add breakglass SSH wrapper tool (for convenience)

cmd/breakglass/breakglass.go

@@ -0,0 +1,224 @@
+// Binary breakglass is a wrapper around SSH, starting breakglass on the
+// destination gokrazy installation <hostname> first.
+//
+// Example:
+//   breakglass gokrazy
+//   breakglass -debug_tarball_pattern=$HOME/gokrazy/debug-\${GOARCH}.tar gokrazy
+package main
+
+import (
+	"archive/tar"
+	"context"
+	"flag"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"log"
+	"net"
+	"net/http"
+	"net/http/cookiejar"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"time"
+)
+
+type bg struct {
+	// config
+	hostname     string
+	pw           string
+	forceRestart bool
+
+	// state
+	GOARCH string
+}
+
+func (bg *bg) startBreakglass() error {
+	jar, err := cookiejar.New(nil)
+	if err != nil {
+		return err
+	}
+	client := &http.Client{Jar: jar}
+	urlPrefix := "http://gokrazy:" + bg.pw + "@" + bg.hostname
+	form, err := client.Get(urlPrefix + "/status?path=/user/breakglass")
+	if err != nil {
+		return err
+	}
+	if form.StatusCode == http.StatusNotFound {
+		fmt.Fprintf(os.Stderr, "Hint: have you installed Go package github.com/gokrazy/breakglass on your gokrazy installation %q?\n", bg.hostname)
+	}
+	if got, want := form.StatusCode, http.StatusOK; got != want {
+		b, _ := ioutil.ReadAll(form.Body)
+		return fmt.Errorf("starting breakglass: unexpected HTTP status: got %v (%s), want %v",
+			form.Status,
+			strings.TrimSpace(string(b)),
+			want)
+	}
+	var xsrfToken string
+	for _, c := range form.Cookies() {
+		if c.Name != "gokrazy_xsrf" {
+			continue
+		}
+		xsrfToken = c.Value
+		break
+	}
+	if xsrfToken == "" {
+		return fmt.Errorf("no gokrazy_xsrf cookie received")
+	}
+
+	bg.GOARCH = form.Header.Get("X-Gokrazy-Goarch")
+
+	if form.Header.Get("X-Gokrazy-Status") == "started" && !bg.forceRestart {
+		return nil // breakglass already running
+	}
+
+	resp, err := client.Post(urlPrefix+"/restart?path=/user/breakglass&xsrftoken="+xsrfToken, "", nil)
+	if err != nil {
+		return err
+	}
+	if got, want := resp.StatusCode, http.StatusOK; got != want {
+		return fmt.Errorf("restarting breakglass: unexpected HTTP status code: got %d, want %d", got, want)
+	}
+	return nil
+}
+
+func pollPort(ctx context.Context, hostname, port string) error {
+	var d net.Dialer
+	for ctx.Err() == nil {
+		conn, err := d.DialContext(ctx, "tcp", net.JoinHostPort(hostname, port))
+		if err != nil {
+			time.Sleep(100 * time.Millisecond)
+			continue
+		}
+		conn.Close()
+		return nil
+	}
+	return ctx.Err()
+}
+
+func (bg *bg) uploadDebugTarball(debugTarballPattern string) error {
+	if debugTarballPattern == "" {
+		return nil // nothing to do
+	}
+	debugTarball := strings.ReplaceAll(
+		debugTarballPattern,
+		"${GOARCH}",
+		bg.GOARCH)
+	st, err := os.Stat(debugTarball)
+	if err != nil {
+		return err
+	}
+	var contents []string
+	f, err := os.Open(debugTarball)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	tr := tar.NewReader(f)
+	for {
+		hdr, err := tr.Next()
+		if err == io.EOF {
+			break // end of archive
+		}
+		if err != nil {
+			return err
+		}
+		contents = append(contents, fmt.Sprintf("%s (%v bytes)", hdr.Name, hdr.Size))
+	}
+	log.Printf("uploading debug tarball:\n\t%s\n\t(last modified: %v, %v ago)\n\t\t%s",
+		debugTarball,
+		st.ModTime().Format("2006-01-02 15:04:05 -0700"),
+		time.Since(st.ModTime()).Round(1*time.Second),
+		strings.Join(contents, "\n\t\t"))
+
+	scp := exec.Command("scp", debugTarball, bg.hostname+":")
+	scp.Stderr = os.Stderr
+	if err := scp.Run(); err != nil {
+		return fmt.Errorf("%v: %v", scp.Args, err)
+	}
+	return nil
+}
+
+func breakglass() error {
+	var (
+		forceRestart = flag.Bool(
+			"force_restart",
+			false,
+			"restart breakglass if it is already running")
+
+		debugTarballPattern = flag.String(
+			"debug_tarball_pattern",
+			"",
+			"If non-empty, a pattern resulting in the path to a debug.tar archive that should be copied to breakglass before starting a shell. This can be used to make additional tools available for debugging. All occurrences of ${GOARCH} will be replaced with the runtime.GOARCH of the remote gokrazy installation.")
+	)
+
+	flag.Usage = func() {
+		fmt.Fprintf(os.Stderr, "Usage of %s:\n\n", os.Args[0])
+
+		fmt.Fprintf(os.Stderr, "  breakglass gokrazy\n")
+		fmt.Fprintf(os.Stderr, "  breakglass -debug_tarball_pattern=$HOME/gokrazy/debug-\\${GOARCH}.tar gokrazy\n")
+
+		fmt.Fprintf(os.Stderr, "\nOptions:\n")
+		flag.PrintDefaults()
+	}
+
+	flag.Parse()
+	if flag.NArg() < 1 {
+		log.Fatalf("syntax: breakglass <hostname> [command]")
+	}
+	hostname := flag.Arg(0)
+
+	dir, err := os.UserConfigDir()
+	if err != nil {
+		return err
+	}
+	b, err := ioutil.ReadFile(filepath.Join(dir, "gokrazy", "http-password.txt"))
+	if err != nil {
+		return err
+	}
+	pw := strings.TrimSpace(string(b))
+	bg := &bg{
+		hostname:     hostname,
+		pw:           pw,
+		forceRestart: *forceRestart,
+	}
+
+	log.Printf("checking breakglass status on gokrazy installation %q", hostname)
+	if err := bg.startBreakglass(); err != nil {
+		return err
+	}
+
+	time.Sleep(250 * time.Millisecond) // give gokrazy some time to restart
+
+	log.Printf("polling SSH port to become available")
+	ctx, canc := context.WithTimeout(context.Background(), 2*time.Second)
+	defer canc()
+	if err := pollPort(ctx, hostname, "ssh"); err != nil {
+		return err
+	}
+
+	if err := bg.uploadDebugTarball(*debugTarballPattern); err != nil {
+		return err
+	}
+
+	ssh := exec.Command("ssh", hostname)
+	if args := flag.Args()[1:]; len(args) > 0 {
+		ssh.Args = append(ssh.Args, args...)
+	}
+	log.Printf("%v", ssh.Args)
+	ssh.Stdin = os.Stdin
+	ssh.Stdout = os.Stdout
+	ssh.Stderr = os.Stderr
+	if err := ssh.Run(); err != nil {
+		return fmt.Errorf("%v: %v", ssh.Args, err)
+	}
+
+	return nil
+}
+
+func main() {
+	if err := breakglass(); err != nil {
+		log.Fatal(err)
+	}
+}