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 func s3ErrorResponse(w http.ResponseWriter, s3code string, message string, resource string, code int) {
 177         w.Header().Set("Content-Type", "application/xml")
 178         w.Header().Set("X-Content-Type-Options", "nosniff")
 179         w.WriteHeader(code)
 180         var errstruct struct {
 181                 Code      string
 182                 Message   string
 183                 Resource  string
 184                 RequestId string
 185         }
 186         errstruct.Code = s3code
 187         errstruct.Message = message
 188         errstruct.Resource = resource
 189         errstruct.RequestId = ""
 190         enc := xml.NewEncoder(w)
 191         fmt.Fprint(w, xml.Header)
 192         enc.EncodeElement(errstruct, xml.StartElement{Name: xml.Name{Local: "Error"}})
 193 }
 194
 195 var NoSuchKey = "NoSuchKey"
 196 var NoSuchBucket = "NoSuchBucket"
 197 var InvalidArgument = "InvalidArgument"
 198 var InternalError = "InternalError"
 199 var UnauthorizedAccess = "UnauthorizedAccess"
 200 var InvalidRequest = "InvalidRequest"
 201 var SignatureDoesNotMatch = "SignatureDoesNotMatch"
 202
 203 // serveS3 handles r and returns true if r is a request from an S3
 204 // client, otherwise it returns false.
 205 func (h *handler) serveS3(w http.ResponseWriter, r *http.Request) bool {
 206         var token string
 207         if auth := r.Header.Get("Authorization"); strings.HasPrefix(auth, "AWS ") {
 208                 split := strings.SplitN(auth[4:], ":", 2)
 209                 if len(split) < 2 {
 210                         s3ErrorResponse(w, InvalidRequest, "malformed Authorization header", r.URL.Path, http.StatusUnauthorized)
 211                         return true
 212                 }
 213                 token = split[0]
 214         } else if strings.HasPrefix(auth, s3SignAlgorithm+" ") {
 215                 t, err := h.checks3signature(r)
 216                 if err != nil {
 217                         s3ErrorResponse(w, SignatureDoesNotMatch, "signature verification failed: "+err.Error(), r.URL.Path, http.StatusForbidden)
 218                         return true
 219                 }
 220                 token = t
 221         } else {
 222                 return false
 223         }
 224
 225         _, kc, client, release, err := h.getClients(r.Header.Get("X-Request-Id"), token)
 226         if err != nil {
 227                 s3ErrorResponse(w, InternalError, "Pool failed: "+h.clientPool.Err().Error(), r.URL.Path, http.StatusInternalServerError)
 228                 return true
 229         }
 230         defer release()
 231
 232         fs := client.SiteFileSystem(kc)
 233         fs.ForwardSlashNameSubstitution(h.Config.cluster.Collections.ForwardSlashNameSubstitution)
 234
 235         objectNameGiven := strings.Count(strings.TrimSuffix(r.URL.Path, "/"), "/") > 1
 236
 237         switch {
 238         case r.Method == http.MethodGet && !objectNameGiven:
 239                 // Path is "/{uuid}" or "/{uuid}/", has no object name
 240                 if _, ok := r.URL.Query()["versioning"]; ok {
 241                         // GetBucketVersioning
 242                         w.Header().Set("Content-Type", "application/xml")
 243                         io.WriteString(w, xml.Header)
 244                         fmt.Fprintln(w, `<VersioningConfiguration xmlns="http://s3.amazonaws.com/doc/2006-03-01/"/>`)
 245                 } else {
 246                         // ListObjects
 247                         h.s3list(w, r, fs)
 248                 }
 249                 return true
 250         case r.Method == http.MethodGet || r.Method == http.MethodHead:
 251                 fspath := "/by_id" + r.URL.Path
 252                 fi, err := fs.Stat(fspath)
 253                 if r.Method == "HEAD" && !objectNameGiven {
 254                         // HeadBucket
 255                         if err == nil && fi.IsDir() {
 256                                 w.WriteHeader(http.StatusOK)
 257                         } else if os.IsNotExist(err) {
 258                                 s3ErrorResponse(w, NoSuchBucket, "The specified bucket does not exist.", r.URL.Path, http.StatusNotFound)
 259                         } else {
 260                                 s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusBadGateway)
 261                         }
 262                         return true
 263                 }
 264                 if err == nil && fi.IsDir() && objectNameGiven && strings.HasSuffix(fspath, "/") && h.Config.cluster.Collections.S3FolderObjects {
 265                         w.Header().Set("Content-Type", "application/x-directory")
 266                         w.WriteHeader(http.StatusOK)
 267                         return true
 268                 }
 269                 if os.IsNotExist(err) ||
 270                         (err != nil && err.Error() == "not a directory") ||
 271                         (fi != nil && fi.IsDir()) {
 272                         s3ErrorResponse(w, NoSuchKey, "The specified key does not exist.", r.URL.Path, http.StatusNotFound)
 273                         return true
 274                 }
 275                 // shallow copy r, and change URL path
 276                 r := *r
 277                 r.URL.Path = fspath
 278                 http.FileServer(fs).ServeHTTP(w, &r)
 279                 return true
 280         case r.Method == http.MethodPut:
 281                 if !objectNameGiven {
 282                         s3ErrorResponse(w, InvalidArgument, "Missing object name in PUT request.", r.URL.Path, http.StatusBadRequest)
 283                         return true
 284                 }
 285                 fspath := "by_id" + r.URL.Path
 286                 var objectIsDir bool
 287                 if strings.HasSuffix(fspath, "/") {
 288                         if !h.Config.cluster.Collections.S3FolderObjects {
 289                                 s3ErrorResponse(w, InvalidArgument, "invalid object name: trailing slash", r.URL.Path, http.StatusBadRequest)
 290                                 return true
 291                         }
 292                         n, err := r.Body.Read(make([]byte, 1))
 293                         if err != nil && err != io.EOF {
 294                                 s3ErrorResponse(w, InternalError, fmt.Sprintf("error reading request body: %s", err), r.URL.Path, http.StatusInternalServerError)
 295                                 return true
 296                         } else if n > 0 {
 297                                 s3ErrorResponse(w, InvalidArgument, "cannot create object with trailing '/' char unless content is empty", r.URL.Path, http.StatusBadRequest)
 298                                 return true
 299                         } else if strings.SplitN(r.Header.Get("Content-Type"), ";", 2)[0] != "application/x-directory" {
 300                                 s3ErrorResponse(w, InvalidArgument, "cannot create object with trailing '/' char unless Content-Type is 'application/x-directory'", r.URL.Path, http.StatusBadRequest)
 301                                 return true
 302                         }
 303                         // Given PUT "foo/bar/", we'll use "foo/bar/."
 304                         // in the "ensure parents exist" block below,
 305                         // and then we'll be done.
 306                         fspath += "."
 307                         objectIsDir = true
 308                 }
 309                 fi, err := fs.Stat(fspath)
 310                 if err != nil && err.Error() == "not a directory" {
 311                         // requested foo/bar, but foo is a file
 312                         s3ErrorResponse(w, InvalidArgument, "object name conflicts with existing object", r.URL.Path, http.StatusBadRequest)
 313                         return true
 314                 }
 315                 if strings.HasSuffix(r.URL.Path, "/") && err == nil && !fi.IsDir() {
 316                         // requested foo/bar/, but foo/bar is a file
 317                         s3ErrorResponse(w, InvalidArgument, "object name conflicts with existing object", r.URL.Path, http.StatusBadRequest)
 318                         return true
 319                 }
 320                 // create missing parent/intermediate directories, if any
 321                 for i, c := range fspath {
 322                         if i > 0 && c == '/' {
 323                                 dir := fspath[:i]
 324                                 if strings.HasSuffix(dir, "/") {
 325                                         err = errors.New("invalid object name (consecutive '/' chars)")
 326                                         s3ErrorResponse(w, InvalidArgument, err.Error(), r.URL.Path, http.StatusBadRequest)
 327                                         return true
 328                                 }
 329                                 err = fs.Mkdir(dir, 0755)
 330                                 if err == arvados.ErrInvalidArgument {
 331                                         // Cannot create a directory
 332                                         // here.
 333                                         err = fmt.Errorf("mkdir %q failed: %w", dir, err)
 334                                         s3ErrorResponse(w, InvalidArgument, err.Error(), r.URL.Path, http.StatusBadRequest)
 335                                         return true
 336                                 } else if err != nil && !os.IsExist(err) {
 337                                         err = fmt.Errorf("mkdir %q failed: %w", dir, err)
 338                                         s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusInternalServerError)
 339                                         return true
 340                                 }
 341                         }
 342                 }
 343                 if !objectIsDir {
 344                         f, err := fs.OpenFile(fspath, os.O_WRONLY|os.O_TRUNC|os.O_CREATE, 0644)
 345                         if os.IsNotExist(err) {
 346                                 f, err = fs.OpenFile(fspath, os.O_WRONLY|os.O_TRUNC|os.O_CREATE, 0644)
 347                         }
 348                         if err != nil {
 349                                 err = fmt.Errorf("open %q failed: %w", r.URL.Path, err)
 350                                 s3ErrorResponse(w, InvalidArgument, err.Error(), r.URL.Path, http.StatusBadRequest)
 351                                 return true
 352                         }
 353                         defer f.Close()
 354                         _, err = io.Copy(f, r.Body)
 355                         if err != nil {
 356                                 err = fmt.Errorf("write to %q failed: %w", r.URL.Path, err)
 357                                 s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusBadGateway)
 358                                 return true
 359                         }
 360                         err = f.Close()
 361                         if err != nil {
 362                                 err = fmt.Errorf("write to %q failed: close: %w", r.URL.Path, err)
 363                                 s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusBadGateway)
 364                                 return true
 365                         }
 366                 }
 367                 err = fs.Sync()
 368                 if err != nil {
 369                         err = fmt.Errorf("sync failed: %w", err)
 370                         s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusInternalServerError)
 371                         return true
 372                 }
 373                 w.WriteHeader(http.StatusOK)
 374                 return true
 375         case r.Method == http.MethodDelete:
 376                 if !objectNameGiven || r.URL.Path == "/" {
 377                         s3ErrorResponse(w, InvalidArgument, "missing object name in DELETE request", r.URL.Path, http.StatusBadRequest)
 378                         return true
 379                 }
 380                 fspath := "by_id" + r.URL.Path
 381                 if strings.HasSuffix(fspath, "/") {
 382                         fspath = strings.TrimSuffix(fspath, "/")
 383                         fi, err := fs.Stat(fspath)
 384                         if os.IsNotExist(err) {
 385                                 w.WriteHeader(http.StatusNoContent)
 386                                 return true
 387                         } else if err != nil {
 388                                 s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusInternalServerError)
 389                                 return true
 390                         } else if !fi.IsDir() {
 391                                 // if "foo" exists and is a file, then
 392                                 // "foo/" doesn't exist, so we say
 393                                 // delete was successful.
 394                                 w.WriteHeader(http.StatusNoContent)
 395                                 return true
 396                         }
 397                 } else if fi, err := fs.Stat(fspath); err == nil && fi.IsDir() {
 398                         // if "foo" is a dir, it is visible via S3
 399                         // only as "foo/", not "foo" -- so we leave
 400                         // the dir alone and return 204 to indicate
 401                         // that "foo" does not exist.
 402                         w.WriteHeader(http.StatusNoContent)
 403                         return true
 404                 }
 405                 err = fs.Remove(fspath)
 406                 if os.IsNotExist(err) {
 407                         w.WriteHeader(http.StatusNoContent)
 408                         return true
 409                 }
 410                 if err != nil {
 411                         err = fmt.Errorf("rm failed: %w", err)
 412                         s3ErrorResponse(w, InvalidArgument, err.Error(), r.URL.Path, http.StatusBadRequest)
 413                         return true
 414                 }
 415                 err = fs.Sync()
 416                 if err != nil {
 417                         err = fmt.Errorf("sync failed: %w", err)
 418                         s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusInternalServerError)
 419                         return true
 420                 }
 421                 w.WriteHeader(http.StatusNoContent)
 422                 return true
 423         default:
 424                 s3ErrorResponse(w, InvalidRequest, "method not allowed", r.URL.Path, http.StatusMethodNotAllowed)
 425
 426                 return true
 427         }
 428 }
 429
 430 // Call fn on the given path (directory) and its contents, in
 431 // lexicographic order.
 432 //
 433 // If isRoot==true and path is not a directory, return nil.
 434 //
 435 // If fn returns filepath.SkipDir when called on a directory, don't
 436 // descend into that directory.
 437 func walkFS(fs arvados.CustomFileSystem, path string, isRoot bool, fn func(path string, fi os.FileInfo) error) error {
 438         if isRoot {
 439                 fi, err := fs.Stat(path)
 440                 if os.IsNotExist(err) || (err == nil && !fi.IsDir()) {
 441                         return nil
 442                 } else if err != nil {
 443                         return err
 444                 }
 445                 err = fn(path, fi)
 446                 if err == filepath.SkipDir {
 447                         return nil
 448                 } else if err != nil {
 449                         return err
 450                 }
 451         }
 452         f, err := fs.Open(path)
 453         if os.IsNotExist(err) && isRoot {
 454                 return nil
 455         } else if err != nil {
 456                 return fmt.Errorf("open %q: %w", path, err)
 457         }
 458         defer f.Close()
 459         if path == "/" {
 460                 path = ""
 461         }
 462         fis, err := f.Readdir(-1)
 463         if err != nil {
 464                 return err
 465         }
 466         sort.Slice(fis, func(i, j int) bool { return fis[i].Name() < fis[j].Name() })
 467         for _, fi := range fis {
 468                 err = fn(path+"/"+fi.Name(), fi)
 469                 if err == filepath.SkipDir {
 470                         continue
 471                 } else if err != nil {
 472                         return err
 473                 }
 474                 if fi.IsDir() {
 475                         err = walkFS(fs, path+"/"+fi.Name(), false, fn)
 476                         if err != nil {
 477                                 return err
 478                         }
 479                 }
 480         }
 481         return nil
 482 }
 483
 484 var errDone = errors.New("done")
 485
 486 func (h *handler) s3list(w http.ResponseWriter, r *http.Request, fs arvados.CustomFileSystem) {
 487         var params struct {
 488                 bucket    string
 489                 delimiter string
 490                 marker    string
 491                 maxKeys   int
 492                 prefix    string
 493         }
 494         params.bucket = strings.SplitN(r.URL.Path[1:], "/", 2)[0]
 495         params.delimiter = r.FormValue("delimiter")
 496         params.marker = r.FormValue("marker")
 497         if mk, _ := strconv.ParseInt(r.FormValue("max-keys"), 10, 64); mk > 0 && mk < s3MaxKeys {
 498                 params.maxKeys = int(mk)
 499         } else {
 500                 params.maxKeys = s3MaxKeys
 501         }
 502         params.prefix = r.FormValue("prefix")
 503
 504         bucketdir := "by_id/" + params.bucket
 505         // walkpath is the directory (relative to bucketdir) we need
 506         // to walk: the innermost directory that is guaranteed to
 507         // contain all paths that have the requested prefix. Examples:
 508         // prefix "foo/bar"  => walkpath "foo"
 509         // prefix "foo/bar/" => walkpath "foo/bar"
 510         // prefix "foo"      => walkpath ""
 511         // prefix ""         => walkpath ""
 512         walkpath := params.prefix
 513         if cut := strings.LastIndex(walkpath, "/"); cut >= 0 {
 514                 walkpath = walkpath[:cut]
 515         } else {
 516                 walkpath = ""
 517         }
 518
 519         type commonPrefix struct {
 520                 Prefix string
 521         }
 522         type listResp struct {
 523                 XMLName string `xml:"http://s3.amazonaws.com/doc/2006-03-01/ ListBucketResult"`
 524                 s3.ListResp
 525                 // s3.ListResp marshals an empty tag when
 526                 // CommonPrefixes is nil, which confuses some clients.
 527                 // Fix by using this nested struct instead.
 528                 CommonPrefixes []commonPrefix
 529                 // Similarly, we need omitempty here, because an empty
 530                 // tag confuses some clients (e.g.,
 531                 // github.com/aws/aws-sdk-net never terminates its
 532                 // paging loop).
 533                 NextMarker string `xml:"NextMarker,omitempty"`
 534                 // ListObjectsV2 has a KeyCount response field.
 535                 KeyCount int
 536         }
 537         resp := listResp{
 538                 ListResp: s3.ListResp{
 539                         Name:      strings.SplitN(r.URL.Path[1:], "/", 2)[0],
 540                         Prefix:    params.prefix,
 541                         Delimiter: params.delimiter,
 542                         Marker:    params.marker,
 543                         MaxKeys:   params.maxKeys,
 544                 },
 545         }
 546         commonPrefixes := map[string]bool{}
 547         err := walkFS(fs, strings.TrimSuffix(bucketdir+"/"+walkpath, "/"), true, func(path string, fi os.FileInfo) error {
 548                 if path == bucketdir {
 549                         return nil
 550                 }
 551                 path = path[len(bucketdir)+1:]
 552                 filesize := fi.Size()
 553                 if fi.IsDir() {
 554                         path += "/"
 555                         filesize = 0
 556                 }
 557                 if len(path) <= len(params.prefix) {
 558                         if path > params.prefix[:len(path)] {
 559                                 // with prefix "foobar", walking "fooz" means we're done
 560                                 return errDone
 561                         }
 562                         if path < params.prefix[:len(path)] {
 563                                 // with prefix "foobar", walking "foobag" is pointless
 564                                 return filepath.SkipDir
 565                         }
 566                         if fi.IsDir() && !strings.HasPrefix(params.prefix+"/", path) {
 567                                 // with prefix "foo/bar", walking "fo"
 568                                 // is pointless (but walking "foo" or
 569                                 // "foo/bar" is necessary)
 570                                 return filepath.SkipDir
 571                         }
 572                         if len(path) < len(params.prefix) {
 573                                 // can't skip anything, and this entry
 574                                 // isn't in the results, so just
 575                                 // continue descent
 576                                 return nil
 577                         }
 578                 } else {
 579                         if path[:len(params.prefix)] > params.prefix {
 580                                 // with prefix "foobar", nothing we
 581                                 // see after "foozzz" is relevant
 582                                 return errDone
 583                         }
 584                 }
 585                 if path < params.marker || path < params.prefix {
 586                         return nil
 587                 }
 588                 if fi.IsDir() && !h.Config.cluster.Collections.S3FolderObjects {
 589                         // Note we don't add anything to
 590                         // commonPrefixes here even if delimiter is
 591                         // "/". We descend into the directory, and
 592                         // return a commonPrefix only if we end up
 593                         // finding a regular file inside it.
 594                         return nil
 595                 }
 596                 if params.delimiter != "" {
 597                         idx := strings.Index(path[len(params.prefix):], params.delimiter)
 598                         if idx >= 0 {
 599                                 // with prefix "foobar" and delimiter
 600                                 // "z", when we hit "foobar/baz", we
 601                                 // add "/baz" to commonPrefixes and
 602                                 // stop descending.
 603                                 commonPrefixes[path[:len(params.prefix)+idx+1]] = true
 604                                 return filepath.SkipDir
 605                         }
 606                 }
 607                 if len(resp.Contents)+len(commonPrefixes) >= params.maxKeys {
 608                         resp.IsTruncated = true
 609                         if params.delimiter != "" {
 610                                 resp.NextMarker = path
 611                         }
 612                         return errDone
 613                 }
 614                 resp.Contents = append(resp.Contents, s3.Key{
 615                         Key:          path,
 616                         LastModified: fi.ModTime().UTC().Format("2006-01-02T15:04:05.999") + "Z",
 617                         Size:         filesize,
 618                 })
 619                 return nil
 620         })
 621         if err != nil && err != errDone {
 622                 http.Error(w, err.Error(), http.StatusInternalServerError)
 623                 return
 624         }
 625         if params.delimiter != "" {
 626                 resp.CommonPrefixes = make([]commonPrefix, 0, len(commonPrefixes))
 627                 for prefix := range commonPrefixes {
 628                         resp.CommonPrefixes = append(resp.CommonPrefixes, commonPrefix{prefix})
 629                 }
 630                 sort.Slice(resp.CommonPrefixes, func(i, j int) bool { return resp.CommonPrefixes[i].Prefix < resp.CommonPrefixes[j].Prefix })
 631         }
 632         resp.KeyCount = len(resp.Contents)
 633         w.Header().Set("Content-Type", "application/xml")
 634         io.WriteString(w, xml.Header)
 635         if err := xml.NewEncoder(w).Encode(resp); err != nil {
 636                 ctxlog.FromContext(r.Context()).WithError(err).Error("error writing xml response")
 637         }
 638 }