// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause

//go:build linux

package main

import (
	"bytes"
	_ "embed"
	"encoding/base64"
	"encoding/json"
	"encoding/pem"
	"errors"
	"fmt"
	"io"
	"io/fs"
	"net"
	"net/http"
	"net/http/httptest"
	"net/netip"
	"os"
	"os/exec"
	"path/filepath"
	"strconv"
	"strings"
	"sync"
	"testing"
	"time"

	"github.com/google/go-cmp/cmp"
	"golang.org/x/sys/unix"
	"tailscale.com/ipn"
	"tailscale.com/tailcfg"
	"tailscale.com/tstest"
	"tailscale.com/types/netmap"
	"tailscale.com/types/ptr"
)

func TestContainerBoot(t *testing.T) {
	d := t.TempDir()

	lapi := localAPI{FSRoot: d}
	if err := lapi.Start(); err != nil {
		t.Fatal(err)
	}
	defer lapi.Close()

	kube := kubeServer{FSRoot: d}
	if err := kube.Start(); err != nil {
		t.Fatal(err)
	}
	defer kube.Close()

	dirs := []string{
		"var/lib",
		"usr/bin",
		"tmp",
		"dev/net",
		"proc/sys/net/ipv4",
		"proc/sys/net/ipv6/conf/all",
	}
	for _, path := range dirs {
		if err := os.MkdirAll(filepath.Join(d, path), 0700); err != nil {
			t.Fatal(err)
		}
	}
	files := map[string][]byte{
		"usr/bin/tailscaled":                    fakeTailscaled,
		"usr/bin/tailscale":                     fakeTailscale,
		"usr/bin/iptables":                      fakeTailscale,
		"usr/bin/ip6tables":                     fakeTailscale,
		"dev/net/tun":                           []byte(""),
		"proc/sys/net/ipv4/ip_forward":          []byte("0"),
		"proc/sys/net/ipv6/conf/all/forwarding": []byte("0"),
	}
	resetFiles := func() {
		for path, content := range files {
			// Making everything executable is a little weird, but the
			// stuff that doesn't need to be executable doesn't care if we
			// do make it executable.
			if err := os.WriteFile(filepath.Join(d, path), content, 0700); err != nil {
				t.Fatal(err)
			}
		}
	}
	resetFiles()

	boot := filepath.Join(d, "containerboot")
	if err := exec.Command("go", "build", "-o", boot, "tailscale.com/cmd/containerboot").Run(); err != nil {
		t.Fatalf("Building containerboot: %v", err)
	}

	argFile := filepath.Join(d, "args")
	runningSockPath := filepath.Join(d, "tmp/tailscaled.sock")

	type phase struct {
		// If non-nil, send this IPN bus notification (and remember it as the
		// initial update for any future new watchers, then wait for all the
		// Waits below to be true before proceeding to the next phase.
		Notify *ipn.Notify

		// WantCmds is the commands that containerboot should run in this phase.
		WantCmds []string
		// WantKubeSecret is the secret keys/values that should exist in the
		// kube secret.
		WantKubeSecret map[string]string
		// WantFiles files that should exist in the container and their
		// contents.
		WantFiles map[string]string
	}
	runningNotify := &ipn.Notify{
		State: ptr.To(ipn.Running),
		NetMap: &netmap.NetworkMap{
			SelfNode: &tailcfg.Node{
				StableID: tailcfg.StableNodeID("myID"),
				Name:     "test-node.test.ts.net",
			},
			Addresses: []netip.Prefix{netip.MustParsePrefix("100.64.0.1/32")},
		},
	}
	tests := []struct {
		Name          string
		Env           map[string]string
		KubeSecret    map[string]string
		KubeDenyPatch bool
		Phases        []phase
	}{
		{
			// Out of the box default: runs in userspace mode, ephemeral storage, interactive login.
			Name: "no_args",
			Env:  nil,
			Phases: []phase{
				{
					WantCmds: []string{
						"/usr/bin/tailscaled --socket=/tmp/tailscaled.sock --state=mem: --statedir=/tmp --tun=userspace-networking",
						"/usr/bin/tailscale --socket=/tmp/tailscaled.sock up --accept-dns=false",
					},
				},
				{
					Notify: runningNotify,
				},
			},
		},
		{
			// Userspace mode, ephemeral storage, authkey provided on every run.
			Name: "authkey",
			Env: map[string]string{
				"TS_AUTHKEY": "tskey-key",
			},
			Phases: []phase{
				{
					WantCmds: []string{
						"/usr/bin/tailscaled --socket=/tmp/tailscaled.sock --state=mem: --statedir=/tmp --tun=userspace-networking",
						"/usr/bin/tailscale --socket=/tmp/tailscaled.sock up --accept-dns=false --authkey=tskey-key",
					},
				},
				{
					Notify: runningNotify,
				},
			},
		},
		{
			// Userspace mode, ephemeral storage, authkey provided on every run.
			Name: "authkey-old-flag",
			Env: map[string]string{
				"TS_AUTH_KEY": "tskey-key",
			},
			Phases: []phase{
				{
					WantCmds: []string{
						"/usr/bin/tailscaled --socket=/tmp/tailscaled.sock --state=mem: --statedir=/tmp --tun=userspace-networking",
						"/usr/bin/tailscale --socket=/tmp/tailscaled.sock up --accept-dns=false --authkey=tskey-key",
					},
				},
				{
					Notify: runningNotify,
				},
			},
		},
		{
			Name: "authkey_disk_state",
			Env: map[string]string{
				"TS_AUTHKEY":   "tskey-key",
				"TS_STATE_DIR": filepath.Join(d, "tmp"),
			},
			Phases: []phase{
				{
					WantCmds: []string{
						"/usr/bin/tailscaled --socket=/tmp/tailscaled.sock --statedir=/tmp --tun=userspace-networking",
						"/usr/bin/tailscale --socket=/tmp/tailscaled.sock up --accept-dns=false --authkey=tskey-key",
					},
				},
				{
					Notify: runningNotify,
				},
			},
		},
		{
			Name: "routes",
			Env: map[string]string{
				"TS_AUTHKEY": "tskey-key",
				"TS_ROUTES":  "1.2.3.0/24,10.20.30.0/24",
			},
			Phases: []phase{
				{
					WantCmds: []string{
						"/usr/bin/tailscaled --socket=/tmp/tailscaled.sock --state=mem: --statedir=/tmp --tun=userspace-networking",
						"/usr/bin/tailscale --socket=/tmp/tailscaled.sock up --accept-dns=false --authkey=tskey-key --advertise-routes=1.2.3.0/24,10.20.30.0/24",
					},
				},
				{
					Notify: runningNotify,
					WantFiles: map[string]string{
						"proc/sys/net/ipv4/ip_forward":          "0",
						"proc/sys/net/ipv6/conf/all/forwarding": "0",
					},
				},
			},
		},
		{
			Name: "routes_kernel_ipv4",
			Env: map[string]string{
				"TS_AUTHKEY":   "tskey-key",
				"TS_ROUTES":    "1.2.3.0/24,10.20.30.0/24",
				"TS_USERSPACE": "false",
			},
			Phases: []phase{
				{
					WantCmds: []string{
						"/usr/bin/tailscaled --socket=/tmp/tailscaled.sock --state=mem: --statedir=/tmp",
						"/usr/bin/tailscale --socket=/tmp/tailscaled.sock up --accept-dns=false --authkey=tskey-key --advertise-routes=1.2.3.0/24,10.20.30.0/24",
					},
				},
				{
					Notify: runningNotify,
					WantFiles: map[string]string{
						"proc/sys/net/ipv4/ip_forward":          "1",
						"proc/sys/net/ipv6/conf/all/forwarding": "0",
					},
				},
			},
		},
		{
			Name: "routes_kernel_ipv6",
			Env: map[string]string{
				"TS_AUTHKEY":   "tskey-key",
				"TS_ROUTES":    "::/64,1::/64",
				"TS_USERSPACE": "false",
			},
			Phases: []phase{
				{
					WantCmds: []string{
						"/usr/bin/tailscaled --socket=/tmp/tailscaled.sock --state=mem: --statedir=/tmp",
						"/usr/bin/tailscale --socket=/tmp/tailscaled.sock up --accept-dns=false --authkey=tskey-key --advertise-routes=::/64,1::/64",
					},
				},
				{
					Notify: runningNotify,
					WantFiles: map[string]string{
						"proc/sys/net/ipv4/ip_forward":          "0",
						"proc/sys/net/ipv6/conf/all/forwarding": "1",
					},
				},
			},
		},
		{
			Name: "routes_kernel_all_families",
			Env: map[string]string{
				"TS_AUTHKEY":   "tskey-key",
				"TS_ROUTES":    "::/64,1.2.3.0/24",
				"TS_USERSPACE": "false",
			},
			Phases: []phase{
				{
					WantCmds: []string{
						"/usr/bin/tailscaled --socket=/tmp/tailscaled.sock --state=mem: --statedir=/tmp",
						"/usr/bin/tailscale --socket=/tmp/tailscaled.sock up --accept-dns=false --authkey=tskey-key --advertise-routes=::/64,1.2.3.0/24",
					},
				},
				{
					Notify: runningNotify,
					WantFiles: map[string]string{
						"proc/sys/net/ipv4/ip_forward":          "1",
						"proc/sys/net/ipv6/conf/all/forwarding": "1",
					},
				},
			},
		},
		{
			Name: "proxy",
			Env: map[string]string{
				"TS_AUTHKEY":   "tskey-key",
				"TS_DEST_IP":   "1.2.3.4",
				"TS_USERSPACE": "false",
			},
			Phases: []phase{
				{
					WantCmds: []string{
						"/usr/bin/tailscaled --socket=/tmp/tailscaled.sock --state=mem: --statedir=/tmp",
						"/usr/bin/tailscale --socket=/tmp/tailscaled.sock up --accept-dns=false --authkey=tskey-key",
					},
				},
				{
					Notify: runningNotify,
					WantCmds: []string{
						"/usr/bin/iptables -t nat -I PREROUTING 1 -d 100.64.0.1 -j DNAT --to-destination 1.2.3.4",
					},
				},
			},
		},
		{
			Name: "authkey_once",
			Env: map[string]string{
				"TS_AUTHKEY":   "tskey-key",
				"TS_AUTH_ONCE": "true",
			},
			Phases: []phase{
				{
					WantCmds: []string{
						"/usr/bin/tailscaled --socket=/tmp/tailscaled.sock --state=mem: --statedir=/tmp --tun=userspace-networking",
					},
				},
				{
					Notify: &ipn.Notify{
						State: ptr.To(ipn.NeedsLogin),
					},
					WantCmds: []string{
						"/usr/bin/tailscale --socket=/tmp/tailscaled.sock up --accept-dns=false --authkey=tskey-key",
					},
				},
				{
					Notify: runningNotify,
				},
			},
		},
		{
			Name: "kube_storage",
			Env: map[string]string{
				"KUBERNETES_SERVICE_HOST":       kube.Host,
				"KUBERNETES_SERVICE_PORT_HTTPS": kube.Port,
			},
			KubeSecret: map[string]string{
				"authkey": "tskey-key",
			},
			Phases: []phase{
				{
					WantCmds: []string{
						"/usr/bin/tailscaled --socket=/tmp/tailscaled.sock --state=kube:tailscale --statedir=/tmp --tun=userspace-networking",
						"/usr/bin/tailscale --socket=/tmp/tailscaled.sock up --accept-dns=false --authkey=tskey-key",
					},
					WantKubeSecret: map[string]string{
						"authkey": "tskey-key",
					},
				},
				{
					Notify: runningNotify,
					WantKubeSecret: map[string]string{
						"authkey":     "tskey-key",
						"device_fqdn": "test-node.test.ts.net",
						"device_id":   "myID",
					},
				},
			},
		},
		{
			Name: "kube_disk_storage",
			Env: map[string]string{
				"KUBERNETES_SERVICE_HOST":       kube.Host,
				"KUBERNETES_SERVICE_PORT_HTTPS": kube.Port,
				// Explicitly set to an empty value, to override the default of "tailscale".
				"TS_KUBE_SECRET": "",
				"TS_STATE_DIR":   filepath.Join(d, "tmp"),
				"TS_AUTHKEY":     "tskey-key",
			},
			KubeSecret: map[string]string{},
			Phases: []phase{
				{
					WantCmds: []string{
						"/usr/bin/tailscaled --socket=/tmp/tailscaled.sock --statedir=/tmp --tun=userspace-networking",
						"/usr/bin/tailscale --socket=/tmp/tailscaled.sock up --accept-dns=false --authkey=tskey-key",
					},
					WantKubeSecret: map[string]string{},
				},
				{
					Notify:         runningNotify,
					WantKubeSecret: map[string]string{},
				},
			},
		},
		{
			Name: "kube_storage_no_patch",
			Env: map[string]string{
				"KUBERNETES_SERVICE_HOST":       kube.Host,
				"KUBERNETES_SERVICE_PORT_HTTPS": kube.Port,
				"TS_AUTHKEY":                    "tskey-key",
			},
			KubeSecret:    map[string]string{},
			KubeDenyPatch: true,
			Phases: []phase{
				{
					WantCmds: []string{
						"/usr/bin/tailscaled --socket=/tmp/tailscaled.sock --state=kube:tailscale --statedir=/tmp --tun=userspace-networking",
						"/usr/bin/tailscale --socket=/tmp/tailscaled.sock up --accept-dns=false --authkey=tskey-key",
					},
					WantKubeSecret: map[string]string{},
				},
				{
					Notify:         runningNotify,
					WantKubeSecret: map[string]string{},
				},
			},
		},
		{
			// Same as previous, but deletes the authkey from the kube secret.
			Name: "kube_storage_auth_once",
			Env: map[string]string{
				"KUBERNETES_SERVICE_HOST":       kube.Host,
				"KUBERNETES_SERVICE_PORT_HTTPS": kube.Port,
				"TS_AUTH_ONCE":                  "true",
			},
			KubeSecret: map[string]string{
				"authkey": "tskey-key",
			},
			Phases: []phase{
				{
					WantCmds: []string{
						"/usr/bin/tailscaled --socket=/tmp/tailscaled.sock --state=kube:tailscale --statedir=/tmp --tun=userspace-networking",
					},
					WantKubeSecret: map[string]string{
						"authkey": "tskey-key",
					},
				},
				{
					Notify: &ipn.Notify{
						State: ptr.To(ipn.NeedsLogin),
					},
					WantCmds: []string{
						"/usr/bin/tailscale --socket=/tmp/tailscaled.sock up --accept-dns=false --authkey=tskey-key",
					},
					WantKubeSecret: map[string]string{
						"authkey": "tskey-key",
					},
				},
				{
					Notify: runningNotify,
					WantKubeSecret: map[string]string{
						"device_fqdn": "test-node.test.ts.net",
						"device_id":   "myID",
					},
				},
			},
		},
		{
			Name: "kube_storage_updates",
			Env: map[string]string{
				"KUBERNETES_SERVICE_HOST":       kube.Host,
				"KUBERNETES_SERVICE_PORT_HTTPS": kube.Port,
			},
			KubeSecret: map[string]string{
				"authkey": "tskey-key",
			},
			Phases: []phase{
				{
					WantCmds: []string{
						"/usr/bin/tailscaled --socket=/tmp/tailscaled.sock --state=kube:tailscale --statedir=/tmp --tun=userspace-networking",
						"/usr/bin/tailscale --socket=/tmp/tailscaled.sock up --accept-dns=false --authkey=tskey-key",
					},
					WantKubeSecret: map[string]string{
						"authkey": "tskey-key",
					},
				},
				{
					Notify: runningNotify,
					WantKubeSecret: map[string]string{
						"authkey":     "tskey-key",
						"device_fqdn": "test-node.test.ts.net",
						"device_id":   "myID",
					},
				},
				{
					Notify: &ipn.Notify{
						State: ptr.To(ipn.Running),
						NetMap: &netmap.NetworkMap{
							SelfNode: &tailcfg.Node{
								StableID: tailcfg.StableNodeID("newID"),
								Name:     "new-name.test.ts.net",
							},
							Addresses: []netip.Prefix{netip.MustParsePrefix("100.64.0.1/32")},
						},
					},
					WantKubeSecret: map[string]string{
						"authkey":     "tskey-key",
						"device_fqdn": "new-name.test.ts.net",
						"device_id":   "newID",
					},
				},
			},
		},
		{
			Name: "proxies",
			Env: map[string]string{
				"TS_SOCKS5_SERVER":              "localhost:1080",
				"TS_OUTBOUND_HTTP_PROXY_LISTEN": "localhost:8080",
			},
			Phases: []phase{
				{
					WantCmds: []string{
						"/usr/bin/tailscaled --socket=/tmp/tailscaled.sock --state=mem: --statedir=/tmp --tun=userspace-networking --socks5-server=localhost:1080 --outbound-http-proxy-listen=localhost:8080",
						"/usr/bin/tailscale --socket=/tmp/tailscaled.sock up --accept-dns=false",
					},
				},
				{
					Notify: runningNotify,
				},
			},
		},
		{
			Name: "dns",
			Env: map[string]string{
				"TS_ACCEPT_DNS": "true",
			},
			Phases: []phase{
				{
					WantCmds: []string{
						"/usr/bin/tailscaled --socket=/tmp/tailscaled.sock --state=mem: --statedir=/tmp --tun=userspace-networking",
						"/usr/bin/tailscale --socket=/tmp/tailscaled.sock up --accept-dns=true",
					},
				},
				{
					Notify: runningNotify,
				},
			},
		},
		{
			Name: "extra_args",
			Env: map[string]string{
				"TS_EXTRA_ARGS":            "--widget=rotated",
				"TS_TAILSCALED_EXTRA_ARGS": "--experiments=widgets",
			},
			Phases: []phase{
				{
					WantCmds: []string{
						"/usr/bin/tailscaled --socket=/tmp/tailscaled.sock --state=mem: --statedir=/tmp --tun=userspace-networking --experiments=widgets",
						"/usr/bin/tailscale --socket=/tmp/tailscaled.sock up --accept-dns=false --widget=rotated",
					},
				}, {
					Notify: runningNotify,
				},
			},
		},
		{
			Name: "hostname",
			Env: map[string]string{
				"TS_HOSTNAME": "my-server",
			},
			Phases: []phase{
				{
					WantCmds: []string{
						"/usr/bin/tailscaled --socket=/tmp/tailscaled.sock --state=mem: --statedir=/tmp --tun=userspace-networking",
						"/usr/bin/tailscale --socket=/tmp/tailscaled.sock up --accept-dns=false --hostname=my-server",
					},
				}, {
					Notify: runningNotify,
				},
			},
		},
	}

	for _, test := range tests {
		t.Run(test.Name, func(t *testing.T) {
			lapi.Reset()
			kube.Reset()
			os.Remove(argFile)
			os.Remove(runningSockPath)
			resetFiles()

			for k, v := range test.KubeSecret {
				kube.SetSecret(k, v)
			}
			kube.SetPatching(!test.KubeDenyPatch)

			cmd := exec.Command(boot)
			cmd.Env = []string{
				fmt.Sprintf("PATH=%s/usr/bin:%s", d, os.Getenv("PATH")),
				fmt.Sprintf("TS_TEST_RECORD_ARGS=%s", argFile),
				fmt.Sprintf("TS_TEST_SOCKET=%s", lapi.Path),
				fmt.Sprintf("TS_SOCKET=%s", runningSockPath),
				fmt.Sprintf("TS_TEST_ONLY_ROOT=%s", d),
			}
			for k, v := range test.Env {
				cmd.Env = append(cmd.Env, fmt.Sprintf("%s=%s", k, v))
			}
			cbOut := &lockingBuffer{}
			defer func() {
				if t.Failed() {
					t.Logf("containerboot output:\n%s", cbOut.String())
				}
			}()
			cmd.Stderr = cbOut
			if err := cmd.Start(); err != nil {
				t.Fatalf("starting containerboot: %v", err)
			}
			defer func() {
				cmd.Process.Signal(unix.SIGTERM)
				cmd.Process.Wait()
			}()

			var wantCmds []string
			for _, p := range test.Phases {
				lapi.Notify(p.Notify)
				wantCmds = append(wantCmds, p.WantCmds...)
				waitArgs(t, 2*time.Second, d, argFile, strings.Join(wantCmds, "\n"))
				err := tstest.WaitFor(2*time.Second, func() error {
					if p.WantKubeSecret != nil {
						got := kube.Secret()
						if diff := cmp.Diff(got, p.WantKubeSecret); diff != "" {
							return fmt.Errorf("unexpected kube secret data (-got+want):\n%s", diff)
						}
					} else {
						got := kube.Secret()
						if len(got) > 0 {
							return fmt.Errorf("kube secret unexpectedly not empty, got %#v", got)
						}
					}
					return nil
				})
				if err != nil {
					t.Fatal(err)
				}
				err = tstest.WaitFor(2*time.Second, func() error {
					for path, want := range p.WantFiles {
						gotBs, err := os.ReadFile(filepath.Join(d, path))
						if err != nil {
							return fmt.Errorf("reading wanted file %q: %v", path, err)
						}
						if got := strings.TrimSpace(string(gotBs)); got != want {
							return fmt.Errorf("wrong file contents for %q, got %q want %q", path, got, want)
						}
					}
					return nil
				})
				if err != nil {
					t.Fatal(err)
				}
			}
			waitLogLine(t, 2*time.Second, cbOut, "Startup complete, waiting for shutdown signal")
		})
	}
}

type lockingBuffer struct {
	sync.Mutex
	b bytes.Buffer
}

func (b *lockingBuffer) Write(bs []byte) (int, error) {
	b.Lock()
	defer b.Unlock()
	return b.b.Write(bs)
}

func (b *lockingBuffer) String() string {
	b.Lock()
	defer b.Unlock()
	return b.b.String()
}

// waitLogLine looks for want in the contents of b.
//
// Only lines starting with 'boot: ' (the output of containerboot
// itself) are considered, and the logged timestamp is ignored.
//
// waitLogLine fails the entire test if path doesn't contain want
// before the timeout.
func waitLogLine(t *testing.T, timeout time.Duration, b *lockingBuffer, want string) {
	deadline := time.Now().Add(timeout)
	for time.Now().Before(deadline) {
		for _, line := range strings.Split(b.String(), "\n") {
			if !strings.HasPrefix(line, "boot: ") {
				continue
			}
			if strings.HasSuffix(line, " "+want) {
				return
			}
		}
		time.Sleep(100 * time.Millisecond)
	}
	t.Fatalf("timed out waiting for wanted output line %q. Output:\n%s", want, b.String())
}

// waitArgs waits until the contents of path matches wantArgs, a set
// of command lines recorded by test_tailscale.sh and
// test_tailscaled.sh.
//
// All occurrences of removeStr are removed from the file prior to
// comparison. This is used to remove the varying temporary root
// directory name from recorded commandlines, so that wantArgs can be
// a constant value.
//
// waitArgs fails the entire test if path doesn't contain wantArgs
// before the timeout.
func waitArgs(t *testing.T, timeout time.Duration, removeStr, path, wantArgs string) {
	t.Helper()
	wantArgs = strings.TrimSpace(wantArgs)
	deadline := time.Now().Add(timeout)
	var got string
	for time.Now().Before(deadline) {
		bs, err := os.ReadFile(path)
		if errors.Is(err, fs.ErrNotExist) {
			// Don't bother logging that the file doesn't exist, it
			// should start existing soon.
			goto loop
		} else if err != nil {
			t.Logf("reading %q: %v", path, err)
			goto loop
		}
		got = strings.TrimSpace(string(bs))
		got = strings.ReplaceAll(got, removeStr, "")
		if got == wantArgs {
			return
		}
	loop:
		time.Sleep(100 * time.Millisecond)
	}
	t.Fatalf("waiting for args file %q to have expected output, got:\n%s\n\nWant: %s", path, got, wantArgs)
}

//go:embed test_tailscaled.sh
var fakeTailscaled []byte

//go:embed test_tailscale.sh
var fakeTailscale []byte

// localAPI is a minimal fake tailscaled LocalAPI server that presents
// just enough functionality for containerboot to function
// correctly. In practice this means it only supports querying
// tailscaled status, and panics on all other uses to make it very
// obvious that something unexpected happened.
type localAPI struct {
	FSRoot string
	Path   string // populated by Start

	srv *http.Server

	sync.Mutex
	cond   *sync.Cond
	notify *ipn.Notify
}

func (l *localAPI) Start() error {
	path := filepath.Join(l.FSRoot, "tmp/tailscaled.sock.fake")
	if err := os.MkdirAll(filepath.Dir(path), 0700); err != nil {
		return err
	}

	ln, err := net.Listen("unix", path)
	if err != nil {
		return err
	}

	l.srv = &http.Server{
		Handler: l,
	}
	l.Path = path
	l.cond = sync.NewCond(&l.Mutex)
	go l.srv.Serve(ln)
	return nil
}

func (l *localAPI) Close() {
	l.srv.Close()
}

func (l *localAPI) Reset() {
	l.Lock()
	defer l.Unlock()
	l.notify = nil
	l.cond.Broadcast()
}

func (l *localAPI) Notify(n *ipn.Notify) {
	if n == nil {
		return
	}
	l.Lock()
	defer l.Unlock()
	l.notify = n
	l.cond.Broadcast()
}

func (l *localAPI) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if r.Method != "GET" {
		panic(fmt.Sprintf("unsupported method %q", r.Method))
	}
	if r.URL.Path != "/localapi/v0/watch-ipn-bus" {
		panic(fmt.Sprintf("unsupported path %q", r.URL.Path))
	}

	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(http.StatusOK)
	if f, ok := w.(http.Flusher); ok {
		f.Flush()
	}
	enc := json.NewEncoder(w)
	l.Lock()
	defer l.Unlock()
	for {
		if l.notify != nil {
			if err := enc.Encode(l.notify); err != nil {
				// Usually broken pipe as the test client disconnects.
				return
			}
			if f, ok := w.(http.Flusher); ok {
				f.Flush()
			}
		}
		l.cond.Wait()
	}
}

// kubeServer is a minimal fake Kubernetes server that presents just
// enough functionality for containerboot to function correctly. In
// practice this means it only supports reading and modifying a single
// kube secret, and panics on all other uses to make it very obvious
// that something unexpected happened.
type kubeServer struct {
	FSRoot     string
	Host, Port string // populated by Start

	srv *httptest.Server

	sync.Mutex
	secret   map[string]string
	canPatch bool
}

func (k *kubeServer) Secret() map[string]string {
	k.Lock()
	defer k.Unlock()
	ret := map[string]string{}
	for k, v := range k.secret {
		ret[k] = v
	}
	return ret
}

func (k *kubeServer) SetSecret(key, val string) {
	k.Lock()
	defer k.Unlock()
	k.secret[key] = val
}

func (k *kubeServer) SetPatching(canPatch bool) {
	k.Lock()
	defer k.Unlock()
	k.canPatch = canPatch
}

func (k *kubeServer) Reset() {
	k.Lock()
	defer k.Unlock()
	k.secret = map[string]string{}
}

func (k *kubeServer) Start() error {
	root := filepath.Join(k.FSRoot, "var/run/secrets/kubernetes.io/serviceaccount")

	if err := os.MkdirAll(root, 0700); err != nil {
		return err
	}

	if err := os.WriteFile(filepath.Join(root, "namespace"), []byte("default"), 0600); err != nil {
		return err
	}
	if err := os.WriteFile(filepath.Join(root, "token"), []byte("bearer_token"), 0600); err != nil {
		return err
	}

	k.srv = httptest.NewTLSServer(k)
	k.Host = k.srv.Listener.Addr().(*net.TCPAddr).IP.String()
	k.Port = strconv.Itoa(k.srv.Listener.Addr().(*net.TCPAddr).Port)

	var cert bytes.Buffer
	if err := pem.Encode(&cert, &pem.Block{Type: "CERTIFICATE", Bytes: k.srv.Certificate().Raw}); err != nil {
		return err
	}
	if err := os.WriteFile(filepath.Join(root, "ca.crt"), cert.Bytes(), 0600); err != nil {
		return err
	}

	return nil
}

func (k *kubeServer) Close() {
	k.srv.Close()
}

func (k *kubeServer) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if r.Header.Get("Authorization") != "Bearer bearer_token" {
		panic("client didn't provide bearer token in request")
	}
	switch r.URL.Path {
	case "/api/v1/namespaces/default/secrets/tailscale":
		k.serveSecret(w, r)
	case "/apis/authorization.k8s.io/v1/selfsubjectaccessreviews":
		k.serveSSAR(w, r)
	default:
		panic(fmt.Sprintf("unhandled fake kube api path %q", r.URL.Path))
	}
}

func (k *kubeServer) serveSSAR(w http.ResponseWriter, r *http.Request) {
	var req struct {
		Spec struct {
			ResourceAttributes struct {
				Verb string `json:"verb"`
			} `json:"resourceAttributes"`
		} `json:"spec"`
	}
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		panic(fmt.Sprintf("decoding SSAR request: %v", err))
	}
	ok := true
	if req.Spec.ResourceAttributes.Verb == "patch" {
		k.Lock()
		defer k.Unlock()
		ok = k.canPatch
	}
	// Just say yes to all SARs, we don't enforce RBAC.
	w.Header().Set("Content-Type", "application/json")
	fmt.Fprintf(w, `{"status":{"allowed":%v}}`, ok)
}

func (k *kubeServer) serveSecret(w http.ResponseWriter, r *http.Request) {
	bs, err := io.ReadAll(r.Body)
	if err != nil {
		http.Error(w, fmt.Sprintf("reading request body: %v", err), http.StatusInternalServerError)
		return
	}

	switch r.Method {
	case "GET":
		w.Header().Set("Content-Type", "application/json")
		ret := map[string]map[string]string{
			"data": {},
		}
		k.Lock()
		defer k.Unlock()
		for k, v := range k.secret {
			v := base64.StdEncoding.EncodeToString([]byte(v))
			if err != nil {
				panic("encode failed")
			}
			ret["data"][k] = v
		}
		if err := json.NewEncoder(w).Encode(ret); err != nil {
			panic("encode failed")
		}
	case "PATCH":
		k.Lock()
		defer k.Unlock()
		if !k.canPatch {
			panic("containerboot tried to patch despite not being allowed")
		}
		switch r.Header.Get("Content-Type") {
		case "application/json-patch+json":
			req := []struct {
				Op   string `json:"op"`
				Path string `json:"path"`
			}{}
			if err := json.Unmarshal(bs, &req); err != nil {
				panic(fmt.Sprintf("json decode failed: %v. Body:\n\n%s", err, string(bs)))
			}
			for _, op := range req {
				if op.Op != "remove" {
					panic(fmt.Sprintf("unsupported json-patch op %q", op.Op))
				}
				if !strings.HasPrefix(op.Path, "/data/") {
					panic(fmt.Sprintf("unsupported json-patch path %q", op.Path))
				}
				delete(k.secret, strings.TrimPrefix(op.Path, "/data/"))
			}
		case "application/strategic-merge-patch+json":
			req := struct {
				Data map[string]string `json:"stringData"`
			}{}
			if err := json.Unmarshal(bs, &req); err != nil {
				panic(fmt.Sprintf("json decode failed: %v. Body:\n\n%s", err, string(bs)))
			}
			for key, val := range req.Data {
				k.secret[key] = val
			}
		default:
			panic(fmt.Sprintf("unknown content type %q", r.Header.Get("Content-Type")))
		}
	default:
		panic(fmt.Sprintf("unhandled HTTP method %q", r.Method))
	}
}