services/keep-web/handler.go

   1 // Copyright (C) The Arvados Authors. All rights reserved.
   2 //
   3 // SPDX-License-Identifier: AGPL-3.0
   4
   5 package main
   6
   7 import (
   8         "encoding/json"
   9         "fmt"
  10         "html"
  11         "html/template"
  12         "io"
  13         "log"
  14         "net/http"
  15         "net/url"
  16         "os"
  17         "sort"
  18         "strconv"
  19         "strings"
  20         "sync"
  21
  22         "git.curoverse.com/arvados.git/sdk/go/arvados"
  23         "git.curoverse.com/arvados.git/sdk/go/arvadosclient"
  24         "git.curoverse.com/arvados.git/sdk/go/auth"
  25         "git.curoverse.com/arvados.git/sdk/go/health"
  26         "git.curoverse.com/arvados.git/sdk/go/httpserver"
  27         "git.curoverse.com/arvados.git/sdk/go/keepclient"
  28         "golang.org/x/net/webdav"
  29 )
  30
  31 type handler struct {
  32         Config        *Config
  33         clientPool    *arvadosclient.ClientPool
  34         setupOnce     sync.Once
  35         healthHandler http.Handler
  36         webdavLS      webdav.LockSystem
  37 }
  38
  39 // parseCollectionIDFromDNSName returns a UUID or PDH if s begins with
  40 // a UUID or URL-encoded PDH; otherwise "".
  41 func parseCollectionIDFromDNSName(s string) string {
  42         // Strip domain.
  43         if i := strings.IndexRune(s, '.'); i >= 0 {
  44                 s = s[:i]
  45         }
  46         // Names like {uuid}--collections.example.com serve the same
  47         // purpose as {uuid}.collections.example.com but can reduce
  48         // cost/effort of using [additional] wildcard certificates.
  49         if i := strings.Index(s, "--"); i >= 0 {
  50                 s = s[:i]
  51         }
  52         if arvadosclient.UUIDMatch(s) {
  53                 return s
  54         }
  55         if pdh := strings.Replace(s, "-", "+", 1); arvadosclient.PDHMatch(pdh) {
  56                 return pdh
  57         }
  58         return ""
  59 }
  60
  61 var urlPDHDecoder = strings.NewReplacer(" ", "+", "-", "+")
  62
  63 // parseCollectionIDFromURL returns a UUID or PDH if s is a UUID or a
  64 // PDH (even if it is a PDH with "+" replaced by " " or "-");
  65 // otherwise "".
  66 func parseCollectionIDFromURL(s string) string {
  67         if arvadosclient.UUIDMatch(s) {
  68                 return s
  69         }
  70         if pdh := urlPDHDecoder.Replace(s); arvadosclient.PDHMatch(pdh) {
  71                 return pdh
  72         }
  73         return ""
  74 }
  75
  76 func (h *handler) setup() {
  77         h.clientPool = arvadosclient.MakeClientPool()
  78
  79         keepclient.RefreshServiceDiscoveryOnSIGHUP()
  80
  81         h.healthHandler = &health.Handler{
  82                 Token:  h.Config.ManagementToken,
  83                 Prefix: "/_health/",
  84         }
  85
  86         // Even though we don't accept LOCK requests, every webdav
  87         // handler must have a non-nil LockSystem.
  88         h.webdavLS = &noLockSystem{}
  89 }
  90
  91 func (h *handler) serveStatus(w http.ResponseWriter, r *http.Request) {
  92         status := struct {
  93                 cacheStats
  94         }{
  95                 cacheStats: h.Config.Cache.Stats(),
  96         }
  97         json.NewEncoder(w).Encode(status)
  98 }
  99
 100 // updateOnSuccess wraps httpserver.ResponseWriter. If the handler
 101 // sends an HTTP header indicating success, updateOnSuccess first
 102 // calls the provided update func. If the update func fails, a 500
 103 // response is sent, and the status code and body sent by the handler
 104 // are ignored (all response writes return the update error).
 105 type updateOnSuccess struct {
 106         httpserver.ResponseWriter
 107         update     func() error
 108         sentHeader bool
 109         err        error
 110 }
 111
 112 func (uos *updateOnSuccess) Write(p []byte) (int, error) {
 113         if uos.err != nil {
 114                 return 0, uos.err
 115         }
 116         if !uos.sentHeader {
 117                 uos.WriteHeader(http.StatusOK)
 118         }
 119         return uos.ResponseWriter.Write(p)
 120 }
 121
 122 func (uos *updateOnSuccess) WriteHeader(code int) {
 123         if !uos.sentHeader {
 124                 uos.sentHeader = true
 125                 if code >= 200 && code < 400 {
 126                         if uos.err = uos.update(); uos.err != nil {
 127                                 code := http.StatusInternalServerError
 128                                 if err, ok := uos.err.(*arvados.TransactionError); ok {
 129                                         code = err.StatusCode
 130                                 }
 131                                 log.Printf("update() changes response to HTTP %d: %T %q", code, uos.err, uos.err)
 132                                 http.Error(uos.ResponseWriter, uos.err.Error(), code)
 133                                 return
 134                         }
 135                 }
 136         }
 137         uos.ResponseWriter.WriteHeader(code)
 138 }
 139
 140 var (
 141         writeMethod = map[string]bool{
 142                 "COPY":   true,
 143                 "DELETE": true,
 144                 "MKCOL":  true,
 145                 "MOVE":   true,
 146                 "PUT":    true,
 147                 "RMCOL":  true,
 148         }
 149         webdavMethod = map[string]bool{
 150                 "COPY":     true,
 151                 "DELETE":   true,
 152                 "MKCOL":    true,
 153                 "MOVE":     true,
 154                 "OPTIONS":  true,
 155                 "PROPFIND": true,
 156                 "PUT":      true,
 157                 "RMCOL":    true,
 158         }
 159         browserMethod = map[string]bool{
 160                 "GET":  true,
 161                 "HEAD": true,
 162                 "POST": true,
 163         }
 164 )
 165
 166 // ServeHTTP implements http.Handler.
 167 func (h *handler) ServeHTTP(wOrig http.ResponseWriter, r *http.Request) {
 168         h.setupOnce.Do(h.setup)
 169
 170         var statusCode = 0
 171         var statusText string
 172
 173         remoteAddr := r.RemoteAddr
 174         if xff := r.Header.Get("X-Forwarded-For"); xff != "" {
 175                 remoteAddr = xff + "," + remoteAddr
 176         }
 177
 178         w := httpserver.WrapResponseWriter(wOrig)
 179         defer func() {
 180                 if statusCode == 0 {
 181                         statusCode = w.WroteStatus()
 182                 } else if w.WroteStatus() == 0 {
 183                         w.WriteHeader(statusCode)
 184                 } else if w.WroteStatus() != statusCode {
 185                         httpserver.Log(r.RemoteAddr, "WARNING",
 186                                 fmt.Sprintf("Our status changed from %d to %d after we sent headers", w.WroteStatus(), statusCode))
 187                 }
 188                 if statusText == "" {
 189                         statusText = http.StatusText(statusCode)
 190                 }
 191                 httpserver.Log(remoteAddr, statusCode, statusText, w.WroteBodyBytes(), r.Method, r.Host, r.URL.Path, r.URL.RawQuery)
 192         }()
 193
 194         if strings.HasPrefix(r.URL.Path, "/_health/") && r.Method == "GET" {
 195                 h.healthHandler.ServeHTTP(w, r)
 196                 return
 197         }
 198
 199         if method := r.Header.Get("Access-Control-Request-Method"); method != "" && r.Method == "OPTIONS" {
 200                 if !browserMethod[method] && !webdavMethod[method] {
 201                         statusCode = http.StatusMethodNotAllowed
 202                         return
 203                 }
 204                 w.Header().Set("Access-Control-Allow-Headers", "Authorization, Content-Type, Range")
 205                 w.Header().Set("Access-Control-Allow-Methods", "COPY, DELETE, GET, MKCOL, MOVE, OPTIONS, POST, PROPFIND, PUT, RMCOL")
 206                 w.Header().Set("Access-Control-Allow-Origin", "*")
 207                 w.Header().Set("Access-Control-Max-Age", "86400")
 208                 statusCode = http.StatusOK
 209                 return
 210         }
 211
 212         if !browserMethod[r.Method] && !webdavMethod[r.Method] {
 213                 statusCode, statusText = http.StatusMethodNotAllowed, r.Method
 214                 return
 215         }
 216
 217         if r.Header.Get("Origin") != "" {
 218                 // Allow simple cross-origin requests without user
 219                 // credentials ("user credentials" as defined by CORS,
 220                 // i.e., cookies, HTTP authentication, and client-side
 221                 // SSL certificates. See
 222                 // http://www.w3.org/TR/cors/#user-credentials).
 223                 w.Header().Set("Access-Control-Allow-Origin", "*")
 224                 w.Header().Set("Access-Control-Expose-Headers", "Content-Range")
 225         }
 226
 227         arv := h.clientPool.Get()
 228         if arv == nil {
 229                 statusCode, statusText = http.StatusInternalServerError, "Pool failed: "+h.clientPool.Err().Error()
 230                 return
 231         }
 232         defer h.clientPool.Put(arv)
 233
 234         pathParts := strings.Split(r.URL.Path[1:], "/")
 235
 236         var stripParts int
 237         var targetID string
 238         var tokens []string
 239         var reqTokens []string
 240         var pathToken bool
 241         var attachment bool
 242         credentialsOK := h.Config.TrustAllContent
 243
 244         if r.Host != "" && r.Host == h.Config.AttachmentOnlyHost {
 245                 credentialsOK = true
 246                 attachment = true
 247         } else if r.FormValue("disposition") == "attachment" {
 248                 attachment = true
 249         }
 250
 251         if targetID = parseCollectionIDFromDNSName(r.Host); targetID != "" {
 252                 // http://ID.collections.example/PATH...
 253                 credentialsOK = true
 254         } else if r.URL.Path == "/status.json" {
 255                 h.serveStatus(w, r)
 256                 return
 257         } else if len(pathParts) >= 1 && strings.HasPrefix(pathParts[0], "c=") {
 258                 // /c=ID[/PATH...]
 259                 targetID = parseCollectionIDFromURL(pathParts[0][2:])
 260                 stripParts = 1
 261         } else if len(pathParts) >= 2 && pathParts[0] == "collections" {
 262                 if len(pathParts) >= 4 && pathParts[1] == "download" {
 263                         // /collections/download/ID/TOKEN/PATH...
 264                         targetID = parseCollectionIDFromURL(pathParts[2])
 265                         tokens = []string{pathParts[3]}
 266                         stripParts = 4
 267                         pathToken = true
 268                 } else {
 269                         // /collections/ID/PATH...
 270                         targetID = parseCollectionIDFromURL(pathParts[1])
 271                         tokens = h.Config.AnonymousTokens
 272                         stripParts = 2
 273                 }
 274         }
 275
 276         if targetID == "" {
 277                 statusCode = http.StatusNotFound
 278                 return
 279         }
 280
 281         formToken := r.FormValue("api_token")
 282         if formToken != "" && r.Header.Get("Origin") != "" && attachment && r.URL.Query().Get("api_token") == "" {
 283                 // The client provided an explicit token in the POST
 284                 // body. The Origin header indicates this *might* be
 285                 // an AJAX request, in which case redirect-with-cookie
 286                 // won't work: we should just serve the content in the
 287                 // POST response. This is safe because:
 288                 //
 289                 // * We're supplying an attachment, not inline
 290                 //   content, so we don't need to convert the POST to
 291                 //   a GET and avoid the "really resubmit form?"
 292                 //   problem.
 293                 //
 294                 // * The token isn't embedded in the URL, so we don't
 295                 //   need to worry about bookmarks and copy/paste.
 296                 tokens = append(tokens, formToken)
 297         } else if formToken != "" && browserMethod[r.Method] {
 298                 // The client provided an explicit token in the query
 299                 // string, or a form in POST body. We must put the
 300                 // token in an HttpOnly cookie, and redirect to the
 301                 // same URL with the query param redacted and method =
 302                 // GET.
 303                 h.seeOtherWithCookie(w, r, "", credentialsOK)
 304                 return
 305         }
 306
 307         targetPath := pathParts[stripParts:]
 308         if tokens == nil && len(targetPath) > 0 && strings.HasPrefix(targetPath[0], "t=") {
 309                 // http://ID.example/t=TOKEN/PATH...
 310                 // /c=ID/t=TOKEN/PATH...
 311                 //
 312                 // This form must only be used to pass scoped tokens
 313                 // that give permission for a single collection. See
 314                 // FormValue case above.
 315                 tokens = []string{targetPath[0][2:]}
 316                 pathToken = true
 317                 targetPath = targetPath[1:]
 318                 stripParts++
 319         }
 320
 321         if tokens == nil {
 322                 if credentialsOK {
 323                         reqTokens = auth.NewCredentialsFromHTTPRequest(r).Tokens
 324                 }
 325                 tokens = append(reqTokens, h.Config.AnonymousTokens...)
 326         }
 327
 328         if len(targetPath) > 0 && targetPath[0] == "_" {
 329                 // If a collection has a directory called "t=foo" or
 330                 // "_", it can be served at
 331                 // //collections.example/_/t=foo/ or
 332                 // //collections.example/_/_/ respectively:
 333                 // //collections.example/t=foo/ won't work because
 334                 // t=foo will be interpreted as a token "foo".
 335                 targetPath = targetPath[1:]
 336                 stripParts++
 337         }
 338
 339         forceReload := false
 340         if cc := r.Header.Get("Cache-Control"); strings.Contains(cc, "no-cache") || strings.Contains(cc, "must-revalidate") {
 341                 forceReload = true
 342         }
 343
 344         var collection *arvados.Collection
 345         tokenResult := make(map[string]int)
 346         for _, arv.ApiToken = range tokens {
 347                 var err error
 348                 collection, err = h.Config.Cache.Get(arv, targetID, forceReload)
 349                 if err == nil {
 350                         // Success
 351                         break
 352                 }
 353                 if srvErr, ok := err.(arvadosclient.APIServerError); ok {
 354                         switch srvErr.HttpStatusCode {
 355                         case 404, 401:
 356                                 // Token broken or insufficient to
 357                                 // retrieve collection
 358                                 tokenResult[arv.ApiToken] = srvErr.HttpStatusCode
 359                                 continue
 360                         }
 361                 }
 362                 // Something more serious is wrong
 363                 statusCode, statusText = http.StatusInternalServerError, err.Error()
 364                 return
 365         }
 366         if collection == nil {
 367                 if pathToken || !credentialsOK {
 368                         // Either the URL is a "secret sharing link"
 369                         // that didn't work out (and asking the client
 370                         // for additional credentials would just be
 371                         // confusing), or we don't even accept
 372                         // credentials at this path.
 373                         statusCode = http.StatusNotFound
 374                         return
 375                 }
 376                 for _, t := range reqTokens {
 377                         if tokenResult[t] == 404 {
 378                                 // The client provided valid token(s), but the
 379                                 // collection was not found.
 380                                 statusCode = http.StatusNotFound
 381                                 return
 382                         }
 383                 }
 384                 // The client's token was invalid (e.g., expired), or
 385                 // the client didn't even provide one.  Propagate the
 386                 // 401 to encourage the client to use a [different]
 387                 // token.
 388                 //
 389                 // TODO(TC): This response would be confusing to
 390                 // someone trying (anonymously) to download public
 391                 // data that has been deleted.  Allow a referrer to
 392                 // provide this context somehow?
 393                 w.Header().Add("WWW-Authenticate", "Basic realm=\"collections\"")
 394                 statusCode = http.StatusUnauthorized
 395                 return
 396         }
 397
 398         kc, err := keepclient.MakeKeepClient(arv)
 399         if err != nil {
 400                 statusCode, statusText = http.StatusInternalServerError, err.Error()
 401                 return
 402         }
 403
 404         var basename string
 405         if len(targetPath) > 0 {
 406                 basename = targetPath[len(targetPath)-1]
 407         }
 408         applyContentDispositionHdr(w, r, basename, attachment)
 409
 410         client := &arvados.Client{
 411                 APIHost:   arv.ApiServer,
 412                 AuthToken: arv.ApiToken,
 413                 Insecure:  arv.ApiInsecure,
 414         }
 415         fs, err := collection.FileSystem(client, kc)
 416         if err != nil {
 417                 statusCode, statusText = http.StatusInternalServerError, err.Error()
 418                 return
 419         }
 420         if webdavMethod[r.Method] {
 421                 writing := !arvadosclient.PDHMatch(targetID) && writeMethod[r.Method]
 422                 if writing {
 423                         // Save the collection only if/when all
 424                         // webdav->filesystem operations succeed --
 425                         // and send a 500 error if the modified
 426                         // collection can't be saved.
 427                         w = &updateOnSuccess{
 428                                 ResponseWriter: w,
 429                                 update: func() error {
 430                                         return h.Config.Cache.Update(client, *collection, fs)
 431                                 }}
 432                 }
 433                 h := webdav.Handler{
 434                         Prefix: "/" + strings.Join(pathParts[:stripParts], "/"),
 435                         FileSystem: &webdavFS{
 436                                 collfs:  fs,
 437                                 writing: writing,
 438                         },
 439                         LockSystem: h.webdavLS,
 440                         Logger: func(_ *http.Request, err error) {
 441                                 if err != nil {
 442                                         log.Printf("error from webdav handler: %q", err)
 443                                 }
 444                         },
 445                 }
 446                 h.ServeHTTP(w, r)
 447                 return
 448         }
 449
 450         openPath := "/" + strings.Join(targetPath, "/")
 451         if f, err := fs.Open(openPath); os.IsNotExist(err) {
 452                 // Requested non-existent path
 453                 statusCode = http.StatusNotFound
 454         } else if err != nil {
 455                 // Some other (unexpected) error
 456                 statusCode, statusText = http.StatusInternalServerError, err.Error()
 457         } else if stat, err := f.Stat(); err != nil {
 458                 // Can't get Size/IsDir (shouldn't happen with a collectionFS!)
 459                 statusCode, statusText = http.StatusInternalServerError, err.Error()
 460         } else if stat.IsDir() && !strings.HasSuffix(r.URL.Path, "/") {
 461                 // If client requests ".../dirname", redirect to
 462                 // ".../dirname/". This way, relative links in the
 463                 // listing for "dirname" can always be "fnm", never
 464                 // "dirname/fnm".
 465                 h.seeOtherWithCookie(w, r, r.URL.Path+"/", credentialsOK)
 466         } else if stat.IsDir() {
 467                 h.serveDirectory(w, r, collection.Name, fs, openPath, stripParts)
 468         } else {
 469                 http.ServeContent(w, r, basename, stat.ModTime(), f)
 470                 if r.Header.Get("Range") == "" && int64(w.WroteBodyBytes()) != stat.Size() {
 471                         // If we wrote fewer bytes than expected, it's
 472                         // too late to change the real response code
 473                         // or send an error message to the client, but
 474                         // at least we can try to put some useful
 475                         // debugging info in the logs.
 476                         n, err := f.Read(make([]byte, 1024))
 477                         statusCode, statusText = http.StatusInternalServerError, fmt.Sprintf("f.Size()==%d but only wrote %d bytes; read(1024) returns %d, %s", stat.Size(), w.WroteBodyBytes(), n, err)
 478
 479                 }
 480         }
 481 }
 482
 483 var dirListingTemplate = `<!DOCTYPE HTML>
 484 <HTML><HEAD>
 485   <META name="robots" content="NOINDEX">
 486   <TITLE>{{ .Collection.Name }}</TITLE>
 487   <STYLE type="text/css">
 488     body {
 489       margin: 1.5em;
 490     }
 491     pre {
 492       background-color: #D9EDF7;
 493       border-radius: .25em;
 494       padding: .75em;
 495       overflow: auto;
 496     }
 497     .footer p {
 498       font-size: 82%;
 499     }
 500     ul {
 501       padding: 0;
 502     }
 503     ul li {
 504       font-family: monospace;
 505       list-style: none;
 506     }
 507   </STYLE>
 508 </HEAD>
 509 <BODY>
 510 <H1>{{ .CollectionName }}</H1>
 511
 512 <P>This collection of data files is being shared with you through
 513 Arvados.  You can download individual files listed below.  To download
 514 the entire collection with wget, try:</P>
 515
 516 <PRE>$ wget --mirror --no-parent --no-host --cut-dirs={{ .StripParts }} https://{{ .Request.Host }}{{ .Request.URL }}</PRE>
 517
 518 <H2>File Listing</H2>
 519
 520 {{if .Files}}
 521 <UL>
 522 {{range .Files}}  <LI>{{.Size | printf "%15d  " | nbsp}}<A href="{{.Name}}">{{.Name}}</A></LI>{{end}}
 523 </UL>
 524 {{else}}
 525 <P>(No files; this collection is empty.)</P>
 526 {{end}}
 527
 528 <HR noshade>
 529 <DIV class="footer">
 530   <P>
 531     About Arvados:
 532     Arvados is a free and open source software bioinformatics platform.
 533     To learn more, visit arvados.org.
 534     Arvados is not responsible for the files listed on this page.
 535   </P>
 536 </DIV>
 537
 538 </BODY>
 539 `
 540
 541 type fileListEnt struct {
 542         Name string
 543         Size int64
 544 }
 545
 546 func (h *handler) serveDirectory(w http.ResponseWriter, r *http.Request, collectionName string, fs http.FileSystem, base string, stripParts int) {
 547         var files []fileListEnt
 548         var walk func(string) error
 549         if !strings.HasSuffix(base, "/") {
 550                 base = base + "/"
 551         }
 552         walk = func(path string) error {
 553                 dirname := base + path
 554                 if dirname != "/" {
 555                         dirname = strings.TrimSuffix(dirname, "/")
 556                 }
 557                 d, err := fs.Open(dirname)
 558                 if err != nil {
 559                         return err
 560                 }
 561                 ents, err := d.Readdir(-1)
 562                 if err != nil {
 563                         return err
 564                 }
 565                 for _, ent := range ents {
 566                         if ent.IsDir() {
 567                                 err = walk(path + ent.Name() + "/")
 568                                 if err != nil {
 569                                         return err
 570                                 }
 571                         } else {
 572                                 files = append(files, fileListEnt{
 573                                         Name: path + ent.Name(),
 574                                         Size: ent.Size(),
 575                                 })
 576                         }
 577                 }
 578                 return nil
 579         }
 580         if err := walk(""); err != nil {
 581                 http.Error(w, err.Error(), http.StatusInternalServerError)
 582                 return
 583         }
 584
 585         funcs := template.FuncMap{
 586                 "nbsp": func(s string) template.HTML {
 587                         return template.HTML(strings.Replace(s, " ", "&nbsp;", -1))
 588                 },
 589         }
 590         tmpl, err := template.New("dir").Funcs(funcs).Parse(dirListingTemplate)
 591         if err != nil {
 592                 http.Error(w, err.Error(), http.StatusInternalServerError)
 593                 return
 594         }
 595         sort.Slice(files, func(i, j int) bool {
 596                 return files[i].Name < files[j].Name
 597         })
 598         w.WriteHeader(http.StatusOK)
 599         tmpl.Execute(w, map[string]interface{}{
 600                 "CollectionName": collectionName,
 601                 "Files":          files,
 602                 "Request":        r,
 603                 "StripParts":     stripParts,
 604         })
 605 }
 606
 607 func applyContentDispositionHdr(w http.ResponseWriter, r *http.Request, filename string, isAttachment bool) {
 608         disposition := "inline"
 609         if isAttachment {
 610                 disposition = "attachment"
 611         }
 612         if strings.ContainsRune(r.RequestURI, '?') {
 613                 // Help the UA realize that the filename is just
 614                 // "filename.txt", not
 615                 // "filename.txt?disposition=attachment".
 616                 //
 617                 // TODO(TC): Follow advice at RFC 6266 appendix D
 618                 disposition += "; filename=" + strconv.QuoteToASCII(filename)
 619         }
 620         if disposition != "inline" {
 621                 w.Header().Set("Content-Disposition", disposition)
 622         }
 623 }
 624
 625 func (h *handler) seeOtherWithCookie(w http.ResponseWriter, r *http.Request, location string, credentialsOK bool) {
 626         if formToken := r.FormValue("api_token"); formToken != "" {
 627                 if !credentialsOK {
 628                         // It is not safe to copy the provided token
 629                         // into a cookie unless the current vhost
 630                         // (origin) serves only a single collection or
 631                         // we are in TrustAllContent mode.
 632                         w.WriteHeader(http.StatusBadRequest)
 633                         return
 634                 }
 635
 636                 // The HttpOnly flag is necessary to prevent
 637                 // JavaScript code (included in, or loaded by, a page
 638                 // in the collection being served) from employing the
 639                 // user's token beyond reading other files in the same
 640                 // domain, i.e., same collection.
 641                 //
 642                 // The 303 redirect is necessary in the case of a GET
 643                 // request to avoid exposing the token in the Location
 644                 // bar, and in the case of a POST request to avoid
 645                 // raising warnings when the user refreshes the
 646                 // resulting page.
 647                 http.SetCookie(w, &http.Cookie{
 648                         Name:     "arvados_api_token",
 649                         Value:    auth.EncodeTokenCookie([]byte(formToken)),
 650                         Path:     "/",
 651                         HttpOnly: true,
 652                 })
 653         }
 654
 655         // Propagate query parameters (except api_token) from
 656         // the original request.
 657         redirQuery := r.URL.Query()
 658         redirQuery.Del("api_token")
 659
 660         u := r.URL
 661         if location != "" {
 662                 newu, err := u.Parse(location)
 663                 if err != nil {
 664                         w.WriteHeader(http.StatusInternalServerError)
 665                         return
 666                 }
 667                 u = newu
 668         }
 669         redir := (&url.URL{
 670                 Host:     r.Host,
 671                 Path:     u.Path,
 672                 RawQuery: redirQuery.Encode(),
 673         }).String()
 674
 675         w.Header().Add("Location", redir)
 676         w.WriteHeader(http.StatusSeeOther)
 677         io.WriteString(w, `<A href="`)
 678         io.WriteString(w, html.EscapeString(redir))
 679         io.WriteString(w, `">Continue</A>`)
 680 }