Move code to hotline dir

1 files changed, 1035 insertions, 0 deletions

diff --git a/hotline/server.go b/hotline/server.go
new file mode 100644
index 0000000..e51f673
--- /dev/null
+++ b/hotline/server.go
@@ -0,0 +1,1035 @@
+package hotline
+
+import (
+	"bytes"
+	"context"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"go.uber.org/zap"
+	"io"
+	"io/ioutil"
+	"log"
+	"math/big"
+	"math/rand"
+	"net"
+	"os"
+	"path"
+	"path/filepath"
+	"runtime/debug"
+	"sort"
+	"strings"
+	"sync"
+	"time"
+
+	"golang.org/x/crypto/bcrypt"
+	"gopkg.in/yaml.v2"
+)
+
+const (
+	userIdleSeconds        = 300 // time in seconds before an inactive user is marked idle
+	idleCheckInterval      = 10  // time in seconds to check for idle users
+	trackerUpdateFrequency = 300 // time in seconds between tracker re-registration
+)
+
+type Server struct {
+	Interface     string
+	Port          int
+	Accounts      map[string]*Account
+	Agreement     []byte
+	Clients       map[uint16]*ClientConn
+	FlatNews      []byte
+	ThreadedNews  *ThreadedNews
+	FileTransfers map[uint32]*FileTransfer
+	Config        *Config
+	ConfigDir     string
+	Logger        *zap.SugaredLogger
+	PrivateChats  map[uint32]*PrivateChat
+	NextGuestID   *uint16
+	TrackerPassID []byte
+	Stats         *Stats
+
+	APIListener  net.Listener
+	FileListener net.Listener
+
+	newsReader io.Reader
+	newsWriter io.WriteCloser
+
+	outbox chan Transaction
+
+	mux         sync.Mutex
+	flatNewsMux sync.Mutex
+}
+
+type PrivateChat struct {
+	Subject    string
+	ClientConn map[uint16]*ClientConn
+}
+
+func (s *Server) ListenAndServe(ctx context.Context, cancelRoot context.CancelFunc) error {
+	s.Logger.Infow("Hotline server started", "version", VERSION)
+	var wg sync.WaitGroup
+
+	wg.Add(1)
+	go func() { s.Logger.Fatal(s.Serve(ctx, cancelRoot, s.APIListener)) }()
+
+	wg.Add(1)
+	go func() { s.Logger.Fatal(s.ServeFileTransfers(s.FileListener)) }()
+
+	wg.Wait()
+
+	return nil
+}
+
+func (s *Server) APIPort() int {
+	return s.APIListener.Addr().(*net.TCPAddr).Port
+}
+
+func (s *Server) ServeFileTransfers(ln net.Listener) error {
+	s.Logger.Infow("Hotline file transfer server started", "Addr", fmt.Sprintf(":%v", s.Port+1))
+
+	for {
+		conn, err := ln.Accept()
+		if err != nil {
+			return err
+		}
+
+		go func() {
+			if err := s.TransferFile(conn); err != nil {
+				s.Logger.Errorw("file transfer error", "reason", err)
+			}
+		}()
+	}
+}
+
+func (s *Server) sendTransaction(t Transaction) error {
+	requestNum := binary.BigEndian.Uint16(t.Type)
+	clientID, err := byteToInt(*t.clientID)
+	if err != nil {
+		return err
+	}
+
+	s.mux.Lock()
+	client := s.Clients[uint16(clientID)]
+	s.mux.Unlock()
+	if client == nil {
+		return errors.New("invalid client")
+	}
+	userName := string(*client.UserName)
+	login := client.Account.Login
+
+	handler := TransactionHandlers[requestNum]
+
+	var n int
+	if n, err = client.Connection.Write(t.Payload()); err != nil {
+		return err
+	}
+	s.Logger.Debugw("Sent Transaction",
+		"name", userName,
+		"login", login,
+		"IsReply", t.IsReply,
+		"type", handler.Name,
+		"sentBytes", n,
+		"remoteAddr", client.Connection.RemoteAddr(),
+	)
+	return nil
+}
+
+func (s *Server) Serve(ctx context.Context, cancelRoot context.CancelFunc, ln net.Listener) error {
+	s.Logger.Infow("Hotline server started", "Addr", fmt.Sprintf(":%v", s.Port))
+
+	for {
+		conn, err := ln.Accept()
+		if err != nil {
+			s.Logger.Errorw("error accepting connection", "err", err)
+		}
+
+		go func() {
+			for {
+				t := <-s.outbox
+				go func() {
+					if err := s.sendTransaction(t); err != nil {
+						s.Logger.Errorw("error sending transaction", "err", err)
+					}
+				}()
+			}
+		}()
+		go func() {
+			if err := s.handleNewConnection(conn); err != nil {
+				if err == io.EOF {
+					s.Logger.Infow("Client disconnected", "RemoteAddr", conn.RemoteAddr())
+				} else {
+					s.Logger.Errorw("error serving request", "RemoteAddr", conn.RemoteAddr(), "err", err)
+				}
+			}
+		}()
+	}
+}
+
+const (
+	agreementFile    = "Agreement.txt"
+	messageBoardFile = "MessageBoard.txt"
+	threadedNewsFile = "ThreadedNews.yaml"
+)
+
+// NewServer constructs a new Server from a config dir
+func NewServer(configDir, netInterface string, netPort int, logger *zap.SugaredLogger) (*Server, error) {
+	server := Server{
+		Port:          netPort,
+		Accounts:      make(map[string]*Account),
+		Config:        new(Config),
+		Clients:       make(map[uint16]*ClientConn),
+		FileTransfers: make(map[uint32]*FileTransfer),
+		PrivateChats:  make(map[uint32]*PrivateChat),
+		ConfigDir:     configDir,
+		Logger:        logger,
+		NextGuestID:   new(uint16),
+		outbox:        make(chan Transaction),
+		Stats:         &Stats{StartTime: time.Now()},
+		ThreadedNews:  &ThreadedNews{},
+		TrackerPassID: make([]byte, 4),
+	}
+
+	ln, err := net.Listen("tcp", fmt.Sprintf("%s:%v", netInterface, netPort))
+	if err != nil {
+		return nil, err
+	}
+	server.APIListener = ln
+
+	if netPort != 0 {
+		netPort += 1
+	}
+
+	ln2, err := net.Listen("tcp", fmt.Sprintf("%s:%v", netInterface, netPort))
+	server.FileListener = ln2
+	if err != nil {
+		return nil, err
+	}
+
+	// generate a new random passID for tracker registration
+	if _, err := rand.Read(server.TrackerPassID); err != nil {
+		return nil, err
+	}
+
+	server.Logger.Debugw("Loading Agreement", "path", configDir+agreementFile)
+	if server.Agreement, err = os.ReadFile(configDir + agreementFile); err != nil {
+		return nil, err
+	}
+
+	if server.FlatNews, err = os.ReadFile(configDir + "MessageBoard.txt"); err != nil {
+		return nil, err
+	}
+
+	if err := server.loadThreadedNews(configDir + "ThreadedNews.yaml"); err != nil {
+		return nil, err
+	}
+
+	if err := server.loadConfig(configDir + "config.yaml"); err != nil {
+		return nil, err
+	}
+
+	if err := server.loadAccounts(configDir + "Users/"); err != nil {
+		return nil, err
+	}
+
+	server.Config.FileRoot = configDir + "Files/"
+
+	*server.NextGuestID = 1
+
+	if server.Config.EnableTrackerRegistration {
+		go func() {
+			for {
+				tr := TrackerRegistration{
+					Port:        []byte{0x15, 0x7c},
+					UserCount:   server.userCount(),
+					PassID:      server.TrackerPassID,
+					Name:        server.Config.Name,
+					Description: server.Config.Description,
+				}
+				for _, t := range server.Config.Trackers {
+					server.Logger.Infof("Registering with tracker %v", t)
+
+					if err := register(t, tr); err != nil {
+						server.Logger.Errorw("unable to register with tracker %v", "error", err)
+					}
+				}
+
+				time.Sleep(trackerUpdateFrequency * time.Second)
+			}
+		}()
+	}
+
+	// Start Client Keepalive go routine
+	go server.keepaliveHandler()
+
+	return &server, nil
+}
+
+func (s *Server) userCount() int {
+	s.mux.Lock()
+	defer s.mux.Unlock()
+
+	return len(s.Clients)
+}
+
+func (s *Server) keepaliveHandler() {
+	for {
+		time.Sleep(idleCheckInterval * time.Second)
+		s.mux.Lock()
+
+		for _, c := range s.Clients {
+			*c.IdleTime += idleCheckInterval
+			if *c.IdleTime > userIdleSeconds && !c.Idle {
+				c.Idle = true
+
+				flagBitmap := big.NewInt(int64(binary.BigEndian.Uint16(*c.Flags)))
+				flagBitmap.SetBit(flagBitmap, userFlagAway, 1)
+				binary.BigEndian.PutUint16(*c.Flags, uint16(flagBitmap.Int64()))
+
+				c.sendAll(
+					tranNotifyChangeUser,
+					NewField(fieldUserID, *c.ID),
+					NewField(fieldUserFlags, *c.Flags),
+					NewField(fieldUserName, *c.UserName),
+					NewField(fieldUserIconID, *c.Icon),
+				)
+			}
+		}
+		s.mux.Unlock()
+	}
+}
+
+func (s *Server) writeThreadedNews() error {
+	s.mux.Lock()
+	defer s.mux.Unlock()
+
+	out, err := yaml.Marshal(s.ThreadedNews)
+	if err != nil {
+		return err
+	}
+	err = ioutil.WriteFile(
+		s.ConfigDir+"ThreadedNews.yaml",
+		out,
+		0666,
+	)
+	return err
+}
+
+func (s *Server) NewClientConn(conn net.Conn) *ClientConn {
+	s.mux.Lock()
+	defer s.mux.Unlock()
+
+	clientConn := &ClientConn{
+		ID:         &[]byte{0, 0},
+		Icon:       &[]byte{0, 0},
+		Flags:      &[]byte{0, 0},
+		UserName:   &[]byte{},
+		Connection: conn,
+		Server:     s,
+		Version:    &[]byte{},
+		IdleTime:   new(int),
+		AutoReply:  &[]byte{},
+		Transfers:  make(map[int][]*FileTransfer),
+	}
+	*s.NextGuestID++
+	ID := *s.NextGuestID
+
+	*clientConn.IdleTime = 0
+
+	binary.BigEndian.PutUint16(*clientConn.ID, ID)
+	s.Clients[ID] = clientConn
+
+	return clientConn
+}
+
+// NewUser creates a new user account entry in the server map and config file
+func (s *Server) NewUser(login, name, password string, access []byte) error {
+	s.mux.Lock()
+	defer s.mux.Unlock()
+
+	account := Account{
+		Login:    login,
+		Name:     name,
+		Password: hashAndSalt([]byte(password)),
+		Access:   &access,
+	}
+	out, err := yaml.Marshal(&account)
+	if err != nil {
+		return err
+	}
+	s.Accounts[login] = &account
+
+	return ioutil.WriteFile(s.ConfigDir+"Users/"+login+".yaml", out, 0666)
+}
+
+// DeleteUser deletes the user account
+func (s *Server) DeleteUser(login string) error {
+	s.mux.Lock()
+	defer s.mux.Unlock()
+
+	delete(s.Accounts, login)
+
+	return os.Remove(s.ConfigDir + "Users/" + login + ".yaml")
+}
+
+func (s *Server) connectedUsers() []Field {
+	s.mux.Lock()
+	defer s.mux.Unlock()
+
+	var connectedUsers []Field
+	for _, c := range s.Clients {
+		user := User{
+			ID:    *c.ID,
+			Icon:  *c.Icon,
+			Flags: *c.Flags,
+			Name:  string(*c.UserName),
+		}
+		connectedUsers = append(connectedUsers, NewField(fieldUsernameWithInfo, user.Payload()))
+	}
+	return connectedUsers
+}
+
+// loadThreadedNews loads the threaded news data from disk
+func (s *Server) loadThreadedNews(threadedNewsPath string) error {
+	fh, err := os.Open(threadedNewsPath)
+	if err != nil {
+		return err
+	}
+	decoder := yaml.NewDecoder(fh)
+	decoder.SetStrict(true)
+
+	return decoder.Decode(s.ThreadedNews)
+}
+
+// loadAccounts loads account data from disk
+func (s *Server) loadAccounts(userDir string) error {
+	matches, err := filepath.Glob(path.Join(userDir, "*.yaml"))
+	if err != nil {
+		return err
+	}
+
+	if len(matches) == 0 {
+		return errors.New("no user accounts found in " + userDir)
+	}
+
+	for _, file := range matches {
+		fh, err := os.Open(file)
+		if err != nil {
+			return err
+		}
+
+		account := Account{}
+		decoder := yaml.NewDecoder(fh)
+		decoder.SetStrict(true)
+		if err := decoder.Decode(&account); err != nil {
+			return err
+		}
+
+		s.Accounts[account.Login] = &account
+	}
+	return nil
+}
+
+func (s *Server) loadConfig(path string) error {
+	fh, err := os.Open(path)
+	if err != nil {
+		return err
+	}
+
+	decoder := yaml.NewDecoder(fh)
+	decoder.SetStrict(true)
+	err = decoder.Decode(s.Config)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+const (
+	minTransactionLen = 22 // minimum length of any transaction
+)
+
+// handleNewConnection takes a new net.Conn and performs the initial login sequence
+func (s *Server) handleNewConnection(conn net.Conn) error {
+	handshakeBuf := make([]byte, 12) // handshakes are always 12 bytes in length
+	if _, err := conn.Read(handshakeBuf); err != nil {
+		return err
+	}
+	if err := Handshake(conn, handshakeBuf[:12]); err != nil {
+		return err
+	}
+
+	buf := make([]byte, 1024)
+	readLen, err := conn.Read(buf)
+	if readLen < minTransactionLen {
+		return err
+	}
+	if err != nil {
+		return err
+	}
+
+	clientLogin, _, err := ReadTransaction(buf[:readLen])
+	if err != nil {
+		return err
+	}
+
+	c := s.NewClientConn(conn)
+	defer c.Disconnect()
+	defer func() {
+		if r := recover(); r != nil {
+			fmt.Println("stacktrace from panic: \n" + string(debug.Stack()))
+			c.Server.Logger.Errorw("PANIC", "err", r, "trace", string(debug.Stack()))
+			c.Disconnect()
+		}
+	}()
+
+	encodedLogin := clientLogin.GetField(fieldUserLogin).Data
+	encodedPassword := clientLogin.GetField(fieldUserPassword).Data
+	*c.Version = clientLogin.GetField(fieldVersion).Data
+
+	var login string
+	for _, char := range encodedLogin {
+		login += string(rune(255 - uint(char)))
+	}
+	if login == "" {
+		login = GuestAccount
+	}
+
+	// If authentication fails, send error reply and close connection
+	if !c.Authenticate(login, encodedPassword) {
+		rep := c.NewErrReply(clientLogin, "Incorrect login.")
+		if _, err := conn.Write(rep.Payload()); err != nil {
+			return err
+		}
+		return fmt.Errorf("incorrect login")
+	}
+
+	if clientLogin.GetField(fieldUserName).Data != nil {
+		*c.UserName = clientLogin.GetField(fieldUserName).Data
+	}
+
+	if clientLogin.GetField(fieldUserIconID).Data != nil {
+		*c.Icon = clientLogin.GetField(fieldUserIconID).Data
+	}
+
+	c.Account = c.Server.Accounts[login]
+
+	if c.Authorize(accessDisconUser) {
+		*c.Flags = []byte{0, 2}
+	}
+
+	s.Logger.Infow("Client connection received", "login", login, "version", *c.Version, "RemoteAddr", conn.RemoteAddr().String())
+
+	s.outbox <- c.NewReply(clientLogin,
+		NewField(fieldVersion, []byte{0x00, 0xbe}),
+		NewField(fieldCommunityBannerID, []byte{0x00, 0x01}),
+		NewField(fieldServerName, []byte(s.Config.Name)),
+	)
+
+	// Send user access privs so client UI knows how to behave
+	c.Server.outbox <- *NewTransaction(tranUserAccess, c.ID, NewField(fieldUserAccess, *c.Account.Access))
+
+	// Show agreement to client
+	c.Server.outbox <- *NewTransaction(tranShowAgreement, c.ID, NewField(fieldData, s.Agreement))
+
+	if _, err := c.notifyNewUserHasJoined(); err != nil {
+		return err
+	}
+	c.Server.Stats.LoginCount += 1
+
+	const readBuffSize = 1024000 // 1KB - TODO: what should this be?
+	const maxTranSize = 1024000
+	tranBuff := make([]byte, 0)
+	tReadlen := 0
+	// Infinite loop where take action on incoming client requests until the connection is closed
+	for {
+		buf = make([]byte, readBuffSize)
+		tranBuff = tranBuff[tReadlen:]
+
+		readLen, err := c.Connection.Read(buf)
+		if err != nil {
+			return err
+		}
+		tranBuff = append(tranBuff, buf[:readLen]...)
+
+		// We may have read multiple requests worth of bytes from Connection.Read.  readTransactions splits them
+		// into a slice of transactions
+		var transactions []Transaction
+		if transactions, tReadlen, err = readTransactions(tranBuff); err != nil {
+			c.Server.Logger.Errorw("Error handling transaction", "err", err)
+		}
+
+		// iterate over all of the transactions that were parsed from the byte slice and handle them
+		for _, t := range transactions {
+			if err := c.handleTransaction(&t); err != nil {
+				c.Server.Logger.Errorw("Error handling transaction", "err", err)
+			}
+		}
+	}
+}
+
+func hashAndSalt(pwd []byte) string {
+	// Use GenerateFromPassword to hash & salt pwd.
+	// MinCost is just an integer constant provided by the bcrypt
+	// package along with DefaultCost & MaxCost.
+	// The cost can be any value you want provided it isn't lower
+	// than the MinCost (4)
+	hash, err := bcrypt.GenerateFromPassword(pwd, bcrypt.MinCost)
+	if err != nil {
+		log.Println(err)
+	}
+	// GenerateFromPassword returns a byte slice so we need to
+	// convert the bytes to a string and return it
+	return string(hash)
+}
+
+// NewTransactionRef generates a random ID for the file transfer.  The Hotline client includes this ID
+// in the file transfer request payload, and the file transfer server will use it to map the request
+// to a transfer
+func (s *Server) NewTransactionRef() []byte {
+	transactionRef := make([]byte, 4)
+	rand.Read(transactionRef)
+
+	return transactionRef
+}
+
+func (s *Server) NewPrivateChat(cc *ClientConn) []byte {
+	s.mux.Lock()
+	defer s.mux.Unlock()
+
+	randID := make([]byte, 4)
+	rand.Read(randID)
+	data := binary.BigEndian.Uint32(randID[:])
+
+	s.PrivateChats[data] = &PrivateChat{
+		Subject:    "",
+		ClientConn: make(map[uint16]*ClientConn),
+	}
+	s.PrivateChats[data].ClientConn[cc.uint16ID()] = cc
+
+	return randID
+}
+
+const dlFldrActionSendFile = 1
+const dlFldrActionResumeFile = 2
+const dlFldrActionNextFile = 3
+
+func (s *Server) TransferFile(conn net.Conn) error {
+	defer func() { _ = conn.Close() }()
+
+	buf := make([]byte, 1024)
+	if _, err := conn.Read(buf); err != nil {
+		return err
+	}
+
+	t, err := NewReadTransfer(buf)
+	if err != nil {
+		return err
+	}
+
+	transferRefNum := binary.BigEndian.Uint32(t.ReferenceNumber[:])
+	fileTransfer := s.FileTransfers[transferRefNum]
+
+	switch fileTransfer.Type {
+	case FileDownload:
+		fullFilePath := fmt.Sprintf("%v/%v", s.Config.FileRoot+string(fileTransfer.FilePath), string(fileTransfer.FileName))
+
+		ffo, err := NewFlattenedFileObject(
+			s.Config.FileRoot+string(fileTransfer.FilePath),
+			string(fileTransfer.FileName),
+		)
+		if err != nil {
+			return err
+		}
+
+		s.Logger.Infow("File download started", "filePath", fullFilePath, "transactionRef", fileTransfer.ReferenceNumber, "RemoteAddr", conn.RemoteAddr().String())
+
+		// Start by sending flat file object to client
+		if _, err := conn.Write(ffo.Payload()); err != nil {
+			return err
+		}
+
+		file, err := os.Open(fullFilePath)
+		if err != nil {
+			return err
+		}
+
+		sendBuffer := make([]byte, 1048576)
+		for {
+			var bytesRead int
+			if bytesRead, err = file.Read(sendBuffer); err == io.EOF {
+				break
+			}
+
+			fileTransfer.BytesSent += bytesRead
+
+			delete(s.FileTransfers, transferRefNum)
+
+			if _, err := conn.Write(sendBuffer[:bytesRead]); err != nil {
+				return err
+			}
+		}
+	case FileUpload:
+		if _, err := conn.Read(buf); err != nil {
+			return err
+		}
+
+		ffo := ReadFlattenedFileObject(buf)
+		payloadLen := len(ffo.Payload())
+		fileSize := int(binary.BigEndian.Uint32(ffo.FlatFileDataForkHeader.DataSize))
+
+		destinationFile := s.Config.FileRoot + ReadFilePath(fileTransfer.FilePath) + "/" + string(fileTransfer.FileName)
+		s.Logger.Infow(
+			"File upload started",
+			"transactionRef", fileTransfer.ReferenceNumber,
+			"RemoteAddr", conn.RemoteAddr().String(),
+			"size", fileSize,
+			"dstFile", destinationFile,
+		)
+
+		newFile, err := os.Create(destinationFile)
+		if err != nil {
+			return err
+		}
+
+		defer func() { _ = newFile.Close() }()
+
+		const buffSize = 1024
+
+		if _, err := newFile.Write(buf[payloadLen:]); err != nil {
+			return err
+		}
+		receivedBytes := buffSize - payloadLen
+
+		for {
+			if (fileSize - receivedBytes) < buffSize {
+				s.Logger.Infow(
+					"File upload complete",
+					"transactionRef", fileTransfer.ReferenceNumber,
+					"RemoteAddr", conn.RemoteAddr().String(),
+					"size", fileSize,
+					"dstFile", destinationFile,
+				)
+
+				if _, err := io.CopyN(newFile, conn, int64(fileSize-receivedBytes)); err != nil {
+					return fmt.Errorf("file transfer failed: %s", err)
+				}
+				return nil
+			}
+
+			// Copy N bytes from conn to upload file
+			n, err := io.CopyN(newFile, conn, buffSize)
+			if err != nil {
+				return err
+			}
+			receivedBytes += int(n)
+		}
+	case FolderDownload:
+		// Folder Download flow:
+		// 1. Get filePath from the Transfer
+		// 2. Iterate over files
+		// 3. For each file:
+		// 	 Send file header to client
+		// The client can reply in 3 ways:
+		//
+		// 1. If type is an odd number (unknown type?), or file download for the current file is completed:
+		//		client sends []byte{0x00, 0x03} to tell the server to continue to the next file
+		//
+		// 2. If download of a file is to be resumed:
+		//		client sends:
+		//			[]byte{0x00, 0x02} // download folder action
+		//			[2]byte // Resume data size
+		//			[]byte file resume data (see myField_FileResumeData)
+		//
+		// 3. Otherwise download of the file is requested and client sends []byte{0x00, 0x01}
+		//
+		// When download is requested (case 2 or 3), server replies with:
+		// 			[4]byte - file size
+		//			[]byte  - Flattened File Object
+		//
+		// After every file download, client could request next file with:
+		// 			[]byte{0x00, 0x03}
+		//
+		// This notifies the server to send the next item header
+
+		fh := NewFilePath(fileTransfer.FilePath)
+		fullFilePath := fmt.Sprintf("%v/%v", s.Config.FileRoot+fh.String(), string(fileTransfer.FileName))
+
+		basePathLen := len(fullFilePath)
+
+		readBuffer := make([]byte, 1024)
+
+		s.Logger.Infow("Start folder download", "path", fullFilePath, "ReferenceNumber", fileTransfer.ReferenceNumber, "RemoteAddr", conn.RemoteAddr())
+
+		i := 0
+		_ = filepath.Walk(fullFilePath+"/", func(path string, info os.FileInfo, _ error) error {
+			i += 1
+			subPath := path[basePathLen-2:]
+			s.Logger.Infow("Sending fileheader", "i", i, "path", path, "fullFilePath", fullFilePath, "subPath", subPath, "IsDir", info.IsDir())
+
+			fileHeader := NewFileHeader(subPath, info.IsDir())
+
+			if i == 1 {
+				return nil
+			}
+
+			// Send the file header to client
+			if _, err := conn.Write(fileHeader.Payload()); err != nil {
+				s.Logger.Errorf("error sending file header: %v", err)
+				return err
+			}
+
+			// Read the client's Next Action request
+			//TODO: Remove hardcoded behavior and switch behaviors based on the next action send
+			if _, err := conn.Read(readBuffer); err != nil {
+				s.Logger.Errorf("error reading next action: %v", err)
+				return err
+			}
+
+			s.Logger.Infow("Client folder download action", "action", fmt.Sprintf("%X", readBuffer[0:2]))
+
+			if info.IsDir() {
+				return nil
+			}
+
+			splitPath := strings.Split(path, "/")
+			//strings.Join(splitPath[:len(splitPath)-1], "/")
+
+			ffo, err := NewFlattenedFileObject(strings.Join(splitPath[:len(splitPath)-1], "/"), info.Name())
+			if err != nil {
+				return err
+			}
+			s.Logger.Infow("File download started",
+				"fileName", info.Name(),
+				"transactionRef", fileTransfer.ReferenceNumber,
+				"RemoteAddr", conn.RemoteAddr().String(),
+				"TransferSize", fmt.Sprintf("%x", ffo.TransferSize()),
+			)
+
+			// Send file size to client
+			if _, err := conn.Write(ffo.TransferSize()); err != nil {
+				s.Logger.Error(err)
+				return err
+			}
+
+			// Send file bytes to client
+			if _, err := conn.Write(ffo.Payload()); err != nil {
+				s.Logger.Error(err)
+				return err
+			}
+
+			file, err := os.Open(path)
+			if err != nil {
+				return err
+			}
+
+			sendBuffer := make([]byte, 1048576)
+			totalBytesSent := len(ffo.Payload())
+
+			for {
+				bytesRead, err := file.Read(sendBuffer)
+				if err == io.EOF {
+					// Read the client's Next Action request
+					//TODO: Remove hardcoded behavior and switch behaviors based on the next action send
+					if _, err := conn.Read(readBuffer); err != nil {
+						s.Logger.Errorf("error reading next action: %v", err)
+						return err
+					}
+					break
+				}
+
+				sentBytes, readErr := conn.Write(sendBuffer[:bytesRead])
+				totalBytesSent += sentBytes
+				if readErr != nil {
+					return err
+				}
+			}
+			return nil
+		})
+
+	case FolderUpload:
+		dstPath := s.Config.FileRoot + ReadFilePath(fileTransfer.FilePath) + "/" + string(fileTransfer.FileName)
+		s.Logger.Infow(
+			"Folder upload started",
+			"transactionRef", fileTransfer.ReferenceNumber,
+			"RemoteAddr", conn.RemoteAddr().String(),
+			"dstPath", dstPath,
+			"TransferSize", fileTransfer.TransferSize,
+			"FolderItemCount", fileTransfer.FolderItemCount,
+		)
+
+		// Check if the target folder exists.  If not, create it.
+		if _, err := os.Stat(dstPath); os.IsNotExist(err) {
+			s.Logger.Infow("Target path does not exist; Creating...", "dstPath", dstPath)
+			if err := os.Mkdir(dstPath, 0777); err != nil {
+				s.Logger.Error(err)
+			}
+		}
+
+		readBuffer := make([]byte, 1024)
+
+		// Begin the folder upload flow by sending the "next file action" to client
+		if _, err := conn.Write([]byte{0, dlFldrActionNextFile}); err != nil {
+			return err
+		}
+
+		fileSize := make([]byte, 4)
+		itemCount := binary.BigEndian.Uint16(fileTransfer.FolderItemCount)
+
+		for i := uint16(0); i < itemCount; i++ {
+			if _, err := conn.Read(readBuffer); err != nil {
+				return err
+			}
+			fu := readFolderUpload(readBuffer)
+
+			s.Logger.Infow(
+				"Folder upload continued",
+				"transactionRef", fmt.Sprintf("%x", fileTransfer.ReferenceNumber),
+				"RemoteAddr", conn.RemoteAddr().String(),
+				"FormattedPath", fu.FormattedPath(),
+				"IsFolder", fmt.Sprintf("%x", fu.IsFolder),
+				"PathItemCount", binary.BigEndian.Uint16(fu.PathItemCount),
+			)
+
+			if bytes.Equal(fu.IsFolder, []byte{0, 1}) {
+				if _, err := os.Stat(dstPath + "/" + fu.FormattedPath()); os.IsNotExist(err) {
+					s.Logger.Infow("Target path does not exist; Creating...", "dstPath", dstPath)
+					if err := os.Mkdir(dstPath+"/"+fu.FormattedPath(), 0777); err != nil {
+						s.Logger.Error(err)
+					}
+				}
+
+				// Tell client to send next file
+				if _, err := conn.Write([]byte{0, dlFldrActionNextFile}); err != nil {
+					s.Logger.Error(err)
+					return err
+				}
+			} else {
+				// TODO: Check if we have the full file already.  If so, send dlFldrAction_NextFile to client to skip.
+				// TODO: Check if we have a partial file already.  If so, send dlFldrAction_ResumeFile to client to resume upload.
+				// Send dlFldrAction_SendFile to client to begin transfer
+				if _, err := conn.Write([]byte{0, dlFldrActionSendFile}); err != nil {
+					return err
+				}
+
+				if _, err := conn.Read(fileSize); err != nil {
+					fmt.Println("Error reading:", err.Error()) // TODO: handle
+				}
+
+				s.Logger.Infow("Starting file transfer", "fileNum", i+1, "totalFiles", itemCount, "fileSize", fileSize)
+
+				if err := transferFile(conn, dstPath+"/"+fu.FormattedPath()); err != nil {
+					s.Logger.Error(err)
+				}
+
+				// Tell client to send next file
+				if _, err := conn.Write([]byte{0, dlFldrActionNextFile}); err != nil {
+					s.Logger.Error(err)
+					return err
+				}
+
+				// Client sends "MACR" after the file.  Read and discard.
+				// TODO: This doesn't seem to be documented.  What is this?  Maybe resource fork?
+				if _, err := conn.Read(readBuffer); err != nil {
+					return err
+				}
+			}
+		}
+		s.Logger.Infof("Folder upload complete")
+	}
+
+	return nil
+}
+
+func transferFile(conn net.Conn, dst string) error {
+	const buffSize = 1024
+	buf := make([]byte, buffSize)
+
+	// Read first chunk of bytes from conn; this will be the Flat File Object and initial chunk of file bytes
+	if _, err := conn.Read(buf); err != nil {
+		return err
+	}
+	ffo := ReadFlattenedFileObject(buf)
+	payloadLen := len(ffo.Payload())
+	fileSize := int(binary.BigEndian.Uint32(ffo.FlatFileDataForkHeader.DataSize))
+
+	newFile, err := os.Create(dst)
+	if err != nil {
+		return err
+	}
+	defer func() { _ = newFile.Close() }()
+	if _, err := newFile.Write(buf[payloadLen:]); err != nil {
+		return err
+	}
+	receivedBytes := buffSize - payloadLen
+
+	for {
+		if (fileSize - receivedBytes) < buffSize {
+			_, err := io.CopyN(newFile, conn, int64(fileSize-receivedBytes))
+			return err
+		}
+
+		// Copy N bytes from conn to upload file
+		n, err := io.CopyN(newFile, conn, buffSize)
+		if err != nil {
+			return err
+		}
+		receivedBytes += int(n)
+	}
+}
+
+// 00 28 // DataSize
+// 00 00 // IsFolder
+// 00 02 // PathItemCount
+//
+// 00 00
+// 09
+// 73 75 62 66 6f 6c 64 65 72 // "subfolder"
+//
+// 00 00
+// 15
+// 73 75 62 66 6f 6c 64 65 72 2d 74 65 73 74 66 69 6c 65 2d 35 6b // "subfolder-testfile-5k"
+func readFolderUpload(buf []byte) folderUpload {
+	dataLen := binary.BigEndian.Uint16(buf[0:2])
+
+	fu := folderUpload{
+		DataSize:      buf[0:2], // Size of this structure (not including data size element itself)
+		IsFolder:      buf[2:4],
+		PathItemCount: buf[4:6],
+		FileNamePath:  buf[6 : dataLen+2],
+	}
+
+	return fu
+}
+
+type folderUpload struct {
+	DataSize      []byte
+	IsFolder      []byte
+	PathItemCount []byte
+	FileNamePath  []byte
+}
+
+func (fu *folderUpload) FormattedPath() string {
+	pathItemLen := binary.BigEndian.Uint16(fu.PathItemCount)
+
+	var pathSegments []string
+	pathData := fu.FileNamePath
+
+	for i := uint16(0); i < pathItemLen; i++ {
+		segLen := pathData[2]
+		pathSegments = append(pathSegments, string(pathData[3:3+segLen]))
+		pathData = pathData[3+segLen:]
+	}
+
+	return strings.Join(pathSegments, pathSeparator)
+}
+
+// sortedClients is a utility function that takes a map of *ClientConn and returns a sorted slice of the values.
+// The purpose of this is to ensure that the ordering of client connections is deterministic so that test assertions work.
+func sortedClients(unsortedClients map[uint16]*ClientConn) (clients []*ClientConn) {
+	for _, c := range unsortedClients {
+		clients = append(clients, c)
+	}
+	sort.Sort(byClientID(clients))
+	return clients
+}