services/keep-web/s3.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         "crypto/hmac"
   9         "crypto/sha256"
  10         "encoding/xml"
  11         "errors"
  12         "fmt"
  13         "hash"
  14         "io"
  15         "net/http"
  16         "net/url"
  17         "os"
  18         "path/filepath"
  19         "sort"
  20         "strconv"
  21         "strings"
  22         "time"
  23
  24         "git.arvados.org/arvados.git/sdk/go/arvados"
  25         "git.arvados.org/arvados.git/sdk/go/ctxlog"
  26         "github.com/AdRoll/goamz/s3"
  27 )
  28
  29 const (
  30         s3MaxKeys       = 1000
  31         s3SignAlgorithm = "AWS4-HMAC-SHA256"
  32         s3MaxClockSkew  = 5 * time.Minute
  33 )
  34
  35 func hmacstring(msg string, key []byte) []byte {
  36         h := hmac.New(sha256.New, key)
  37         io.WriteString(h, msg)
  38         return h.Sum(nil)
  39 }
  40
  41 func hashdigest(h hash.Hash, payload string) string {
  42         io.WriteString(h, payload)
  43         return fmt.Sprintf("%x", h.Sum(nil))
  44 }
  45
  46 // Signing key for given secret key and request attrs.
  47 func s3signatureKey(key, datestamp, regionName, serviceName string) []byte {
  48         return hmacstring("aws4_request",
  49                 hmacstring(serviceName,
  50                         hmacstring(regionName,
  51                                 hmacstring(datestamp, []byte("AWS4"+key)))))
  52 }
  53
  54 // Canonical query string for S3 V4 signature: sorted keys, spaces
  55 // escaped as %20 instead of +, keyvalues joined with &.
  56 func s3querystring(u *url.URL) string {
  57         keys := make([]string, 0, len(u.Query()))
  58         values := make(map[string]string, len(u.Query()))
  59         for k, vs := range u.Query() {
  60                 k = strings.Replace(url.QueryEscape(k), "+", "%20", -1)
  61                 keys = append(keys, k)
  62                 for _, v := range vs {
  63                         v = strings.Replace(url.QueryEscape(v), "+", "%20", -1)
  64                         if values[k] != "" {
  65                                 values[k] += "&"
  66                         }
  67                         values[k] += k + "=" + v
  68                 }
  69         }
  70         sort.Strings(keys)
  71         for i, k := range keys {
  72                 keys[i] = values[k]
  73         }
  74         return strings.Join(keys, "&")
  75 }
  76
  77 func s3stringToSign(alg, scope, signedHeaders string, r *http.Request) (string, error) {
  78         timefmt, timestr := "20060102T150405Z", r.Header.Get("X-Amz-Date")
  79         if timestr == "" {
  80                 timefmt, timestr = time.RFC1123, r.Header.Get("Date")
  81         }
  82         t, err := time.Parse(timefmt, timestr)
  83         if err != nil {
  84                 return "", fmt.Errorf("invalid timestamp %q: %s", timestr, err)
  85         }
  86         if skew := time.Now().Sub(t); skew < -s3MaxClockSkew || skew > s3MaxClockSkew {
  87                 return "", errors.New("exceeded max clock skew")
  88         }
  89
  90         var canonicalHeaders string
  91         for _, h := range strings.Split(signedHeaders, ";") {
  92                 if h == "host" {
  93                         canonicalHeaders += h + ":" + r.Host + "\n"
  94                 } else {
  95                         canonicalHeaders += h + ":" + r.Header.Get(h) + "\n"
  96                 }
  97         }
  98
  99         canonicalRequest := fmt.Sprintf("%s\n%s\n%s\n%s\n%s\n%s", r.Method, r.URL.EscapedPath(), s3querystring(r.URL), canonicalHeaders, signedHeaders, r.Header.Get("X-Amz-Content-Sha256"))
 100         ctxlog.FromContext(r.Context()).Debugf("s3stringToSign: canonicalRequest %s", canonicalRequest)
 101         return fmt.Sprintf("%s\n%s\n%s\n%s", alg, r.Header.Get("X-Amz-Date"), scope, hashdigest(sha256.New(), canonicalRequest)), nil
 102 }
 103
 104 func s3signature(secretKey, scope, signedHeaders, stringToSign string) (string, error) {
 105         // scope is {datestamp}/{region}/{service}/aws4_request
 106         drs := strings.Split(scope, "/")
 107         if len(drs) != 4 {
 108                 return "", fmt.Errorf("invalid scope %q", scope)
 109         }
 110         key := s3signatureKey(secretKey, drs[0], drs[1], drs[2])
 111         return hashdigest(hmac.New(sha256.New, key), stringToSign), nil
 112 }
 113
 114 // checks3signature verifies the given S3 V4 signature and returns the
 115 // Arvados token that corresponds to the given accessKey. An error is
 116 // returned if accessKey is not a valid token UUID or the signature
 117 // does not match.
 118 func (h *handler) checks3signature(r *http.Request) (string, error) {
 119         var key, scope, signedHeaders, signature string
 120         authstring := strings.TrimPrefix(r.Header.Get("Authorization"), s3SignAlgorithm+" ")
 121         for _, cmpt := range strings.Split(authstring, ",") {
 122                 cmpt = strings.TrimSpace(cmpt)
 123                 split := strings.SplitN(cmpt, "=", 2)
 124                 switch {
 125                 case len(split) != 2:
 126                         // (?) ignore
 127                 case split[0] == "Credential":
 128                         keyandscope := strings.SplitN(split[1], "/", 2)
 129                         if len(keyandscope) == 2 {
 130                                 key, scope = keyandscope[0], keyandscope[1]
 131                         }
 132                 case split[0] == "SignedHeaders":
 133                         signedHeaders = split[1]
 134                 case split[0] == "Signature":
 135                         signature = split[1]
 136                 }
 137         }
 138
 139         client := (&arvados.Client{
 140                 APIHost:  h.Config.cluster.Services.Controller.ExternalURL.Host,
 141                 Insecure: h.Config.cluster.TLS.Insecure,
 142         }).WithRequestID(r.Header.Get("X-Request-Id"))
 143         var aca arvados.APIClientAuthorization
 144         var secret string
 145         var err error
 146         if len(key) == 27 && key[5:12] == "-gj3su-" {
 147                 // Access key is the UUID of an Arvados token, secret
 148                 // key is the secret part.
 149                 ctx := arvados.ContextWithAuthorization(r.Context(), "Bearer "+h.Config.cluster.SystemRootToken)
 150                 err = client.RequestAndDecodeContext(ctx, &aca, "GET", "arvados/v1/api_client_authorizations/"+key, nil, nil)
 151                 secret = aca.APIToken
 152         } else {
 153                 // Access key and secret key are both an entire
 154                 // Arvados token or OIDC access token.
 155                 ctx := arvados.ContextWithAuthorization(r.Context(), "Bearer "+key)
 156                 err = client.RequestAndDecodeContext(ctx, &aca, "GET", "arvados/v1/api_client_authorizations/current", nil, nil)
 157                 secret = key
 158         }
 159         if err != nil {
 160                 ctxlog.FromContext(r.Context()).WithError(err).WithField("UUID", key).Info("token lookup failed")
 161                 return "", errors.New("invalid access key")
 162         }
 163         stringToSign, err := s3stringToSign(s3SignAlgorithm, scope, signedHeaders, r)
 164         if err != nil {
 165                 return "", err
 166         }
 167         expect, err := s3signature(secret, scope, signedHeaders, stringToSign)
 168         if err != nil {
 169                 return "", err
 170         } else if expect != signature {
 171                 return "", fmt.Errorf("signature does not match (scope %q signedHeaders %q stringToSign %q)", scope, signedHeaders, stringToSign)
 172         }
 173         return secret, nil
 174 }
 175
 176 // serveS3 handles r and returns true if r is a request from an S3
 177 // client, otherwise it returns false.
 178 func (h *handler) serveS3(w http.ResponseWriter, r *http.Request) bool {
 179         var token string
 180         if auth := r.Header.Get("Authorization"); strings.HasPrefix(auth, "AWS ") {
 181                 split := strings.SplitN(auth[4:], ":", 2)
 182                 if len(split) < 2 {
 183                         http.Error(w, "malformed Authorization header", http.StatusUnauthorized)
 184                         return true
 185                 }
 186                 token = split[0]
 187         } else if strings.HasPrefix(auth, s3SignAlgorithm+" ") {
 188                 t, err := h.checks3signature(r)
 189                 if err != nil {
 190                         http.Error(w, "signature verification failed: "+err.Error(), http.StatusForbidden)
 191                         return true
 192                 }
 193                 token = t
 194         } else {
 195                 return false
 196         }
 197
 198         _, kc, client, release, err := h.getClients(r.Header.Get("X-Request-Id"), token)
 199         if err != nil {
 200                 http.Error(w, "Pool failed: "+h.clientPool.Err().Error(), http.StatusInternalServerError)
 201                 return true
 202         }
 203         defer release()
 204
 205         fs := client.SiteFileSystem(kc)
 206         fs.ForwardSlashNameSubstitution(h.Config.cluster.Collections.ForwardSlashNameSubstitution)
 207
 208         objectNameGiven := strings.Count(strings.TrimSuffix(r.URL.Path, "/"), "/") > 1
 209
 210         switch {
 211         case r.Method == http.MethodGet && !objectNameGiven:
 212                 // Path is "/{uuid}" or "/{uuid}/", has no object name
 213                 if _, ok := r.URL.Query()["versioning"]; ok {
 214                         // GetBucketVersioning
 215                         w.Header().Set("Content-Type", "application/xml")
 216                         io.WriteString(w, xml.Header)
 217                         fmt.Fprintln(w, `<VersioningConfiguration xmlns="http://s3.amazonaws.com/doc/2006-03-01/"/>`)
 218                 } else {
 219                         // ListObjects
 220                         h.s3list(w, r, fs)
 221                 }
 222                 return true
 223         case r.Method == http.MethodGet || r.Method == http.MethodHead:
 224                 fspath := "/by_id" + r.URL.Path
 225                 fi, err := fs.Stat(fspath)
 226                 if r.Method == "HEAD" && !objectNameGiven {
 227                         // HeadBucket
 228                         if err == nil && fi.IsDir() {
 229                                 w.WriteHeader(http.StatusOK)
 230                         } else if os.IsNotExist(err) {
 231                                 w.WriteHeader(http.StatusNotFound)
 232                         } else {
 233                                 http.Error(w, err.Error(), http.StatusBadGateway)
 234                         }
 235                         return true
 236                 }
 237                 if err == nil && fi.IsDir() && objectNameGiven && strings.HasSuffix(fspath, "/") && h.Config.cluster.Collections.S3FolderObjects {
 238                         w.Header().Set("Content-Type", "application/x-directory")
 239                         w.WriteHeader(http.StatusOK)
 240                         return true
 241                 }
 242                 if os.IsNotExist(err) ||
 243                         (err != nil && err.Error() == "not a directory") ||
 244                         (fi != nil && fi.IsDir()) {
 245                         http.Error(w, "not found", http.StatusNotFound)
 246                         return true
 247                 }
 248                 // shallow copy r, and change URL path
 249                 r := *r
 250                 r.URL.Path = fspath
 251                 http.FileServer(fs).ServeHTTP(w, &r)
 252                 return true
 253         case r.Method == http.MethodPut:
 254                 if !objectNameGiven {
 255                         http.Error(w, "missing object name in PUT request", http.StatusBadRequest)
 256                         return true
 257                 }
 258                 fspath := "by_id" + r.URL.Path
 259                 var objectIsDir bool
 260                 if strings.HasSuffix(fspath, "/") {
 261                         if !h.Config.cluster.Collections.S3FolderObjects {
 262                                 http.Error(w, "invalid object name: trailing slash", http.StatusBadRequest)
 263                                 return true
 264                         }
 265                         n, err := r.Body.Read(make([]byte, 1))
 266                         if err != nil && err != io.EOF {
 267                                 http.Error(w, fmt.Sprintf("error reading request body: %s", err), http.StatusInternalServerError)
 268                                 return true
 269                         } else if n > 0 {
 270                                 http.Error(w, "cannot create object with trailing '/' char unless content is empty", http.StatusBadRequest)
 271                                 return true
 272                         } else if strings.SplitN(r.Header.Get("Content-Type"), ";", 2)[0] != "application/x-directory" {
 273                                 http.Error(w, "cannot create object with trailing '/' char unless Content-Type is 'application/x-directory'", http.StatusBadRequest)
 274                                 return true
 275                         }
 276                         // Given PUT "foo/bar/", we'll use "foo/bar/."
 277                         // in the "ensure parents exist" block below,
 278                         // and then we'll be done.
 279                         fspath += "."
 280                         objectIsDir = true
 281                 }
 282                 fi, err := fs.Stat(fspath)
 283                 if err != nil && err.Error() == "not a directory" {
 284                         // requested foo/bar, but foo is a file
 285                         http.Error(w, "object name conflicts with existing object", http.StatusBadRequest)
 286                         return true
 287                 }
 288                 if strings.HasSuffix(r.URL.Path, "/") && err == nil && !fi.IsDir() {
 289                         // requested foo/bar/, but foo/bar is a file
 290                         http.Error(w, "object name conflicts with existing object", http.StatusBadRequest)
 291                         return true
 292                 }
 293                 // create missing parent/intermediate directories, if any
 294                 for i, c := range fspath {
 295                         if i > 0 && c == '/' {
 296                                 dir := fspath[:i]
 297                                 if strings.HasSuffix(dir, "/") {
 298                                         err = errors.New("invalid object name (consecutive '/' chars)")
 299                                         http.Error(w, err.Error(), http.StatusBadRequest)
 300                                         return true
 301                                 }
 302                                 err = fs.Mkdir(dir, 0755)
 303                                 if err == arvados.ErrInvalidArgument {
 304                                         // Cannot create a directory
 305                                         // here.
 306                                         err = fmt.Errorf("mkdir %q failed: %w", dir, err)
 307                                         http.Error(w, err.Error(), http.StatusBadRequest)
 308                                         return true
 309                                 } else if err != nil && !os.IsExist(err) {
 310                                         err = fmt.Errorf("mkdir %q failed: %w", dir, err)
 311                                         http.Error(w, err.Error(), http.StatusInternalServerError)
 312                                         return true
 313                                 }
 314                         }
 315                 }
 316                 if !objectIsDir {
 317                         f, err := fs.OpenFile(fspath, os.O_WRONLY|os.O_TRUNC|os.O_CREATE, 0644)
 318                         if os.IsNotExist(err) {
 319                                 f, err = fs.OpenFile(fspath, os.O_WRONLY|os.O_TRUNC|os.O_CREATE, 0644)
 320                         }
 321                         if err != nil {
 322                                 err = fmt.Errorf("open %q failed: %w", r.URL.Path, err)
 323                                 http.Error(w, err.Error(), http.StatusBadRequest)
 324                                 return true
 325                         }
 326                         defer f.Close()
 327                         _, err = io.Copy(f, r.Body)
 328                         if err != nil {
 329                                 err = fmt.Errorf("write to %q failed: %w", r.URL.Path, err)
 330                                 http.Error(w, err.Error(), http.StatusBadGateway)
 331                                 return true
 332                         }
 333                         err = f.Close()
 334                         if err != nil {
 335                                 err = fmt.Errorf("write to %q failed: close: %w", r.URL.Path, err)
 336                                 http.Error(w, err.Error(), http.StatusBadGateway)
 337                                 return true
 338                         }
 339                 }
 340                 err = fs.Sync()
 341                 if err != nil {
 342                         err = fmt.Errorf("sync failed: %w", err)
 343                         http.Error(w, err.Error(), http.StatusInternalServerError)
 344                         return true
 345                 }
 346                 w.WriteHeader(http.StatusOK)
 347                 return true
 348         case r.Method == http.MethodDelete:
 349                 if !objectNameGiven || r.URL.Path == "/" {
 350                         http.Error(w, "missing object name in DELETE request", http.StatusBadRequest)
 351                         return true
 352                 }
 353                 fspath := "by_id" + r.URL.Path
 354                 if strings.HasSuffix(fspath, "/") {
 355                         fspath = strings.TrimSuffix(fspath, "/")
 356                         fi, err := fs.Stat(fspath)
 357                         if os.IsNotExist(err) {
 358                                 w.WriteHeader(http.StatusNoContent)
 359                                 return true
 360                         } else if err != nil {
 361                                 http.Error(w, err.Error(), http.StatusInternalServerError)
 362                                 return true
 363                         } else if !fi.IsDir() {
 364                                 // if "foo" exists and is a file, then
 365                                 // "foo/" doesn't exist, so we say
 366                                 // delete was successful.
 367                                 w.WriteHeader(http.StatusNoContent)
 368                                 return true
 369                         }
 370                 } else if fi, err := fs.Stat(fspath); err == nil && fi.IsDir() {
 371                         // if "foo" is a dir, it is visible via S3
 372                         // only as "foo/", not "foo" -- so we leave
 373                         // the dir alone and return 204 to indicate
 374                         // that "foo" does not exist.
 375                         w.WriteHeader(http.StatusNoContent)
 376                         return true
 377                 }
 378                 err = fs.Remove(fspath)
 379                 if os.IsNotExist(err) {
 380                         w.WriteHeader(http.StatusNoContent)
 381                         return true
 382                 }
 383                 if err != nil {
 384                         err = fmt.Errorf("rm failed: %w", err)
 385                         http.Error(w, err.Error(), http.StatusBadRequest)
 386                         return true
 387                 }
 388                 err = fs.Sync()
 389                 if err != nil {
 390                         err = fmt.Errorf("sync failed: %w", err)
 391                         http.Error(w, err.Error(), http.StatusInternalServerError)
 392                         return true
 393                 }
 394                 w.WriteHeader(http.StatusNoContent)
 395                 return true
 396         default:
 397                 http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
 398                 return true
 399         }
 400 }
 401
 402 // Call fn on the given path (directory) and its contents, in
 403 // lexicographic order.
 404 //
 405 // If isRoot==true and path is not a directory, return nil.
 406 //
 407 // If fn returns filepath.SkipDir when called on a directory, don't
 408 // descend into that directory.
 409 func walkFS(fs arvados.CustomFileSystem, path string, isRoot bool, fn func(path string, fi os.FileInfo) error) error {
 410         if isRoot {
 411                 fi, err := fs.Stat(path)
 412                 if os.IsNotExist(err) || (err == nil && !fi.IsDir()) {
 413                         return nil
 414                 } else if err != nil {
 415                         return err
 416                 }
 417                 err = fn(path, fi)
 418                 if err == filepath.SkipDir {
 419                         return nil
 420                 } else if err != nil {
 421                         return err
 422                 }
 423         }
 424         f, err := fs.Open(path)
 425         if os.IsNotExist(err) && isRoot {
 426                 return nil
 427         } else if err != nil {
 428                 return fmt.Errorf("open %q: %w", path, err)
 429         }
 430         defer f.Close()
 431         if path == "/" {
 432                 path = ""
 433         }
 434         fis, err := f.Readdir(-1)
 435         if err != nil {
 436                 return err
 437         }
 438         sort.Slice(fis, func(i, j int) bool { return fis[i].Name() < fis[j].Name() })
 439         for _, fi := range fis {
 440                 err = fn(path+"/"+fi.Name(), fi)
 441                 if err == filepath.SkipDir {
 442                         continue
 443                 } else if err != nil {
 444                         return err
 445                 }
 446                 if fi.IsDir() {
 447                         err = walkFS(fs, path+"/"+fi.Name(), false, fn)
 448                         if err != nil {
 449                                 return err
 450                         }
 451                 }
 452         }
 453         return nil
 454 }
 455
 456 var errDone = errors.New("done")
 457
 458 func (h *handler) s3list(w http.ResponseWriter, r *http.Request, fs arvados.CustomFileSystem) {
 459         var params struct {
 460                 bucket    string
 461                 delimiter string
 462                 marker    string
 463                 maxKeys   int
 464                 prefix    string
 465         }
 466         params.bucket = strings.SplitN(r.URL.Path[1:], "/", 2)[0]
 467         params.delimiter = r.FormValue("delimiter")
 468         params.marker = r.FormValue("marker")
 469         if mk, _ := strconv.ParseInt(r.FormValue("max-keys"), 10, 64); mk > 0 && mk < s3MaxKeys {
 470                 params.maxKeys = int(mk)
 471         } else {
 472                 params.maxKeys = s3MaxKeys
 473         }
 474         params.prefix = r.FormValue("prefix")
 475
 476         bucketdir := "by_id/" + params.bucket
 477         // walkpath is the directory (relative to bucketdir) we need
 478         // to walk: the innermost directory that is guaranteed to
 479         // contain all paths that have the requested prefix. Examples:
 480         // prefix "foo/bar"  => walkpath "foo"
 481         // prefix "foo/bar/" => walkpath "foo/bar"
 482         // prefix "foo"      => walkpath ""
 483         // prefix ""         => walkpath ""
 484         walkpath := params.prefix
 485         if cut := strings.LastIndex(walkpath, "/"); cut >= 0 {
 486                 walkpath = walkpath[:cut]
 487         } else {
 488                 walkpath = ""
 489         }
 490
 491         type commonPrefix struct {
 492                 Prefix string
 493         }
 494         type listResp struct {
 495                 XMLName string `xml:"http://s3.amazonaws.com/doc/2006-03-01/ ListBucketResult"`
 496                 s3.ListResp
 497                 // s3.ListResp marshals an empty tag when
 498                 // CommonPrefixes is nil, which confuses some clients.
 499                 // Fix by using this nested struct instead.
 500                 CommonPrefixes []commonPrefix
 501                 // Similarly, we need omitempty here, because an empty
 502                 // tag confuses some clients (e.g.,
 503                 // github.com/aws/aws-sdk-net never terminates its
 504                 // paging loop).
 505                 NextMarker string `xml:"NextMarker,omitempty"`
 506                 // ListObjectsV2 has a KeyCount response field.
 507                 KeyCount int
 508         }
 509         resp := listResp{
 510                 ListResp: s3.ListResp{
 511                         Name:      strings.SplitN(r.URL.Path[1:], "/", 2)[0],
 512                         Prefix:    params.prefix,
 513                         Delimiter: params.delimiter,
 514                         Marker:    params.marker,
 515                         MaxKeys:   params.maxKeys,
 516                 },
 517         }
 518         commonPrefixes := map[string]bool{}
 519         err := walkFS(fs, strings.TrimSuffix(bucketdir+"/"+walkpath, "/"), true, func(path string, fi os.FileInfo) error {
 520                 if path == bucketdir {
 521                         return nil
 522                 }
 523                 path = path[len(bucketdir)+1:]
 524                 filesize := fi.Size()
 525                 if fi.IsDir() {
 526                         path += "/"
 527                         filesize = 0
 528                 }
 529                 if len(path) <= len(params.prefix) {
 530                         if path > params.prefix[:len(path)] {
 531                                 // with prefix "foobar", walking "fooz" means we're done
 532                                 return errDone
 533                         }
 534                         if path < params.prefix[:len(path)] {
 535                                 // with prefix "foobar", walking "foobag" is pointless
 536                                 return filepath.SkipDir
 537                         }
 538                         if fi.IsDir() && !strings.HasPrefix(params.prefix+"/", path) {
 539                                 // with prefix "foo/bar", walking "fo"
 540                                 // is pointless (but walking "foo" or
 541                                 // "foo/bar" is necessary)
 542                                 return filepath.SkipDir
 543                         }
 544                         if len(path) < len(params.prefix) {
 545                                 // can't skip anything, and this entry
 546                                 // isn't in the results, so just
 547                                 // continue descent
 548                                 return nil
 549                         }
 550                 } else {
 551                         if path[:len(params.prefix)] > params.prefix {
 552                                 // with prefix "foobar", nothing we
 553                                 // see after "foozzz" is relevant
 554                                 return errDone
 555                         }
 556                 }
 557                 if path < params.marker || path < params.prefix {
 558                         return nil
 559                 }
 560                 if fi.IsDir() && !h.Config.cluster.Collections.S3FolderObjects {
 561                         // Note we don't add anything to
 562                         // commonPrefixes here even if delimiter is
 563                         // "/". We descend into the directory, and
 564                         // return a commonPrefix only if we end up
 565                         // finding a regular file inside it.
 566                         return nil
 567                 }
 568                 if params.delimiter != "" {
 569                         idx := strings.Index(path[len(params.prefix):], params.delimiter)
 570                         if idx >= 0 {
 571                                 // with prefix "foobar" and delimiter
 572                                 // "z", when we hit "foobar/baz", we
 573                                 // add "/baz" to commonPrefixes and
 574                                 // stop descending.
 575                                 commonPrefixes[path[:len(params.prefix)+idx+1]] = true
 576                                 return filepath.SkipDir
 577                         }
 578                 }
 579                 if len(resp.Contents)+len(commonPrefixes) >= params.maxKeys {
 580                         resp.IsTruncated = true
 581                         if params.delimiter != "" {
 582                                 resp.NextMarker = path
 583                         }
 584                         return errDone
 585                 }
 586                 resp.Contents = append(resp.Contents, s3.Key{
 587                         Key:          path,
 588                         LastModified: fi.ModTime().UTC().Format("2006-01-02T15:04:05.999") + "Z",
 589                         Size:         filesize,
 590                 })
 591                 return nil
 592         })
 593         if err != nil && err != errDone {
 594                 http.Error(w, err.Error(), http.StatusInternalServerError)
 595                 return
 596         }
 597         if params.delimiter != "" {
 598                 resp.CommonPrefixes = make([]commonPrefix, 0, len(commonPrefixes))
 599                 for prefix := range commonPrefixes {
 600                         resp.CommonPrefixes = append(resp.CommonPrefixes, commonPrefix{prefix})
 601                 }
 602                 sort.Slice(resp.CommonPrefixes, func(i, j int) bool { return resp.CommonPrefixes[i].Prefix < resp.CommonPrefixes[j].Prefix })
 603         }
 604         resp.KeyCount = len(resp.Contents)
 605         w.Header().Set("Content-Type", "application/xml")
 606         io.WriteString(w, xml.Header)
 607         if err := xml.NewEncoder(w).Encode(resp); err != nil {
 608                 ctxlog.FromContext(r.Context()).WithError(err).Error("error writing xml response")
 609         }
 610 }