.Duration
		maxTime           time.Duration
		retry             int
		retryDelay        time.Duration
		retryMaxTime      time.Duration
	}
)

// WithCurlConnectionTimeout sets the timeout for each connection started
// by curl.
func WithCurlConnectionTimeout(timeout time.Duration) CurlOption {
	return func(args *curlArgs) {
		args.connectionTimeout = timeout
	}
}

// WithCurlMaxTime sets the max time for a transfer for each connection started
// by curl.
func WithCurlMaxTime(t time.Duration) CurlOption {
	return func(args *curlArgs) {
		args.maxTime = t
	}
}

// WithCurlRetry sets the number of retries a connection is attempted by curl.
func WithCurlRetry(ret int) CurlOption {
	return func(args *curlArgs) {
		args.retry = ret
	}
}

const (
	defaultConnectionTimeout = 3 * time.Second
	defaultMaxTime           = 10 * time.Second
	defaultRetry             = 5
	defaultRetryDelay        = 0 * time.Second
	defaultRetryMaxTime      = 50 * time.Second
)

// Curl executes the Tailscale curl command and curls a hostname
// or IP. It accepts a series of CurlOption.
func (t *TailscaleInContainer) Curl(url string, opts ...CurlOption) (string, error) {
	args := curlArgs{
		connectionTimeout: defaultConnectionTimeout,
		maxTime:           defaultMaxTime,
		retry:             defaultRetry,
		retryDelay:        defaultRetryDelay,
		retryMaxTime:      defaultRetryMaxTime,
	}

	for _, opt := range opts {
		opt(&args)
	}

	command := []string{
		"curl",
		"--silent",
		"--connect-timeout", fmt.Sprintf("%d", int(args.connectionTimeout.Seconds())),
		"--max-time", fmt.Sprintf("%d", int(args.maxTime.Seconds())),
		"--retry", fmt.Sprintf("%d", args.retry),
		"--retry-delay", fmt.Sprintf("%d", int(args.retryDelay.Seconds())),
		"--retry-max-time", fmt.Sprintf("%d", int(args.retryMaxTime.Seconds())),
		url,
	}

	var result string
	result, _, err := t.Execute(command)
	if err != nil {
		log.Printf(
			"failed to run curl command from %s to %s, err: %s",
			t.Hostname(),
			url,
			err,
		)

		return result, err
	}

	return result, nil
}

// WriteFile save file inside the Tailscale container.
func (t *TailscaleInContainer) WriteFile(path string, data []byte) error {
	return integrationutil.WriteFileToContainer(t.pool, t.container, path, data)
}

// SaveLog saves the current stdout log of the container to a path
// on the host system.
func (t *TailscaleInContainer) SaveLog(path string) error {
	return dockertestutil.SaveLog(t.pool, t.container, path)
}