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tailscale/control/controlclient/direct.go

809 lines
21 KiB
Go

// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package controlclient
import (
"bytes"
"context"
"crypto/rand"
"encoding/binary"
"encoding/json"
"errors"
"fmt"
"io"
"io/ioutil"
"log"
"net/http"
"net/url"
"os"
"reflect"
"strconv"
"strings"
"sync"
"time"
"github.com/tailscale/wireguard-go/wgcfg"
"golang.org/x/crypto/nacl/box"
"golang.org/x/oauth2"
"tailscale.com/log/logheap"
"tailscale.com/net/netns"
"tailscale.com/net/tlsdial"
"tailscale.com/tailcfg"
"tailscale.com/types/logger"
"tailscale.com/types/structs"
"tailscale.com/version"
)
type Persist struct {
_ structs.Incomparable
PrivateMachineKey wgcfg.PrivateKey
PrivateNodeKey wgcfg.PrivateKey
OldPrivateNodeKey wgcfg.PrivateKey // needed to request key rotation
Provider string
LoginName string
}
func (p *Persist) Equals(p2 *Persist) bool {
if p == nil && p2 == nil {
return true
}
if p == nil || p2 == nil {
return false
}
return p.PrivateMachineKey.Equal(p2.PrivateMachineKey) &&
p.PrivateNodeKey.Equal(p2.PrivateNodeKey) &&
p.OldPrivateNodeKey.Equal(p2.OldPrivateNodeKey) &&
p.Provider == p2.Provider &&
p.LoginName == p2.LoginName
}
func (p *Persist) Pretty() string {
var mk, ok, nk wgcfg.Key
if !p.PrivateMachineKey.IsZero() {
mk = p.PrivateMachineKey.Public()
}
if !p.OldPrivateNodeKey.IsZero() {
ok = p.OldPrivateNodeKey.Public()
}
if !p.PrivateNodeKey.IsZero() {
nk = p.PrivateNodeKey.Public()
}
return fmt.Sprintf("Persist{m=%v, o=%v, n=%v u=%#v}",
mk.ShortString(), ok.ShortString(), nk.ShortString(),
p.LoginName)
}
// Direct is the client that connects to a tailcontrol server for a node.
type Direct struct {
httpc *http.Client // HTTP client used to talk to tailcontrol
serverURL string // URL of the tailcontrol server
timeNow func() time.Time
lastPrintMap time.Time
newDecompressor func() (Decompressor, error)
keepAlive bool
logf logger.Logf
discoPubKey tailcfg.DiscoKey
mu sync.Mutex // mutex guards the following fields
serverKey wgcfg.Key
persist Persist
authKey string
tryingNewKey wgcfg.PrivateKey
expiry *time.Time
// hostinfo is mutated in-place while mu is held.
hostinfo *tailcfg.Hostinfo // always non-nil
endpoints []string
localPort uint16 // or zero to mean auto
}
type Options struct {
Persist Persist // initial persistent data
ServerURL string // URL of the tailcontrol server
AuthKey string // optional node auth key for auto registration
TimeNow func() time.Time // time.Now implementation used by Client
Hostinfo *tailcfg.Hostinfo // non-nil passes ownership, nil means to use default using os.Hostname, etc
DiscoPublicKey tailcfg.DiscoKey
NewDecompressor func() (Decompressor, error)
KeepAlive bool
Logf logger.Logf
HTTPTestClient *http.Client // optional HTTP client to use (for tests only)
}
type Decompressor interface {
DecodeAll(input, dst []byte) ([]byte, error)
Close()
}
// NewDirect returns a new Direct client.
func NewDirect(opts Options) (*Direct, error) {
if opts.ServerURL == "" {
return nil, errors.New("controlclient.New: no server URL specified")
}
opts.ServerURL = strings.TrimRight(opts.ServerURL, "/")
serverURL, err := url.Parse(opts.ServerURL)
if err != nil {
return nil, err
}
if opts.TimeNow == nil {
opts.TimeNow = time.Now
}
if opts.Logf == nil {
// TODO(apenwarr): remove this default and fail instead.
// TODO(bradfitz): ... but then it shouldn't be in Options.
opts.Logf = log.Printf
}
httpc := opts.HTTPTestClient
if httpc == nil {
dialer := netns.NewDialer()
tr := http.DefaultTransport.(*http.Transport).Clone()
tr.DialContext = dialer.DialContext
tr.ForceAttemptHTTP2 = true
tr.TLSClientConfig = tlsdial.Config(serverURL.Host, tr.TLSClientConfig)
httpc = &http.Client{Transport: tr}
}
c := &Direct{
httpc: httpc,
serverURL: opts.ServerURL,
timeNow: opts.TimeNow,
logf: opts.Logf,
newDecompressor: opts.NewDecompressor,
keepAlive: opts.KeepAlive,
persist: opts.Persist,
authKey: opts.AuthKey,
discoPubKey: opts.DiscoPublicKey,
}
if opts.Hostinfo == nil {
c.SetHostinfo(NewHostinfo())
} else {
c.SetHostinfo(opts.Hostinfo)
}
return c, nil
}
func NewHostinfo() *tailcfg.Hostinfo {
hostname, _ := os.Hostname()
return &tailcfg.Hostinfo{
IPNVersion: version.LONG,
Hostname: hostname,
OS: version.OS(),
}
}
// SetHostinfo clones the provided Hostinfo and remembers it for the
// next update. It reports whether the Hostinfo has changed.
func (c *Direct) SetHostinfo(hi *tailcfg.Hostinfo) bool {
if hi == nil {
panic("nil Hostinfo")
}
c.mu.Lock()
defer c.mu.Unlock()
if hi.Equal(c.hostinfo) {
return false
}
c.hostinfo = hi.Clone()
return true
}
// SetNetInfo clones the provided NetInfo and remembers it for the
// next update. It reports whether the NetInfo has changed.
func (c *Direct) SetNetInfo(ni *tailcfg.NetInfo) bool {
if ni == nil {
panic("nil NetInfo")
}
c.mu.Lock()
defer c.mu.Unlock()
if c.hostinfo == nil {
c.logf("[unexpected] SetNetInfo called with no HostInfo; ignoring NetInfo update: %+v", ni)
return false
}
if reflect.DeepEqual(ni, c.hostinfo.NetInfo) {
return false
}
c.hostinfo.NetInfo = ni.Clone()
return true
}
func (c *Direct) GetPersist() Persist {
c.mu.Lock()
defer c.mu.Unlock()
return c.persist
}
type LoginFlags int
const (
LoginDefault = LoginFlags(0)
LoginInteractive = LoginFlags(1 << iota) // force user login and key refresh
)
func (c *Direct) TryLogout(ctx context.Context) error {
c.logf("direct.TryLogout()")
c.mu.Lock()
defer c.mu.Unlock()
// TODO(crawshaw): Tell the server. This node key should be
// immediately invalidated.
//if c.persist.PrivateNodeKey != (wgcfg.PrivateKey{}) {
//}
c.persist = Persist{
PrivateMachineKey: c.persist.PrivateMachineKey,
}
return nil
}
func (c *Direct) TryLogin(ctx context.Context, t *oauth2.Token, flags LoginFlags) (url string, err error) {
c.logf("direct.TryLogin(%v, %v)", t != nil, flags)
return c.doLoginOrRegen(ctx, t, flags, false, "")
}
func (c *Direct) WaitLoginURL(ctx context.Context, url string) (newUrl string, err error) {
c.logf("direct.WaitLoginURL")
return c.doLoginOrRegen(ctx, nil, LoginDefault, false, url)
}
func (c *Direct) doLoginOrRegen(ctx context.Context, t *oauth2.Token, flags LoginFlags, regen bool, url string) (newUrl string, err error) {
mustregen, url, err := c.doLogin(ctx, t, flags, regen, url)
if err != nil {
return url, err
}
if mustregen {
_, url, err = c.doLogin(ctx, t, flags, true, url)
}
return url, err
}
func (c *Direct) doLogin(ctx context.Context, t *oauth2.Token, flags LoginFlags, regen bool, url string) (mustregen bool, newurl string, err error) {
c.mu.Lock()
persist := c.persist
tryingNewKey := c.tryingNewKey
serverKey := c.serverKey
authKey := c.authKey
hostinfo := c.hostinfo
backendLogID := hostinfo.BackendLogID
expired := c.expiry != nil && !c.expiry.IsZero() && c.expiry.Before(c.timeNow())
c.mu.Unlock()
if persist.PrivateMachineKey == (wgcfg.PrivateKey{}) {
c.logf("Generating a new machinekey.")
mkey, err := wgcfg.NewPrivateKey()
if err != nil {
log.Fatal(err)
}
persist.PrivateMachineKey = mkey
}
if expired {
c.logf("Old key expired -> regen=true")
regen = true
}
if (flags & LoginInteractive) != 0 {
c.logf("LoginInteractive -> regen=true")
regen = true
}
c.logf("doLogin(regen=%v, hasUrl=%v)", regen, url != "")
if serverKey == (wgcfg.Key{}) {
var err error
serverKey, err = loadServerKey(ctx, c.httpc, c.serverURL)
if err != nil {
return regen, url, err
}
c.mu.Lock()
c.serverKey = serverKey
c.mu.Unlock()
}
var oldNodeKey wgcfg.Key
if url != "" {
} else if regen || persist.PrivateNodeKey == (wgcfg.PrivateKey{}) {
c.logf("Generating a new nodekey.")
persist.OldPrivateNodeKey = persist.PrivateNodeKey
key, err := wgcfg.NewPrivateKey()
if err != nil {
c.logf("login keygen: %v", err)
return regen, url, err
}
tryingNewKey = key
} else {
// Try refreshing the current key first
tryingNewKey = persist.PrivateNodeKey
}
if persist.OldPrivateNodeKey != (wgcfg.PrivateKey{}) {
oldNodeKey = persist.OldPrivateNodeKey.Public()
}
if tryingNewKey == (wgcfg.PrivateKey{}) {
log.Fatalf("tryingNewKey is empty, give up")
}
if backendLogID == "" {
err = errors.New("hostinfo: BackendLogID missing")
return regen, url, err
}
request := tailcfg.RegisterRequest{
Version: 1,
OldNodeKey: tailcfg.NodeKey(oldNodeKey),
NodeKey: tailcfg.NodeKey(tryingNewKey.Public()),
Hostinfo: hostinfo,
Followup: url,
}
c.logf("RegisterReq: onode=%v node=%v fup=%v",
request.OldNodeKey.ShortString(),
request.NodeKey.ShortString(), url != "")
request.Auth.Oauth2Token = t
request.Auth.Provider = persist.Provider
request.Auth.LoginName = persist.LoginName
request.Auth.AuthKey = authKey
bodyData, err := encode(request, &serverKey, &persist.PrivateMachineKey)
if err != nil {
return regen, url, err
}
body := bytes.NewReader(bodyData)
u := fmt.Sprintf("%s/machine/%s", c.serverURL, persist.PrivateMachineKey.Public().HexString())
req, err := http.NewRequest("POST", u, body)
if err != nil {
return regen, url, err
}
req = req.WithContext(ctx)
res, err := c.httpc.Do(req)
if err != nil {
return regen, url, fmt.Errorf("register request: %v", err)
}
c.logf("RegisterReq: returned.")
resp := tailcfg.RegisterResponse{}
if err := decode(res, &resp, &serverKey, &persist.PrivateMachineKey); err != nil {
return regen, url, fmt.Errorf("register request: %v", err)
}
if resp.NodeKeyExpired {
if regen {
return true, "", fmt.Errorf("weird: regen=true but server says NodeKeyExpired: %v", request.NodeKey)
}
c.logf("server reports new node key %v has expired",
request.NodeKey.ShortString())
return true, "", nil
}
if persist.Provider == "" {
persist.Provider = resp.Login.Provider
}
if persist.LoginName == "" {
persist.LoginName = resp.Login.LoginName
}
// TODO(crawshaw): RegisterResponse should be able to mechanically
// communicate some extra instructions from the server:
// - new node key required
// - machine key no longer supported
// - user is disabled
if resp.AuthURL != "" {
c.logf("AuthURL is %v", resp.AuthURL)
} else {
c.logf("No AuthURL")
}
c.mu.Lock()
if resp.AuthURL == "" {
// key rotation is complete
persist.PrivateNodeKey = tryingNewKey
} else {
// save it for the retry-with-URL
c.tryingNewKey = tryingNewKey
}
c.persist = persist
c.mu.Unlock()
if err != nil {
return regen, "", err
}
if ctx.Err() != nil {
return regen, "", ctx.Err()
}
return false, resp.AuthURL, nil
}
func sameStrings(a, b []string) bool {
if len(a) != len(b) {
return false
}
for i := range a {
if a[i] != b[i] {
return false
}
}
return true
}
// newEndpoints acquires c.mu and sets the local port and endpoints and reports
// whether they've changed.
//
// It does not retain the provided slice.
func (c *Direct) newEndpoints(localPort uint16, endpoints []string) (changed bool) {
c.mu.Lock()
defer c.mu.Unlock()
// Nothing new?
if c.localPort == localPort && sameStrings(c.endpoints, endpoints) {
return false // unchanged
}
c.logf("client.newEndpoints(%v, %v)", localPort, endpoints)
c.localPort = localPort
c.endpoints = append(c.endpoints[:0], endpoints...)
return true // changed
}
// SetEndpoints updates the list of locally advertised endpoints.
// It won't be replicated to the server until a *fresh* call to PollNetMap().
// You don't need to restart PollNetMap if we return changed==false.
func (c *Direct) SetEndpoints(localPort uint16, endpoints []string) (changed bool) {
// (no log message on function entry, because it clutters the logs
// if endpoints haven't changed. newEndpoints() will log it.)
return c.newEndpoints(localPort, endpoints)
}
func (c *Direct) PollNetMap(ctx context.Context, maxPolls int, cb func(*NetworkMap)) error {
c.mu.Lock()
persist := c.persist
serverURL := c.serverURL
serverKey := c.serverKey
hostinfo := c.hostinfo
backendLogID := hostinfo.BackendLogID
localPort := c.localPort
ep := append([]string(nil), c.endpoints...)
c.mu.Unlock()
if backendLogID == "" {
return errors.New("hostinfo: BackendLogID missing")
}
allowStream := maxPolls != 1
c.logf("PollNetMap: stream=%v :%v %v", maxPolls, localPort, ep)
vlogf := logger.Discard
if Debug.NetMap {
vlogf = c.logf
}
request := tailcfg.MapRequest{
Version: 4,
IncludeIPv6: true,
KeepAlive: c.keepAlive,
NodeKey: tailcfg.NodeKey(persist.PrivateNodeKey.Public()),
DiscoKey: c.discoPubKey,
Endpoints: ep,
Stream: allowStream,
Hostinfo: hostinfo,
}
if c.newDecompressor != nil {
request.Compress = "zstd"
}
bodyData, err := encode(request, &serverKey, &persist.PrivateMachineKey)
if err != nil {
vlogf("netmap: encode: %v", err)
return err
}
t0 := time.Now()
u := fmt.Sprintf("%s/machine/%s/map", serverURL, persist.PrivateMachineKey.Public().HexString())
req, err := http.NewRequest("POST", u, bytes.NewReader(bodyData))
if err != nil {
return err
}
ctx, cancel := context.WithCancel(ctx)
defer cancel()
req = req.WithContext(ctx)
res, err := c.httpc.Do(req)
if err != nil {
vlogf("netmap: Do: %v", err)
return err
}
vlogf("netmap: Do = %v after %v", res.StatusCode, time.Since(t0).Round(time.Millisecond))
if res.StatusCode != 200 {
msg, _ := ioutil.ReadAll(res.Body)
res.Body.Close()
return fmt.Errorf("initial fetch failed %d: %s",
res.StatusCode, strings.TrimSpace(string(msg)))
}
defer res.Body.Close()
// If we go more than pollTimeout without hearing from the server,
// end the long poll. We should be receiving a keep alive ping
// every minute.
const pollTimeout = 120 * time.Second
timeout := time.NewTimer(pollTimeout)
timeoutReset := make(chan struct{})
pollDone := make(chan struct{})
defer close(pollDone)
go func() {
for {
select {
case <-pollDone:
vlogf("netmap: ending timeout goroutine")
return
case <-timeout.C:
c.logf("map response long-poll timed out!")
cancel()
return
case <-timeoutReset:
if !timeout.Stop() {
select {
case <-timeout.C:
case <-pollDone:
vlogf("netmap: ending timeout goroutine")
return
}
}
vlogf("netmap: reset timeout timer")
timeout.Reset(pollTimeout)
}
}
}()
var lastDERPMap *tailcfg.DERPMap
// If allowStream, then the server will use an HTTP long poll to
// return incremental results. There is always one response right
// away, followed by a delay, and eventually others.
// If !allowStream, it'll still send the first result in exactly
// the same format before just closing the connection.
// We can use this same read loop either way.
var msg []byte
for i := 0; i < maxPolls || maxPolls < 0; i++ {
vlogf("netmap: starting size read after %v (poll %v)", time.Since(t0).Round(time.Millisecond), i)
var siz [4]byte
if _, err := io.ReadFull(res.Body, siz[:]); err != nil {
vlogf("netmap: size read error after %v: %v", time.Since(t0).Round(time.Millisecond), err)
return err
}
size := binary.LittleEndian.Uint32(siz[:])
vlogf("netmap: read size %v after %v", size, time.Since(t0).Round(time.Millisecond))
msg = append(msg[:0], make([]byte, size)...)
if _, err := io.ReadFull(res.Body, msg); err != nil {
vlogf("netmap: body read error: %v", err)
return err
}
vlogf("netmap: read body after %v", time.Since(t0).Round(time.Millisecond))
var resp tailcfg.MapResponse
if err := c.decodeMsg(msg, &resp); err != nil {
vlogf("netmap: decode error: %v")
return err
}
if resp.KeepAlive {
vlogf("netmap: got keep-alive")
select {
case timeoutReset <- struct{}{}:
vlogf("netmap: sent keep-alive timer reset")
case <-ctx.Done():
c.logf("netmap: not resetting timer for keep-alive due to: %v", ctx.Err())
return ctx.Err()
}
continue
}
vlogf("netmap: got new map")
if resp.DERPMap != nil {
vlogf("netmap: new map contains DERP map")
lastDERPMap = resp.DERPMap
}
if resp.Debug != nil && resp.Debug.LogHeapPprof {
go logheap.LogHeap(resp.Debug.LogHeapURL)
}
// Temporarily (2020-06-29) support removing all but
// discovery-supporting nodes during development, for
// less noise.
if Debug.OnlyDisco {
filtered := resp.Peers[:0]
for _, p := range resp.Peers {
if !p.DiscoKey.IsZero() {
filtered = append(filtered, p)
}
}
resp.Peers = filtered
}
nm := &NetworkMap{
NodeKey: tailcfg.NodeKey(persist.PrivateNodeKey.Public()),
PrivateKey: persist.PrivateNodeKey,
Expiry: resp.Node.KeyExpiry,
Addresses: resp.Node.Addresses,
Peers: resp.Peers,
LocalPort: localPort,
User: resp.Node.User,
UserProfiles: make(map[tailcfg.UserID]tailcfg.UserProfile),
Domain: resp.Domain,
Roles: resp.Roles,
DNS: resp.DNS,
DNSDomains: resp.SearchPaths,
Hostinfo: resp.Node.Hostinfo,
PacketFilter: c.parsePacketFilter(resp.PacketFilter),
DERPMap: lastDERPMap,
Debug: resp.Debug,
}
for _, profile := range resp.UserProfiles {
nm.UserProfiles[profile.ID] = profile
}
if resp.Node.MachineAuthorized {
nm.MachineStatus = tailcfg.MachineAuthorized
} else {
nm.MachineStatus = tailcfg.MachineUnauthorized
}
// Printing the netmap can be extremely verbose, but is very
// handy for debugging. Let's limit how often we do it.
// Code elsewhere prints netmap diffs every time, so this
// occasional full dump, plus incremental diffs, should do
// the job.
now := c.timeNow()
if now.Sub(c.lastPrintMap) >= 5*time.Minute {
c.lastPrintMap = now
c.logf("new network map[%d]:\n%s", i, nm.Concise())
}
c.mu.Lock()
c.expiry = &nm.Expiry
c.mu.Unlock()
cb(nm)
}
if ctx.Err() != nil {
return ctx.Err()
}
return nil
}
func decode(res *http.Response, v interface{}, serverKey *wgcfg.Key, mkey *wgcfg.PrivateKey) error {
defer res.Body.Close()
msg, err := ioutil.ReadAll(io.LimitReader(res.Body, 1<<20))
if err != nil {
return err
}
if res.StatusCode != 200 {
return fmt.Errorf("%d: %v", res.StatusCode, string(msg))
}
return decodeMsg(msg, v, serverKey, mkey)
}
func (c *Direct) decodeMsg(msg []byte, v interface{}) error {
mkey := c.persist.PrivateMachineKey
serverKey := c.serverKey
decrypted, err := decryptMsg(msg, &serverKey, &mkey)
if err != nil {
return err
}
var b []byte
if c.newDecompressor == nil {
b = decrypted
} else {
decoder, err := c.newDecompressor()
if err != nil {
return err
}
defer decoder.Close()
b, err = decoder.DecodeAll(decrypted, nil)
if err != nil {
return err
}
}
if err := json.Unmarshal(b, v); err != nil {
return fmt.Errorf("response: %v", err)
}
return nil
}
func decodeMsg(msg []byte, v interface{}, serverKey *wgcfg.Key, mkey *wgcfg.PrivateKey) error {
decrypted, err := decryptMsg(msg, serverKey, mkey)
if err != nil {
return err
}
if err := json.Unmarshal(decrypted, v); err != nil {
return fmt.Errorf("response: %v", err)
}
return nil
}
func decryptMsg(msg []byte, serverKey *wgcfg.Key, mkey *wgcfg.PrivateKey) ([]byte, error) {
var nonce [24]byte
if len(msg) < len(nonce)+1 {
return nil, fmt.Errorf("response missing nonce, len=%d", len(msg))
}
copy(nonce[:], msg)
msg = msg[len(nonce):]
pub, pri := (*[32]byte)(serverKey), (*[32]byte)(mkey)
decrypted, ok := box.Open(nil, msg, &nonce, pub, pri)
if !ok {
return nil, fmt.Errorf("cannot decrypt response")
}
return decrypted, nil
}
func encode(v interface{}, serverKey *wgcfg.Key, mkey *wgcfg.PrivateKey) ([]byte, error) {
b, err := json.Marshal(v)
if err != nil {
return nil, err
}
const debugMapRequests = false
if debugMapRequests {
if _, ok := v.(tailcfg.MapRequest); ok {
log.Printf("MapRequest: %s", b)
}
}
var nonce [24]byte
if _, err := io.ReadFull(rand.Reader, nonce[:]); err != nil {
panic(err)
}
pub, pri := (*[32]byte)(serverKey), (*[32]byte)(mkey)
msg := box.Seal(nonce[:], b, &nonce, pub, pri)
return msg, nil
}
func loadServerKey(ctx context.Context, httpc *http.Client, serverURL string) (wgcfg.Key, error) {
req, err := http.NewRequest("GET", serverURL+"/key", nil)
if err != nil {
return wgcfg.Key{}, fmt.Errorf("create control key request: %v", err)
}
req = req.WithContext(ctx)
res, err := httpc.Do(req)
if err != nil {
return wgcfg.Key{}, fmt.Errorf("fetch control key: %v", err)
}
defer res.Body.Close()
b, err := ioutil.ReadAll(io.LimitReader(res.Body, 1<<16))
if err != nil {
return wgcfg.Key{}, fmt.Errorf("fetch control key response: %v", err)
}
if res.StatusCode != 200 {
return wgcfg.Key{}, fmt.Errorf("fetch control key: %d: %s", res.StatusCode, string(b))
}
key, err := wgcfg.ParseHexKey(string(b))
if err != nil {
return wgcfg.Key{}, fmt.Errorf("fetch control key: %v", err)
}
return key, nil
}
// Debug contains temporary internal-only debug knobs.
// They're unexported to not draw attention to them.
var Debug = initDebug()
type debug struct {
NetMap bool
OnlyDisco bool
Disco bool
}
func initDebug() debug {
return debug{
NetMap: envBool("TS_DEBUG_NETMAP"),
OnlyDisco: os.Getenv("TS_DEBUG_USE_DISCO") == "only",
Disco: os.Getenv("TS_DEBUG_USE_DISCO") == "only" || envBool("TS_DEBUG_USE_DISCO"),
}
}
func envBool(k string) bool {
e := os.Getenv(k)
if e == "" {
return false
}
v, err := strconv.ParseBool(e)
if err != nil {
panic(fmt.Sprintf("invalid non-bool %q for env var %q", e, k))
}
return v
}