byre/internal/tailscale/tailscale.go

package tailscale

import (
	"context"
	"encoding/json"
	"fmt"
	"os"
	"os/exec"
	"strconv"
	"strings"
)

const cli = "/Applications/Tailscale.app/Contents/MacOS/Tailscale"

func Serve(ctx context.Context, port int) error {
	_, err := serve(ctx, port, "http://127.0.0.1:"+strconv.Itoa(port))
	return err
}

func ServeRoot(ctx context.Context, target string) (string, error) {
	host, err := serve(ctx, 443, target)
	if err != nil {
		return "", err
	}
	return "https://" + strings.TrimSuffix(host, ":443"), nil
}

func serve(ctx context.Context, port int, target string) (string, error) {
	_, err := run(ctx, "serve", "--bg", "--https="+strconv.Itoa(port), target)
	if err != nil {
		return "", err
	}
	out, err := run(ctx, "serve", "status", "--json")
	if err != nil {
		return "", err
	}
	status := struct {
		Web map[string]json.RawMessage
	}{}
	err = json.Unmarshal(out, &status)
	if err != nil {
		return "", fmt.Errorf("parse tailscale serve status: %w", err)
	}
	suffix := ":" + strconv.Itoa(port)
	for host := range status.Web {
		if strings.HasSuffix(host, suffix) {
			return host, nil
		}
	}
	return "", fmt.Errorf("tailscale serve --https=%d exited 0 but port %d is not in serve status", port, port)
}

func Problem(ctx context.Context) string {
	_, err := os.Stat(cli)
	if err != nil {
		return "Install the Tailscale app from https://tailscale.com/download/mac and sign in."
	}
	out, err := run(ctx, "status", "--json", "--peers=false")
	if err != nil {
		return "Open Tailscale and sign in (" + err.Error() + ")."
	}
	status := struct {
		BackendState string
		CertDomains  []string
	}{}
	err = json.Unmarshal(out, &status)
	if err != nil {
		return "Parse tailscale status: " + err.Error()
	}
	if status.BackendState != "Running" {
		return "Open Tailscale and sign in (it is " + status.BackendState + ")."
	}
	if len(status.CertDomains) == 0 {
		return "Turn on HTTPS Certificates on the DNS page of Tailscale's admin console, https://login.tailscale.com/admin/dns."
	}
	return ""
}

func Off(ctx context.Context, port int) error {
	_, err := run(ctx, "serve", "--https="+strconv.Itoa(port), "off")
	return err
}

func run(ctx context.Context, args ...string) ([]byte, error) {
	cmd := exec.CommandContext(ctx, cli, args...)
	cmd.Env = append(os.Environ(), "TAILSCALE_BE_CLI=1")
	stderr := strings.Builder{}
	cmd.Stderr = &stderr
	out, err := cmd.Output()
	if err != nil {
		return nil, fmt.Errorf("tailscale %s: %w: %s", strings.Join(args, " "), err, strings.TrimSpace(stderr.String()+string(out)))
	}
	return out, nil
}