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 var reMultipleSlashChars = regexp.MustCompile(`//+`)
  79
  80 func s3stringToSign(alg, scope, signedHeaders string, r *http.Request) (string, error) {
  81         timefmt, timestr := "20060102T150405Z", r.Header.Get("X-Amz-Date")
  82         if timestr == "" {
  83                 timefmt, timestr = time.RFC1123, r.Header.Get("Date")
  84         }
  85         t, err := time.Parse(timefmt, timestr)
  86         if err != nil {
  87                 return "", fmt.Errorf("invalid timestamp %q: %s", timestr, err)
  88         }
  89         if skew := time.Now().Sub(t); skew < -s3MaxClockSkew || skew > s3MaxClockSkew {
  90                 return "", errors.New("exceeded max clock skew")
  91         }
  92
  93         var canonicalHeaders string
  94         for _, h := range strings.Split(signedHeaders, ";") {
  95                 if h == "host" {
  96                         canonicalHeaders += h + ":" + r.Host + "\n"
  97                 } else {
  98                         canonicalHeaders += h + ":" + r.Header.Get(h) + "\n"
  99                 }
 100         }
 101
 102         normalizedURL := *r.URL
 103         normalizedURL.RawPath = ""
 104         normalizedURL.Path = reMultipleSlashChars.ReplaceAllString(normalizedURL.Path, "/")
 105         canonicalRequest := fmt.Sprintf("%s\n%s\n%s\n%s\n%s\n%s", r.Method, normalizedURL.EscapedPath(), s3querystring(r.URL), canonicalHeaders, signedHeaders, r.Header.Get("X-Amz-Content-Sha256"))
 106         ctxlog.FromContext(r.Context()).Debugf("s3stringToSign: canonicalRequest %s", canonicalRequest)
 107         return fmt.Sprintf("%s\n%s\n%s\n%s", alg, r.Header.Get("X-Amz-Date"), scope, hashdigest(sha256.New(), canonicalRequest)), nil
 108 }
 109
 110 func s3signature(secretKey, scope, signedHeaders, stringToSign string) (string, error) {
 111         // scope is {datestamp}/{region}/{service}/aws4_request
 112         drs := strings.Split(scope, "/")
 113         if len(drs) != 4 {
 114                 return "", fmt.Errorf("invalid scope %q", scope)
 115         }
 116         key := s3signatureKey(secretKey, drs[0], drs[1], drs[2])
 117         return hashdigest(hmac.New(sha256.New, key), stringToSign), nil
 118 }
 119
 120 var v2tokenUnderscore = regexp.MustCompile(`^v2_[a-z0-9]{5}-gj3su-[a-z0-9]{15}_`)
 121
 122 func unescapeKey(key string) string {
 123         if v2tokenUnderscore.MatchString(key) {
 124                 // Entire Arvados token, with "/" replaced by "_" to
 125                 // avoid colliding with the Authorization header
 126                 // format.
 127                 return strings.Replace(key, "_", "/", -1)
 128         } else if s, err := url.PathUnescape(key); err == nil {
 129                 return s
 130         } else {
 131                 return key
 132         }
 133 }
 134
 135 // checks3signature verifies the given S3 V4 signature and returns the
 136 // Arvados token that corresponds to the given accessKey. An error is
 137 // returned if accessKey is not a valid token UUID or the signature
 138 // does not match.
 139 func (h *handler) checks3signature(r *http.Request) (string, error) {
 140         var key, scope, signedHeaders, signature string
 141         authstring := strings.TrimPrefix(r.Header.Get("Authorization"), s3SignAlgorithm+" ")
 142         for _, cmpt := range strings.Split(authstring, ",") {
 143                 cmpt = strings.TrimSpace(cmpt)
 144                 split := strings.SplitN(cmpt, "=", 2)
 145                 switch {
 146                 case len(split) != 2:
 147                         // (?) ignore
 148                 case split[0] == "Credential":
 149                         keyandscope := strings.SplitN(split[1], "/", 2)
 150                         if len(keyandscope) == 2 {
 151                                 key, scope = keyandscope[0], keyandscope[1]
 152                         }
 153                 case split[0] == "SignedHeaders":
 154                         signedHeaders = split[1]
 155                 case split[0] == "Signature":
 156                         signature = split[1]
 157                 }
 158         }
 159
 160         client := (&arvados.Client{
 161                 APIHost:  h.Config.cluster.Services.Controller.ExternalURL.Host,
 162                 Insecure: h.Config.cluster.TLS.Insecure,
 163         }).WithRequestID(r.Header.Get("X-Request-Id"))
 164         var aca arvados.APIClientAuthorization
 165         var secret string
 166         var err error
 167         if len(key) == 27 && key[5:12] == "-gj3su-" {
 168                 // Access key is the UUID of an Arvados token, secret
 169                 // key is the secret part.
 170                 ctx := arvados.ContextWithAuthorization(r.Context(), "Bearer "+h.Config.cluster.SystemRootToken)
 171                 err = client.RequestAndDecodeContext(ctx, &aca, "GET", "arvados/v1/api_client_authorizations/"+key, nil, nil)
 172                 secret = aca.APIToken
 173         } else {
 174                 // Access key and secret key are both an entire
 175                 // Arvados token or OIDC access token.
 176                 ctx := arvados.ContextWithAuthorization(r.Context(), "Bearer "+unescapeKey(key))
 177                 err = client.RequestAndDecodeContext(ctx, &aca, "GET", "arvados/v1/api_client_authorizations/current", nil, nil)
 178                 secret = key
 179         }
 180         if err != nil {
 181                 ctxlog.FromContext(r.Context()).WithError(err).WithField("UUID", key).Info("token lookup failed")
 182                 return "", errors.New("invalid access key")
 183         }
 184         stringToSign, err := s3stringToSign(s3SignAlgorithm, scope, signedHeaders, r)
 185         if err != nil {
 186                 return "", err
 187         }
 188         expect, err := s3signature(secret, scope, signedHeaders, stringToSign)
 189         if err != nil {
 190                 return "", err
 191         } else if expect != signature {
 192                 return "", fmt.Errorf("signature does not match (scope %q signedHeaders %q stringToSign %q)", scope, signedHeaders, stringToSign)
 193         }
 194         return aca.TokenV2(), nil
 195 }
 196
 197 func s3ErrorResponse(w http.ResponseWriter, s3code string, message string, resource string, code int) {
 198         w.Header().Set("Content-Type", "application/xml")
 199         w.Header().Set("X-Content-Type-Options", "nosniff")
 200         w.WriteHeader(code)
 201         var errstruct struct {
 202                 Code      string
 203                 Message   string
 204                 Resource  string
 205                 RequestId string
 206         }
 207         errstruct.Code = s3code
 208         errstruct.Message = message
 209         errstruct.Resource = resource
 210         errstruct.RequestId = ""
 211         enc := xml.NewEncoder(w)
 212         fmt.Fprint(w, xml.Header)
 213         enc.EncodeElement(errstruct, xml.StartElement{Name: xml.Name{Local: "Error"}})
 214 }
 215
 216 var NoSuchKey = "NoSuchKey"
 217 var NoSuchBucket = "NoSuchBucket"
 218 var InvalidArgument = "InvalidArgument"
 219 var InternalError = "InternalError"
 220 var UnauthorizedAccess = "UnauthorizedAccess"
 221 var InvalidRequest = "InvalidRequest"
 222 var SignatureDoesNotMatch = "SignatureDoesNotMatch"
 223
 224 // serveS3 handles r and returns true if r is a request from an S3
 225 // client, otherwise it returns false.
 226 func (h *handler) serveS3(w http.ResponseWriter, r *http.Request) bool {
 227         var token string
 228         if auth := r.Header.Get("Authorization"); strings.HasPrefix(auth, "AWS ") {
 229                 split := strings.SplitN(auth[4:], ":", 2)
 230                 if len(split) < 2 {
 231                         s3ErrorResponse(w, InvalidRequest, "malformed Authorization header", r.URL.Path, http.StatusUnauthorized)
 232                         return true
 233                 }
 234                 token = unescapeKey(split[0])
 235         } else if strings.HasPrefix(auth, s3SignAlgorithm+" ") {
 236                 t, err := h.checks3signature(r)
 237                 if err != nil {
 238                         s3ErrorResponse(w, SignatureDoesNotMatch, "signature verification failed: "+err.Error(), r.URL.Path, http.StatusForbidden)
 239                         return true
 240                 }
 241                 token = t
 242         } else {
 243                 return false
 244         }
 245
 246         _, kc, client, release, err := h.getClients(r.Header.Get("X-Request-Id"), token)
 247         if err != nil {
 248                 s3ErrorResponse(w, InternalError, "Pool failed: "+h.clientPool.Err().Error(), r.URL.Path, http.StatusInternalServerError)
 249                 return true
 250         }
 251         defer release()
 252
 253         fs := client.SiteFileSystem(kc)
 254         fs.ForwardSlashNameSubstitution(h.Config.cluster.Collections.ForwardSlashNameSubstitution)
 255
 256         var objectNameGiven bool
 257         var bucketName string
 258         fspath := "/by_id"
 259         if id := parseCollectionIDFromDNSName(r.Host); id != "" {
 260                 fspath += "/" + id
 261                 bucketName = id
 262                 objectNameGiven = strings.Count(strings.TrimSuffix(r.URL.Path, "/"), "/") > 0
 263         } else {
 264                 bucketName = strings.SplitN(strings.TrimPrefix(r.URL.Path, "/"), "/", 2)[0]
 265                 objectNameGiven = strings.Count(strings.TrimSuffix(r.URL.Path, "/"), "/") > 1
 266         }
 267         fspath += reMultipleSlashChars.ReplaceAllString(r.URL.Path, "/")
 268
 269         switch {
 270         case r.Method == http.MethodGet && !objectNameGiven:
 271                 // Path is "/{uuid}" or "/{uuid}/", has no object name
 272                 if _, ok := r.URL.Query()["versioning"]; ok {
 273                         // GetBucketVersioning
 274                         w.Header().Set("Content-Type", "application/xml")
 275                         io.WriteString(w, xml.Header)
 276                         fmt.Fprintln(w, `<VersioningConfiguration xmlns="http://s3.amazonaws.com/doc/2006-03-01/"/>`)
 277                 } else {
 278                         // ListObjects
 279                         h.s3list(bucketName, w, r, fs)
 280                 }
 281                 return true
 282         case r.Method == http.MethodGet || r.Method == http.MethodHead:
 283                 fi, err := fs.Stat(fspath)
 284                 if r.Method == "HEAD" && !objectNameGiven {
 285                         // HeadBucket
 286                         if err == nil && fi.IsDir() {
 287                                 w.WriteHeader(http.StatusOK)
 288                         } else if os.IsNotExist(err) {
 289                                 s3ErrorResponse(w, NoSuchBucket, "The specified bucket does not exist.", r.URL.Path, http.StatusNotFound)
 290                         } else {
 291                                 s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusBadGateway)
 292                         }
 293                         return true
 294                 }
 295                 if err == nil && fi.IsDir() && objectNameGiven && strings.HasSuffix(fspath, "/") && h.Config.cluster.Collections.S3FolderObjects {
 296                         w.Header().Set("Content-Type", "application/x-directory")
 297                         w.WriteHeader(http.StatusOK)
 298                         return true
 299                 }
 300                 if os.IsNotExist(err) ||
 301                         (err != nil && err.Error() == "not a directory") ||
 302                         (fi != nil && fi.IsDir()) {
 303                         s3ErrorResponse(w, NoSuchKey, "The specified key does not exist.", r.URL.Path, http.StatusNotFound)
 304                         return true
 305                 }
 306                 // shallow copy r, and change URL path
 307                 r := *r
 308                 r.URL.Path = fspath
 309                 http.FileServer(fs).ServeHTTP(w, &r)
 310                 return true
 311         case r.Method == http.MethodPut:
 312                 if !objectNameGiven {
 313                         s3ErrorResponse(w, InvalidArgument, "Missing object name in PUT request.", r.URL.Path, http.StatusBadRequest)
 314                         return true
 315                 }
 316                 var objectIsDir bool
 317                 if strings.HasSuffix(fspath, "/") {
 318                         if !h.Config.cluster.Collections.S3FolderObjects {
 319                                 s3ErrorResponse(w, InvalidArgument, "invalid object name: trailing slash", r.URL.Path, http.StatusBadRequest)
 320                                 return true
 321                         }
 322                         n, err := r.Body.Read(make([]byte, 1))
 323                         if err != nil && err != io.EOF {
 324                                 s3ErrorResponse(w, InternalError, fmt.Sprintf("error reading request body: %s", err), r.URL.Path, http.StatusInternalServerError)
 325                                 return true
 326                         } else if n > 0 {
 327                                 s3ErrorResponse(w, InvalidArgument, "cannot create object with trailing '/' char unless content is empty", r.URL.Path, http.StatusBadRequest)
 328                                 return true
 329                         } else if strings.SplitN(r.Header.Get("Content-Type"), ";", 2)[0] != "application/x-directory" {
 330                                 s3ErrorResponse(w, InvalidArgument, "cannot create object with trailing '/' char unless Content-Type is 'application/x-directory'", r.URL.Path, http.StatusBadRequest)
 331                                 return true
 332                         }
 333                         // Given PUT "foo/bar/", we'll use "foo/bar/."
 334                         // in the "ensure parents exist" block below,
 335                         // and then we'll be done.
 336                         fspath += "."
 337                         objectIsDir = true
 338                 }
 339                 fi, err := fs.Stat(fspath)
 340                 if err != nil && err.Error() == "not a directory" {
 341                         // requested foo/bar, but foo is a file
 342                         s3ErrorResponse(w, InvalidArgument, "object name conflicts with existing object", r.URL.Path, http.StatusBadRequest)
 343                         return true
 344                 }
 345                 if strings.HasSuffix(r.URL.Path, "/") && err == nil && !fi.IsDir() {
 346                         // requested foo/bar/, but foo/bar is a file
 347                         s3ErrorResponse(w, InvalidArgument, "object name conflicts with existing object", r.URL.Path, http.StatusBadRequest)
 348                         return true
 349                 }
 350                 // create missing parent/intermediate directories, if any
 351                 for i, c := range fspath {
 352                         if i > 0 && c == '/' {
 353                                 dir := fspath[:i]
 354                                 if strings.HasSuffix(dir, "/") {
 355                                         err = errors.New("invalid object name (consecutive '/' chars)")
 356                                         s3ErrorResponse(w, InvalidArgument, err.Error(), r.URL.Path, http.StatusBadRequest)
 357                                         return true
 358                                 }
 359                                 err = fs.Mkdir(dir, 0755)
 360                                 if err == arvados.ErrInvalidArgument {
 361                                         // Cannot create a directory
 362                                         // here.
 363                                         err = fmt.Errorf("mkdir %q failed: %w", dir, err)
 364                                         s3ErrorResponse(w, InvalidArgument, err.Error(), r.URL.Path, http.StatusBadRequest)
 365                                         return true
 366                                 } else if err != nil && !os.IsExist(err) {
 367                                         err = fmt.Errorf("mkdir %q failed: %w", dir, err)
 368                                         s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusInternalServerError)
 369                                         return true
 370                                 }
 371                         }
 372                 }
 373                 if !objectIsDir {
 374                         f, err := fs.OpenFile(fspath, os.O_WRONLY|os.O_TRUNC|os.O_CREATE, 0644)
 375                         if os.IsNotExist(err) {
 376                                 f, err = fs.OpenFile(fspath, os.O_WRONLY|os.O_TRUNC|os.O_CREATE, 0644)
 377                         }
 378                         if err != nil {
 379                                 err = fmt.Errorf("open %q failed: %w", r.URL.Path, err)
 380                                 s3ErrorResponse(w, InvalidArgument, err.Error(), r.URL.Path, http.StatusBadRequest)
 381                                 return true
 382                         }
 383                         defer f.Close()
 384                         _, err = io.Copy(f, r.Body)
 385                         if err != nil {
 386                                 err = fmt.Errorf("write to %q failed: %w", r.URL.Path, err)
 387                                 s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusBadGateway)
 388                                 return true
 389                         }
 390                         err = f.Close()
 391                         if err != nil {
 392                                 err = fmt.Errorf("write to %q failed: close: %w", r.URL.Path, err)
 393                                 s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusBadGateway)
 394                                 return true
 395                         }
 396                 }
 397                 err = fs.Sync()
 398                 if err != nil {
 399                         err = fmt.Errorf("sync failed: %w", err)
 400                         s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusInternalServerError)
 401                         return true
 402                 }
 403                 w.WriteHeader(http.StatusOK)
 404                 return true
 405         case r.Method == http.MethodDelete:
 406                 if !objectNameGiven || r.URL.Path == "/" {
 407                         s3ErrorResponse(w, InvalidArgument, "missing object name in DELETE request", r.URL.Path, http.StatusBadRequest)
 408                         return true
 409                 }
 410                 if strings.HasSuffix(fspath, "/") {
 411                         fspath = strings.TrimSuffix(fspath, "/")
 412                         fi, err := fs.Stat(fspath)
 413                         if os.IsNotExist(err) {
 414                                 w.WriteHeader(http.StatusNoContent)
 415                                 return true
 416                         } else if err != nil {
 417                                 s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusInternalServerError)
 418                                 return true
 419                         } else if !fi.IsDir() {
 420                                 // if "foo" exists and is a file, then
 421                                 // "foo/" doesn't exist, so we say
 422                                 // delete was successful.
 423                                 w.WriteHeader(http.StatusNoContent)
 424                                 return true
 425                         }
 426                 } else if fi, err := fs.Stat(fspath); err == nil && fi.IsDir() {
 427                         // if "foo" is a dir, it is visible via S3
 428                         // only as "foo/", not "foo" -- so we leave
 429                         // the dir alone and return 204 to indicate
 430                         // that "foo" does not exist.
 431                         w.WriteHeader(http.StatusNoContent)
 432                         return true
 433                 }
 434                 err = fs.Remove(fspath)
 435                 if os.IsNotExist(err) {
 436                         w.WriteHeader(http.StatusNoContent)
 437                         return true
 438                 }
 439                 if err != nil {
 440                         err = fmt.Errorf("rm failed: %w", err)
 441                         s3ErrorResponse(w, InvalidArgument, err.Error(), r.URL.Path, http.StatusBadRequest)
 442                         return true
 443                 }
 444                 err = fs.Sync()
 445                 if err != nil {
 446                         err = fmt.Errorf("sync failed: %w", err)
 447                         s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusInternalServerError)
 448                         return true
 449                 }
 450                 w.WriteHeader(http.StatusNoContent)
 451                 return true
 452         default:
 453                 s3ErrorResponse(w, InvalidRequest, "method not allowed", r.URL.Path, http.StatusMethodNotAllowed)
 454
 455                 return true
 456         }
 457 }
 458
 459 // Call fn on the given path (directory) and its contents, in
 460 // lexicographic order.
 461 //
 462 // If isRoot==true and path is not a directory, return nil.
 463 //
 464 // If fn returns filepath.SkipDir when called on a directory, don't
 465 // descend into that directory.
 466 func walkFS(fs arvados.CustomFileSystem, path string, isRoot bool, fn func(path string, fi os.FileInfo) error) error {
 467         if isRoot {
 468                 fi, err := fs.Stat(path)
 469                 if os.IsNotExist(err) || (err == nil && !fi.IsDir()) {
 470                         return nil
 471                 } else if err != nil {
 472                         return err
 473                 }
 474                 err = fn(path, fi)
 475                 if err == filepath.SkipDir {
 476                         return nil
 477                 } else if err != nil {
 478                         return err
 479                 }
 480         }
 481         f, err := fs.Open(path)
 482         if os.IsNotExist(err) && isRoot {
 483                 return nil
 484         } else if err != nil {
 485                 return fmt.Errorf("open %q: %w", path, err)
 486         }
 487         defer f.Close()
 488         if path == "/" {
 489                 path = ""
 490         }
 491         fis, err := f.Readdir(-1)
 492         if err != nil {
 493                 return err
 494         }
 495         sort.Slice(fis, func(i, j int) bool { return fis[i].Name() < fis[j].Name() })
 496         for _, fi := range fis {
 497                 err = fn(path+"/"+fi.Name(), fi)
 498                 if err == filepath.SkipDir {
 499                         continue
 500                 } else if err != nil {
 501                         return err
 502                 }
 503                 if fi.IsDir() {
 504                         err = walkFS(fs, path+"/"+fi.Name(), false, fn)
 505                         if err != nil {
 506                                 return err
 507                         }
 508                 }
 509         }
 510         return nil
 511 }
 512
 513 var errDone = errors.New("done")
 514
 515 func (h *handler) s3list(bucket string, w http.ResponseWriter, r *http.Request, fs arvados.CustomFileSystem) {
 516         var params struct {
 517                 delimiter string
 518                 marker    string
 519                 maxKeys   int
 520                 prefix    string
 521         }
 522         params.delimiter = r.FormValue("delimiter")
 523         params.marker = r.FormValue("marker")
 524         if mk, _ := strconv.ParseInt(r.FormValue("max-keys"), 10, 64); mk > 0 && mk < s3MaxKeys {
 525                 params.maxKeys = int(mk)
 526         } else {
 527                 params.maxKeys = s3MaxKeys
 528         }
 529         params.prefix = r.FormValue("prefix")
 530
 531         bucketdir := "by_id/" + bucket
 532         // walkpath is the directory (relative to bucketdir) we need
 533         // to walk: the innermost directory that is guaranteed to
 534         // contain all paths that have the requested prefix. Examples:
 535         // prefix "foo/bar"  => walkpath "foo"
 536         // prefix "foo/bar/" => walkpath "foo/bar"
 537         // prefix "foo"      => walkpath ""
 538         // prefix ""         => walkpath ""
 539         walkpath := params.prefix
 540         if cut := strings.LastIndex(walkpath, "/"); cut >= 0 {
 541                 walkpath = walkpath[:cut]
 542         } else {
 543                 walkpath = ""
 544         }
 545
 546         type commonPrefix struct {
 547                 Prefix string
 548         }
 549         type listResp struct {
 550                 XMLName string `xml:"http://s3.amazonaws.com/doc/2006-03-01/ ListBucketResult"`
 551                 s3.ListResp
 552                 // s3.ListResp marshals an empty tag when
 553                 // CommonPrefixes is nil, which confuses some clients.
 554                 // Fix by using this nested struct instead.
 555                 CommonPrefixes []commonPrefix
 556                 // Similarly, we need omitempty here, because an empty
 557                 // tag confuses some clients (e.g.,
 558                 // github.com/aws/aws-sdk-net never terminates its
 559                 // paging loop).
 560                 NextMarker string `xml:"NextMarker,omitempty"`
 561                 // ListObjectsV2 has a KeyCount response field.
 562                 KeyCount int
 563         }
 564         resp := listResp{
 565                 ListResp: s3.ListResp{
 566                         Name:      bucket,
 567                         Prefix:    params.prefix,
 568                         Delimiter: params.delimiter,
 569                         Marker:    params.marker,
 570                         MaxKeys:   params.maxKeys,
 571                 },
 572         }
 573         commonPrefixes := map[string]bool{}
 574         err := walkFS(fs, strings.TrimSuffix(bucketdir+"/"+walkpath, "/"), true, func(path string, fi os.FileInfo) error {
 575                 if path == bucketdir {
 576                         return nil
 577                 }
 578                 path = path[len(bucketdir)+1:]
 579                 filesize := fi.Size()
 580                 if fi.IsDir() {
 581                         path += "/"
 582                         filesize = 0
 583                 }
 584                 if len(path) <= len(params.prefix) {
 585                         if path > params.prefix[:len(path)] {
 586                                 // with prefix "foobar", walking "fooz" means we're done
 587                                 return errDone
 588                         }
 589                         if path < params.prefix[:len(path)] {
 590                                 // with prefix "foobar", walking "foobag" is pointless
 591                                 return filepath.SkipDir
 592                         }
 593                         if fi.IsDir() && !strings.HasPrefix(params.prefix+"/", path) {
 594                                 // with prefix "foo/bar", walking "fo"
 595                                 // is pointless (but walking "foo" or
 596                                 // "foo/bar" is necessary)
 597                                 return filepath.SkipDir
 598                         }
 599                         if len(path) < len(params.prefix) {
 600                                 // can't skip anything, and this entry
 601                                 // isn't in the results, so just
 602                                 // continue descent
 603                                 return nil
 604                         }
 605                 } else {
 606                         if path[:len(params.prefix)] > params.prefix {
 607                                 // with prefix "foobar", nothing we
 608                                 // see after "foozzz" is relevant
 609                                 return errDone
 610                         }
 611                 }
 612                 if path < params.marker || path < params.prefix {
 613                         return nil
 614                 }
 615                 if fi.IsDir() && !h.Config.cluster.Collections.S3FolderObjects {
 616                         // Note we don't add anything to
 617                         // commonPrefixes here even if delimiter is
 618                         // "/". We descend into the directory, and
 619                         // return a commonPrefix only if we end up
 620                         // finding a regular file inside it.
 621                         return nil
 622                 }
 623                 if params.delimiter != "" {
 624                         idx := strings.Index(path[len(params.prefix):], params.delimiter)
 625                         if idx >= 0 {
 626                                 // with prefix "foobar" and delimiter
 627                                 // "z", when we hit "foobar/baz", we
 628                                 // add "/baz" to commonPrefixes and
 629                                 // stop descending.
 630                                 commonPrefixes[path[:len(params.prefix)+idx+1]] = true
 631                                 return filepath.SkipDir
 632                         }
 633                 }
 634                 if len(resp.Contents)+len(commonPrefixes) >= params.maxKeys {
 635                         resp.IsTruncated = true
 636                         if params.delimiter != "" {
 637                                 resp.NextMarker = path
 638                         }
 639                         return errDone
 640                 }
 641                 resp.Contents = append(resp.Contents, s3.Key{
 642                         Key:          path,
 643                         LastModified: fi.ModTime().UTC().Format("2006-01-02T15:04:05.999") + "Z",
 644                         Size:         filesize,
 645                 })
 646                 return nil
 647         })
 648         if err != nil && err != errDone {
 649                 http.Error(w, err.Error(), http.StatusInternalServerError)
 650                 return
 651         }
 652         if params.delimiter != "" {
 653                 resp.CommonPrefixes = make([]commonPrefix, 0, len(commonPrefixes))
 654                 for prefix := range commonPrefixes {
 655                         resp.CommonPrefixes = append(resp.CommonPrefixes, commonPrefix{prefix})
 656                 }
 657                 sort.Slice(resp.CommonPrefixes, func(i, j int) bool { return resp.CommonPrefixes[i].Prefix < resp.CommonPrefixes[j].Prefix })
 658         }
 659         resp.KeyCount = len(resp.Contents)
 660         w.Header().Set("Content-Type", "application/xml")
 661         io.WriteString(w, xml.Header)
 662         if err := xml.NewEncoder(w).Encode(resp); err != nil {
 663                 ctxlog.FromContext(r.Context()).WithError(err).Error("error writing xml response")
 664         }
 665 }