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         var err error
 232         var fs arvados.CustomFileSystem
 233         if r.Method == http.MethodGet || r.Method == http.MethodHead {
 234                 // Use a single session (cached FileSystem) across
 235                 // multiple read requests.
 236                 fs, err = h.Config.Cache.GetSession(token)
 237                 if err != nil {
 238                         s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusInternalServerError)
 239                         return true
 240                 }
 241         } else {
 242                 // Create a FileSystem for this request, to avoid
 243                 // exposing incomplete write operations to concurrent
 244                 // requests.
 245                 _, kc, client, release, err := h.getClients(r.Header.Get("X-Request-Id"), token)
 246                 if err != nil {
 247                         s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusInternalServerError)
 248                         return true
 249                 }
 250                 defer release()
 251                 fs = client.SiteFileSystem(kc)
 252                 fs.ForwardSlashNameSubstitution(h.Config.cluster.Collections.ForwardSlashNameSubstitution)
 253         }
 254
 255         var objectNameGiven bool
 256         var bucketName string
 257         fspath := "/by_id"
 258         if id := parseCollectionIDFromDNSName(r.Host); id != "" {
 259                 fspath += "/" + id
 260                 bucketName = id
 261                 objectNameGiven = strings.Count(strings.TrimSuffix(r.URL.Path, "/"), "/") > 0
 262         } else {
 263                 bucketName = strings.SplitN(strings.TrimPrefix(r.URL.Path, "/"), "/", 2)[0]
 264                 objectNameGiven = strings.Count(strings.TrimSuffix(r.URL.Path, "/"), "/") > 1
 265         }
 266         fspath += reMultipleSlashChars.ReplaceAllString(r.URL.Path, "/")
 267
 268         switch {
 269         case r.Method == http.MethodGet && !objectNameGiven:
 270                 // Path is "/{uuid}" or "/{uuid}/", has no object name
 271                 if _, ok := r.URL.Query()["versioning"]; ok {
 272                         // GetBucketVersioning
 273                         w.Header().Set("Content-Type", "application/xml")
 274                         io.WriteString(w, xml.Header)
 275                         fmt.Fprintln(w, `<VersioningConfiguration xmlns="http://s3.amazonaws.com/doc/2006-03-01/"/>`)
 276                 } else if _, ok = r.URL.Query()["location"]; ok {
 277                         // GetBucketLocation
 278                         w.Header().Set("Content-Type", "application/xml")
 279                         io.WriteString(w, xml.Header)
 280                         fmt.Fprintln(w, `<LocationConstraint xmlns="http://s3.amazonaws.com/doc/2006-03-01/">`+h.Config.cluster.ClusterID+`</LocationConstraint>`)
 281                 } else {
 282                         // ListObjects
 283                         h.s3list(bucketName, w, r, fs)
 284                 }
 285                 return true
 286         case r.Method == http.MethodGet || r.Method == http.MethodHead:
 287                 fi, err := fs.Stat(fspath)
 288                 if r.Method == "HEAD" && !objectNameGiven {
 289                         // HeadBucket
 290                         if err == nil && fi.IsDir() {
 291                                 w.WriteHeader(http.StatusOK)
 292                         } else if os.IsNotExist(err) {
 293                                 s3ErrorResponse(w, NoSuchBucket, "The specified bucket does not exist.", r.URL.Path, http.StatusNotFound)
 294                         } else {
 295                                 s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusBadGateway)
 296                         }
 297                         return true
 298                 }
 299                 if err == nil && fi.IsDir() && objectNameGiven && strings.HasSuffix(fspath, "/") && h.Config.cluster.Collections.S3FolderObjects {
 300                         w.Header().Set("Content-Type", "application/x-directory")
 301                         w.WriteHeader(http.StatusOK)
 302                         return true
 303                 }
 304                 if os.IsNotExist(err) ||
 305                         (err != nil && err.Error() == "not a directory") ||
 306                         (fi != nil && fi.IsDir()) {
 307                         s3ErrorResponse(w, NoSuchKey, "The specified key does not exist.", r.URL.Path, http.StatusNotFound)
 308                         return true
 309                 }
 310                 // shallow copy r, and change URL path
 311                 r := *r
 312                 r.URL.Path = fspath
 313                 http.FileServer(fs).ServeHTTP(w, &r)
 314                 return true
 315         case r.Method == http.MethodPut:
 316                 if !objectNameGiven {
 317                         s3ErrorResponse(w, InvalidArgument, "Missing object name in PUT request.", r.URL.Path, http.StatusBadRequest)
 318                         return true
 319                 }
 320                 var objectIsDir bool
 321                 if strings.HasSuffix(fspath, "/") {
 322                         if !h.Config.cluster.Collections.S3FolderObjects {
 323                                 s3ErrorResponse(w, InvalidArgument, "invalid object name: trailing slash", r.URL.Path, http.StatusBadRequest)
 324                                 return true
 325                         }
 326                         n, err := r.Body.Read(make([]byte, 1))
 327                         if err != nil && err != io.EOF {
 328                                 s3ErrorResponse(w, InternalError, fmt.Sprintf("error reading request body: %s", err), r.URL.Path, http.StatusInternalServerError)
 329                                 return true
 330                         } else if n > 0 {
 331                                 s3ErrorResponse(w, InvalidArgument, "cannot create object with trailing '/' char unless content is empty", r.URL.Path, http.StatusBadRequest)
 332                                 return true
 333                         } else if strings.SplitN(r.Header.Get("Content-Type"), ";", 2)[0] != "application/x-directory" {
 334                                 s3ErrorResponse(w, InvalidArgument, "cannot create object with trailing '/' char unless Content-Type is 'application/x-directory'", r.URL.Path, http.StatusBadRequest)
 335                                 return true
 336                         }
 337                         // Given PUT "foo/bar/", we'll use "foo/bar/."
 338                         // in the "ensure parents exist" block below,
 339                         // and then we'll be done.
 340                         fspath += "."
 341                         objectIsDir = true
 342                 }
 343                 fi, err := fs.Stat(fspath)
 344                 if err != nil && err.Error() == "not a directory" {
 345                         // requested foo/bar, but foo is a file
 346                         s3ErrorResponse(w, InvalidArgument, "object name conflicts with existing object", r.URL.Path, http.StatusBadRequest)
 347                         return true
 348                 }
 349                 if strings.HasSuffix(r.URL.Path, "/") && err == nil && !fi.IsDir() {
 350                         // requested foo/bar/, but foo/bar is a file
 351                         s3ErrorResponse(w, InvalidArgument, "object name conflicts with existing object", r.URL.Path, http.StatusBadRequest)
 352                         return true
 353                 }
 354                 // create missing parent/intermediate directories, if any
 355                 for i, c := range fspath {
 356                         if i > 0 && c == '/' {
 357                                 dir := fspath[:i]
 358                                 if strings.HasSuffix(dir, "/") {
 359                                         err = errors.New("invalid object name (consecutive '/' chars)")
 360                                         s3ErrorResponse(w, InvalidArgument, err.Error(), r.URL.Path, http.StatusBadRequest)
 361                                         return true
 362                                 }
 363                                 err = fs.Mkdir(dir, 0755)
 364                                 if err == arvados.ErrInvalidArgument {
 365                                         // Cannot create a directory
 366                                         // here.
 367                                         err = fmt.Errorf("mkdir %q failed: %w", dir, err)
 368                                         s3ErrorResponse(w, InvalidArgument, err.Error(), r.URL.Path, http.StatusBadRequest)
 369                                         return true
 370                                 } else if err != nil && !os.IsExist(err) {
 371                                         err = fmt.Errorf("mkdir %q failed: %w", dir, err)
 372                                         s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusInternalServerError)
 373                                         return true
 374                                 }
 375                         }
 376                 }
 377                 if !objectIsDir {
 378                         f, err := fs.OpenFile(fspath, os.O_WRONLY|os.O_TRUNC|os.O_CREATE, 0644)
 379                         if os.IsNotExist(err) {
 380                                 f, err = fs.OpenFile(fspath, os.O_WRONLY|os.O_TRUNC|os.O_CREATE, 0644)
 381                         }
 382                         if err != nil {
 383                                 err = fmt.Errorf("open %q failed: %w", r.URL.Path, err)
 384                                 s3ErrorResponse(w, InvalidArgument, err.Error(), r.URL.Path, http.StatusBadRequest)
 385                                 return true
 386                         }
 387                         defer f.Close()
 388                         _, err = io.Copy(f, r.Body)
 389                         if err != nil {
 390                                 err = fmt.Errorf("write to %q failed: %w", r.URL.Path, err)
 391                                 s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusBadGateway)
 392                                 return true
 393                         }
 394                         err = f.Close()
 395                         if err != nil {
 396                                 err = fmt.Errorf("write to %q failed: close: %w", r.URL.Path, err)
 397                                 s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusBadGateway)
 398                                 return true
 399                         }
 400                 }
 401                 err = fs.Sync()
 402                 if err != nil {
 403                         err = fmt.Errorf("sync failed: %w", err)
 404                         s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusInternalServerError)
 405                         return true
 406                 }
 407                 // Ensure a subsequent read operation will see the changes.
 408                 h.Config.Cache.ResetSession(token)
 409                 w.WriteHeader(http.StatusOK)
 410                 return true
 411         case r.Method == http.MethodDelete:
 412                 if !objectNameGiven || r.URL.Path == "/" {
 413                         s3ErrorResponse(w, InvalidArgument, "missing object name in DELETE request", r.URL.Path, http.StatusBadRequest)
 414                         return true
 415                 }
 416                 if strings.HasSuffix(fspath, "/") {
 417                         fspath = strings.TrimSuffix(fspath, "/")
 418                         fi, err := fs.Stat(fspath)
 419                         if os.IsNotExist(err) {
 420                                 w.WriteHeader(http.StatusNoContent)
 421                                 return true
 422                         } else if err != nil {
 423                                 s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusInternalServerError)
 424                                 return true
 425                         } else if !fi.IsDir() {
 426                                 // if "foo" exists and is a file, then
 427                                 // "foo/" doesn't exist, so we say
 428                                 // delete was successful.
 429                                 w.WriteHeader(http.StatusNoContent)
 430                                 return true
 431                         }
 432                 } else if fi, err := fs.Stat(fspath); err == nil && fi.IsDir() {
 433                         // if "foo" is a dir, it is visible via S3
 434                         // only as "foo/", not "foo" -- so we leave
 435                         // the dir alone and return 204 to indicate
 436                         // that "foo" does not exist.
 437                         w.WriteHeader(http.StatusNoContent)
 438                         return true
 439                 }
 440                 err = fs.Remove(fspath)
 441                 if os.IsNotExist(err) {
 442                         w.WriteHeader(http.StatusNoContent)
 443                         return true
 444                 }
 445                 if err != nil {
 446                         err = fmt.Errorf("rm failed: %w", err)
 447                         s3ErrorResponse(w, InvalidArgument, err.Error(), r.URL.Path, http.StatusBadRequest)
 448                         return true
 449                 }
 450                 err = fs.Sync()
 451                 if err != nil {
 452                         err = fmt.Errorf("sync failed: %w", err)
 453                         s3ErrorResponse(w, InternalError, err.Error(), r.URL.Path, http.StatusInternalServerError)
 454                         return true
 455                 }
 456                 // Ensure a subsequent read operation will see the changes.
 457                 h.Config.Cache.ResetSession(token)
 458                 w.WriteHeader(http.StatusNoContent)
 459                 return true
 460         default:
 461                 s3ErrorResponse(w, InvalidRequest, "method not allowed", r.URL.Path, http.StatusMethodNotAllowed)
 462                 return true
 463         }
 464 }
 465
 466 // Call fn on the given path (directory) and its contents, in
 467 // lexicographic order.
 468 //
 469 // If isRoot==true and path is not a directory, return nil.
 470 //
 471 // If fn returns filepath.SkipDir when called on a directory, don't
 472 // descend into that directory.
 473 func walkFS(fs arvados.CustomFileSystem, path string, isRoot bool, fn func(path string, fi os.FileInfo) error) error {
 474         if isRoot {
 475                 fi, err := fs.Stat(path)
 476                 if os.IsNotExist(err) || (err == nil && !fi.IsDir()) {
 477                         return nil
 478                 } else if err != nil {
 479                         return err
 480                 }
 481                 err = fn(path, fi)
 482                 if err == filepath.SkipDir {
 483                         return nil
 484                 } else if err != nil {
 485                         return err
 486                 }
 487         }
 488         f, err := fs.Open(path)
 489         if os.IsNotExist(err) && isRoot {
 490                 return nil
 491         } else if err != nil {
 492                 return fmt.Errorf("open %q: %w", path, err)
 493         }
 494         defer f.Close()
 495         if path == "/" {
 496                 path = ""
 497         }
 498         fis, err := f.Readdir(-1)
 499         if err != nil {
 500                 return err
 501         }
 502         sort.Slice(fis, func(i, j int) bool { return fis[i].Name() < fis[j].Name() })
 503         for _, fi := range fis {
 504                 err = fn(path+"/"+fi.Name(), fi)
 505                 if err == filepath.SkipDir {
 506                         continue
 507                 } else if err != nil {
 508                         return err
 509                 }
 510                 if fi.IsDir() {
 511                         err = walkFS(fs, path+"/"+fi.Name(), false, fn)
 512                         if err != nil {
 513                                 return err
 514                         }
 515                 }
 516         }
 517         return nil
 518 }
 519
 520 var errDone = errors.New("done")
 521
 522 func (h *handler) s3list(bucket string, w http.ResponseWriter, r *http.Request, fs arvados.CustomFileSystem) {
 523         var params struct {
 524                 delimiter string
 525                 marker    string
 526                 maxKeys   int
 527                 prefix    string
 528         }
 529         params.delimiter = r.FormValue("delimiter")
 530         params.marker = r.FormValue("marker")
 531         if mk, _ := strconv.ParseInt(r.FormValue("max-keys"), 10, 64); mk > 0 && mk < s3MaxKeys {
 532                 params.maxKeys = int(mk)
 533         } else {
 534                 params.maxKeys = s3MaxKeys
 535         }
 536         params.prefix = r.FormValue("prefix")
 537
 538         bucketdir := "by_id/" + bucket
 539         // walkpath is the directory (relative to bucketdir) we need
 540         // to walk: the innermost directory that is guaranteed to
 541         // contain all paths that have the requested prefix. Examples:
 542         // prefix "foo/bar"  => walkpath "foo"
 543         // prefix "foo/bar/" => walkpath "foo/bar"
 544         // prefix "foo"      => walkpath ""
 545         // prefix ""         => walkpath ""
 546         walkpath := params.prefix
 547         if cut := strings.LastIndex(walkpath, "/"); cut >= 0 {
 548                 walkpath = walkpath[:cut]
 549         } else {
 550                 walkpath = ""
 551         }
 552
 553         type commonPrefix struct {
 554                 Prefix string
 555         }
 556         type listResp struct {
 557                 XMLName string `xml:"http://s3.amazonaws.com/doc/2006-03-01/ ListBucketResult"`
 558                 s3.ListResp
 559                 // s3.ListResp marshals an empty tag when
 560                 // CommonPrefixes is nil, which confuses some clients.
 561                 // Fix by using this nested struct instead.
 562                 CommonPrefixes []commonPrefix
 563                 // Similarly, we need omitempty here, because an empty
 564                 // tag confuses some clients (e.g.,
 565                 // github.com/aws/aws-sdk-net never terminates its
 566                 // paging loop).
 567                 NextMarker string `xml:"NextMarker,omitempty"`
 568                 // ListObjectsV2 has a KeyCount response field.
 569                 KeyCount int
 570         }
 571         resp := listResp{
 572                 ListResp: s3.ListResp{
 573                         Name:      bucket,
 574                         Prefix:    params.prefix,
 575                         Delimiter: params.delimiter,
 576                         Marker:    params.marker,
 577                         MaxKeys:   params.maxKeys,
 578                 },
 579         }
 580         commonPrefixes := map[string]bool{}
 581         err := walkFS(fs, strings.TrimSuffix(bucketdir+"/"+walkpath, "/"), true, func(path string, fi os.FileInfo) error {
 582                 if path == bucketdir {
 583                         return nil
 584                 }
 585                 path = path[len(bucketdir)+1:]
 586                 filesize := fi.Size()
 587                 if fi.IsDir() {
 588                         path += "/"
 589                         filesize = 0
 590                 }
 591                 if len(path) <= len(params.prefix) {
 592                         if path > params.prefix[:len(path)] {
 593                                 // with prefix "foobar", walking "fooz" means we're done
 594                                 return errDone
 595                         }
 596                         if path < params.prefix[:len(path)] {
 597                                 // with prefix "foobar", walking "foobag" is pointless
 598                                 return filepath.SkipDir
 599                         }
 600                         if fi.IsDir() && !strings.HasPrefix(params.prefix+"/", path) {
 601                                 // with prefix "foo/bar", walking "fo"
 602                                 // is pointless (but walking "foo" or
 603                                 // "foo/bar" is necessary)
 604                                 return filepath.SkipDir
 605                         }
 606                         if len(path) < len(params.prefix) {
 607                                 // can't skip anything, and this entry
 608                                 // isn't in the results, so just
 609                                 // continue descent
 610                                 return nil
 611                         }
 612                 } else {
 613                         if path[:len(params.prefix)] > params.prefix {
 614                                 // with prefix "foobar", nothing we
 615                                 // see after "foozzz" is relevant
 616                                 return errDone
 617                         }
 618                 }
 619                 if path < params.marker || path < params.prefix {
 620                         return nil
 621                 }
 622                 if fi.IsDir() && !h.Config.cluster.Collections.S3FolderObjects {
 623                         // Note we don't add anything to
 624                         // commonPrefixes here even if delimiter is
 625                         // "/". We descend into the directory, and
 626                         // return a commonPrefix only if we end up
 627                         // finding a regular file inside it.
 628                         return nil
 629                 }
 630                 if params.delimiter != "" {
 631                         idx := strings.Index(path[len(params.prefix):], params.delimiter)
 632                         if idx >= 0 {
 633                                 // with prefix "foobar" and delimiter
 634                                 // "z", when we hit "foobar/baz", we
 635                                 // add "/baz" to commonPrefixes and
 636                                 // stop descending.
 637                                 commonPrefixes[path[:len(params.prefix)+idx+1]] = true
 638                                 return filepath.SkipDir
 639                         }
 640                 }
 641                 if len(resp.Contents)+len(commonPrefixes) >= params.maxKeys {
 642                         resp.IsTruncated = true
 643                         if params.delimiter != "" {
 644                                 resp.NextMarker = path
 645                         }
 646                         return errDone
 647                 }
 648                 resp.Contents = append(resp.Contents, s3.Key{
 649                         Key:          path,
 650                         LastModified: fi.ModTime().UTC().Format("2006-01-02T15:04:05.999") + "Z",
 651                         Size:         filesize,
 652                 })
 653                 return nil
 654         })
 655         if err != nil && err != errDone {
 656                 http.Error(w, err.Error(), http.StatusInternalServerError)
 657                 return
 658         }
 659         if params.delimiter != "" {
 660                 resp.CommonPrefixes = make([]commonPrefix, 0, len(commonPrefixes))
 661                 for prefix := range commonPrefixes {
 662                         resp.CommonPrefixes = append(resp.CommonPrefixes, commonPrefix{prefix})
 663                 }
 664                 sort.Slice(resp.CommonPrefixes, func(i, j int) bool { return resp.CommonPrefixes[i].Prefix < resp.CommonPrefixes[j].Prefix })
 665         }
 666         resp.KeyCount = len(resp.Contents)
 667         w.Header().Set("Content-Type", "application/xml")
 668         io.WriteString(w, xml.Header)
 669         if err := xml.NewEncoder(w).Encode(resp); err != nil {
 670                 ctxlog.FromContext(r.Context()).WithError(err).Error("error writing xml response")
 671         }
 672 }