git.r.bdr.sh - rbdr/mobius/blob - hotline/server.go

   1 package hotline
   2
   3 import (
   4         "bufio"
   5         "bytes"
   6         "context"
   7         "encoding/binary"
   8         "errors"
   9         "fmt"
  10         "github.com/go-playground/validator/v10"
  11         "go.uber.org/zap"
  12         "gopkg.in/yaml.v3"
  13         "io"
  14         "io/fs"
  15         "io/ioutil"
  16         "math/big"
  17         "math/rand"
  18         "net"
  19         "os"
  20         "path/filepath"
  21         "runtime/debug"
  22         "strings"
  23         "sync"
  24         "time"
  25 )
  26
  27 type contextKey string
  28
  29 var contextKeyReq = contextKey("req")
  30
  31 type requestCtx struct {
  32         remoteAddr string
  33         login      string
  34         name       string
  35 }
  36
  37 const (
  38         userIdleSeconds        = 300 // time in seconds before an inactive user is marked idle
  39         idleCheckInterval      = 10  // time in seconds to check for idle users
  40         trackerUpdateFrequency = 300 // time in seconds between tracker re-registration
  41 )
  42
  43 var nostalgiaVersion = []byte{0, 0, 2, 0x2c} // version ID used by the Nostalgia client
  44
  45 type Server struct {
  46         Port         int
  47         Accounts     map[string]*Account
  48         Agreement    []byte
  49         Clients      map[uint16]*ClientConn
  50         ThreadedNews *ThreadedNews
  51
  52         fileTransfers map[[4]byte]*FileTransfer
  53
  54         Config        *Config
  55         ConfigDir     string
  56         Logger        *zap.SugaredLogger
  57         PrivateChats  map[uint32]*PrivateChat
  58         NextGuestID   *uint16
  59         TrackerPassID [4]byte
  60         Stats         *Stats
  61
  62         FS FileStore // Storage backend to use for File storage
  63
  64         outbox chan Transaction
  65         mux    sync.Mutex
  66
  67         flatNewsMux sync.Mutex
  68         FlatNews    []byte
  69 }
  70
  71 type PrivateChat struct {
  72         Subject    string
  73         ClientConn map[uint16]*ClientConn
  74 }
  75
  76 func (s *Server) ListenAndServe(ctx context.Context, cancelRoot context.CancelFunc) error {
  77         s.Logger.Infow("Hotline server started",
  78                 "version", VERSION,
  79                 "API port", fmt.Sprintf(":%v", s.Port),
  80                 "Transfer port", fmt.Sprintf(":%v", s.Port+1),
  81         )
  82
  83         var wg sync.WaitGroup
  84
  85         wg.Add(1)
  86         go func() {
  87                 ln, err := net.Listen("tcp", fmt.Sprintf("%s:%v", "", s.Port))
  88                 if err != nil {
  89                         s.Logger.Fatal(err)
  90                 }
  91
  92                 s.Logger.Fatal(s.Serve(ctx, ln))
  93         }()
  94
  95         wg.Add(1)
  96         go func() {
  97                 ln, err := net.Listen("tcp", fmt.Sprintf("%s:%v", "", s.Port+1))
  98                 if err != nil {
  99                         s.Logger.Fatal(err)
 100
 101                 }
 102
 103                 s.Logger.Fatal(s.ServeFileTransfers(ctx, ln))
 104         }()
 105
 106         wg.Wait()
 107
 108         return nil
 109 }
 110
 111 func (s *Server) ServeFileTransfers(ctx context.Context, ln net.Listener) error {
 112         for {
 113                 conn, err := ln.Accept()
 114                 if err != nil {
 115                         return err
 116                 }
 117
 118                 go func() {
 119                         defer func() { _ = conn.Close() }()
 120
 121                         err = s.handleFileTransfer(
 122                                 context.WithValue(ctx, contextKeyReq, requestCtx{
 123                                         remoteAddr: conn.RemoteAddr().String(),
 124                                 }),
 125                                 conn,
 126                         )
 127
 128                         if err != nil {
 129                                 s.Logger.Errorw("file transfer error", "reason", err)
 130                         }
 131                 }()
 132         }
 133 }
 134
 135 func (s *Server) sendTransaction(t Transaction) error {
 136         clientID, err := byteToInt(*t.clientID)
 137         if err != nil {
 138                 return err
 139         }
 140
 141         s.mux.Lock()
 142         client := s.Clients[uint16(clientID)]
 143         if client == nil {
 144                 return fmt.Errorf("invalid client id %v", *t.clientID)
 145         }
 146
 147         s.mux.Unlock()
 148
 149         b, err := t.MarshalBinary()
 150         if err != nil {
 151                 return err
 152         }
 153
 154         if _, err := client.Connection.Write(b); err != nil {
 155                 return err
 156         }
 157
 158         return nil
 159 }
 160
 161 func (s *Server) processOutbox() {
 162         for {
 163                 t := <-s.outbox
 164                 go func() {
 165                         if err := s.sendTransaction(t); err != nil {
 166                                 s.Logger.Errorw("error sending transaction", "err", err)
 167                         }
 168                 }()
 169         }
 170 }
 171
 172 func (s *Server) Serve(ctx context.Context, ln net.Listener) error {
 173         go s.processOutbox()
 174
 175         for {
 176                 conn, err := ln.Accept()
 177                 if err != nil {
 178                         s.Logger.Errorw("error accepting connection", "err", err)
 179                 }
 180                 connCtx := context.WithValue(ctx, contextKeyReq, requestCtx{
 181                         remoteAddr: conn.RemoteAddr().String(),
 182                 })
 183
 184                 go func() {
 185                         s.Logger.Infow("Connection established", "RemoteAddr", conn.RemoteAddr())
 186
 187                         if err := s.handleNewConnection(connCtx, conn, conn.RemoteAddr().String()); err != nil {
 188                                 if err == io.EOF {
 189                                         s.Logger.Infow("Client disconnected", "RemoteAddr", conn.RemoteAddr())
 190                                 } else {
 191                                         s.Logger.Errorw("error serving request", "RemoteAddr", conn.RemoteAddr(), "err", err)
 192                                 }
 193                         }
 194                 }()
 195         }
 196 }
 197
 198 const (
 199         agreementFile = "Agreement.txt"
 200 )
 201
 202 // NewServer constructs a new Server from a config dir
 203 func NewServer(configDir string, netPort int, logger *zap.SugaredLogger, FS FileStore) (*Server, error) {
 204         server := Server{
 205                 Port:          netPort,
 206                 Accounts:      make(map[string]*Account),
 207                 Config:        new(Config),
 208                 Clients:       make(map[uint16]*ClientConn),
 209                 fileTransfers: make(map[[4]byte]*FileTransfer),
 210                 PrivateChats:  make(map[uint32]*PrivateChat),
 211                 ConfigDir:     configDir,
 212                 Logger:        logger,
 213                 NextGuestID:   new(uint16),
 214                 outbox:        make(chan Transaction),
 215                 Stats:         &Stats{StartTime: time.Now()},
 216                 ThreadedNews:  &ThreadedNews{},
 217                 FS:            FS,
 218         }
 219
 220         var err error
 221
 222         // generate a new random passID for tracker registration
 223         if _, err := rand.Read(server.TrackerPassID[:]); err != nil {
 224                 return nil, err
 225         }
 226
 227         server.Agreement, err = os.ReadFile(filepath.Join(configDir, agreementFile))
 228         if err != nil {
 229                 return nil, err
 230         }
 231
 232         if server.FlatNews, err = os.ReadFile(filepath.Join(configDir, "MessageBoard.txt")); err != nil {
 233                 return nil, err
 234         }
 235
 236         if err := server.loadThreadedNews(filepath.Join(configDir, "ThreadedNews.yaml")); err != nil {
 237                 return nil, err
 238         }
 239
 240         if err := server.loadConfig(filepath.Join(configDir, "config.yaml")); err != nil {
 241                 return nil, err
 242         }
 243
 244         if err := server.loadAccounts(filepath.Join(configDir, "Users/")); err != nil {
 245                 return nil, err
 246         }
 247
 248         server.Config.FileRoot = filepath.Join(configDir, "Files")
 249
 250         *server.NextGuestID = 1
 251
 252         if server.Config.EnableTrackerRegistration {
 253                 server.Logger.Infow(
 254                         "Tracker registration enabled",
 255                         "frequency", fmt.Sprintf("%vs", trackerUpdateFrequency),
 256                         "trackers", server.Config.Trackers,
 257                 )
 258
 259                 go func() {
 260                         for {
 261                                 tr := &TrackerRegistration{
 262                                         UserCount:   server.userCount(),
 263                                         PassID:      server.TrackerPassID[:],
 264                                         Name:        server.Config.Name,
 265                                         Description: server.Config.Description,
 266                                 }
 267                                 binary.BigEndian.PutUint16(tr.Port[:], uint16(server.Port))
 268                                 for _, t := range server.Config.Trackers {
 269                                         if err := register(t, tr); err != nil {
 270                                                 server.Logger.Errorw("unable to register with tracker %v", "error", err)
 271                                         }
 272                                         server.Logger.Infow("Sent Tracker registration", "data", tr)
 273                                 }
 274
 275                                 time.Sleep(trackerUpdateFrequency * time.Second)
 276                         }
 277                 }()
 278         }
 279
 280         // Start Client Keepalive go routine
 281         go server.keepaliveHandler()
 282
 283         return &server, nil
 284 }
 285
 286 func (s *Server) userCount() int {
 287         s.mux.Lock()
 288         defer s.mux.Unlock()
 289
 290         return len(s.Clients)
 291 }
 292
 293 func (s *Server) keepaliveHandler() {
 294         for {
 295                 time.Sleep(idleCheckInterval * time.Second)
 296                 s.mux.Lock()
 297
 298                 for _, c := range s.Clients {
 299                         c.IdleTime += idleCheckInterval
 300                         if c.IdleTime > userIdleSeconds && !c.Idle {
 301                                 c.Idle = true
 302
 303                                 flagBitmap := big.NewInt(int64(binary.BigEndian.Uint16(*c.Flags)))
 304                                 flagBitmap.SetBit(flagBitmap, userFlagAway, 1)
 305                                 binary.BigEndian.PutUint16(*c.Flags, uint16(flagBitmap.Int64()))
 306
 307                                 c.sendAll(
 308                                         tranNotifyChangeUser,
 309                                         NewField(fieldUserID, *c.ID),
 310                                         NewField(fieldUserFlags, *c.Flags),
 311                                         NewField(fieldUserName, c.UserName),
 312                                         NewField(fieldUserIconID, *c.Icon),
 313                                 )
 314                         }
 315                 }
 316                 s.mux.Unlock()
 317         }
 318 }
 319
 320 func (s *Server) writeThreadedNews() error {
 321         s.mux.Lock()
 322         defer s.mux.Unlock()
 323
 324         out, err := yaml.Marshal(s.ThreadedNews)
 325         if err != nil {
 326                 return err
 327         }
 328         err = ioutil.WriteFile(
 329                 filepath.Join(s.ConfigDir, "ThreadedNews.yaml"),
 330                 out,
 331                 0666,
 332         )
 333         return err
 334 }
 335
 336 func (s *Server) NewClientConn(conn io.ReadWriteCloser, remoteAddr string) *ClientConn {
 337         s.mux.Lock()
 338         defer s.mux.Unlock()
 339
 340         clientConn := &ClientConn{
 341                 ID:         &[]byte{0, 0},
 342                 Icon:       &[]byte{0, 0},
 343                 Flags:      &[]byte{0, 0},
 344                 UserName:   []byte{},
 345                 Connection: conn,
 346                 Server:     s,
 347                 Version:    &[]byte{},
 348                 AutoReply:  []byte{},
 349                 transfers:  map[int]map[[4]byte]*FileTransfer{},
 350                 Agreed:     false,
 351                 RemoteAddr: remoteAddr,
 352         }
 353         clientConn.transfers = map[int]map[[4]byte]*FileTransfer{
 354                 FileDownload:   {},
 355                 FileUpload:     {},
 356                 FolderDownload: {},
 357                 FolderUpload:   {},
 358                 bannerDownload: {},
 359         }
 360
 361         *s.NextGuestID++
 362         ID := *s.NextGuestID
 363
 364         binary.BigEndian.PutUint16(*clientConn.ID, ID)
 365         s.Clients[ID] = clientConn
 366
 367         return clientConn
 368 }
 369
 370 // NewUser creates a new user account entry in the server map and config file
 371 func (s *Server) NewUser(login, name, password string, access []byte) error {
 372         s.mux.Lock()
 373         defer s.mux.Unlock()
 374
 375         account := Account{
 376                 Login:    login,
 377                 Name:     name,
 378                 Password: hashAndSalt([]byte(password)),
 379                 Access:   &access,
 380         }
 381         out, err := yaml.Marshal(&account)
 382         if err != nil {
 383                 return err
 384         }
 385         s.Accounts[login] = &account
 386
 387         return s.FS.WriteFile(filepath.Join(s.ConfigDir, "Users", login+".yaml"), out, 0666)
 388 }
 389
 390 func (s *Server) UpdateUser(login, newLogin, name, password string, access []byte) error {
 391         s.mux.Lock()
 392         defer s.mux.Unlock()
 393
 394         // update renames the user login
 395         if login != newLogin {
 396                 err := os.Rename(filepath.Join(s.ConfigDir, "Users", login+".yaml"), filepath.Join(s.ConfigDir, "Users", newLogin+".yaml"))
 397                 if err != nil {
 398                         return err
 399                 }
 400                 s.Accounts[newLogin] = s.Accounts[login]
 401                 delete(s.Accounts, login)
 402         }
 403
 404         account := s.Accounts[newLogin]
 405         account.Access = &access
 406         account.Name = name
 407         account.Password = password
 408
 409         out, err := yaml.Marshal(&account)
 410         if err != nil {
 411                 return err
 412         }
 413
 414         if err := os.WriteFile(filepath.Join(s.ConfigDir, "Users", newLogin+".yaml"), out, 0666); err != nil {
 415                 return err
 416         }
 417
 418         return nil
 419 }
 420
 421 // DeleteUser deletes the user account
 422 func (s *Server) DeleteUser(login string) error {
 423         s.mux.Lock()
 424         defer s.mux.Unlock()
 425
 426         delete(s.Accounts, login)
 427
 428         return s.FS.Remove(filepath.Join(s.ConfigDir, "Users", login+".yaml"))
 429 }
 430
 431 func (s *Server) connectedUsers() []Field {
 432         s.mux.Lock()
 433         defer s.mux.Unlock()
 434
 435         var connectedUsers []Field
 436         for _, c := range sortedClients(s.Clients) {
 437                 if !c.Agreed {
 438                         continue
 439                 }
 440                 user := User{
 441                         ID:    *c.ID,
 442                         Icon:  *c.Icon,
 443                         Flags: *c.Flags,
 444                         Name:  string(c.UserName),
 445                 }
 446                 connectedUsers = append(connectedUsers, NewField(fieldUsernameWithInfo, user.Payload()))
 447         }
 448         return connectedUsers
 449 }
 450
 451 // loadThreadedNews loads the threaded news data from disk
 452 func (s *Server) loadThreadedNews(threadedNewsPath string) error {
 453         fh, err := os.Open(threadedNewsPath)
 454         if err != nil {
 455                 return err
 456         }
 457         decoder := yaml.NewDecoder(fh)
 458
 459         return decoder.Decode(s.ThreadedNews)
 460 }
 461
 462 // loadAccounts loads account data from disk
 463 func (s *Server) loadAccounts(userDir string) error {
 464         matches, err := filepath.Glob(filepath.Join(userDir, "*.yaml"))
 465         if err != nil {
 466                 return err
 467         }
 468
 469         if len(matches) == 0 {
 470                 return errors.New("no user accounts found in " + userDir)
 471         }
 472
 473         for _, file := range matches {
 474                 fh, err := s.FS.Open(file)
 475                 if err != nil {
 476                         return err
 477                 }
 478
 479                 account := Account{}
 480                 decoder := yaml.NewDecoder(fh)
 481                 if err := decoder.Decode(&account); err != nil {
 482                         return err
 483                 }
 484
 485                 s.Accounts[account.Login] = &account
 486         }
 487         return nil
 488 }
 489
 490 func (s *Server) loadConfig(path string) error {
 491         fh, err := s.FS.Open(path)
 492         if err != nil {
 493                 return err
 494         }
 495
 496         decoder := yaml.NewDecoder(fh)
 497         err = decoder.Decode(s.Config)
 498         if err != nil {
 499                 return err
 500         }
 501
 502         validate := validator.New()
 503         err = validate.Struct(s.Config)
 504         if err != nil {
 505                 return err
 506         }
 507         return nil
 508 }
 509
 510 // dontPanic logs panics instead of crashing
 511 func dontPanic(logger *zap.SugaredLogger) {
 512         if r := recover(); r != nil {
 513                 fmt.Println("stacktrace from panic: \n" + string(debug.Stack()))
 514                 logger.Errorw("PANIC", "err", r, "trace", string(debug.Stack()))
 515         }
 516 }
 517
 518 // handleNewConnection takes a new net.Conn and performs the initial login sequence
 519 func (s *Server) handleNewConnection(ctx context.Context, rwc io.ReadWriteCloser, remoteAddr string) error {
 520         defer dontPanic(s.Logger)
 521
 522         if err := Handshake(rwc); err != nil {
 523                 return err
 524         }
 525
 526         // Create a new scanner for parsing incoming bytes into transaction tokens
 527         scanner := bufio.NewScanner(rwc)
 528         scanner.Split(transactionScanner)
 529
 530         scanner.Scan()
 531
 532         clientLogin, _, err := ReadTransaction(scanner.Bytes())
 533         if err != nil {
 534                 panic(err)
 535         }
 536
 537         c := s.NewClientConn(rwc, remoteAddr)
 538         defer c.Disconnect()
 539
 540         encodedLogin := clientLogin.GetField(fieldUserLogin).Data
 541         encodedPassword := clientLogin.GetField(fieldUserPassword).Data
 542         *c.Version = clientLogin.GetField(fieldVersion).Data
 543
 544         var login string
 545         for _, char := range encodedLogin {
 546                 login += string(rune(255 - uint(char)))
 547         }
 548         if login == "" {
 549                 login = GuestAccount
 550         }
 551
 552         c.logger = s.Logger.With("remoteAddr", remoteAddr, "login", login)
 553
 554         // If authentication fails, send error reply and close connection
 555         if !c.Authenticate(login, encodedPassword) {
 556                 t := c.NewErrReply(clientLogin, "Incorrect login.")
 557                 b, err := t.MarshalBinary()
 558                 if err != nil {
 559                         return err
 560                 }
 561                 if _, err := rwc.Write(b); err != nil {
 562                         return err
 563                 }
 564
 565                 c.logger.Infow("Login failed", "clientVersion", fmt.Sprintf("%x", *c.Version))
 566
 567                 return nil
 568         }
 569
 570         if clientLogin.GetField(fieldUserName).Data != nil {
 571                 c.UserName = clientLogin.GetField(fieldUserName).Data
 572         }
 573
 574         if clientLogin.GetField(fieldUserIconID).Data != nil {
 575                 *c.Icon = clientLogin.GetField(fieldUserIconID).Data
 576         }
 577
 578         c.Account = c.Server.Accounts[login]
 579
 580         if c.Authorize(accessDisconUser) {
 581                 *c.Flags = []byte{0, 2}
 582         }
 583
 584         s.outbox <- c.NewReply(clientLogin,
 585                 NewField(fieldVersion, []byte{0x00, 0xbe}),
 586                 NewField(fieldCommunityBannerID, []byte{0, 0}),
 587                 NewField(fieldServerName, []byte(s.Config.Name)),
 588         )
 589
 590         // Send user access privs so client UI knows how to behave
 591         c.Server.outbox <- *NewTransaction(tranUserAccess, c.ID, NewField(fieldUserAccess, *c.Account.Access))
 592
 593         // Show agreement to client
 594         c.Server.outbox <- *NewTransaction(tranShowAgreement, c.ID, NewField(fieldData, s.Agreement))
 595
 596         // Used simplified hotline v1.2.3 login flow for clients that do not send login info in tranAgreed
 597         if *c.Version == nil || bytes.Equal(*c.Version, nostalgiaVersion) {
 598                 c.Agreed = true
 599                 c.logger = c.logger.With("name", string(c.UserName))
 600                 c.logger.Infow("Login successful", "clientVersion", fmt.Sprintf("%x", *c.Version))
 601
 602                 for _, t := range c.notifyOthers(
 603                         *NewTransaction(
 604                                 tranNotifyChangeUser, nil,
 605                                 NewField(fieldUserName, c.UserName),
 606                                 NewField(fieldUserID, *c.ID),
 607                                 NewField(fieldUserIconID, *c.Icon),
 608                                 NewField(fieldUserFlags, *c.Flags),
 609                         ),
 610                 ) {
 611                         c.Server.outbox <- t
 612                 }
 613         }
 614
 615         c.Server.Stats.LoginCount += 1
 616
 617         // Scan for new transactions and handle them as they come in.
 618         for scanner.Scan() {
 619                 // Make a new []byte slice and copy the scanner bytes to it.  This is critical to avoid a data race as the
 620                 // scanner re-uses the buffer for subsequent scans.
 621                 buf := make([]byte, len(scanner.Bytes()))
 622                 copy(buf, scanner.Bytes())
 623
 624                 t, _, err := ReadTransaction(buf)
 625                 if err != nil {
 626                         panic(err)
 627                 }
 628                 if err := c.handleTransaction(*t); err != nil {
 629                         c.logger.Errorw("Error handling transaction", "err", err)
 630                 }
 631         }
 632         return nil
 633 }
 634
 635 func (s *Server) NewPrivateChat(cc *ClientConn) []byte {
 636         s.mux.Lock()
 637         defer s.mux.Unlock()
 638
 639         randID := make([]byte, 4)
 640         rand.Read(randID)
 641         data := binary.BigEndian.Uint32(randID[:])
 642
 643         s.PrivateChats[data] = &PrivateChat{
 644                 Subject:    "",
 645                 ClientConn: make(map[uint16]*ClientConn),
 646         }
 647         s.PrivateChats[data].ClientConn[cc.uint16ID()] = cc
 648
 649         return randID
 650 }
 651
 652 const dlFldrActionSendFile = 1
 653 const dlFldrActionResumeFile = 2
 654 const dlFldrActionNextFile = 3
 655
 656 // handleFileTransfer receives a client net.Conn from the file transfer server, performs the requested transfer type, then closes the connection
 657 func (s *Server) handleFileTransfer(ctx context.Context, rwc io.ReadWriter) error {
 658         defer dontPanic(s.Logger)
 659
 660         txBuf := make([]byte, 16)
 661         if _, err := io.ReadFull(rwc, txBuf); err != nil {
 662                 return err
 663         }
 664
 665         var t transfer
 666         if _, err := t.Write(txBuf); err != nil {
 667                 return err
 668         }
 669
 670         defer func() {
 671                 s.mux.Lock()
 672                 delete(s.fileTransfers, t.ReferenceNumber)
 673                 s.mux.Unlock()
 674
 675         }()
 676
 677         s.mux.Lock()
 678         fileTransfer, ok := s.fileTransfers[t.ReferenceNumber]
 679         s.mux.Unlock()
 680         if !ok {
 681                 return errors.New("invalid transaction ID")
 682         }
 683
 684         defer func() {
 685                 fileTransfer.ClientConn.transfersMU.Lock()
 686                 delete(fileTransfer.ClientConn.transfers[fileTransfer.Type], t.ReferenceNumber)
 687                 fileTransfer.ClientConn.transfersMU.Unlock()
 688         }()
 689
 690         rLogger := s.Logger.With(
 691                 "remoteAddr", ctx.Value(contextKeyReq).(requestCtx).remoteAddr,
 692                 "login", fileTransfer.ClientConn.Account.Login,
 693                 "name", string(fileTransfer.ClientConn.UserName),
 694         )
 695
 696         fullPath, err := readPath(s.Config.FileRoot, fileTransfer.FilePath, fileTransfer.FileName)
 697         if err != nil {
 698                 return err
 699         }
 700
 701         switch fileTransfer.Type {
 702         case bannerDownload:
 703                 if err := s.bannerDownload(rwc); err != nil {
 704                         panic(err)
 705                         return err
 706                 }
 707         case FileDownload:
 708                 s.Stats.DownloadCounter += 1
 709
 710                 var dataOffset int64
 711                 if fileTransfer.fileResumeData != nil {
 712                         dataOffset = int64(binary.BigEndian.Uint32(fileTransfer.fileResumeData.ForkInfoList[0].DataSize[:]))
 713                 }
 714
 715                 fw, err := newFileWrapper(s.FS, fullPath, 0)
 716                 if err != nil {
 717                         return err
 718                 }
 719
 720                 rLogger.Infow("File download started", "filePath", fullPath)
 721
 722                 // if file transfer options are included, that means this is a "quick preview" request from a 1.5+ client
 723                 if fileTransfer.options == nil {
 724                         // Start by sending flat file object to client
 725                         if _, err := rwc.Write(fw.ffo.BinaryMarshal()); err != nil {
 726                                 return err
 727                         }
 728                 }
 729
 730                 file, err := fw.dataForkReader()
 731                 if err != nil {
 732                         return err
 733                 }
 734
 735                 br := bufio.NewReader(file)
 736                 if _, err := br.Discard(int(dataOffset)); err != nil {
 737                         return err
 738                 }
 739
 740                 if _, err = io.Copy(rwc, io.TeeReader(br, fileTransfer.bytesSentCounter)); err != nil {
 741                         return err
 742                 }
 743
 744                 // if the client requested to resume transfer, do not send the resource fork header, or it will be appended into the fileWrapper data
 745                 if fileTransfer.fileResumeData == nil {
 746                         err = binary.Write(rwc, binary.BigEndian, fw.rsrcForkHeader())
 747                         if err != nil {
 748                                 return err
 749                         }
 750                 }
 751
 752                 rFile, err := fw.rsrcForkFile()
 753                 if err != nil {
 754                         return nil
 755                 }
 756
 757                 if _, err = io.Copy(rwc, io.TeeReader(rFile, fileTransfer.bytesSentCounter)); err != nil {
 758                         return err
 759                 }
 760
 761         case FileUpload:
 762                 s.Stats.UploadCounter += 1
 763
 764                 var file *os.File
 765
 766                 // A file upload has three possible cases:
 767                 // 1) Upload a new file
 768                 // 2) Resume a partially transferred file
 769                 // 3) Replace a fully uploaded file
 770                 //  We have to infer which case applies by inspecting what is already on the filesystem
 771
 772                 // 1) Check for existing file:
 773                 _, err = os.Stat(fullPath)
 774                 if err == nil {
 775                         return errors.New("existing file found at " + fullPath)
 776                 }
 777                 if errors.Is(err, fs.ErrNotExist) {
 778                         // If not found, open or create a new .incomplete file
 779                         file, err = os.OpenFile(fullPath+incompleteFileSuffix, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0644)
 780                         if err != nil {
 781                                 return err
 782                         }
 783                 }
 784
 785                 f, err := newFileWrapper(s.FS, fullPath, 0)
 786                 if err != nil {
 787                         return err
 788                 }
 789
 790                 rLogger.Infow("File upload started", "dstFile", fullPath)
 791
 792                 rForkWriter := io.Discard
 793                 iForkWriter := io.Discard
 794                 if s.Config.PreserveResourceForks {
 795                         rForkWriter, err = f.rsrcForkWriter()
 796                         if err != nil {
 797                                 return err
 798                         }
 799
 800                         iForkWriter, err = f.infoForkWriter()
 801                         if err != nil {
 802                                 return err
 803                         }
 804                 }
 805
 806                 if err := receiveFile(rwc, file, rForkWriter, iForkWriter, fileTransfer.bytesSentCounter); err != nil {
 807                         s.Logger.Error(err)
 808                 }
 809
 810                 if err := file.Close(); err != nil {
 811                         return err
 812                 }
 813
 814                 if err := s.FS.Rename(fullPath+".incomplete", fullPath); err != nil {
 815                         return err
 816                 }
 817
 818                 rLogger.Infow("File upload complete", "dstFile", fullPath)
 819         case FolderDownload:
 820                 // Folder Download flow:
 821                 // 1. Get filePath from the transfer
 822                 // 2. Iterate over files
 823                 // 3. For each fileWrapper:
 824                 //       Send fileWrapper header to client
 825                 // The client can reply in 3 ways:
 826                 //
 827                 // 1. If type is an odd number (unknown type?), or fileWrapper download for the current fileWrapper is completed:
 828                 //              client sends []byte{0x00, 0x03} to tell the server to continue to the next fileWrapper
 829                 //
 830                 // 2. If download of a fileWrapper is to be resumed:
 831                 //              client sends:
 832                 //                      []byte{0x00, 0x02} // download folder action
 833                 //                      [2]byte // Resume data size
 834                 //                      []byte fileWrapper resume data (see myField_FileResumeData)
 835                 //
 836                 // 3. Otherwise, download of the fileWrapper is requested and client sends []byte{0x00, 0x01}
 837                 //
 838                 // When download is requested (case 2 or 3), server replies with:
 839                 //                      [4]byte - fileWrapper size
 840                 //                      []byte  - Flattened File Object
 841                 //
 842                 // After every fileWrapper download, client could request next fileWrapper with:
 843                 //                      []byte{0x00, 0x03}
 844                 //
 845                 // This notifies the server to send the next item header
 846
 847                 basePathLen := len(fullPath)
 848
 849                 rLogger.Infow("Start folder download", "path", fullPath)
 850
 851                 nextAction := make([]byte, 2)
 852                 if _, err := io.ReadFull(rwc, nextAction); err != nil {
 853                         return err
 854                 }
 855
 856                 i := 0
 857                 err = filepath.Walk(fullPath+"/", func(path string, info os.FileInfo, err error) error {
 858                         s.Stats.DownloadCounter += 1
 859                         i += 1
 860
 861                         if err != nil {
 862                                 return err
 863                         }
 864
 865                         // skip dot files
 866                         if strings.HasPrefix(info.Name(), ".") {
 867                                 return nil
 868                         }
 869
 870                         hlFile, err := newFileWrapper(s.FS, path, 0)
 871                         if err != nil {
 872                                 return err
 873                         }
 874
 875                         subPath := path[basePathLen+1:]
 876                         rLogger.Debugw("Sending fileheader", "i", i, "path", path, "fullFilePath", fullPath, "subPath", subPath, "IsDir", info.IsDir())
 877
 878                         if i == 1 {
 879                                 return nil
 880                         }
 881
 882                         fileHeader := NewFileHeader(subPath, info.IsDir())
 883
 884                         // Send the fileWrapper header to client
 885                         if _, err := rwc.Write(fileHeader.Payload()); err != nil {
 886                                 s.Logger.Errorf("error sending file header: %v", err)
 887                                 return err
 888                         }
 889
 890                         // Read the client's Next Action request
 891                         if _, err := io.ReadFull(rwc, nextAction); err != nil {
 892                                 return err
 893                         }
 894
 895                         rLogger.Debugw("Client folder download action", "action", fmt.Sprintf("%X", nextAction[0:2]))
 896
 897                         var dataOffset int64
 898
 899                         switch nextAction[1] {
 900                         case dlFldrActionResumeFile:
 901                                 // get size of resumeData
 902                                 resumeDataByteLen := make([]byte, 2)
 903                                 if _, err := io.ReadFull(rwc, resumeDataByteLen); err != nil {
 904                                         return err
 905                                 }
 906
 907                                 resumeDataLen := binary.BigEndian.Uint16(resumeDataByteLen)
 908                                 resumeDataBytes := make([]byte, resumeDataLen)
 909                                 if _, err := io.ReadFull(rwc, resumeDataBytes); err != nil {
 910                                         return err
 911                                 }
 912
 913                                 var frd FileResumeData
 914                                 if err := frd.UnmarshalBinary(resumeDataBytes); err != nil {
 915                                         return err
 916                                 }
 917                                 dataOffset = int64(binary.BigEndian.Uint32(frd.ForkInfoList[0].DataSize[:]))
 918                         case dlFldrActionNextFile:
 919                                 // client asked to skip this file
 920                                 return nil
 921                         }
 922
 923                         if info.IsDir() {
 924                                 return nil
 925                         }
 926
 927                         rLogger.Infow("File download started",
 928                                 "fileName", info.Name(),
 929                                 "TransferSize", fmt.Sprintf("%x", hlFile.ffo.TransferSize(dataOffset)),
 930                         )
 931
 932                         // Send file size to client
 933                         if _, err := rwc.Write(hlFile.ffo.TransferSize(dataOffset)); err != nil {
 934                                 s.Logger.Error(err)
 935                                 return err
 936                         }
 937
 938                         // Send ffo bytes to client
 939                         if _, err := rwc.Write(hlFile.ffo.BinaryMarshal()); err != nil {
 940                                 s.Logger.Error(err)
 941                                 return err
 942                         }
 943
 944                         file, err := s.FS.Open(path)
 945                         if err != nil {
 946                                 return err
 947                         }
 948
 949                         // wr := bufio.NewWriterSize(rwc, 1460)
 950                         if _, err = io.Copy(rwc, io.TeeReader(file, fileTransfer.bytesSentCounter)); err != nil {
 951                                 return err
 952                         }
 953
 954                         if nextAction[1] != 2 && hlFile.ffo.FlatFileHeader.ForkCount[1] == 3 {
 955                                 err = binary.Write(rwc, binary.BigEndian, hlFile.rsrcForkHeader())
 956                                 if err != nil {
 957                                         return err
 958                                 }
 959
 960                                 rFile, err := hlFile.rsrcForkFile()
 961                                 if err != nil {
 962                                         return err
 963                                 }
 964
 965                                 if _, err = io.Copy(rwc, io.TeeReader(rFile, fileTransfer.bytesSentCounter)); err != nil {
 966                                         return err
 967                                 }
 968                         }
 969
 970                         // Read the client's Next Action request.  This is always 3, I think?
 971                         if _, err := io.ReadFull(rwc, nextAction); err != nil {
 972                                 return err
 973                         }
 974
 975                         return nil
 976                 })
 977
 978                 if err != nil {
 979                         return err
 980                 }
 981
 982         case FolderUpload:
 983                 rLogger.Infow(
 984                         "Folder upload started",
 985                         "dstPath", fullPath,
 986                         "TransferSize", binary.BigEndian.Uint32(fileTransfer.TransferSize),
 987                         "FolderItemCount", fileTransfer.FolderItemCount,
 988                 )
 989
 990                 // Check if the target folder exists.  If not, create it.
 991                 if _, err := s.FS.Stat(fullPath); os.IsNotExist(err) {
 992                         if err := s.FS.Mkdir(fullPath, 0777); err != nil {
 993                                 return err
 994                         }
 995                 }
 996
 997                 // Begin the folder upload flow by sending the "next file action" to client
 998                 if _, err := rwc.Write([]byte{0, dlFldrActionNextFile}); err != nil {
 999                         return err
1000                 }
1001
1002                 fileSize := make([]byte, 4)
1003
1004                 for i := 0; i < fileTransfer.ItemCount(); i++ {
1005                         s.Stats.UploadCounter += 1
1006
1007                         var fu folderUpload
1008                         if _, err := io.ReadFull(rwc, fu.DataSize[:]); err != nil {
1009                                 return err
1010                         }
1011                         if _, err := io.ReadFull(rwc, fu.IsFolder[:]); err != nil {
1012                                 return err
1013                         }
1014                         if _, err := io.ReadFull(rwc, fu.PathItemCount[:]); err != nil {
1015                                 return err
1016                         }
1017
1018                         fu.FileNamePath = make([]byte, binary.BigEndian.Uint16(fu.DataSize[:])-4) // -4 to subtract the path separator bytes
1019
1020                         if _, err := io.ReadFull(rwc, fu.FileNamePath); err != nil {
1021                                 return err
1022                         }
1023
1024                         rLogger.Infow(
1025                                 "Folder upload continued",
1026                                 "FormattedPath", fu.FormattedPath(),
1027                                 "IsFolder", fmt.Sprintf("%x", fu.IsFolder),
1028                                 "PathItemCount", binary.BigEndian.Uint16(fu.PathItemCount[:]),
1029                         )
1030
1031                         if fu.IsFolder == [2]byte{0, 1} {
1032                                 if _, err := os.Stat(filepath.Join(fullPath, fu.FormattedPath())); os.IsNotExist(err) {
1033                                         if err := os.Mkdir(filepath.Join(fullPath, fu.FormattedPath()), 0777); err != nil {
1034                                                 return err
1035                                         }
1036                                 }
1037
1038                                 // Tell client to send next file
1039                                 if _, err := rwc.Write([]byte{0, dlFldrActionNextFile}); err != nil {
1040                                         return err
1041                                 }
1042                         } else {
1043                                 nextAction := dlFldrActionSendFile
1044
1045                                 // Check if we have the full file already.  If so, send dlFldrAction_NextFile to client to skip.
1046                                 _, err = os.Stat(filepath.Join(fullPath, fu.FormattedPath()))
1047                                 if err != nil && !errors.Is(err, fs.ErrNotExist) {
1048                                         return err
1049                                 }
1050                                 if err == nil {
1051                                         nextAction = dlFldrActionNextFile
1052                                 }
1053
1054                                 //  Check if we have a partial file already.  If so, send dlFldrAction_ResumeFile to client to resume upload.
1055                                 incompleteFile, err := os.Stat(filepath.Join(fullPath, fu.FormattedPath()+incompleteFileSuffix))
1056                                 if err != nil && !errors.Is(err, fs.ErrNotExist) {
1057                                         return err
1058                                 }
1059                                 if err == nil {
1060                                         nextAction = dlFldrActionResumeFile
1061                                 }
1062
1063                                 if _, err := rwc.Write([]byte{0, uint8(nextAction)}); err != nil {
1064                                         return err
1065                                 }
1066
1067                                 switch nextAction {
1068                                 case dlFldrActionNextFile:
1069                                         continue
1070                                 case dlFldrActionResumeFile:
1071                                         offset := make([]byte, 4)
1072                                         binary.BigEndian.PutUint32(offset, uint32(incompleteFile.Size()))
1073
1074                                         file, err := os.OpenFile(fullPath+"/"+fu.FormattedPath()+incompleteFileSuffix, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
1075                                         if err != nil {
1076                                                 return err
1077                                         }
1078
1079                                         fileResumeData := NewFileResumeData([]ForkInfoList{*NewForkInfoList(offset)})
1080
1081                                         b, _ := fileResumeData.BinaryMarshal()
1082
1083                                         bs := make([]byte, 2)
1084                                         binary.BigEndian.PutUint16(bs, uint16(len(b)))
1085
1086                                         if _, err := rwc.Write(append(bs, b...)); err != nil {
1087                                                 return err
1088                                         }
1089
1090                                         if _, err := io.ReadFull(rwc, fileSize); err != nil {
1091                                                 return err
1092                                         }
1093
1094                                         if err := receiveFile(rwc, file, ioutil.Discard, ioutil.Discard, fileTransfer.bytesSentCounter); err != nil {
1095                                                 s.Logger.Error(err)
1096                                         }
1097
1098                                         err = os.Rename(fullPath+"/"+fu.FormattedPath()+".incomplete", fullPath+"/"+fu.FormattedPath())
1099                                         if err != nil {
1100                                                 return err
1101                                         }
1102
1103                                 case dlFldrActionSendFile:
1104                                         if _, err := io.ReadFull(rwc, fileSize); err != nil {
1105                                                 return err
1106                                         }
1107
1108                                         filePath := filepath.Join(fullPath, fu.FormattedPath())
1109
1110                                         hlFile, err := newFileWrapper(s.FS, filePath, 0)
1111                                         if err != nil {
1112                                                 return err
1113                                         }
1114
1115                                         rLogger.Infow("Starting file transfer", "path", filePath, "fileNum", i+1, "fileSize", binary.BigEndian.Uint32(fileSize))
1116
1117                                         incWriter, err := hlFile.incFileWriter()
1118                                         if err != nil {
1119                                                 return err
1120                                         }
1121
1122                                         rForkWriter := io.Discard
1123                                         iForkWriter := io.Discard
1124                                         if s.Config.PreserveResourceForks {
1125                                                 iForkWriter, err = hlFile.infoForkWriter()
1126                                                 if err != nil {
1127                                                         return err
1128                                                 }
1129
1130                                                 rForkWriter, err = hlFile.rsrcForkWriter()
1131                                                 if err != nil {
1132                                                         return err
1133                                                 }
1134                                         }
1135                                         if err := receiveFile(rwc, incWriter, rForkWriter, iForkWriter, fileTransfer.bytesSentCounter); err != nil {
1136                                                 return err
1137                                         }
1138
1139                                         if err := os.Rename(filePath+".incomplete", filePath); err != nil {
1140                                                 return err
1141                                         }
1142                                 }
1143
1144                                 // Tell client to send next fileWrapper
1145                                 if _, err := rwc.Write([]byte{0, dlFldrActionNextFile}); err != nil {
1146                                         return err
1147                                 }
1148                         }
1149                 }
1150                 rLogger.Infof("Folder upload complete")
1151         }
1152
1153         return nil
1154 }