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 func s3ErrorResponse(w http.ResponseWriter, s3code string, message string, resource string, code int) {
 193         w.Header().Set("Content-Type", "application/xml")
 194         w.Header().Set("X-Content-Type-Options", "nosniff")
 195         w.WriteHeader(code)
 196         var errstruct struct {
 197                 Code      string
 198                 Message   string
 199                 Resource  string
 200                 RequestId string
 201         }
 202         errstruct.Code = s3code
 203         errstruct.Message = message
 204         errstruct.Resource = resource
 205         errstruct.RequestId = ""
 206         enc := xml.NewEncoder(w)
 207         fmt.Fprint(w, xml.Header)
 208         enc.EncodeElement(errstruct, xml.StartElement{Name: xml.Name{Local: "Error"}})
 209 }
 210
 211 var NoSuchKey = "NoSuchKey"
 212 var NoSuchBucket = "NoSuchBucket"
 213 var InvalidArgument = "InvalidArgument"
 214 var InternalError = "InternalError"
 215 var UnauthorizedAccess = "UnauthorizedAccess"
 216 var InvalidRequest = "InvalidRequest"
 217 var SignatureDoesNotMatch = "SignatureDoesNotMatch"
 218
 219 // serveS3 handles r and returns true if r is a request from an S3
 220 // client, otherwise it returns false.
 221 func (h *handler) serveS3(w http.ResponseWriter, r *http.Request) bool {
 222         var token string
 223         if auth := r.Header.Get("Authorization"); strings.HasPrefix(auth, "AWS ") {
 224                 split := strings.SplitN(auth[4:], ":", 2)
 225                 if len(split) < 2 {
 226                         s3ErrorResponse(w, InvalidRequest, "malformed Authorization header", r.URL.Path, http.StatusUnauthorized)
 227                         return true
 228                 }
 229                 token = unescapeKey(split[0])
 230         } else if strings.HasPrefix(auth, s3SignAlgorithm+" ") {
 231                 t, err := h.checks3signature(r)
 232                 if err != nil {
 233                         s3ErrorResponse(w, SignatureDoesNotMatch, "signature verification failed: "+err.Error(), r.URL.Path, http.StatusForbidden)
 234                         return true
 235                 }
 236                 token = t
 237         } else {
 238                 return false
 239         }
 240
 241         _, kc, client, release, err := h.getClients(r.Header.Get("X-Request-Id"), token)
 242         if err != nil {
 243                 s3ErrorResponse(w, InternalError, "Pool failed: "+h.clientPool.Err().Error(), r.URL.Path, http.StatusInternalServerError)
 244                 return true
 245         }
 246         defer release()
 247
 248         fs := client.SiteFileSystem(kc)
 249         fs.ForwardSlashNameSubstitution(h.Config.cluster.Collections.ForwardSlashNameSubstitution)
 250
 251         var objectNameGiven bool
 252         var bucketName string
 253         fspath := "/by_id"
 254         if id := parseCollectionIDFromDNSName(r.Host); id != "" {
 255                 fspath += "/" + id
 256                 bucketName = id
 257                 objectNameGiven = strings.Count(strings.TrimSuffix(r.URL.Path, "/"), "/") > 0
 258         } else {
 259                 bucketName = strings.SplitN(strings.TrimPrefix(r.URL.Path, "/"), "/", 2)[0]
 260                 objectNameGiven = strings.Count(strings.TrimSuffix(r.URL.Path, "/"), "/") > 1
 261         }
 262         fspath += r.URL.Path
 263
 264         switch {
 265         case r.Method == http.MethodGet && !objectNameGiven:
 266                 // Path is "/{uuid}" or "/{uuid}/", has no object name
 267                 if _, ok := r.URL.Query()["versioning"]; ok {
 268                         // GetBucketVersioning
 269                         w.Header().Set("Content-Type", "application/xml")
 270                         io.WriteString(w, xml.Header)
 271                         fmt.Fprintln(w, `<VersioningConfiguration xmlns="http://s3.amazonaws.com/doc/2006-03-01/"/>`)
 272                 } else {
 273                         // ListObjects
 274                         h.s3list(bucketName, w, r, fs)
 275                 }
 276                 return true
 277         case r.Method == http.MethodGet || r.Method == http.MethodHead:
 278                 fi, err := fs.Stat(fspath)
 279                 if r.Method == "HEAD" && !objectNameGiven {
 280                         // HeadBucket
 281                         if err == nil && fi.IsDir() {
 282                                 w.WriteHeader(http.StatusOK)
 283                         } else if os.IsNotExist(err) {
 284                                 s3ErrorResponse(w, NoSuchBucket, "The specified bucket does not exist.", r.URL.Path, http.StatusNotFound)
 285                         } else {
 286                                 s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusBadGateway)
 287                         }
 288                         return true
 289                 }
 290                 if err == nil && fi.IsDir() && objectNameGiven && strings.HasSuffix(fspath, "/") && h.Config.cluster.Collections.S3FolderObjects {
 291                         w.Header().Set("Content-Type", "application/x-directory")
 292                         w.WriteHeader(http.StatusOK)
 293                         return true
 294                 }
 295                 if os.IsNotExist(err) ||
 296                         (err != nil && err.Error() == "not a directory") ||
 297                         (fi != nil && fi.IsDir()) {
 298                         s3ErrorResponse(w, NoSuchKey, "The specified key does not exist.", r.URL.Path, http.StatusNotFound)
 299                         return true
 300                 }
 301                 // shallow copy r, and change URL path
 302                 r := *r
 303                 r.URL.Path = fspath
 304                 http.FileServer(fs).ServeHTTP(w, &r)
 305                 return true
 306         case r.Method == http.MethodPut:
 307                 if !objectNameGiven {
 308                         s3ErrorResponse(w, InvalidArgument, "Missing object name in PUT request.", r.URL.Path, http.StatusBadRequest)
 309                         return true
 310                 }
 311                 var objectIsDir bool
 312                 if strings.HasSuffix(fspath, "/") {
 313                         if !h.Config.cluster.Collections.S3FolderObjects {
 314                                 s3ErrorResponse(w, InvalidArgument, "invalid object name: trailing slash", r.URL.Path, http.StatusBadRequest)
 315                                 return true
 316                         }
 317                         n, err := r.Body.Read(make([]byte, 1))
 318                         if err != nil && err != io.EOF {
 319                                 s3ErrorResponse(w, InternalError, fmt.Sprintf("error reading request body: %s", err), r.URL.Path, http.StatusInternalServerError)
 320                                 return true
 321                         } else if n > 0 {
 322                                 s3ErrorResponse(w, InvalidArgument, "cannot create object with trailing '/' char unless content is empty", r.URL.Path, http.StatusBadRequest)
 323                                 return true
 324                         } else if strings.SplitN(r.Header.Get("Content-Type"), ";", 2)[0] != "application/x-directory" {
 325                                 s3ErrorResponse(w, InvalidArgument, "cannot create object with trailing '/' char unless Content-Type is 'application/x-directory'", r.URL.Path, http.StatusBadRequest)
 326                                 return true
 327                         }
 328                         // Given PUT "foo/bar/", we'll use "foo/bar/."
 329                         // in the "ensure parents exist" block below,
 330                         // and then we'll be done.
 331                         fspath += "."
 332                         objectIsDir = true
 333                 }
 334                 fi, err := fs.Stat(fspath)
 335                 if err != nil && err.Error() == "not a directory" {
 336                         // requested foo/bar, but foo is a file
 337                         s3ErrorResponse(w, InvalidArgument, "object name conflicts with existing object", r.URL.Path, http.StatusBadRequest)
 338                         return true
 339                 }
 340                 if strings.HasSuffix(r.URL.Path, "/") && err == nil && !fi.IsDir() {
 341                         // requested foo/bar/, but foo/bar is a file
 342                         s3ErrorResponse(w, InvalidArgument, "object name conflicts with existing object", r.URL.Path, http.StatusBadRequest)
 343                         return true
 344                 }
 345                 // create missing parent/intermediate directories, if any
 346                 for i, c := range fspath {
 347                         if i > 0 && c == '/' {
 348                                 dir := fspath[:i]
 349                                 if strings.HasSuffix(dir, "/") {
 350                                         err = errors.New("invalid object name (consecutive '/' chars)")
 351                                         s3ErrorResponse(w, InvalidArgument, err.Error(), r.URL.Path, http.StatusBadRequest)
 352                                         return true
 353                                 }
 354                                 err = fs.Mkdir(dir, 0755)
 355                                 if err == arvados.ErrInvalidArgument {
 356                                         // Cannot create a directory
 357                                         // here.
 358                                         err = fmt.Errorf("mkdir %q failed: %w", dir, err)
 359                                         s3ErrorResponse(w, InvalidArgument, err.Error(), r.URL.Path, http.StatusBadRequest)
 360                                         return true
 361                                 } else if err != nil && !os.IsExist(err) {
 362                                         err = fmt.Errorf("mkdir %q failed: %w", dir, err)
 363                                         s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusInternalServerError)
 364                                         return true
 365                                 }
 366                         }
 367                 }
 368                 if !objectIsDir {
 369                         f, err := fs.OpenFile(fspath, os.O_WRONLY|os.O_TRUNC|os.O_CREATE, 0644)
 370                         if os.IsNotExist(err) {
 371                                 f, err = fs.OpenFile(fspath, os.O_WRONLY|os.O_TRUNC|os.O_CREATE, 0644)
 372                         }
 373                         if err != nil {
 374                                 err = fmt.Errorf("open %q failed: %w", r.URL.Path, err)
 375                                 s3ErrorResponse(w, InvalidArgument, err.Error(), r.URL.Path, http.StatusBadRequest)
 376                                 return true
 377                         }
 378                         defer f.Close()
 379                         _, err = io.Copy(f, r.Body)
 380                         if err != nil {
 381                                 err = fmt.Errorf("write to %q failed: %w", r.URL.Path, err)
 382                                 s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusBadGateway)
 383                                 return true
 384                         }
 385                         err = f.Close()
 386                         if err != nil {
 387                                 err = fmt.Errorf("write to %q failed: close: %w", r.URL.Path, err)
 388                                 s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusBadGateway)
 389                                 return true
 390                         }
 391                 }
 392                 err = fs.Sync()
 393                 if err != nil {
 394                         err = fmt.Errorf("sync failed: %w", err)
 395                         s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusInternalServerError)
 396                         return true
 397                 }
 398                 w.WriteHeader(http.StatusOK)
 399                 return true
 400         case r.Method == http.MethodDelete:
 401                 if !objectNameGiven || r.URL.Path == "/" {
 402                         s3ErrorResponse(w, InvalidArgument, "missing object name in DELETE request", r.URL.Path, http.StatusBadRequest)
 403                         return true
 404                 }
 405                 if strings.HasSuffix(fspath, "/") {
 406                         fspath = strings.TrimSuffix(fspath, "/")
 407                         fi, err := fs.Stat(fspath)
 408                         if os.IsNotExist(err) {
 409                                 w.WriteHeader(http.StatusNoContent)
 410                                 return true
 411                         } else if err != nil {
 412                                 s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusInternalServerError)
 413                                 return true
 414                         } else if !fi.IsDir() {
 415                                 // if "foo" exists and is a file, then
 416                                 // "foo/" doesn't exist, so we say
 417                                 // delete was successful.
 418                                 w.WriteHeader(http.StatusNoContent)
 419                                 return true
 420                         }
 421                 } else if fi, err := fs.Stat(fspath); err == nil && fi.IsDir() {
 422                         // if "foo" is a dir, it is visible via S3
 423                         // only as "foo/", not "foo" -- so we leave
 424                         // the dir alone and return 204 to indicate
 425                         // that "foo" does not exist.
 426                         w.WriteHeader(http.StatusNoContent)
 427                         return true
 428                 }
 429                 err = fs.Remove(fspath)
 430                 if os.IsNotExist(err) {
 431                         w.WriteHeader(http.StatusNoContent)
 432                         return true
 433                 }
 434                 if err != nil {
 435                         err = fmt.Errorf("rm failed: %w", err)
 436                         s3ErrorResponse(w, InvalidArgument, err.Error(), r.URL.Path, http.StatusBadRequest)
 437                         return true
 438                 }
 439                 err = fs.Sync()
 440                 if err != nil {
 441                         err = fmt.Errorf("sync failed: %w", err)
 442                         s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusInternalServerError)
 443                         return true
 444                 }
 445                 w.WriteHeader(http.StatusNoContent)
 446                 return true
 447         default:
 448                 s3ErrorResponse(w, InvalidRequest, "method not allowed", r.URL.Path, http.StatusMethodNotAllowed)
 449
 450                 return true
 451         }
 452 }
 453
 454 // Call fn on the given path (directory) and its contents, in
 455 // lexicographic order.
 456 //
 457 // If isRoot==true and path is not a directory, return nil.
 458 //
 459 // If fn returns filepath.SkipDir when called on a directory, don't
 460 // descend into that directory.
 461 func walkFS(fs arvados.CustomFileSystem, path string, isRoot bool, fn func(path string, fi os.FileInfo) error) error {
 462         if isRoot {
 463                 fi, err := fs.Stat(path)
 464                 if os.IsNotExist(err) || (err == nil && !fi.IsDir()) {
 465                         return nil
 466                 } else if err != nil {
 467                         return err
 468                 }
 469                 err = fn(path, fi)
 470                 if err == filepath.SkipDir {
 471                         return nil
 472                 } else if err != nil {
 473                         return err
 474                 }
 475         }
 476         f, err := fs.Open(path)
 477         if os.IsNotExist(err) && isRoot {
 478                 return nil
 479         } else if err != nil {
 480                 return fmt.Errorf("open %q: %w", path, err)
 481         }
 482         defer f.Close()
 483         if path == "/" {
 484                 path = ""
 485         }
 486         fis, err := f.Readdir(-1)
 487         if err != nil {
 488                 return err
 489         }
 490         sort.Slice(fis, func(i, j int) bool { return fis[i].Name() < fis[j].Name() })
 491         for _, fi := range fis {
 492                 err = fn(path+"/"+fi.Name(), fi)
 493                 if err == filepath.SkipDir {
 494                         continue
 495                 } else if err != nil {
 496                         return err
 497                 }
 498                 if fi.IsDir() {
 499                         err = walkFS(fs, path+"/"+fi.Name(), false, fn)
 500                         if err != nil {
 501                                 return err
 502                         }
 503                 }
 504         }
 505         return nil
 506 }
 507
 508 var errDone = errors.New("done")
 509
 510 func (h *handler) s3list(bucket string, w http.ResponseWriter, r *http.Request, fs arvados.CustomFileSystem) {
 511         var params struct {
 512                 delimiter string
 513                 marker    string
 514                 maxKeys   int
 515                 prefix    string
 516         }
 517         params.delimiter = r.FormValue("delimiter")
 518         params.marker = r.FormValue("marker")
 519         if mk, _ := strconv.ParseInt(r.FormValue("max-keys"), 10, 64); mk > 0 && mk < s3MaxKeys {
 520                 params.maxKeys = int(mk)
 521         } else {
 522                 params.maxKeys = s3MaxKeys
 523         }
 524         params.prefix = r.FormValue("prefix")
 525
 526         bucketdir := "by_id/" + bucket
 527         // walkpath is the directory (relative to bucketdir) we need
 528         // to walk: the innermost directory that is guaranteed to
 529         // contain all paths that have the requested prefix. Examples:
 530         // prefix "foo/bar"  => walkpath "foo"
 531         // prefix "foo/bar/" => walkpath "foo/bar"
 532         // prefix "foo"      => walkpath ""
 533         // prefix ""         => walkpath ""
 534         walkpath := params.prefix
 535         if cut := strings.LastIndex(walkpath, "/"); cut >= 0 {
 536                 walkpath = walkpath[:cut]
 537         } else {
 538                 walkpath = ""
 539         }
 540
 541         type commonPrefix struct {
 542                 Prefix string
 543         }
 544         type listResp struct {
 545                 XMLName string `xml:"http://s3.amazonaws.com/doc/2006-03-01/ ListBucketResult"`
 546                 s3.ListResp
 547                 // s3.ListResp marshals an empty tag when
 548                 // CommonPrefixes is nil, which confuses some clients.
 549                 // Fix by using this nested struct instead.
 550                 CommonPrefixes []commonPrefix
 551                 // Similarly, we need omitempty here, because an empty
 552                 // tag confuses some clients (e.g.,
 553                 // github.com/aws/aws-sdk-net never terminates its
 554                 // paging loop).
 555                 NextMarker string `xml:"NextMarker,omitempty"`
 556                 // ListObjectsV2 has a KeyCount response field.
 557                 KeyCount int
 558         }
 559         resp := listResp{
 560                 ListResp: s3.ListResp{
 561                         Name:      bucket,
 562                         Prefix:    params.prefix,
 563                         Delimiter: params.delimiter,
 564                         Marker:    params.marker,
 565                         MaxKeys:   params.maxKeys,
 566                 },
 567         }
 568         commonPrefixes := map[string]bool{}
 569         err := walkFS(fs, strings.TrimSuffix(bucketdir+"/"+walkpath, "/"), true, func(path string, fi os.FileInfo) error {
 570                 if path == bucketdir {
 571                         return nil
 572                 }
 573                 path = path[len(bucketdir)+1:]
 574                 filesize := fi.Size()
 575                 if fi.IsDir() {
 576                         path += "/"
 577                         filesize = 0
 578                 }
 579                 if len(path) <= len(params.prefix) {
 580                         if path > params.prefix[:len(path)] {
 581                                 // with prefix "foobar", walking "fooz" means we're done
 582                                 return errDone
 583                         }
 584                         if path < params.prefix[:len(path)] {
 585                                 // with prefix "foobar", walking "foobag" is pointless
 586                                 return filepath.SkipDir
 587                         }
 588                         if fi.IsDir() && !strings.HasPrefix(params.prefix+"/", path) {
 589                                 // with prefix "foo/bar", walking "fo"
 590                                 // is pointless (but walking "foo" or
 591                                 // "foo/bar" is necessary)
 592                                 return filepath.SkipDir
 593                         }
 594                         if len(path) < len(params.prefix) {
 595                                 // can't skip anything, and this entry
 596                                 // isn't in the results, so just
 597                                 // continue descent
 598                                 return nil
 599                         }
 600                 } else {
 601                         if path[:len(params.prefix)] > params.prefix {
 602                                 // with prefix "foobar", nothing we
 603                                 // see after "foozzz" is relevant
 604                                 return errDone
 605                         }
 606                 }
 607                 if path < params.marker || path < params.prefix {
 608                         return nil
 609                 }
 610                 if fi.IsDir() && !h.Config.cluster.Collections.S3FolderObjects {
 611                         // Note we don't add anything to
 612                         // commonPrefixes here even if delimiter is
 613                         // "/". We descend into the directory, and
 614                         // return a commonPrefix only if we end up
 615                         // finding a regular file inside it.
 616                         return nil
 617                 }
 618                 if params.delimiter != "" {
 619                         idx := strings.Index(path[len(params.prefix):], params.delimiter)
 620                         if idx >= 0 {
 621                                 // with prefix "foobar" and delimiter
 622                                 // "z", when we hit "foobar/baz", we
 623                                 // add "/baz" to commonPrefixes and
 624                                 // stop descending.
 625                                 commonPrefixes[path[:len(params.prefix)+idx+1]] = true
 626                                 return filepath.SkipDir
 627                         }
 628                 }
 629                 if len(resp.Contents)+len(commonPrefixes) >= params.maxKeys {
 630                         resp.IsTruncated = true
 631                         if params.delimiter != "" {
 632                                 resp.NextMarker = path
 633                         }
 634                         return errDone
 635                 }
 636                 resp.Contents = append(resp.Contents, s3.Key{
 637                         Key:          path,
 638                         LastModified: fi.ModTime().UTC().Format("2006-01-02T15:04:05.999") + "Z",
 639                         Size:         filesize,
 640                 })
 641                 return nil
 642         })
 643         if err != nil && err != errDone {
 644                 http.Error(w, err.Error(), http.StatusInternalServerError)
 645                 return
 646         }
 647         if params.delimiter != "" {
 648                 resp.CommonPrefixes = make([]commonPrefix, 0, len(commonPrefixes))
 649                 for prefix := range commonPrefixes {
 650                         resp.CommonPrefixes = append(resp.CommonPrefixes, commonPrefix{prefix})
 651                 }
 652                 sort.Slice(resp.CommonPrefixes, func(i, j int) bool { return resp.CommonPrefixes[i].Prefix < resp.CommonPrefixes[j].Prefix })
 653         }
 654         resp.KeyCount = len(resp.Contents)
 655         w.Header().Set("Content-Type", "application/xml")
 656         io.WriteString(w, xml.Header)
 657         if err := xml.NewEncoder(w).Encode(resp); err != nil {
 658                 ctxlog.FromContext(r.Context()).WithError(err).Error("error writing xml response")
 659         }
 660 }