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

   1 package hotline
   2
   3 import (
   4         "context"
   5         "encoding/binary"
   6         "errors"
   7         "fmt"
   8         "github.com/go-playground/validator/v10"
   9         "go.uber.org/zap"
  10         "io"
  11         "io/fs"
  12         "io/ioutil"
  13         "math/big"
  14         "math/rand"
  15         "net"
  16         "os"
  17         "path"
  18         "path/filepath"
  19         "runtime/debug"
  20         "sort"
  21         "strings"
  22         "sync"
  23         "time"
  24
  25         "gopkg.in/yaml.v3"
  26 )
  27
  28 const (
  29         userIdleSeconds        = 300 // time in seconds before an inactive user is marked idle
  30         idleCheckInterval      = 10  // time in seconds to check for idle users
  31         trackerUpdateFrequency = 300 // time in seconds between tracker re-registration
  32 )
  33
  34 type Server struct {
  35         Port          int
  36         Accounts      map[string]*Account
  37         Agreement     []byte
  38         Clients       map[uint16]*ClientConn
  39         FlatNews      []byte
  40         ThreadedNews  *ThreadedNews
  41         FileTransfers map[uint32]*FileTransfer
  42         Config        *Config
  43         ConfigDir     string
  44         Logger        *zap.SugaredLogger
  45         PrivateChats  map[uint32]*PrivateChat
  46         NextGuestID   *uint16
  47         TrackerPassID []byte
  48         Stats         *Stats
  49
  50         APIListener  net.Listener
  51         FileListener net.Listener
  52
  53         // newsReader io.Reader
  54         // newsWriter io.WriteCloser
  55
  56         outbox chan Transaction
  57
  58         mux         sync.Mutex
  59         flatNewsMux sync.Mutex
  60 }
  61
  62 type PrivateChat struct {
  63         Subject    string
  64         ClientConn map[uint16]*ClientConn
  65 }
  66
  67 func (s *Server) ListenAndServe(ctx context.Context, cancelRoot context.CancelFunc) error {
  68         s.Logger.Infow("Hotline server started", "version", VERSION)
  69         var wg sync.WaitGroup
  70
  71         wg.Add(1)
  72         go func() { s.Logger.Fatal(s.Serve(ctx, cancelRoot, s.APIListener)) }()
  73
  74         wg.Add(1)
  75         go func() { s.Logger.Fatal(s.ServeFileTransfers(s.FileListener)) }()
  76
  77         wg.Wait()
  78
  79         return nil
  80 }
  81
  82 func (s *Server) APIPort() int {
  83         return s.APIListener.Addr().(*net.TCPAddr).Port
  84 }
  85
  86 func (s *Server) ServeFileTransfers(ln net.Listener) error {
  87         s.Logger.Infow("Hotline file transfer server started", "Addr", fmt.Sprintf(":%v", s.Port+1))
  88
  89         for {
  90                 conn, err := ln.Accept()
  91                 if err != nil {
  92                         return err
  93                 }
  94
  95                 go func() {
  96                         if err := s.handleFileTransfer(conn); err != nil {
  97                                 s.Logger.Errorw("file transfer error", "reason", err)
  98                         }
  99                 }()
 100         }
 101 }
 102
 103 func (s *Server) sendTransaction(t Transaction) error {
 104         requestNum := binary.BigEndian.Uint16(t.Type)
 105         clientID, err := byteToInt(*t.clientID)
 106         if err != nil {
 107                 return err
 108         }
 109
 110         s.mux.Lock()
 111         client := s.Clients[uint16(clientID)]
 112         s.mux.Unlock()
 113         if client == nil {
 114                 return fmt.Errorf("invalid client id %v", *t.clientID)
 115         }
 116         userName := string(client.UserName)
 117         login := client.Account.Login
 118
 119         handler := TransactionHandlers[requestNum]
 120
 121         b, err := t.MarshalBinary()
 122         if err != nil {
 123                 return err
 124         }
 125         var n int
 126         if n, err = client.Connection.Write(b); err != nil {
 127                 return err
 128         }
 129         s.Logger.Debugw("Sent Transaction",
 130                 "name", userName,
 131                 "login", login,
 132                 "IsReply", t.IsReply,
 133                 "type", handler.Name,
 134                 "sentBytes", n,
 135                 "remoteAddr", client.RemoteAddr,
 136         )
 137         return nil
 138 }
 139
 140 func (s *Server) Serve(ctx context.Context, cancelRoot context.CancelFunc, ln net.Listener) error {
 141         s.Logger.Infow("Hotline server started", "Addr", fmt.Sprintf(":%v", s.Port))
 142
 143         for {
 144                 conn, err := ln.Accept()
 145                 if err != nil {
 146                         s.Logger.Errorw("error accepting connection", "err", err)
 147                 }
 148
 149                 go func() {
 150                         for {
 151                                 t := <-s.outbox
 152                                 go func() {
 153                                         if err := s.sendTransaction(t); err != nil {
 154                                                 s.Logger.Errorw("error sending transaction", "err", err)
 155                                         }
 156                                 }()
 157                         }
 158                 }()
 159                 go func() {
 160                         if err := s.handleNewConnection(conn, conn.RemoteAddr().String()); err != nil {
 161                                 if err == io.EOF {
 162                                         s.Logger.Infow("Client disconnected", "RemoteAddr", conn.RemoteAddr())
 163                                 } else {
 164                                         s.Logger.Errorw("error serving request", "RemoteAddr", conn.RemoteAddr(), "err", err)
 165                                 }
 166                         }
 167                 }()
 168         }
 169 }
 170
 171 const (
 172         agreementFile = "Agreement.txt"
 173 )
 174
 175 // NewServer constructs a new Server from a config dir
 176 func NewServer(configDir, netInterface string, netPort int, logger *zap.SugaredLogger) (*Server, error) {
 177         server := Server{
 178                 Port:          netPort,
 179                 Accounts:      make(map[string]*Account),
 180                 Config:        new(Config),
 181                 Clients:       make(map[uint16]*ClientConn),
 182                 FileTransfers: make(map[uint32]*FileTransfer),
 183                 PrivateChats:  make(map[uint32]*PrivateChat),
 184                 ConfigDir:     configDir,
 185                 Logger:        logger,
 186                 NextGuestID:   new(uint16),
 187                 outbox:        make(chan Transaction),
 188                 Stats:         &Stats{StartTime: time.Now()},
 189                 ThreadedNews:  &ThreadedNews{},
 190                 TrackerPassID: make([]byte, 4),
 191         }
 192
 193         ln, err := net.Listen("tcp", fmt.Sprintf("%s:%v", netInterface, netPort))
 194         if err != nil {
 195                 return nil, err
 196         }
 197         server.APIListener = ln
 198
 199         if netPort != 0 {
 200                 netPort += 1
 201         }
 202
 203         ln2, err := net.Listen("tcp", fmt.Sprintf("%s:%v", netInterface, netPort))
 204         server.FileListener = ln2
 205         if err != nil {
 206                 return nil, err
 207         }
 208
 209         // generate a new random passID for tracker registration
 210         if _, err := rand.Read(server.TrackerPassID); err != nil {
 211                 return nil, err
 212         }
 213
 214         server.Logger.Debugw("Loading Agreement", "path", configDir+agreementFile)
 215         if server.Agreement, err = os.ReadFile(configDir + agreementFile); err != nil {
 216                 return nil, err
 217         }
 218
 219         if server.FlatNews, err = os.ReadFile(configDir + "MessageBoard.txt"); err != nil {
 220                 return nil, err
 221         }
 222
 223         if err := server.loadThreadedNews(configDir + "ThreadedNews.yaml"); err != nil {
 224                 return nil, err
 225         }
 226
 227         if err := server.loadConfig(configDir + "config.yaml"); err != nil {
 228                 return nil, err
 229         }
 230
 231         if err := server.loadAccounts(configDir + "Users/"); err != nil {
 232                 return nil, err
 233         }
 234
 235         server.Config.FileRoot = configDir + "Files/"
 236
 237         *server.NextGuestID = 1
 238
 239         if server.Config.EnableTrackerRegistration {
 240                 server.Logger.Infow(
 241                         "Tracker registration enabled",
 242                         "frequency", fmt.Sprintf("%vs", trackerUpdateFrequency),
 243                         "trackers", server.Config.Trackers,
 244                 )
 245
 246                 go func() {
 247                         for {
 248                                 tr := &TrackerRegistration{
 249                                         Port:        []byte{0x15, 0x7c},
 250                                         UserCount:   server.userCount(),
 251                                         PassID:      server.TrackerPassID,
 252                                         Name:        server.Config.Name,
 253                                         Description: server.Config.Description,
 254                                 }
 255                                 for _, t := range server.Config.Trackers {
 256                                         if err := register(t, tr); err != nil {
 257                                                 server.Logger.Errorw("unable to register with tracker %v", "error", err)
 258                                         }
 259                                         server.Logger.Infow("Sent Tracker registration", "data", tr)
 260                                 }
 261
 262                                 time.Sleep(trackerUpdateFrequency * time.Second)
 263                         }
 264                 }()
 265         }
 266
 267         // Start Client Keepalive go routine
 268         go server.keepaliveHandler()
 269
 270         return &server, nil
 271 }
 272
 273 func (s *Server) userCount() int {
 274         s.mux.Lock()
 275         defer s.mux.Unlock()
 276
 277         return len(s.Clients)
 278 }
 279
 280 func (s *Server) keepaliveHandler() {
 281         for {
 282                 time.Sleep(idleCheckInterval * time.Second)
 283                 s.mux.Lock()
 284
 285                 for _, c := range s.Clients {
 286                         c.IdleTime += idleCheckInterval
 287                         if c.IdleTime > userIdleSeconds && !c.Idle {
 288                                 c.Idle = true
 289
 290                                 flagBitmap := big.NewInt(int64(binary.BigEndian.Uint16(*c.Flags)))
 291                                 flagBitmap.SetBit(flagBitmap, userFlagAway, 1)
 292                                 binary.BigEndian.PutUint16(*c.Flags, uint16(flagBitmap.Int64()))
 293
 294                                 c.sendAll(
 295                                         tranNotifyChangeUser,
 296                                         NewField(fieldUserID, *c.ID),
 297                                         NewField(fieldUserFlags, *c.Flags),
 298                                         NewField(fieldUserName, c.UserName),
 299                                         NewField(fieldUserIconID, *c.Icon),
 300                                 )
 301                         }
 302                 }
 303                 s.mux.Unlock()
 304         }
 305 }
 306
 307 func (s *Server) writeThreadedNews() error {
 308         s.mux.Lock()
 309         defer s.mux.Unlock()
 310
 311         out, err := yaml.Marshal(s.ThreadedNews)
 312         if err != nil {
 313                 return err
 314         }
 315         err = ioutil.WriteFile(
 316                 s.ConfigDir+"ThreadedNews.yaml",
 317                 out,
 318                 0666,
 319         )
 320         return err
 321 }
 322
 323 func (s *Server) NewClientConn(conn net.Conn, remoteAddr string) *ClientConn {
 324         s.mux.Lock()
 325         defer s.mux.Unlock()
 326
 327         clientConn := &ClientConn{
 328                 ID:         &[]byte{0, 0},
 329                 Icon:       &[]byte{0, 0},
 330                 Flags:      &[]byte{0, 0},
 331                 UserName:   []byte{},
 332                 Connection: conn,
 333                 Server:     s,
 334                 Version:    &[]byte{},
 335                 AutoReply:  []byte{},
 336                 Transfers:  make(map[int][]*FileTransfer),
 337                 Agreed:     false,
 338                 RemoteAddr: remoteAddr,
 339         }
 340         *s.NextGuestID++
 341         ID := *s.NextGuestID
 342
 343         binary.BigEndian.PutUint16(*clientConn.ID, ID)
 344         s.Clients[ID] = clientConn
 345
 346         return clientConn
 347 }
 348
 349 // NewUser creates a new user account entry in the server map and config file
 350 func (s *Server) NewUser(login, name, password string, access []byte) error {
 351         s.mux.Lock()
 352         defer s.mux.Unlock()
 353
 354         account := Account{
 355                 Login:    login,
 356                 Name:     name,
 357                 Password: hashAndSalt([]byte(password)),
 358                 Access:   &access,
 359         }
 360         out, err := yaml.Marshal(&account)
 361         if err != nil {
 362                 return err
 363         }
 364         s.Accounts[login] = &account
 365
 366         return FS.WriteFile(s.ConfigDir+"Users/"+login+".yaml", out, 0666)
 367 }
 368
 369 func (s *Server) UpdateUser(login, newLogin, name, password string, access []byte) error {
 370         s.mux.Lock()
 371         defer s.mux.Unlock()
 372
 373         fmt.Printf("login: %v, newLogin: %v: ", login, newLogin)
 374
 375         // update renames the user login
 376         if login != newLogin {
 377                 err := os.Rename(s.ConfigDir+"Users/"+login+".yaml", s.ConfigDir+"Users/"+newLogin+".yaml")
 378                 if err != nil {
 379                         return err
 380                 }
 381                 s.Accounts[newLogin] = s.Accounts[login]
 382                 delete(s.Accounts, login)
 383         }
 384
 385         account := s.Accounts[newLogin]
 386         account.Access = &access
 387         account.Name = name
 388         account.Password = password
 389
 390         out, err := yaml.Marshal(&account)
 391         if err != nil {
 392                 return err
 393         }
 394         if err := os.WriteFile(s.ConfigDir+"Users/"+newLogin+".yaml", out, 0666); err != nil {
 395                 return err
 396         }
 397
 398         return nil
 399 }
 400
 401 // DeleteUser deletes the user account
 402 func (s *Server) DeleteUser(login string) error {
 403         s.mux.Lock()
 404         defer s.mux.Unlock()
 405
 406         delete(s.Accounts, login)
 407
 408         return FS.Remove(s.ConfigDir + "Users/" + login + ".yaml")
 409 }
 410
 411 func (s *Server) connectedUsers() []Field {
 412         s.mux.Lock()
 413         defer s.mux.Unlock()
 414
 415         var connectedUsers []Field
 416         for _, c := range sortedClients(s.Clients) {
 417                 if !c.Agreed {
 418                         continue
 419                 }
 420                 user := User{
 421                         ID:    *c.ID,
 422                         Icon:  *c.Icon,
 423                         Flags: *c.Flags,
 424                         Name:  string(c.UserName),
 425                 }
 426                 connectedUsers = append(connectedUsers, NewField(fieldUsernameWithInfo, user.Payload()))
 427         }
 428         return connectedUsers
 429 }
 430
 431 // loadThreadedNews loads the threaded news data from disk
 432 func (s *Server) loadThreadedNews(threadedNewsPath string) error {
 433         fh, err := os.Open(threadedNewsPath)
 434         if err != nil {
 435                 return err
 436         }
 437         decoder := yaml.NewDecoder(fh)
 438
 439         return decoder.Decode(s.ThreadedNews)
 440 }
 441
 442 // loadAccounts loads account data from disk
 443 func (s *Server) loadAccounts(userDir string) error {
 444         matches, err := filepath.Glob(path.Join(userDir, "*.yaml"))
 445         if err != nil {
 446                 return err
 447         }
 448
 449         if len(matches) == 0 {
 450                 return errors.New("no user accounts found in " + userDir)
 451         }
 452
 453         for _, file := range matches {
 454                 fh, err := FS.Open(file)
 455                 if err != nil {
 456                         return err
 457                 }
 458
 459                 account := Account{}
 460                 decoder := yaml.NewDecoder(fh)
 461                 if err := decoder.Decode(&account); err != nil {
 462                         return err
 463                 }
 464
 465                 s.Accounts[account.Login] = &account
 466         }
 467         return nil
 468 }
 469
 470 func (s *Server) loadConfig(path string) error {
 471         fh, err := FS.Open(path)
 472         if err != nil {
 473                 return err
 474         }
 475
 476         decoder := yaml.NewDecoder(fh)
 477         err = decoder.Decode(s.Config)
 478         if err != nil {
 479                 return err
 480         }
 481
 482         validate := validator.New()
 483         err = validate.Struct(s.Config)
 484         if err != nil {
 485                 return err
 486         }
 487         return nil
 488 }
 489
 490 const (
 491         minTransactionLen = 22 // minimum length of any transaction
 492 )
 493
 494 // dontPanic recovers and logs panics instead of crashing
 495 // TODO: remove this after known issues are fixed
 496 func dontPanic(logger *zap.SugaredLogger) {
 497         if r := recover(); r != nil {
 498                 fmt.Println("stacktrace from panic: \n" + string(debug.Stack()))
 499                 logger.Errorw("PANIC", "err", r, "trace", string(debug.Stack()))
 500         }
 501 }
 502
 503 // handleNewConnection takes a new net.Conn and performs the initial login sequence
 504 func (s *Server) handleNewConnection(conn net.Conn, remoteAddr string) error {
 505         defer dontPanic(s.Logger)
 506
 507         if err := Handshake(conn); err != nil {
 508                 return err
 509         }
 510
 511         buf := make([]byte, 1024)
 512         // TODO: fix potential short read with io.ReadFull
 513         readLen, err := conn.Read(buf)
 514         if readLen < minTransactionLen {
 515                 return err
 516         }
 517         if err != nil {
 518                 return err
 519         }
 520
 521         clientLogin, _, err := ReadTransaction(buf[:readLen])
 522         if err != nil {
 523                 return err
 524         }
 525
 526         c := s.NewClientConn(conn, remoteAddr)
 527         defer c.Disconnect()
 528
 529         encodedLogin := clientLogin.GetField(fieldUserLogin).Data
 530         encodedPassword := clientLogin.GetField(fieldUserPassword).Data
 531         *c.Version = clientLogin.GetField(fieldVersion).Data
 532
 533         var login string
 534         for _, char := range encodedLogin {
 535                 login += string(rune(255 - uint(char)))
 536         }
 537         if login == "" {
 538                 login = GuestAccount
 539         }
 540
 541         // If authentication fails, send error reply and close connection
 542         if !c.Authenticate(login, encodedPassword) {
 543                 t := c.NewErrReply(clientLogin, "Incorrect login.")
 544                 b, err := t.MarshalBinary()
 545                 if err != nil {
 546                         return err
 547                 }
 548                 if _, err := conn.Write(b); err != nil {
 549                         return err
 550                 }
 551                 return fmt.Errorf("incorrect login")
 552         }
 553
 554         if clientLogin.GetField(fieldUserName).Data != nil {
 555                 c.UserName = clientLogin.GetField(fieldUserName).Data
 556         }
 557
 558         if clientLogin.GetField(fieldUserIconID).Data != nil {
 559                 *c.Icon = clientLogin.GetField(fieldUserIconID).Data
 560         }
 561
 562         c.Account = c.Server.Accounts[login]
 563
 564         if c.Authorize(accessDisconUser) {
 565                 *c.Flags = []byte{0, 2}
 566         }
 567
 568         s.Logger.Infow("Client connection received", "login", login, "version", *c.Version, "RemoteAddr", remoteAddr)
 569
 570         s.outbox <- c.NewReply(clientLogin,
 571                 NewField(fieldVersion, []byte{0x00, 0xbe}),
 572                 NewField(fieldCommunityBannerID, []byte{0x00, 0x01}),
 573                 NewField(fieldServerName, []byte(s.Config.Name)),
 574         )
 575
 576         // Send user access privs so client UI knows how to behave
 577         c.Server.outbox <- *NewTransaction(tranUserAccess, c.ID, NewField(fieldUserAccess, *c.Account.Access))
 578
 579         // Show agreement to client
 580         c.Server.outbox <- *NewTransaction(tranShowAgreement, c.ID, NewField(fieldData, s.Agreement))
 581
 582         // assume simplified hotline v1.2.3 login flow that does not require agreement
 583         if *c.Version == nil {
 584                 c.Agreed = true
 585
 586                 c.notifyOthers(
 587                         *NewTransaction(
 588                                 tranNotifyChangeUser, nil,
 589                                 NewField(fieldUserName, c.UserName),
 590                                 NewField(fieldUserID, *c.ID),
 591                                 NewField(fieldUserIconID, *c.Icon),
 592                                 NewField(fieldUserFlags, *c.Flags),
 593                         ),
 594                 )
 595         }
 596
 597         c.Server.Stats.LoginCount += 1
 598
 599         const readBuffSize = 1024000 // 1KB - TODO: what should this be?
 600         tranBuff := make([]byte, 0)
 601         tReadlen := 0
 602         // Infinite loop where take action on incoming client requests until the connection is closed
 603         for {
 604                 buf = make([]byte, readBuffSize)
 605                 tranBuff = tranBuff[tReadlen:]
 606
 607                 readLen, err := c.Connection.Read(buf)
 608                 if err != nil {
 609                         return err
 610                 }
 611                 tranBuff = append(tranBuff, buf[:readLen]...)
 612
 613                 // We may have read multiple requests worth of bytes from Connection.Read.  readTransactions splits them
 614                 // into a slice of transactions
 615                 var transactions []Transaction
 616                 if transactions, tReadlen, err = readTransactions(tranBuff); err != nil {
 617                         c.Server.Logger.Errorw("Error handling transaction", "err", err)
 618                 }
 619
 620                 // iterate over all of the transactions that were parsed from the byte slice and handle them
 621                 for _, t := range transactions {
 622                         if err := c.handleTransaction(&t); err != nil {
 623                                 c.Server.Logger.Errorw("Error handling transaction", "err", err)
 624                         }
 625                 }
 626         }
 627 }
 628
 629 // NewTransactionRef generates a random ID for the file transfer.  The Hotline client includes this ID
 630 // in the file transfer request payload, and the file transfer server will use it to map the request
 631 // to a transfer
 632 func (s *Server) NewTransactionRef() []byte {
 633         transactionRef := make([]byte, 4)
 634         rand.Read(transactionRef)
 635
 636         return transactionRef
 637 }
 638
 639 func (s *Server) NewPrivateChat(cc *ClientConn) []byte {
 640         s.mux.Lock()
 641         defer s.mux.Unlock()
 642
 643         randID := make([]byte, 4)
 644         rand.Read(randID)
 645         data := binary.BigEndian.Uint32(randID[:])
 646
 647         s.PrivateChats[data] = &PrivateChat{
 648                 Subject:    "",
 649                 ClientConn: make(map[uint16]*ClientConn),
 650         }
 651         s.PrivateChats[data].ClientConn[cc.uint16ID()] = cc
 652
 653         return randID
 654 }
 655
 656 const dlFldrActionSendFile = 1
 657 const dlFldrActionResumeFile = 2
 658 const dlFldrActionNextFile = 3
 659
 660 // handleFileTransfer receives a client net.Conn from the file transfer server, performs the requested transfer type, then closes the connection
 661 func (s *Server) handleFileTransfer(conn io.ReadWriteCloser) error {
 662         defer func() {
 663
 664                 if err := conn.Close(); err != nil {
 665                         s.Logger.Errorw("error closing connection", "error", err)
 666                 }
 667         }()
 668
 669         defer dontPanic(s.Logger)
 670
 671         txBuf := make([]byte, 16)
 672         if _, err := io.ReadFull(conn, txBuf); err != nil {
 673                 return err
 674         }
 675
 676         var t transfer
 677         if _, err := t.Write(txBuf); err != nil {
 678                 return err
 679         }
 680
 681         transferRefNum := binary.BigEndian.Uint32(t.ReferenceNumber[:])
 682         defer func() {
 683                 s.mux.Lock()
 684                 delete(s.FileTransfers, transferRefNum)
 685                 s.mux.Unlock()
 686         }()
 687
 688         s.mux.Lock()
 689         fileTransfer, ok := s.FileTransfers[transferRefNum]
 690         s.mux.Unlock()
 691         if !ok {
 692                 return errors.New("invalid transaction ID")
 693         }
 694
 695         switch fileTransfer.Type {
 696         case FileDownload:
 697                 fullFilePath, err := readPath(s.Config.FileRoot, fileTransfer.FilePath, fileTransfer.FileName)
 698                 if err != nil {
 699                         return err
 700                 }
 701
 702                 var dataOffset int64
 703                 if fileTransfer.fileResumeData != nil {
 704                         dataOffset = int64(binary.BigEndian.Uint32(fileTransfer.fileResumeData.ForkInfoList[0].DataSize[:]))
 705                 }
 706
 707                 ffo, err := NewFlattenedFileObject(s.Config.FileRoot, fileTransfer.FilePath, fileTransfer.FileName, dataOffset)
 708                 if err != nil {
 709                         return err
 710                 }
 711
 712                 s.Logger.Infow("File download started", "filePath", fullFilePath, "transactionRef", fileTransfer.ReferenceNumber)
 713
 714                 if fileTransfer.options == nil {
 715                         // Start by sending flat file object to client
 716                         if _, err := conn.Write(ffo.BinaryMarshal()); err != nil {
 717                                 return err
 718                         }
 719                 }
 720
 721                 file, err := FS.Open(fullFilePath)
 722                 if err != nil {
 723                         return err
 724                 }
 725
 726                 sendBuffer := make([]byte, 1048576)
 727                 var totalSent int64
 728                 for {
 729                         var bytesRead int
 730                         if bytesRead, err = file.ReadAt(sendBuffer, dataOffset+totalSent); err == io.EOF {
 731                                 if _, err := conn.Write(sendBuffer[:bytesRead]); err != nil {
 732                                         return err
 733                                 }
 734                                 break
 735                         }
 736                         if err != nil {
 737                                 return err
 738                         }
 739                         totalSent += int64(bytesRead)
 740
 741                         fileTransfer.BytesSent += bytesRead
 742
 743                         if _, err := conn.Write(sendBuffer[:bytesRead]); err != nil {
 744                                 return err
 745                         }
 746                 }
 747         case FileUpload:
 748                 destinationFile := s.Config.FileRoot + ReadFilePath(fileTransfer.FilePath) + "/" + string(fileTransfer.FileName)
 749
 750                 var file *os.File
 751
 752                 // A file upload has three possible cases:
 753                 // 1) Upload a new file
 754                 // 2) Resume a partially transferred file
 755                 // 3) Replace a fully uploaded file
 756                 // Unfortunately we have to infer which case applies by inspecting what is already on the file system
 757
 758                 // 1) Check for existing file:
 759                 _, err := os.Stat(destinationFile)
 760                 if err == nil {
 761                         // If found, that means this upload is intended to replace the file
 762                         if err = os.Remove(destinationFile); err != nil {
 763                                 return err
 764                         }
 765                         file, err = os.Create(destinationFile + incompleteFileSuffix)
 766                 }
 767                 if errors.Is(err, fs.ErrNotExist) {
 768                         // If not found, open or create a new incomplete file
 769                         file, err = os.OpenFile(destinationFile+incompleteFileSuffix, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0644)
 770                         if err != nil {
 771                                 return err
 772                         }
 773                 }
 774
 775                 defer func() { _ = file.Close() }()
 776
 777                 s.Logger.Infow("File upload started", "transactionRef", fileTransfer.ReferenceNumber, "dstFile", destinationFile)
 778
 779                 // TODO: replace io.Discard with a real file when ready to implement storing of resource fork data
 780                 if err := receiveFile(conn, file, io.Discard); err != nil {
 781                         return err
 782                 }
 783
 784                 if err := os.Rename(destinationFile+".incomplete", destinationFile); err != nil {
 785                         return err
 786                 }
 787
 788                 s.Logger.Infow("File upload complete", "transactionRef", fileTransfer.ReferenceNumber, "dstFile", destinationFile)
 789         case FolderDownload:
 790                 // Folder Download flow:
 791                 // 1. Get filePath from the transfer
 792                 // 2. Iterate over files
 793                 // 3. For each file:
 794                 //       Send file header to client
 795                 // The client can reply in 3 ways:
 796                 //
 797                 // 1. If type is an odd number (unknown type?), or file download for the current file is completed:
 798                 //              client sends []byte{0x00, 0x03} to tell the server to continue to the next file
 799                 //
 800                 // 2. If download of a file is to be resumed:
 801                 //              client sends:
 802                 //                      []byte{0x00, 0x02} // download folder action
 803                 //                      [2]byte // Resume data size
 804                 //                      []byte file resume data (see myField_FileResumeData)
 805                 //
 806                 // 3. Otherwise, download of the file is requested and client sends []byte{0x00, 0x01}
 807                 //
 808                 // When download is requested (case 2 or 3), server replies with:
 809                 //                      [4]byte - file size
 810                 //                      []byte  - Flattened File Object
 811                 //
 812                 // After every file download, client could request next file with:
 813                 //                      []byte{0x00, 0x03}
 814                 //
 815                 // This notifies the server to send the next item header
 816
 817                 fullFilePath, err := readPath(s.Config.FileRoot, fileTransfer.FilePath, fileTransfer.FileName)
 818                 if err != nil {
 819                         return err
 820                 }
 821
 822                 basePathLen := len(fullFilePath)
 823
 824                 s.Logger.Infow("Start folder download", "path", fullFilePath, "ReferenceNumber", fileTransfer.ReferenceNumber)
 825
 826                 nextAction := make([]byte, 2)
 827                 if _, err := io.ReadFull(conn, nextAction); err != nil {
 828                         return err
 829                 }
 830
 831                 i := 0
 832                 err = filepath.Walk(fullFilePath+"/", func(path string, info os.FileInfo, err error) error {
 833                         if err != nil {
 834                                 return err
 835                         }
 836                         i += 1
 837                         subPath := path[basePathLen+1:]
 838                         s.Logger.Infow("Sending fileheader", "i", i, "path", path, "fullFilePath", fullFilePath, "subPath", subPath, "IsDir", info.IsDir())
 839
 840                         if i == 1 {
 841                                 return nil
 842                         }
 843
 844                         fileHeader := NewFileHeader(subPath, info.IsDir())
 845
 846                         // Send the file header to client
 847                         if _, err := conn.Write(fileHeader.Payload()); err != nil {
 848                                 s.Logger.Errorf("error sending file header: %v", err)
 849                                 return err
 850                         }
 851
 852                         // Read the client's Next Action request
 853                         if _, err := io.ReadFull(conn, nextAction); err != nil {
 854                                 return err
 855                         }
 856
 857                         s.Logger.Infow("Client folder download action", "action", fmt.Sprintf("%X", nextAction[0:2]))
 858
 859                         var dataOffset int64
 860
 861                         switch nextAction[1] {
 862                         case dlFldrActionResumeFile:
 863                                 // client asked to resume this file
 864                                 var frd FileResumeData
 865                                 // get size of resumeData
 866                                 if _, err := io.ReadFull(conn, nextAction); err != nil {
 867                                         return err
 868                                 }
 869
 870                                 resumeDataLen := binary.BigEndian.Uint16(nextAction)
 871                                 resumeDataBytes := make([]byte, resumeDataLen)
 872                                 if _, err := io.ReadFull(conn, resumeDataBytes); err != nil {
 873                                         return err
 874                                 }
 875
 876                                 if err := frd.UnmarshalBinary(resumeDataBytes); err != nil {
 877                                         return err
 878                                 }
 879                                 dataOffset = int64(binary.BigEndian.Uint32(frd.ForkInfoList[0].DataSize[:]))
 880                         case dlFldrActionNextFile:
 881                                 // client asked to skip this file
 882                                 return nil
 883                         }
 884
 885                         if info.IsDir() {
 886                                 return nil
 887                         }
 888
 889                         splitPath := strings.Split(path, "/")
 890
 891                         ffo, err := NewFlattenedFileObject(strings.Join(splitPath[:len(splitPath)-1], "/"), nil, []byte(info.Name()), dataOffset)
 892                         if err != nil {
 893                                 return err
 894                         }
 895                         s.Logger.Infow("File download started",
 896                                 "fileName", info.Name(),
 897                                 "transactionRef", fileTransfer.ReferenceNumber,
 898                                 "TransferSize", fmt.Sprintf("%x", ffo.TransferSize()),
 899                         )
 900
 901                         // Send file size to client
 902                         if _, err := conn.Write(ffo.TransferSize()); err != nil {
 903                                 s.Logger.Error(err)
 904                                 return err
 905                         }
 906
 907                         // Send ffo bytes to client
 908                         if _, err := conn.Write(ffo.BinaryMarshal()); err != nil {
 909                                 s.Logger.Error(err)
 910                                 return err
 911                         }
 912
 913                         file, err := FS.Open(path)
 914                         if err != nil {
 915                                 return err
 916                         }
 917
 918                         // // Copy N bytes from file to connection
 919                         // _, err = io.CopyN(conn, file, int64(binary.BigEndian.Uint32(ffo.FlatFileDataForkHeader.DataSize[:])))
 920                         // if err != nil {
 921                         //      return err
 922                         // }
 923                         // file.Close()
 924                         sendBuffer := make([]byte, 1048576)
 925                         var totalSent int64
 926                         for {
 927                                 var bytesRead int
 928                                 if bytesRead, err = file.ReadAt(sendBuffer, dataOffset+totalSent); err == io.EOF {
 929                                         if _, err := conn.Write(sendBuffer[:bytesRead]); err != nil {
 930                                                 return err
 931                                         }
 932                                         break
 933                                 }
 934                                 if err != nil {
 935                                         panic(err)
 936                                 }
 937                                 totalSent += int64(bytesRead)
 938
 939                                 fileTransfer.BytesSent += bytesRead
 940
 941                                 if _, err := conn.Write(sendBuffer[:bytesRead]); err != nil {
 942                                         return err
 943                                 }
 944                         }
 945
 946                         // TODO: optionally send resource fork header and resource fork data
 947
 948                         // Read the client's Next Action request.  This is always 3, I think?
 949                         if _, err := io.ReadFull(conn, nextAction); err != nil {
 950                                 return err
 951                         }
 952
 953                         return nil
 954                 })
 955
 956         case FolderUpload:
 957                 dstPath, err := readPath(s.Config.FileRoot, fileTransfer.FilePath, fileTransfer.FileName)
 958                 if err != nil {
 959                         return err
 960                 }
 961                 s.Logger.Infow(
 962                         "Folder upload started",
 963                         "transactionRef", fileTransfer.ReferenceNumber,
 964                         "dstPath", dstPath,
 965                         "TransferSize", fmt.Sprintf("%x", fileTransfer.TransferSize),
 966                         "FolderItemCount", fileTransfer.FolderItemCount,
 967                 )
 968
 969                 // Check if the target folder exists.  If not, create it.
 970                 if _, err := FS.Stat(dstPath); os.IsNotExist(err) {
 971                         if err := FS.Mkdir(dstPath, 0777); err != nil {
 972                                 return err
 973                         }
 974                 }
 975
 976                 // Begin the folder upload flow by sending the "next file action" to client
 977                 if _, err := conn.Write([]byte{0, dlFldrActionNextFile}); err != nil {
 978                         return err
 979                 }
 980
 981                 fileSize := make([]byte, 4)
 982                 readBuffer := make([]byte, 1024)
 983
 984                 for i := 0; i < fileTransfer.ItemCount(); i++ {
 985                         // TODO: fix potential short read with io.ReadFull
 986                         _, err := conn.Read(readBuffer)
 987                         if err != nil {
 988                                 return err
 989                         }
 990                         fu := readFolderUpload(readBuffer)
 991
 992                         s.Logger.Infow(
 993                                 "Folder upload continued",
 994                                 "transactionRef", fmt.Sprintf("%x", fileTransfer.ReferenceNumber),
 995                                 "FormattedPath", fu.FormattedPath(),
 996                                 "IsFolder", fmt.Sprintf("%x", fu.IsFolder),
 997                                 "PathItemCount", binary.BigEndian.Uint16(fu.PathItemCount[:]),
 998                         )
 999
1000                         if fu.IsFolder == [2]byte{0, 1} {
1001                                 if _, err := os.Stat(dstPath + "/" + fu.FormattedPath()); os.IsNotExist(err) {
1002                                         if err := os.Mkdir(dstPath+"/"+fu.FormattedPath(), 0777); err != nil {
1003                                                 return err
1004                                         }
1005                                 }
1006
1007                                 // Tell client to send next file
1008                                 if _, err := conn.Write([]byte{0, dlFldrActionNextFile}); err != nil {
1009                                         return err
1010                                 }
1011                         } else {
1012                                 nextAction := dlFldrActionSendFile
1013
1014                                 // Check if we have the full file already.  If so, send dlFldrAction_NextFile to client to skip.
1015                                 _, err := os.Stat(dstPath + "/" + fu.FormattedPath())
1016                                 if err != nil && !errors.Is(err, fs.ErrNotExist) {
1017                                         return err
1018                                 }
1019                                 if err == nil {
1020                                         nextAction = dlFldrActionNextFile
1021                                 }
1022
1023                                 //  Check if we have a partial file already.  If so, send dlFldrAction_ResumeFile to client to resume upload.
1024                                 inccompleteFile, err := os.Stat(dstPath + "/" + fu.FormattedPath() + incompleteFileSuffix)
1025                                 if err != nil && !errors.Is(err, fs.ErrNotExist) {
1026                                         return err
1027                                 }
1028                                 if err == nil {
1029                                         nextAction = dlFldrActionResumeFile
1030                                 }
1031
1032                                 fmt.Printf("Next Action: %v\n", nextAction)
1033
1034                                 if _, err := conn.Write([]byte{0, uint8(nextAction)}); err != nil {
1035                                         return err
1036                                 }
1037
1038                                 switch nextAction {
1039                                 case dlFldrActionNextFile:
1040                                         continue
1041                                 case dlFldrActionResumeFile:
1042                                         offset := make([]byte, 4)
1043                                         binary.BigEndian.PutUint32(offset, uint32(inccompleteFile.Size()))
1044
1045                                         file, err := os.OpenFile(dstPath+"/"+fu.FormattedPath()+incompleteFileSuffix, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
1046                                         if err != nil {
1047                                                 return err
1048                                         }
1049
1050                                         fileResumeData := NewFileResumeData([]ForkInfoList{
1051                                                 *NewForkInfoList(offset),
1052                                         })
1053
1054                                         b, _ := fileResumeData.BinaryMarshal()
1055
1056                                         bs := make([]byte, 2)
1057                                         binary.BigEndian.PutUint16(bs, uint16(len(b)))
1058
1059                                         if _, err := conn.Write(append(bs, b...)); err != nil {
1060                                                 return err
1061                                         }
1062
1063                                         if _, err := io.ReadFull(conn, fileSize); err != nil {
1064                                                 return err
1065                                         }
1066
1067                                         if err := receiveFile(conn, file, ioutil.Discard); err != nil {
1068                                                 s.Logger.Error(err)
1069                                         }
1070
1071                                         err = os.Rename(dstPath+"/"+fu.FormattedPath()+".incomplete", dstPath+"/"+fu.FormattedPath())
1072                                         if err != nil {
1073                                                 return err
1074                                         }
1075
1076                                 case dlFldrActionSendFile:
1077                                         if _, err := conn.Read(fileSize); err != nil {
1078                                                 return err
1079                                         }
1080
1081                                         filePath := dstPath + "/" + fu.FormattedPath()
1082                                         s.Logger.Infow("Starting file transfer", "path", filePath, "fileNum", i+1, "totalFiles", "zz", "fileSize", binary.BigEndian.Uint32(fileSize))
1083
1084                                         newFile, err := FS.Create(filePath + ".incomplete")
1085                                         if err != nil {
1086                                                 return err
1087                                         }
1088
1089                                         if err := receiveFile(conn, newFile, ioutil.Discard); err != nil {
1090                                                 s.Logger.Error(err)
1091                                         }
1092                                         _ = newFile.Close()
1093                                         if err := os.Rename(filePath+".incomplete", filePath); err != nil {
1094                                                 return err
1095                                         }
1096                                 }
1097
1098                                 // Tell client to send next file
1099                                 if _, err := conn.Write([]byte{0, dlFldrActionNextFile}); err != nil {
1100                                         return err
1101                                 }
1102                         }
1103                 }
1104                 s.Logger.Infof("Folder upload complete")
1105         }
1106
1107         return nil
1108 }
1109
1110 // sortedClients is a utility function that takes a map of *ClientConn and returns a sorted slice of the values.
1111 // The purpose of this is to ensure that the ordering of client connections is deterministic so that test assertions work.
1112 func sortedClients(unsortedClients map[uint16]*ClientConn) (clients []*ClientConn) {
1113         for _, c := range unsortedClients {
1114                 clients = append(clients, c)
1115         }
1116         sort.Sort(byClientID(clients))
1117         return clients
1118 }