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