lib/crunchrun/container_gateway.go

   1 // Copyright (C) The Arvados Authors. All rights reserved.
   2 //
   3 // SPDX-License-Identifier: AGPL-3.0
   4
   5 package crunchrun
   6
   7 import (
   8         "context"
   9         "crypto/hmac"
  10         "crypto/rand"
  11         "crypto/rsa"
  12         "crypto/sha256"
  13         "crypto/tls"
  14         "fmt"
  15         "io"
  16         "net"
  17         "net/http"
  18         "net/url"
  19         "os"
  20         "os/exec"
  21         "strings"
  22         "sync"
  23         "syscall"
  24         "time"
  25
  26         "git.arvados.org/arvados.git/lib/controller/rpc"
  27         "git.arvados.org/arvados.git/lib/selfsigned"
  28         "git.arvados.org/arvados.git/lib/webdavfs"
  29         "git.arvados.org/arvados.git/sdk/go/arvados"
  30         "git.arvados.org/arvados.git/sdk/go/auth"
  31         "git.arvados.org/arvados.git/sdk/go/ctxlog"
  32         "git.arvados.org/arvados.git/sdk/go/httpserver"
  33         "github.com/creack/pty"
  34         "github.com/google/shlex"
  35         "github.com/hashicorp/yamux"
  36         "golang.org/x/crypto/ssh"
  37         "golang.org/x/net/webdav"
  38 )
  39
  40 type GatewayTarget interface {
  41         // Command that will execute cmd inside the container
  42         InjectCommand(ctx context.Context, detachKeys, username string, usingTTY bool, cmd []string) (*exec.Cmd, error)
  43
  44         // IP address inside container
  45         IPAddress() (string, error)
  46 }
  47
  48 type GatewayTargetStub struct{}
  49
  50 func (GatewayTargetStub) IPAddress() (string, error) { return "127.0.0.1", nil }
  51 func (GatewayTargetStub) InjectCommand(ctx context.Context, detachKeys, username string, usingTTY bool, cmd []string) (*exec.Cmd, error) {
  52         return exec.CommandContext(ctx, cmd[0], cmd[1:]...), nil
  53 }
  54
  55 type Gateway struct {
  56         ContainerUUID string
  57         // Caller should set Address to "", or "host:0" or "host:port"
  58         // where host is a known external IP address; port is a
  59         // desired port number to listen on; and ":0" chooses an
  60         // available dynamic port.
  61         //
  62         // If Address is "", Start() listens only on the loopback
  63         // interface (and changes Address to "127.0.0.1:port").
  64         // Otherwise it listens on all interfaces.
  65         //
  66         // If Address is "host:0", Start() updates Address to
  67         // "host:port".
  68         Address    string
  69         AuthSecret string
  70         Target     GatewayTarget
  71         Log        interface {
  72                 Printf(fmt string, args ...interface{})
  73         }
  74         // If non-nil, set up a ContainerGatewayTunnel, so that the
  75         // controller can connect to us even if our external IP
  76         // address is unknown or not routable from controller.
  77         ArvadosClient *arvados.Client
  78
  79         // When a tunnel is connected or reconnected, this func (if
  80         // not nil) will be called with the InternalURL of the
  81         // controller process at the other end of the tunnel.
  82         UpdateTunnelURL func(url string)
  83
  84         // Source for serving WebDAV requests at
  85         // /arvados/v1/containers/{uuid}/log/
  86         LogCollection arvados.CollectionFileSystem
  87
  88         sshConfig   ssh.ServerConfig
  89         requestAuth string
  90         respondAuth string
  91         logPath     string
  92 }
  93
  94 // Start starts an http server that allows authenticated clients to open an
  95 // interactive "docker exec" session and (in future) connect to tcp ports
  96 // inside the docker container.
  97 func (gw *Gateway) Start() error {
  98         gw.sshConfig = ssh.ServerConfig{
  99                 NoClientAuth: true,
 100                 PasswordCallback: func(c ssh.ConnMetadata, pass []byte) (*ssh.Permissions, error) {
 101                         if c.User() == "_" {
 102                                 return nil, nil
 103                         }
 104                         return nil, fmt.Errorf("cannot specify user %q via ssh client", c.User())
 105                 },
 106                 PublicKeyCallback: func(c ssh.ConnMetadata, pubKey ssh.PublicKey) (*ssh.Permissions, error) {
 107                         if c.User() == "_" {
 108                                 return &ssh.Permissions{
 109                                         Extensions: map[string]string{
 110                                                 "pubkey-fp": ssh.FingerprintSHA256(pubKey),
 111                                         },
 112                                 }, nil
 113                         }
 114                         return nil, fmt.Errorf("cannot specify user %q via ssh client", c.User())
 115                 },
 116         }
 117         pvt, err := rsa.GenerateKey(rand.Reader, 2048)
 118         if err != nil {
 119                 return err
 120         }
 121         err = pvt.Validate()
 122         if err != nil {
 123                 return err
 124         }
 125         signer, err := ssh.NewSignerFromKey(pvt)
 126         if err != nil {
 127                 return err
 128         }
 129         gw.sshConfig.AddHostKey(signer)
 130
 131         // Address (typically provided by arvados-dispatch-cloud) is
 132         // HOST:PORT where HOST is our IP address or hostname as seen
 133         // from arvados-controller, and PORT is either the desired
 134         // port where we should run our gateway server, or "0" if we
 135         // should choose an available port.
 136         extAddr := gw.Address
 137         // Generally we can't know which local interface corresponds
 138         // to an externally reachable IP address, so if we expect to
 139         // be reachable by external hosts, we listen on all
 140         // interfaces.
 141         listenHost := ""
 142         if extAddr == "" {
 143                 // If the dispatcher doesn't tell us our external IP
 144                 // address, controller will only be able to connect
 145                 // through the tunnel (see runTunnel), so our gateway
 146                 // server only needs to listen on the loopback
 147                 // interface.
 148                 extAddr = "127.0.0.1:0"
 149                 listenHost = "127.0.0.1"
 150         }
 151         extHost, extPort, err := net.SplitHostPort(extAddr)
 152         if err != nil {
 153                 return err
 154         }
 155         cert, err := selfsigned.CertGenerator{}.Generate()
 156         if err != nil {
 157                 return err
 158         }
 159         h := hmac.New(sha256.New, []byte(gw.AuthSecret))
 160         h.Write(cert.Certificate[0])
 161         gw.requestAuth = fmt.Sprintf("%x", h.Sum(nil))
 162         h.Reset()
 163         h.Write([]byte(gw.requestAuth))
 164         gw.respondAuth = fmt.Sprintf("%x", h.Sum(nil))
 165
 166         gw.logPath = "/arvados/v1/containers/" + gw.ContainerUUID + "/log"
 167
 168         srv := &httpserver.Server{
 169                 Server: http.Server{
 170                         Handler: gw,
 171                         TLSConfig: &tls.Config{
 172                                 Certificates: []tls.Certificate{cert},
 173                         },
 174                 },
 175                 Addr: net.JoinHostPort(listenHost, extPort),
 176         }
 177         err = srv.Start()
 178         if err != nil {
 179                 return err
 180         }
 181         go func() {
 182                 err := srv.Wait()
 183                 gw.Log.Printf("gateway server stopped: %s", err)
 184         }()
 185         // Get the port number we are listening on (extPort might be
 186         // "0" or a port name, in which case this will be different).
 187         _, listenPort, err := net.SplitHostPort(srv.Addr)
 188         if err != nil {
 189                 return err
 190         }
 191         // When changing state to Running, the caller will want to set
 192         // gateway_address to a "HOST:PORT" that, if controller
 193         // connects to it, will reach this gateway server.
 194         //
 195         // The most likely thing to work is: HOST is our external
 196         // hostname/IP as provided by the caller
 197         // (arvados-dispatch-cloud) or 127.0.0.1 to indicate
 198         // non-tunnel connections aren't available; and PORT is the
 199         // port number we are listening on.
 200         gw.Address = net.JoinHostPort(extHost, listenPort)
 201         gw.Log.Printf("gateway server listening at %s", gw.Address)
 202         if gw.ArvadosClient != nil {
 203                 go gw.maintainTunnel(gw.Address)
 204         }
 205         return nil
 206 }
 207
 208 func (gw *Gateway) maintainTunnel(addr string) {
 209         for ; ; time.Sleep(5 * time.Second) {
 210                 err := gw.runTunnel(addr)
 211                 gw.Log.Printf("runTunnel: %s", err)
 212         }
 213 }
 214
 215 // runTunnel connects to controller and sets up a tunnel through
 216 // which controller can connect to the gateway server at the given
 217 // addr.
 218 func (gw *Gateway) runTunnel(addr string) error {
 219         ctx := auth.NewContext(context.Background(), auth.NewCredentials(gw.ArvadosClient.AuthToken))
 220         arpc := rpc.NewConn("", &url.URL{Scheme: "https", Host: gw.ArvadosClient.APIHost}, gw.ArvadosClient.Insecure, rpc.PassthroughTokenProvider)
 221         tun, err := arpc.ContainerGatewayTunnel(ctx, arvados.ContainerGatewayTunnelOptions{
 222                 UUID:       gw.ContainerUUID,
 223                 AuthSecret: gw.AuthSecret,
 224         })
 225         if err != nil {
 226                 return fmt.Errorf("error creating gateway tunnel: %s", err)
 227         }
 228         mux, err := yamux.Client(tun.Conn, nil)
 229         if err != nil {
 230                 return fmt.Errorf("error setting up mux client end: %s", err)
 231         }
 232         if url := tun.Header.Get("X-Arvados-Internal-Url"); url != "" && gw.UpdateTunnelURL != nil {
 233                 gw.UpdateTunnelURL(url)
 234         }
 235         for {
 236                 muxconn, err := mux.AcceptStream()
 237                 if err != nil {
 238                         return err
 239                 }
 240                 gw.Log.Printf("tunnel connection %d started", muxconn.StreamID())
 241                 go func() {
 242                         defer muxconn.Close()
 243                         gwconn, err := net.Dial("tcp", addr)
 244                         if err != nil {
 245                                 gw.Log.Printf("tunnel connection %d: error connecting to %s: %s", muxconn.StreamID(), addr, err)
 246                                 return
 247                         }
 248                         defer gwconn.Close()
 249                         var wg sync.WaitGroup
 250                         wg.Add(2)
 251                         go func() {
 252                                 defer wg.Done()
 253                                 _, err := io.Copy(gwconn, muxconn)
 254                                 if err != nil {
 255                                         gw.Log.Printf("tunnel connection %d: mux end: %s", muxconn.StreamID(), err)
 256                                 }
 257                                 gwconn.Close()
 258                         }()
 259                         go func() {
 260                                 defer wg.Done()
 261                                 _, err := io.Copy(muxconn, gwconn)
 262                                 if err != nil {
 263                                         gw.Log.Printf("tunnel connection %d: gateway end: %s", muxconn.StreamID(), err)
 264                                 }
 265                                 muxconn.Close()
 266                         }()
 267                         wg.Wait()
 268                         gw.Log.Printf("tunnel connection %d finished", muxconn.StreamID())
 269                 }()
 270         }
 271 }
 272
 273 var webdavMethod = map[string]bool{
 274         "GET":      true,
 275         "OPTIONS":  true,
 276         "PROPFIND": true,
 277 }
 278
 279 func (gw *Gateway) ServeHTTP(w http.ResponseWriter, req *http.Request) {
 280         reqUUID := req.Header.Get("X-Arvados-Container-Gateway-Uuid")
 281         if reqUUID == "" {
 282                 // older controller versions only send UUID as query param
 283                 req.ParseForm()
 284                 reqUUID = req.Form.Get("uuid")
 285         }
 286         if reqUUID != gw.ContainerUUID {
 287                 http.Error(w, fmt.Sprintf("misdirected request: meant for %q but received by crunch-run %q", reqUUID, gw.ContainerUUID), http.StatusBadGateway)
 288                 return
 289         }
 290         if req.Header.Get("X-Arvados-Authorization") != gw.requestAuth {
 291                 http.Error(w, "bad X-Arvados-Authorization header", http.StatusUnauthorized)
 292                 return
 293         }
 294         w.Header().Set("X-Arvados-Authorization-Response", gw.respondAuth)
 295         switch {
 296         case req.Method == "POST" && req.Header.Get("Upgrade") == "ssh":
 297                 gw.handleSSH(w, req)
 298         case req.URL.Path == gw.logPath || strings.HasPrefix(req.URL.Path, gw.logPath):
 299                 if !webdavMethod[req.Method] {
 300                         http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
 301                         return
 302                 }
 303                 gw.handleLogsWebDAV(w, req)
 304         default:
 305                 http.Error(w, "path not found", http.StatusNotFound)
 306         }
 307 }
 308
 309 func (gw *Gateway) handleLogsWebDAV(w http.ResponseWriter, r *http.Request) {
 310         if gw.LogCollection == nil {
 311                 http.Error(w, "Not found", http.StatusNotFound)
 312                 return
 313         }
 314         wh := webdav.Handler{
 315                 Prefix: gw.logPath,
 316                 FileSystem: &webdavfs.FS{
 317                         FileSystem:    gw.LogCollection,
 318                         Prefix:        "",
 319                         Writing:       false,
 320                         AlwaysReadEOF: r.Method == "PROPFIND",
 321                 },
 322                 LockSystem: webdavfs.NoLockSystem,
 323                 Logger:     gw.webdavLogger,
 324         }
 325         wh.ServeHTTP(w, r)
 326 }
 327
 328 func (gw *Gateway) webdavLogger(r *http.Request, err error) {
 329         if err != nil && !os.IsNotExist(err) {
 330                 ctxlog.FromContext(r.Context()).WithError(err).Info("error reported by webdav handler")
 331         } else {
 332                 ctxlog.FromContext(r.Context()).WithError(err).Debug("webdav request log")
 333         }
 334 }
 335
 336 // handleSSH connects to an SSH server that allows the caller to run
 337 // interactive commands as root (or any other desired user) inside the
 338 // container. The tunnel itself can only be created by an
 339 // authenticated caller, so the SSH server itself is wide open (any
 340 // password or key will be accepted).
 341 //
 342 // Requests must have path "/ssh" and the following headers:
 343 //
 344 // Connection: upgrade
 345 // Upgrade: ssh
 346 // X-Arvados-Target-Uuid: uuid of container
 347 // X-Arvados-Authorization: must match
 348 // hmac(AuthSecret,certfingerprint) (this prevents other containers
 349 // and shell nodes from connecting directly)
 350 //
 351 // Optional headers:
 352 //
 353 // X-Arvados-Detach-Keys: argument to "docker exec --detach-keys",
 354 // e.g., "ctrl-p,ctrl-q"
 355 // X-Arvados-Login-Username: argument to "docker exec --user": account
 356 // used to run command(s) inside the container.
 357 func (gw *Gateway) handleSSH(w http.ResponseWriter, req *http.Request) {
 358         req.ParseForm()
 359         detachKeys := req.Form.Get("detach_keys")
 360         username := req.Form.Get("login_username")
 361         if username == "" {
 362                 username = "root"
 363         }
 364         hj, ok := w.(http.Hijacker)
 365         if !ok {
 366                 http.Error(w, "ResponseWriter does not support connection upgrade", http.StatusInternalServerError)
 367                 return
 368         }
 369         netconn, _, err := hj.Hijack()
 370         if !ok {
 371                 http.Error(w, err.Error(), http.StatusInternalServerError)
 372                 return
 373         }
 374         defer netconn.Close()
 375         w.Header().Set("Connection", "upgrade")
 376         w.Header().Set("Upgrade", "ssh")
 377         netconn.Write([]byte("HTTP/1.1 101 Switching Protocols\r\n"))
 378         w.Header().Write(netconn)
 379         netconn.Write([]byte("\r\n"))
 380
 381         ctx := req.Context()
 382
 383         conn, newchans, reqs, err := ssh.NewServerConn(netconn, &gw.sshConfig)
 384         if err == io.EOF {
 385                 return
 386         } else if err != nil {
 387                 gw.Log.Printf("ssh.NewServerConn: %s", err)
 388                 return
 389         }
 390         defer conn.Close()
 391         go ssh.DiscardRequests(reqs)
 392         for newch := range newchans {
 393                 switch newch.ChannelType() {
 394                 case "direct-tcpip":
 395                         go gw.handleDirectTCPIP(ctx, newch)
 396                 case "session":
 397                         go gw.handleSession(ctx, newch, detachKeys, username)
 398                 default:
 399                         go newch.Reject(ssh.UnknownChannelType, fmt.Sprintf("unsupported channel type %q", newch.ChannelType()))
 400                 }
 401         }
 402 }
 403
 404 func (gw *Gateway) handleDirectTCPIP(ctx context.Context, newch ssh.NewChannel) {
 405         ch, reqs, err := newch.Accept()
 406         if err != nil {
 407                 gw.Log.Printf("accept direct-tcpip channel: %s", err)
 408                 return
 409         }
 410         defer ch.Close()
 411         go ssh.DiscardRequests(reqs)
 412
 413         // RFC 4254 7.2 (copy of channelOpenDirectMsg in
 414         // golang.org/x/crypto/ssh)
 415         var msg struct {
 416                 Raddr string
 417                 Rport uint32
 418                 Laddr string
 419                 Lport uint32
 420         }
 421         err = ssh.Unmarshal(newch.ExtraData(), &msg)
 422         if err != nil {
 423                 fmt.Fprintf(ch.Stderr(), "unmarshal direct-tcpip extradata: %s\n", err)
 424                 return
 425         }
 426         switch msg.Raddr {
 427         case "localhost", "0.0.0.0", "127.0.0.1", "::1", "::":
 428         default:
 429                 fmt.Fprintf(ch.Stderr(), "cannot forward to ports on %q, only localhost\n", msg.Raddr)
 430                 return
 431         }
 432
 433         dstaddr, err := gw.Target.IPAddress()
 434         if err != nil {
 435                 fmt.Fprintf(ch.Stderr(), "container has no IP address: %s\n", err)
 436                 return
 437         } else if dstaddr == "" {
 438                 fmt.Fprintf(ch.Stderr(), "container has no IP address\n")
 439                 return
 440         }
 441
 442         dst := net.JoinHostPort(dstaddr, fmt.Sprintf("%d", msg.Rport))
 443         tcpconn, err := net.Dial("tcp", dst)
 444         if err != nil {
 445                 fmt.Fprintf(ch.Stderr(), "%s: %s\n", dst, err)
 446                 return
 447         }
 448         go func() {
 449                 n, _ := io.Copy(ch, tcpconn)
 450                 ctxlog.FromContext(ctx).Debugf("tcpip: sent %d bytes\n", n)
 451                 ch.CloseWrite()
 452         }()
 453         n, _ := io.Copy(tcpconn, ch)
 454         ctxlog.FromContext(ctx).Debugf("tcpip: received %d bytes\n", n)
 455 }
 456
 457 func (gw *Gateway) handleSession(ctx context.Context, newch ssh.NewChannel, detachKeys, username string) {
 458         ch, reqs, err := newch.Accept()
 459         if err != nil {
 460                 gw.Log.Printf("error accepting session channel: %s", err)
 461                 return
 462         }
 463         defer ch.Close()
 464
 465         var pty0, tty0 *os.File
 466         // Where to send errors/messages for the client to see
 467         logw := io.Writer(ch.Stderr())
 468         // How to end lines when sending errors/messages to the client
 469         // (changes to \r\n when using a pty)
 470         eol := "\n"
 471         // Env vars to add to child process
 472         termEnv := []string(nil)
 473
 474         started := 0
 475         wantClose := make(chan struct{})
 476         for {
 477                 var req *ssh.Request
 478                 select {
 479                 case r, ok := <-reqs:
 480                         if !ok {
 481                                 return
 482                         }
 483                         req = r
 484                 case <-wantClose:
 485                         return
 486                 }
 487                 ok := false
 488                 switch req.Type {
 489                 case "shell", "exec":
 490                         if started++; started != 1 {
 491                                 // RFC 4254 6.5: "Only one of these
 492                                 // requests can succeed per channel."
 493                                 break
 494                         }
 495                         ok = true
 496                         var payload struct {
 497                                 Command string
 498                         }
 499                         ssh.Unmarshal(req.Payload, &payload)
 500                         execargs, err := shlex.Split(payload.Command)
 501                         if err != nil {
 502                                 fmt.Fprintf(logw, "error parsing supplied command: %s"+eol, err)
 503                                 return
 504                         }
 505                         if len(execargs) == 0 {
 506                                 execargs = []string{"/bin/bash", "-login"}
 507                         }
 508                         go func() {
 509                                 var resp struct {
 510                                         Status uint32
 511                                 }
 512                                 defer func() {
 513                                         ch.SendRequest("exit-status", false, ssh.Marshal(&resp))
 514                                         close(wantClose)
 515                                 }()
 516
 517                                 cmd, err := gw.Target.InjectCommand(ctx, detachKeys, username, tty0 != nil, execargs)
 518                                 if err != nil {
 519                                         fmt.Fprintln(ch.Stderr(), err)
 520                                         ch.CloseWrite()
 521                                         resp.Status = 1
 522                                         return
 523                                 }
 524                                 if tty0 != nil {
 525                                         cmd.Stdin = tty0
 526                                         cmd.Stdout = tty0
 527                                         cmd.Stderr = tty0
 528                                         go io.Copy(ch, pty0)
 529                                         go io.Copy(pty0, ch)
 530                                         // Send our own debug messages to tty as well.
 531                                         logw = tty0
 532                                 } else {
 533                                         // StdinPipe may seem
 534                                         // superfluous here, but it's
 535                                         // not: it causes cmd.Run() to
 536                                         // return when the subprocess
 537                                         // exits. Without it, Run()
 538                                         // waits for stdin to close,
 539                                         // which causes "ssh ... echo
 540                                         // ok" (with the client's
 541                                         // stdin connected to a
 542                                         // terminal or something) to
 543                                         // hang.
 544                                         stdin, err := cmd.StdinPipe()
 545                                         if err != nil {
 546                                                 fmt.Fprintln(ch.Stderr(), err)
 547                                                 ch.CloseWrite()
 548                                                 resp.Status = 1
 549                                                 return
 550                                         }
 551                                         go func() {
 552                                                 io.Copy(stdin, ch)
 553                                                 stdin.Close()
 554                                         }()
 555                                         cmd.Stdout = ch
 556                                         cmd.Stderr = ch.Stderr()
 557                                 }
 558                                 cmd.SysProcAttr = &syscall.SysProcAttr{
 559                                         Setctty: tty0 != nil,
 560                                         Setsid:  true,
 561                                 }
 562                                 cmd.Env = append(os.Environ(), termEnv...)
 563                                 err = cmd.Run()
 564                                 if exiterr, ok := err.(*exec.ExitError); ok {
 565                                         if status, ok := exiterr.Sys().(syscall.WaitStatus); ok {
 566                                                 resp.Status = uint32(status.ExitStatus())
 567                                         }
 568                                 } else if err != nil {
 569                                         // Propagate errors like `exec: "docker": executable file not found in $PATH`
 570                                         fmt.Fprintln(ch.Stderr(), err)
 571                                 }
 572                                 errClose := ch.CloseWrite()
 573                                 if resp.Status == 0 && (err != nil || errClose != nil) {
 574                                         resp.Status = 1
 575                                 }
 576                         }()
 577                 case "pty-req":
 578                         eol = "\r\n"
 579                         p, t, err := pty.Open()
 580                         if err != nil {
 581                                 fmt.Fprintf(ch.Stderr(), "pty failed: %s"+eol, err)
 582                                 break
 583                         }
 584                         defer p.Close()
 585                         defer t.Close()
 586                         pty0, tty0 = p, t
 587                         ok = true
 588                         var payload struct {
 589                                 Term string
 590                                 Cols uint32
 591                                 Rows uint32
 592                                 X    uint32
 593                                 Y    uint32
 594                         }
 595                         ssh.Unmarshal(req.Payload, &payload)
 596                         termEnv = []string{"TERM=" + payload.Term, "USE_TTY=1"}
 597                         err = pty.Setsize(pty0, &pty.Winsize{Rows: uint16(payload.Rows), Cols: uint16(payload.Cols), X: uint16(payload.X), Y: uint16(payload.Y)})
 598                         if err != nil {
 599                                 fmt.Fprintf(logw, "pty-req: setsize failed: %s"+eol, err)
 600                         }
 601                 case "window-change":
 602                         var payload struct {
 603                                 Cols uint32
 604                                 Rows uint32
 605                                 X    uint32
 606                                 Y    uint32
 607                         }
 608                         ssh.Unmarshal(req.Payload, &payload)
 609                         err := pty.Setsize(pty0, &pty.Winsize{Rows: uint16(payload.Rows), Cols: uint16(payload.Cols), X: uint16(payload.X), Y: uint16(payload.Y)})
 610                         if err != nil {
 611                                 fmt.Fprintf(logw, "window-change: setsize failed: %s"+eol, err)
 612                                 break
 613                         }
 614                         ok = true
 615                 case "env":
 616                         // TODO: implement "env"
 617                         // requests by setting env
 618                         // vars in the docker-exec
 619                         // command (not docker-exec's
 620                         // own environment, which
 621                         // would be a gaping security
 622                         // hole).
 623                 default:
 624                         // fmt.Fprintf(logw, "declined request %q on ssh channel"+eol, req.Type)
 625                 }
 626                 if req.WantReply {
 627                         req.Reply(ok, nil)
 628                 }
 629         }
 630 }