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         "regexp"
  20         "sort"
  21         "strconv"
  22         "strings"
  23         "time"
  24
  25         "git.arvados.org/arvados.git/sdk/go/arvados"
  26         "git.arvados.org/arvados.git/sdk/go/ctxlog"
  27         "github.com/AdRoll/goamz/s3"
  28 )
  29
  30 const (
  31         s3MaxKeys       = 1000
  32         s3SignAlgorithm = "AWS4-HMAC-SHA256"
  33         s3MaxClockSkew  = 5 * time.Minute
  34 )
  35
  36 func hmacstring(msg string, key []byte) []byte {
  37         h := hmac.New(sha256.New, key)
  38         io.WriteString(h, msg)
  39         return h.Sum(nil)
  40 }
  41
  42 func hashdigest(h hash.Hash, payload string) string {
  43         io.WriteString(h, payload)
  44         return fmt.Sprintf("%x", h.Sum(nil))
  45 }
  46
  47 // Signing key for given secret key and request attrs.
  48 func s3signatureKey(key, datestamp, regionName, serviceName string) []byte {
  49         return hmacstring("aws4_request",
  50                 hmacstring(serviceName,
  51                         hmacstring(regionName,
  52                                 hmacstring(datestamp, []byte("AWS4"+key)))))
  53 }
  54
  55 // Canonical query string for S3 V4 signature: sorted keys, spaces
  56 // escaped as %20 instead of +, keyvalues joined with &.
  57 func s3querystring(u *url.URL) string {
  58         keys := make([]string, 0, len(u.Query()))
  59         values := make(map[string]string, len(u.Query()))
  60         for k, vs := range u.Query() {
  61                 k = strings.Replace(url.QueryEscape(k), "+", "%20", -1)
  62                 keys = append(keys, k)
  63                 for _, v := range vs {
  64                         v = strings.Replace(url.QueryEscape(v), "+", "%20", -1)
  65                         if values[k] != "" {
  66                                 values[k] += "&"
  67                         }
  68                         values[k] += k + "=" + v
  69                 }
  70         }
  71         sort.Strings(keys)
  72         for i, k := range keys {
  73                 keys[i] = values[k]
  74         }
  75         return strings.Join(keys, "&")
  76 }
  77
  78 func s3stringToSign(alg, scope, signedHeaders string, r *http.Request) (string, error) {
  79         timefmt, timestr := "20060102T150405Z", r.Header.Get("X-Amz-Date")
  80         if timestr == "" {
  81                 timefmt, timestr = time.RFC1123, r.Header.Get("Date")
  82         }
  83         t, err := time.Parse(timefmt, timestr)
  84         if err != nil {
  85                 return "", fmt.Errorf("invalid timestamp %q: %s", timestr, err)
  86         }
  87         if skew := time.Now().Sub(t); skew < -s3MaxClockSkew || skew > s3MaxClockSkew {
  88                 return "", errors.New("exceeded max clock skew")
  89         }
  90
  91         var canonicalHeaders string
  92         for _, h := range strings.Split(signedHeaders, ";") {
  93                 if h == "host" {
  94                         canonicalHeaders += h + ":" + r.Host + "\n"
  95                 } else {
  96                         canonicalHeaders += h + ":" + r.Header.Get(h) + "\n"
  97                 }
  98         }
  99
 100         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"))
 101         ctxlog.FromContext(r.Context()).Debugf("s3stringToSign: canonicalRequest %s", canonicalRequest)
 102         return fmt.Sprintf("%s\n%s\n%s\n%s", alg, r.Header.Get("X-Amz-Date"), scope, hashdigest(sha256.New(), canonicalRequest)), nil
 103 }
 104
 105 func s3signature(secretKey, scope, signedHeaders, stringToSign string) (string, error) {
 106         // scope is {datestamp}/{region}/{service}/aws4_request
 107         drs := strings.Split(scope, "/")
 108         if len(drs) != 4 {
 109                 return "", fmt.Errorf("invalid scope %q", scope)
 110         }
 111         key := s3signatureKey(secretKey, drs[0], drs[1], drs[2])
 112         return hashdigest(hmac.New(sha256.New, key), stringToSign), nil
 113 }
 114
 115 var v2tokenUnderscore = regexp.MustCompile(`^v2_[a-z0-9]{5}-gj3su-[a-z0-9]{15}_`)
 116
 117 func unescapeKey(key string) string {
 118         if v2tokenUnderscore.MatchString(key) {
 119                 // Entire Arvados token, with "/" replaced by "_" to
 120                 // avoid colliding with the Authorization header
 121                 // format.
 122                 return strings.Replace(key, "_", "/", -1)
 123         } else if s, err := url.PathUnescape(key); err == nil {
 124                 return s
 125         } else {
 126                 return key
 127         }
 128 }
 129
 130 // checks3signature verifies the given S3 V4 signature and returns the
 131 // Arvados token that corresponds to the given accessKey. An error is
 132 // returned if accessKey is not a valid token UUID or the signature
 133 // does not match.
 134 func (h *handler) checks3signature(r *http.Request) (string, error) {
 135         var key, scope, signedHeaders, signature string
 136         authstring := strings.TrimPrefix(r.Header.Get("Authorization"), s3SignAlgorithm+" ")
 137         for _, cmpt := range strings.Split(authstring, ",") {
 138                 cmpt = strings.TrimSpace(cmpt)
 139                 split := strings.SplitN(cmpt, "=", 2)
 140                 switch {
 141                 case len(split) != 2:
 142                         // (?) ignore
 143                 case split[0] == "Credential":
 144                         keyandscope := strings.SplitN(split[1], "/", 2)
 145                         if len(keyandscope) == 2 {
 146                                 key, scope = keyandscope[0], keyandscope[1]
 147                         }
 148                 case split[0] == "SignedHeaders":
 149                         signedHeaders = split[1]
 150                 case split[0] == "Signature":
 151                         signature = split[1]
 152                 }
 153         }
 154
 155         client := (&arvados.Client{
 156                 APIHost:  h.Config.cluster.Services.Controller.ExternalURL.Host,
 157                 Insecure: h.Config.cluster.TLS.Insecure,
 158         }).WithRequestID(r.Header.Get("X-Request-Id"))
 159         var aca arvados.APIClientAuthorization
 160         var secret string
 161         var err error
 162         if len(key) == 27 && key[5:12] == "-gj3su-" {
 163                 // Access key is the UUID of an Arvados token, secret
 164                 // key is the secret part.
 165                 ctx := arvados.ContextWithAuthorization(r.Context(), "Bearer "+h.Config.cluster.SystemRootToken)
 166                 err = client.RequestAndDecodeContext(ctx, &aca, "GET", "arvados/v1/api_client_authorizations/"+key, nil, nil)
 167                 secret = aca.APIToken
 168         } else {
 169                 // Access key and secret key are both an entire
 170                 // Arvados token or OIDC access token.
 171                 ctx := arvados.ContextWithAuthorization(r.Context(), "Bearer "+unescapeKey(key))
 172                 err = client.RequestAndDecodeContext(ctx, &aca, "GET", "arvados/v1/api_client_authorizations/current", nil, nil)
 173                 secret = key
 174         }
 175         if err != nil {
 176                 ctxlog.FromContext(r.Context()).WithError(err).WithField("UUID", key).Info("token lookup failed")
 177                 return "", errors.New("invalid access key")
 178         }
 179         stringToSign, err := s3stringToSign(s3SignAlgorithm, scope, signedHeaders, r)
 180         if err != nil {
 181                 return "", err
 182         }
 183         expect, err := s3signature(secret, scope, signedHeaders, stringToSign)
 184         if err != nil {
 185                 return "", err
 186         } else if expect != signature {
 187                 return "", fmt.Errorf("signature does not match (scope %q signedHeaders %q stringToSign %q)", scope, signedHeaders, stringToSign)
 188         }
 189         return aca.TokenV2(), nil
 190 }
 191
 192 // serveS3 handles r and returns true if r is a request from an S3
 193 // client, otherwise it returns false.
 194 func (h *handler) serveS3(w http.ResponseWriter, r *http.Request) bool {
 195         var token string
 196         if auth := r.Header.Get("Authorization"); strings.HasPrefix(auth, "AWS ") {
 197                 split := strings.SplitN(auth[4:], ":", 2)
 198                 if len(split) < 2 {
 199                         http.Error(w, "malformed Authorization header", http.StatusUnauthorized)
 200                         return true
 201                 }
 202                 token = unescapeKey(split[0])
 203         } else if strings.HasPrefix(auth, s3SignAlgorithm+" ") {
 204                 t, err := h.checks3signature(r)
 205                 if err != nil {
 206                         http.Error(w, "signature verification failed: "+err.Error(), http.StatusForbidden)
 207                         return true
 208                 }
 209                 token = t
 210         } else {
 211                 return false
 212         }
 213
 214         _, kc, client, release, err := h.getClients(r.Header.Get("X-Request-Id"), token)
 215         if err != nil {
 216                 http.Error(w, "Pool failed: "+h.clientPool.Err().Error(), http.StatusInternalServerError)
 217                 return true
 218         }
 219         defer release()
 220
 221         fs := client.SiteFileSystem(kc)
 222         fs.ForwardSlashNameSubstitution(h.Config.cluster.Collections.ForwardSlashNameSubstitution)
 223
 224         var objectNameGiven bool
 225         fspath := "/by_id"
 226         if id := parseCollectionIDFromDNSName(r.Host); id != "" {
 227                 fspath += "/" + id
 228                 objectNameGiven = strings.Count(strings.TrimSuffix(r.URL.Path, "/"), "/") > 0
 229         } else {
 230                 objectNameGiven = strings.Count(strings.TrimSuffix(r.URL.Path, "/"), "/") > 1
 231         }
 232         fspath += r.URL.Path
 233
 234         switch {
 235         case r.Method == http.MethodGet && !objectNameGiven:
 236                 // Path is "/{uuid}" or "/{uuid}/", has no object name
 237                 if _, ok := r.URL.Query()["versioning"]; ok {
 238                         // GetBucketVersioning
 239                         w.Header().Set("Content-Type", "application/xml")
 240                         io.WriteString(w, xml.Header)
 241                         fmt.Fprintln(w, `<VersioningConfiguration xmlns="http://s3.amazonaws.com/doc/2006-03-01/"/>`)
 242                 } else {
 243                         // ListObjects
 244                         h.s3list(w, r, fs)
 245                 }
 246                 return true
 247         case r.Method == http.MethodGet || r.Method == http.MethodHead:
 248                 fi, err := fs.Stat(fspath)
 249                 if r.Method == "HEAD" && !objectNameGiven {
 250                         // HeadBucket
 251                         if err == nil && fi.IsDir() {
 252                                 w.WriteHeader(http.StatusOK)
 253                         } else if os.IsNotExist(err) {
 254                                 w.WriteHeader(http.StatusNotFound)
 255                         } else {
 256                                 http.Error(w, err.Error(), http.StatusBadGateway)
 257                         }
 258                         return true
 259                 }
 260                 if err == nil && fi.IsDir() && objectNameGiven && strings.HasSuffix(fspath, "/") && h.Config.cluster.Collections.S3FolderObjects {
 261                         w.Header().Set("Content-Type", "application/x-directory")
 262                         w.WriteHeader(http.StatusOK)
 263                         return true
 264                 }
 265                 if os.IsNotExist(err) ||
 266                         (err != nil && err.Error() == "not a directory") ||
 267                         (fi != nil && fi.IsDir()) {
 268                         http.Error(w, "not found", http.StatusNotFound)
 269                         return true
 270                 }
 271                 // shallow copy r, and change URL path
 272                 r := *r
 273                 r.URL.Path = fspath
 274                 http.FileServer(fs).ServeHTTP(w, &r)
 275                 return true
 276         case r.Method == http.MethodPut:
 277                 if !objectNameGiven {
 278                         http.Error(w, "missing object name in PUT request", http.StatusBadRequest)
 279                         return true
 280                 }
 281                 var objectIsDir bool
 282                 if strings.HasSuffix(fspath, "/") {
 283                         if !h.Config.cluster.Collections.S3FolderObjects {
 284                                 http.Error(w, "invalid object name: trailing slash", http.StatusBadRequest)
 285                                 return true
 286                         }
 287                         n, err := r.Body.Read(make([]byte, 1))
 288                         if err != nil && err != io.EOF {
 289                                 http.Error(w, fmt.Sprintf("error reading request body: %s", err), http.StatusInternalServerError)
 290                                 return true
 291                         } else if n > 0 {
 292                                 http.Error(w, "cannot create object with trailing '/' char unless content is empty", http.StatusBadRequest)
 293                                 return true
 294                         } else if strings.SplitN(r.Header.Get("Content-Type"), ";", 2)[0] != "application/x-directory" {
 295                                 http.Error(w, "cannot create object with trailing '/' char unless Content-Type is 'application/x-directory'", http.StatusBadRequest)
 296                                 return true
 297                         }
 298                         // Given PUT "foo/bar/", we'll use "foo/bar/."
 299                         // in the "ensure parents exist" block below,
 300                         // and then we'll be done.
 301                         fspath += "."
 302                         objectIsDir = true
 303                 }
 304                 fi, err := fs.Stat(fspath)
 305                 if err != nil && err.Error() == "not a directory" {
 306                         // requested foo/bar, but foo is a file
 307                         http.Error(w, "object name conflicts with existing object", http.StatusBadRequest)
 308                         return true
 309                 }
 310                 if strings.HasSuffix(r.URL.Path, "/") && err == nil && !fi.IsDir() {
 311                         // requested foo/bar/, but foo/bar is a file
 312                         http.Error(w, "object name conflicts with existing object", http.StatusBadRequest)
 313                         return true
 314                 }
 315                 // create missing parent/intermediate directories, if any
 316                 for i, c := range fspath {
 317                         if i > 0 && c == '/' {
 318                                 dir := fspath[:i]
 319                                 if strings.HasSuffix(dir, "/") {
 320                                         err = errors.New("invalid object name (consecutive '/' chars)")
 321                                         http.Error(w, err.Error(), http.StatusBadRequest)
 322                                         return true
 323                                 }
 324                                 err = fs.Mkdir(dir, 0755)
 325                                 if err == arvados.ErrInvalidArgument {
 326                                         // Cannot create a directory
 327                                         // here.
 328                                         err = fmt.Errorf("mkdir %q failed: %w", dir, err)
 329                                         http.Error(w, err.Error(), http.StatusBadRequest)
 330                                         return true
 331                                 } else if err != nil && !os.IsExist(err) {
 332                                         err = fmt.Errorf("mkdir %q failed: %w", dir, err)
 333                                         http.Error(w, err.Error(), http.StatusInternalServerError)
 334                                         return true
 335                                 }
 336                         }
 337                 }
 338                 if !objectIsDir {
 339                         f, err := fs.OpenFile(fspath, os.O_WRONLY|os.O_TRUNC|os.O_CREATE, 0644)
 340                         if os.IsNotExist(err) {
 341                                 f, err = fs.OpenFile(fspath, os.O_WRONLY|os.O_TRUNC|os.O_CREATE, 0644)
 342                         }
 343                         if err != nil {
 344                                 err = fmt.Errorf("open %q failed: %w", r.URL.Path, err)
 345                                 http.Error(w, err.Error(), http.StatusBadRequest)
 346                                 return true
 347                         }
 348                         defer f.Close()
 349                         _, err = io.Copy(f, r.Body)
 350                         if err != nil {
 351                                 err = fmt.Errorf("write to %q failed: %w", r.URL.Path, err)
 352                                 http.Error(w, err.Error(), http.StatusBadGateway)
 353                                 return true
 354                         }
 355                         err = f.Close()
 356                         if err != nil {
 357                                 err = fmt.Errorf("write to %q failed: close: %w", r.URL.Path, err)
 358                                 http.Error(w, err.Error(), http.StatusBadGateway)
 359                                 return true
 360                         }
 361                 }
 362                 err = fs.Sync()
 363                 if err != nil {
 364                         err = fmt.Errorf("sync failed: %w", err)
 365                         http.Error(w, err.Error(), http.StatusInternalServerError)
 366                         return true
 367                 }
 368                 w.WriteHeader(http.StatusOK)
 369                 return true
 370         case r.Method == http.MethodDelete:
 371                 if !objectNameGiven || r.URL.Path == "/" {
 372                         http.Error(w, "missing object name in DELETE request", http.StatusBadRequest)
 373                         return true
 374                 }
 375                 if strings.HasSuffix(fspath, "/") {
 376                         fspath = strings.TrimSuffix(fspath, "/")
 377                         fi, err := fs.Stat(fspath)
 378                         if os.IsNotExist(err) {
 379                                 w.WriteHeader(http.StatusNoContent)
 380                                 return true
 381                         } else if err != nil {
 382                                 http.Error(w, err.Error(), http.StatusInternalServerError)
 383                                 return true
 384                         } else if !fi.IsDir() {
 385                                 // if "foo" exists and is a file, then
 386                                 // "foo/" doesn't exist, so we say
 387                                 // delete was successful.
 388                                 w.WriteHeader(http.StatusNoContent)
 389                                 return true
 390                         }
 391                 } else if fi, err := fs.Stat(fspath); err == nil && fi.IsDir() {
 392                         // if "foo" is a dir, it is visible via S3
 393                         // only as "foo/", not "foo" -- so we leave
 394                         // the dir alone and return 204 to indicate
 395                         // that "foo" does not exist.
 396                         w.WriteHeader(http.StatusNoContent)
 397                         return true
 398                 }
 399                 err = fs.Remove(fspath)
 400                 if os.IsNotExist(err) {
 401                         w.WriteHeader(http.StatusNoContent)
 402                         return true
 403                 }
 404                 if err != nil {
 405                         err = fmt.Errorf("rm failed: %w", err)
 406                         http.Error(w, err.Error(), http.StatusBadRequest)
 407                         return true
 408                 }
 409                 err = fs.Sync()
 410                 if err != nil {
 411                         err = fmt.Errorf("sync failed: %w", err)
 412                         http.Error(w, err.Error(), http.StatusInternalServerError)
 413                         return true
 414                 }
 415                 w.WriteHeader(http.StatusNoContent)
 416                 return true
 417         default:
 418                 http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
 419                 return true
 420         }
 421 }
 422
 423 // Call fn on the given path (directory) and its contents, in
 424 // lexicographic order.
 425 //
 426 // If isRoot==true and path is not a directory, return nil.
 427 //
 428 // If fn returns filepath.SkipDir when called on a directory, don't
 429 // descend into that directory.
 430 func walkFS(fs arvados.CustomFileSystem, path string, isRoot bool, fn func(path string, fi os.FileInfo) error) error {
 431         if isRoot {
 432                 fi, err := fs.Stat(path)
 433                 if os.IsNotExist(err) || (err == nil && !fi.IsDir()) {
 434                         return nil
 435                 } else if err != nil {
 436                         return err
 437                 }
 438                 err = fn(path, fi)
 439                 if err == filepath.SkipDir {
 440                         return nil
 441                 } else if err != nil {
 442                         return err
 443                 }
 444         }
 445         f, err := fs.Open(path)
 446         if os.IsNotExist(err) && isRoot {
 447                 return nil
 448         } else if err != nil {
 449                 return fmt.Errorf("open %q: %w", path, err)
 450         }
 451         defer f.Close()
 452         if path == "/" {
 453                 path = ""
 454         }
 455         fis, err := f.Readdir(-1)
 456         if err != nil {
 457                 return err
 458         }
 459         sort.Slice(fis, func(i, j int) bool { return fis[i].Name() < fis[j].Name() })
 460         for _, fi := range fis {
 461                 err = fn(path+"/"+fi.Name(), fi)
 462                 if err == filepath.SkipDir {
 463                         continue
 464                 } else if err != nil {
 465                         return err
 466                 }
 467                 if fi.IsDir() {
 468                         err = walkFS(fs, path+"/"+fi.Name(), false, fn)
 469                         if err != nil {
 470                                 return err
 471                         }
 472                 }
 473         }
 474         return nil
 475 }
 476
 477 var errDone = errors.New("done")
 478
 479 func (h *handler) s3list(w http.ResponseWriter, r *http.Request, fs arvados.CustomFileSystem) {
 480         var params struct {
 481                 bucket    string
 482                 delimiter string
 483                 marker    string
 484                 maxKeys   int
 485                 prefix    string
 486         }
 487         params.bucket = strings.SplitN(r.URL.Path[1:], "/", 2)[0]
 488         params.delimiter = r.FormValue("delimiter")
 489         params.marker = r.FormValue("marker")
 490         if mk, _ := strconv.ParseInt(r.FormValue("max-keys"), 10, 64); mk > 0 && mk < s3MaxKeys {
 491                 params.maxKeys = int(mk)
 492         } else {
 493                 params.maxKeys = s3MaxKeys
 494         }
 495         params.prefix = r.FormValue("prefix")
 496
 497         bucketdir := "by_id/" + params.bucket
 498         // walkpath is the directory (relative to bucketdir) we need
 499         // to walk: the innermost directory that is guaranteed to
 500         // contain all paths that have the requested prefix. Examples:
 501         // prefix "foo/bar"  => walkpath "foo"
 502         // prefix "foo/bar/" => walkpath "foo/bar"
 503         // prefix "foo"      => walkpath ""
 504         // prefix ""         => walkpath ""
 505         walkpath := params.prefix
 506         if cut := strings.LastIndex(walkpath, "/"); cut >= 0 {
 507                 walkpath = walkpath[:cut]
 508         } else {
 509                 walkpath = ""
 510         }
 511
 512         type commonPrefix struct {
 513                 Prefix string
 514         }
 515         type listResp struct {
 516                 XMLName string `xml:"http://s3.amazonaws.com/doc/2006-03-01/ ListBucketResult"`
 517                 s3.ListResp
 518                 // s3.ListResp marshals an empty tag when
 519                 // CommonPrefixes is nil, which confuses some clients.
 520                 // Fix by using this nested struct instead.
 521                 CommonPrefixes []commonPrefix
 522                 // Similarly, we need omitempty here, because an empty
 523                 // tag confuses some clients (e.g.,
 524                 // github.com/aws/aws-sdk-net never terminates its
 525                 // paging loop).
 526                 NextMarker string `xml:"NextMarker,omitempty"`
 527                 // ListObjectsV2 has a KeyCount response field.
 528                 KeyCount int
 529         }
 530         resp := listResp{
 531                 ListResp: s3.ListResp{
 532                         Name:      strings.SplitN(r.URL.Path[1:], "/", 2)[0],
 533                         Prefix:    params.prefix,
 534                         Delimiter: params.delimiter,
 535                         Marker:    params.marker,
 536                         MaxKeys:   params.maxKeys,
 537                 },
 538         }
 539         commonPrefixes := map[string]bool{}
 540         err := walkFS(fs, strings.TrimSuffix(bucketdir+"/"+walkpath, "/"), true, func(path string, fi os.FileInfo) error {
 541                 if path == bucketdir {
 542                         return nil
 543                 }
 544                 path = path[len(bucketdir)+1:]
 545                 filesize := fi.Size()
 546                 if fi.IsDir() {
 547                         path += "/"
 548                         filesize = 0
 549                 }
 550                 if len(path) <= len(params.prefix) {
 551                         if path > params.prefix[:len(path)] {
 552                                 // with prefix "foobar", walking "fooz" means we're done
 553                                 return errDone
 554                         }
 555                         if path < params.prefix[:len(path)] {
 556                                 // with prefix "foobar", walking "foobag" is pointless
 557                                 return filepath.SkipDir
 558                         }
 559                         if fi.IsDir() && !strings.HasPrefix(params.prefix+"/", path) {
 560                                 // with prefix "foo/bar", walking "fo"
 561                                 // is pointless (but walking "foo" or
 562                                 // "foo/bar" is necessary)
 563                                 return filepath.SkipDir
 564                         }
 565                         if len(path) < len(params.prefix) {
 566                                 // can't skip anything, and this entry
 567                                 // isn't in the results, so just
 568                                 // continue descent
 569                                 return nil
 570                         }
 571                 } else {
 572                         if path[:len(params.prefix)] > params.prefix {
 573                                 // with prefix "foobar", nothing we
 574                                 // see after "foozzz" is relevant
 575                                 return errDone
 576                         }
 577                 }
 578                 if path < params.marker || path < params.prefix {
 579                         return nil
 580                 }
 581                 if fi.IsDir() && !h.Config.cluster.Collections.S3FolderObjects {
 582                         // Note we don't add anything to
 583                         // commonPrefixes here even if delimiter is
 584                         // "/". We descend into the directory, and
 585                         // return a commonPrefix only if we end up
 586                         // finding a regular file inside it.
 587                         return nil
 588                 }
 589                 if params.delimiter != "" {
 590                         idx := strings.Index(path[len(params.prefix):], params.delimiter)
 591                         if idx >= 0 {
 592                                 // with prefix "foobar" and delimiter
 593                                 // "z", when we hit "foobar/baz", we
 594                                 // add "/baz" to commonPrefixes and
 595                                 // stop descending.
 596                                 commonPrefixes[path[:len(params.prefix)+idx+1]] = true
 597                                 return filepath.SkipDir
 598                         }
 599                 }
 600                 if len(resp.Contents)+len(commonPrefixes) >= params.maxKeys {
 601                         resp.IsTruncated = true
 602                         if params.delimiter != "" {
 603                                 resp.NextMarker = path
 604                         }
 605                         return errDone
 606                 }
 607                 resp.Contents = append(resp.Contents, s3.Key{
 608                         Key:          path,
 609                         LastModified: fi.ModTime().UTC().Format("2006-01-02T15:04:05.999") + "Z",
 610                         Size:         filesize,
 611                 })
 612                 return nil
 613         })
 614         if err != nil && err != errDone {
 615                 http.Error(w, err.Error(), http.StatusInternalServerError)
 616                 return
 617         }
 618         if params.delimiter != "" {
 619                 resp.CommonPrefixes = make([]commonPrefix, 0, len(commonPrefixes))
 620                 for prefix := range commonPrefixes {
 621                         resp.CommonPrefixes = append(resp.CommonPrefixes, commonPrefix{prefix})
 622                 }
 623                 sort.Slice(resp.CommonPrefixes, func(i, j int) bool { return resp.CommonPrefixes[i].Prefix < resp.CommonPrefixes[j].Prefix })
 624         }
 625         resp.KeyCount = len(resp.Contents)
 626         w.Header().Set("Content-Type", "application/xml")
 627         io.WriteString(w, xml.Header)
 628         if err := xml.NewEncoder(w).Encode(resp); err != nil {
 629                 ctxlog.FromContext(r.Context()).WithError(err).Error("error writing xml response")
 630         }
 631 }