Refactor listener setup

[rbdr/mobius] / hotline / server.go

diff --git a/hotline/server.go b/hotline/server.go
index 2ee31cf610627dc66956d04f1a1f74852e9315f8..b1d8849032cce8db50159a453f8273ac89f14381 100644 (file)
--- a/hotline/server.go
+++ b/hotline/server.go
@@ -1,14 +1,16 @@
 package hotline
 
 import (
 package hotline
 
 import (

+       "bytes"

        "context"
        "encoding/binary"
        "errors"
        "fmt"
        "context"
        "encoding/binary"
        "errors"
        "fmt"

+       "github.com/go-playground/validator/v10"

        "go.uber.org/zap"
        "io"
        "go.uber.org/zap"
        "io"

+       "io/fs"

        "io/ioutil"
        "io/ioutil"

-       "log"

        "math/big"
        "math/rand"
        "net"
        "math/big"
        "math/rand"
        "net"


@@ -21,8 +23,7 @@ import (
        "sync"
        "time"
 
        "sync"
        "time"
 

-       "golang.org/x/crypto/bcrypt"
-       "gopkg.in/yaml.v2"
+       "gopkg.in/yaml.v3"

 )
 
 const (
 )
 
 const (


@@ -31,6 +32,8 @@ const (
        trackerUpdateFrequency = 300 // time in seconds between tracker re-registration
 )
 
        trackerUpdateFrequency = 300 // time in seconds between tracker re-registration
 )
 

+var nostalgiaVersion = []byte{0, 0, 2, 0x2c} // version ID used by the Nostalgia client
+

 type Server struct {
        Port          int
        Accounts      map[string]*Account
 type Server struct {
        Port          int
        Accounts      map[string]*Account


@@ -44,14 +47,12 @@ type Server struct {
        Logger        *zap.SugaredLogger
        PrivateChats  map[uint32]*PrivateChat
        NextGuestID   *uint16
        Logger        *zap.SugaredLogger
        PrivateChats  map[uint32]*PrivateChat
        NextGuestID   *uint16

-       TrackerPassID []byte
+       TrackerPassID [4]byte

        Stats         *Stats
 
        Stats         *Stats
 

-       APIListener  net.Listener
-       FileListener net.Listener

 
 

-       newsReader io.Reader
-       newsWriter io.WriteCloser
+       // newsReader io.Reader
+       // newsWriter io.WriteCloser

 
        outbox chan Transaction
 
 
        outbox chan Transaction
 


@@ -65,27 +66,41 @@ type PrivateChat struct {
 }
 
 func (s *Server) ListenAndServe(ctx context.Context, cancelRoot context.CancelFunc) error {
 }
 
 func (s *Server) ListenAndServe(ctx context.Context, cancelRoot context.CancelFunc) error {

-       s.Logger.Infow("Hotline server started", "version", VERSION)
+       s.Logger.Infow("Hotline server started",
+               "version", VERSION,
+               "API port", fmt.Sprintf(":%v", s.Port),
+               "Transfer port", fmt.Sprintf(":%v", s.Port+1),
+       )
+

        var wg sync.WaitGroup
 
        wg.Add(1)
        var wg sync.WaitGroup
 
        wg.Add(1)

-       go func() { s.Logger.Fatal(s.Serve(ctx, cancelRoot, s.APIListener)) }()
+       go func() {
+               ln, err := net.Listen("tcp", fmt.Sprintf("%s:%v", "", s.Port))
+               if err != nil {
+                       s.Logger.Fatal(err)
+               }
+
+               s.Logger.Fatal(s.Serve(ctx, cancelRoot, ln))
+       }()

 
        wg.Add(1)
 
        wg.Add(1)

-       go func() { s.Logger.Fatal(s.ServeFileTransfers(s.FileListener)) }()
+       go func() {
+               ln, err := net.Listen("tcp", fmt.Sprintf("%s:%v", "", s.Port+1))
+               if err != nil {
+                       s.Logger.Fatal(err)
+
+               }
+
+               s.Logger.Fatal(s.ServeFileTransfers(ln))
+       }()

 
        wg.Wait()
 
        return nil
 }
 
 
        wg.Wait()
 
        return nil
 }
 

-func (s *Server) APIPort() int {
-       return s.APIListener.Addr().(*net.TCPAddr).Port
-}
-

 func (s *Server) ServeFileTransfers(ln net.Listener) error {
 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 {
        for {
                conn, err := ln.Accept()
                if err != nil {


@@ -93,7 +108,7 @@ func (s *Server) ServeFileTransfers(ln net.Listener) error {
                }
 
                go func() {
                }
 
                go func() {

-                       if err := s.TransferFile(conn); err != nil {
+                       if err := s.handleFileTransfer(conn); err != nil {

                                s.Logger.Errorw("file transfer error", "reason", err)
                        }
                }()
                                s.Logger.Errorw("file transfer error", "reason", err)
                        }
                }()


@@ -111,7 +126,7 @@ func (s *Server) sendTransaction(t Transaction) error {
        client := s.Clients[uint16(clientID)]
        s.mux.Unlock()
        if client == nil {
        client := s.Clients[uint16(clientID)]
        s.mux.Unlock()
        if client == nil {

-               return errors.New("invalid client")
+               return fmt.Errorf("invalid client id %v", *t.clientID)

        }
        userName := string(client.UserName)
        login := client.Account.Login
        }
        userName := string(client.UserName)
        login := client.Account.Login


@@ -132,13 +147,12 @@ func (s *Server) sendTransaction(t Transaction) error {
                "IsReply", t.IsReply,
                "type", handler.Name,
                "sentBytes", n,
                "IsReply", t.IsReply,
                "type", handler.Name,
                "sentBytes", n,

-               "remoteAddr", client.Connection.RemoteAddr(),
+               "remoteAddr", client.RemoteAddr,

        )
        return nil
 }
 
 func (s *Server) Serve(ctx context.Context, cancelRoot context.CancelFunc, ln net.Listener) error {
        )
        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()
 
        for {
                conn, err := ln.Accept()


@@ -157,7 +171,7 @@ func (s *Server) Serve(ctx context.Context, cancelRoot context.CancelFunc, ln ne
                        }
                }()
                go func() {
                        }
                }()
                go func() {

-                       if err := s.handleNewConnection(conn); err != nil {
+                       if err := s.handleNewConnection(conn, conn.RemoteAddr().String()); err != nil {

                                if err == io.EOF {
                                        s.Logger.Infow("Client disconnected", "RemoteAddr", conn.RemoteAddr())
                                } else {
                                if err == io.EOF {
                                        s.Logger.Infow("Client disconnected", "RemoteAddr", conn.RemoteAddr())
                                } else {


@@ -169,7 +183,7 @@ func (s *Server) Serve(ctx context.Context, cancelRoot context.CancelFunc, ln ne
 }
 
 const (
 }
 
 const (

-       agreementFile    = "Agreement.txt"
+       agreementFile = "Agreement.txt"

 )
 
 // NewServer constructs a new Server from a config dir
 )
 
 // NewServer constructs a new Server from a config dir


@@ -187,31 +201,15 @@ func NewServer(configDir, netInterface string, netPort int, logger *zap.SugaredL
                outbox:        make(chan Transaction),
                Stats:         &Stats{StartTime: time.Now()},
                ThreadedNews:  &ThreadedNews{},
                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
-       }
+       var err error

 
        // generate a new random passID for tracker registration
 
        // generate a new random passID for tracker registration

-       if _, err := rand.Read(server.TrackerPassID); err != nil {
+       if _, err := rand.Read(server.TrackerPassID[:]); err != nil {

                return nil, err
        }
 
                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.Agreement, err = os.ReadFile(configDir + agreementFile); err != nil {
                return nil, err
        }


@@ -237,21 +235,26 @@ func NewServer(configDir, netInterface string, netPort int, logger *zap.SugaredL
        *server.NextGuestID = 1
 
        if server.Config.EnableTrackerRegistration {
        *server.NextGuestID = 1
 
        if server.Config.EnableTrackerRegistration {

+               server.Logger.Infow(
+                       "Tracker registration enabled",
+                       "frequency", fmt.Sprintf("%vs", trackerUpdateFrequency),
+                       "trackers", server.Config.Trackers,
+               )
+

                go func() {
                        for {
                go func() {
                        for {

-                               tr := TrackerRegistration{
-                                       Port:        []byte{0x15, 0x7c},
+                               tr := &TrackerRegistration{

                                        UserCount:   server.userCount(),
                                        UserCount:   server.userCount(),

-                                       PassID:      server.TrackerPassID,
+                                       PassID:      server.TrackerPassID[:],

                                        Name:        server.Config.Name,
                                        Description: server.Config.Description,
                                }
                                        Name:        server.Config.Name,
                                        Description: server.Config.Description,
                                }

+                               binary.BigEndian.PutUint16(tr.Port[:], uint16(server.Port))

                                for _, t := range server.Config.Trackers {
                                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)
                                        }
                                        if err := register(t, tr); err != nil {
                                                server.Logger.Errorw("unable to register with tracker %v", "error", err)
                                        }

+                                       server.Logger.Infow("Sent Tracker registration", "data", tr)

                                }
 
                                time.Sleep(trackerUpdateFrequency * time.Second)
                                }
 
                                time.Sleep(trackerUpdateFrequency * time.Second)


@@ -278,8 +281,8 @@ func (s *Server) keepaliveHandler() {
                s.mux.Lock()
 
                for _, c := range s.Clients {
                s.mux.Lock()
 
                for _, c := range s.Clients {

-                       *c.IdleTime += idleCheckInterval
-                       if *c.IdleTime > userIdleSeconds && !c.Idle {
+                       c.IdleTime += idleCheckInterval
+                       if c.IdleTime > userIdleSeconds && !c.Idle {

                                c.Idle = true
 
                                flagBitmap := big.NewInt(int64(binary.BigEndian.Uint16(*c.Flags)))
                                c.Idle = true
 
                                flagBitmap := big.NewInt(int64(binary.BigEndian.Uint16(*c.Flags)))


@@ -315,7 +318,7 @@ func (s *Server) writeThreadedNews() error {
        return err
 }
 
        return err
 }
 

-func (s *Server) NewClientConn(conn net.Conn) *ClientConn {
+func (s *Server) NewClientConn(conn net.Conn, remoteAddr string) *ClientConn {

        s.mux.Lock()
        defer s.mux.Unlock()
 
        s.mux.Lock()
        defer s.mux.Unlock()
 


@@ -327,15 +330,14 @@ func (s *Server) NewClientConn(conn net.Conn) *ClientConn {
                Connection: conn,
                Server:     s,
                Version:    &[]byte{},
                Connection: conn,
                Server:     s,
                Version:    &[]byte{},

-               IdleTime:   new(int),
-               AutoReply:  &[]byte{},
+               AutoReply:  []byte{},

                Transfers:  make(map[int][]*FileTransfer),
                Transfers:  make(map[int][]*FileTransfer),

+               Agreed:     false,
+               RemoteAddr: remoteAddr,

        }
        *s.NextGuestID++
        ID := *s.NextGuestID
 
        }
        *s.NextGuestID++
        ID := *s.NextGuestID
 

-       *clientConn.IdleTime = 0
-

        binary.BigEndian.PutUint16(*clientConn.ID, ID)
        s.Clients[ID] = clientConn
 
        binary.BigEndian.PutUint16(*clientConn.ID, ID)
        s.Clients[ID] = clientConn
 


@@ -359,7 +361,37 @@ func (s *Server) NewUser(login, name, password string, access []byte) error {
        }
        s.Accounts[login] = &account
 
        }
        s.Accounts[login] = &account
 

-       return ioutil.WriteFile(s.ConfigDir+"Users/"+login+".yaml", out, 0666)
+       return FS.WriteFile(s.ConfigDir+"Users/"+login+".yaml", out, 0666)
+}
+
+func (s *Server) UpdateUser(login, newLogin, name, password string, access []byte) error {
+       s.mux.Lock()
+       defer s.mux.Unlock()
+
+       // update renames the user login
+       if login != newLogin {
+               err := os.Rename(s.ConfigDir+"Users/"+login+".yaml", s.ConfigDir+"Users/"+newLogin+".yaml")
+               if err != nil {
+                       return err
+               }
+               s.Accounts[newLogin] = s.Accounts[login]
+               delete(s.Accounts, login)
+       }
+
+       account := s.Accounts[newLogin]
+       account.Access = &access
+       account.Name = name
+       account.Password = password
+
+       out, err := yaml.Marshal(&account)
+       if err != nil {
+               return err
+       }
+       if err := os.WriteFile(s.ConfigDir+"Users/"+newLogin+".yaml", out, 0666); err != nil {
+               return err
+       }
+
+       return nil

 }
 
 // DeleteUser deletes the user account
 }
 
 // DeleteUser deletes the user account


@@ -369,7 +401,7 @@ func (s *Server) DeleteUser(login string) error {
 
        delete(s.Accounts, login)
 
 
        delete(s.Accounts, login)
 

-       return os.Remove(s.ConfigDir + "Users/" + login + ".yaml")
+       return FS.Remove(s.ConfigDir + "Users/" + login + ".yaml")

 }
 
 func (s *Server) connectedUsers() []Field {
 }
 
 func (s *Server) connectedUsers() []Field {


@@ -377,7 +409,10 @@ func (s *Server) connectedUsers() []Field {
        defer s.mux.Unlock()
 
        var connectedUsers []Field
        defer s.mux.Unlock()
 
        var connectedUsers []Field

-       for _, c := range s.Clients {
+       for _, c := range sortedClients(s.Clients) {
+               if !c.Agreed {
+                       continue
+               }

                user := User{
                        ID:    *c.ID,
                        Icon:  *c.Icon,
                user := User{
                        ID:    *c.ID,
                        Icon:  *c.Icon,


@@ -396,7 +431,6 @@ func (s *Server) loadThreadedNews(threadedNewsPath string) error {
                return err
        }
        decoder := yaml.NewDecoder(fh)
                return err
        }
        decoder := yaml.NewDecoder(fh)

-       decoder.SetStrict(true)

 
        return decoder.Decode(s.ThreadedNews)
 }
 
        return decoder.Decode(s.ThreadedNews)
 }


@@ -413,14 +447,13 @@ func (s *Server) loadAccounts(userDir string) error {
        }
 
        for _, file := range matches {
        }
 
        for _, file := range matches {

-               fh, err := os.Open(file)
+               fh, err := FS.Open(file)

                if err != nil {
                        return err
                }
 
                account := Account{}
                decoder := yaml.NewDecoder(fh)
                if err != nil {
                        return err
                }
 
                account := Account{}
                decoder := yaml.NewDecoder(fh)

-               decoder.SetStrict(true)

                if err := decoder.Decode(&account); err != nil {
                        return err
                }
                if err := decoder.Decode(&account); err != nil {
                        return err
                }


@@ -431,17 +464,22 @@ func (s *Server) loadAccounts(userDir string) error {
 }
 
 func (s *Server) loadConfig(path string) error {
 }
 
 func (s *Server) loadConfig(path string) error {

-       fh, err := os.Open(path)
+       fh, err := FS.Open(path)

        if err != nil {
                return err
        }
 
        decoder := yaml.NewDecoder(fh)
        if err != nil {
                return err
        }
 
        decoder := yaml.NewDecoder(fh)

-       decoder.SetStrict(true)

        err = decoder.Decode(s.Config)
        if err != nil {
                return err
        }
        err = decoder.Decode(s.Config)
        if err != nil {
                return err
        }

+
+       validate := validator.New()
+       err = validate.Struct(s.Config)
+       if err != nil {
+               return err
+       }

        return nil
 }
 
        return nil
 }
 


@@ -449,17 +487,25 @@ const (
        minTransactionLen = 22 // minimum length of any transaction
 )
 
        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
+// dontPanic recovers and logs panics instead of crashing
+// TODO: remove this after known issues are fixed
+func dontPanic(logger *zap.SugaredLogger) {
+       if r := recover(); r != nil {
+               fmt.Println("stacktrace from panic: \n" + string(debug.Stack()))
+               logger.Errorw("PANIC", "err", r, "trace", string(debug.Stack()))

        }
        }

-       if err := Handshake(conn, handshakeBuf[:12]); err != nil {
+}
+
+// handleNewConnection takes a new net.Conn and performs the initial login sequence
+func (s *Server) handleNewConnection(conn net.Conn, remoteAddr string) error {
+       defer dontPanic(s.Logger)
+
+       if err := Handshake(conn); err != nil {

                return err
        }
 
        buf := make([]byte, 1024)
                return err
        }
 
        buf := make([]byte, 1024)

+       // TODO: fix potential short read with io.ReadFull

        readLen, err := conn.Read(buf)
        if readLen < minTransactionLen {
                return err
        readLen, err := conn.Read(buf)
        if readLen < minTransactionLen {
                return err


@@ -473,15 +519,8 @@ func (s *Server) handleNewConnection(conn net.Conn) error {
                return err
        }
 
                return err
        }
 

-       c := s.NewClientConn(conn)
+       c := s.NewClientConn(conn, remoteAddr)

        defer c.Disconnect()
        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
 
        encodedLogin := clientLogin.GetField(fieldUserLogin).Data
        encodedPassword := clientLogin.GetField(fieldUserPassword).Data


@@ -522,7 +561,7 @@ func (s *Server) handleNewConnection(conn net.Conn) error {
                *c.Flags = []byte{0, 2}
        }
 
                *c.Flags = []byte{0, 2}
        }
 

-       s.Logger.Infow("Client connection received", "login", login, "version", *c.Version, "RemoteAddr", conn.RemoteAddr().String())
+       s.Logger.Infow("Client connection received", "login", login, "version", *c.Version, "RemoteAddr", remoteAddr)

 
        s.outbox <- c.NewReply(clientLogin,
                NewField(fieldVersion, []byte{0x00, 0xbe}),
 
        s.outbox <- c.NewReply(clientLogin,
                NewField(fieldVersion, []byte{0x00, 0xbe}),


@@ -536,9 +575,21 @@ func (s *Server) handleNewConnection(conn net.Conn) error {
        // Show agreement to client
        c.Server.outbox <- *NewTransaction(tranShowAgreement, c.ID, NewField(fieldData, s.Agreement))
 
        // Show agreement to client
        c.Server.outbox <- *NewTransaction(tranShowAgreement, c.ID, NewField(fieldData, s.Agreement))
 

-       if _, err := c.notifyNewUserHasJoined(); err != nil {
-               return err
+       // Used simplified hotline v1.2.3 login flow for clients that do not send login info in tranAgreed
+       if *c.Version == nil || bytes.Equal(*c.Version, nostalgiaVersion) {
+               c.Agreed = true
+
+               c.notifyOthers(
+                       *NewTransaction(
+                               tranNotifyChangeUser, nil,
+                               NewField(fieldUserName, c.UserName),
+                               NewField(fieldUserID, *c.ID),
+                               NewField(fieldUserIconID, *c.Icon),
+                               NewField(fieldUserFlags, *c.Flags),
+                       ),
+               )

        }
        }

+

        c.Server.Stats.LoginCount += 1
 
        const readBuffSize = 1024000 // 1KB - TODO: what should this be?
        c.Server.Stats.LoginCount += 1
 
        const readBuffSize = 1024000 // 1KB - TODO: what should this be?


@@ -571,21 +622,6 @@ func (s *Server) handleNewConnection(conn net.Conn) error {
        }
 }
 
        }
 }
 

-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
 // 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


@@ -617,22 +653,40 @@ const dlFldrActionSendFile = 1
 const dlFldrActionResumeFile = 2
 const dlFldrActionNextFile = 3
 
 const dlFldrActionResumeFile = 2
 const dlFldrActionNextFile = 3
 

-func (s *Server) TransferFile(conn net.Conn) error {
-       defer func() { _ = conn.Close() }()
+// handleFileTransfer receives a client net.Conn from the file transfer server, performs the requested transfer type, then closes the connection
+func (s *Server) handleFileTransfer(conn io.ReadWriteCloser) error {
+       defer func() {

 
 

-       buf := make([]byte, 1024)
-       if _, err := conn.Read(buf); err != nil {
+               if err := conn.Close(); err != nil {
+                       s.Logger.Errorw("error closing connection", "error", err)
+               }
+       }()
+
+       defer dontPanic(s.Logger)
+
+       txBuf := make([]byte, 16)
+       if _, err := io.ReadFull(conn, txBuf); err != nil {

                return err
        }
 
        var t transfer
                return err
        }
 
        var t transfer

-       _, err := t.Write(buf[:16])
-       if err != nil {
+       if _, err := t.Write(txBuf); err != nil {

                return err
        }
 
        transferRefNum := binary.BigEndian.Uint32(t.ReferenceNumber[:])
                return err
        }
 
        transferRefNum := binary.BigEndian.Uint32(t.ReferenceNumber[:])

-       fileTransfer := s.FileTransfers[transferRefNum]
+       defer func() {
+               s.mux.Lock()
+               delete(s.FileTransfers, transferRefNum)
+               s.mux.Unlock()
+       }()
+
+       s.mux.Lock()
+       fileTransfer, ok := s.FileTransfers[transferRefNum]
+       s.mux.Unlock()
+       if !ok {
+               return errors.New("invalid transaction ID")
+       }

 
        switch fileTransfer.Type {
        case FileDownload:
 
        switch fileTransfer.Type {
        case FileDownload:


@@ -641,20 +695,23 @@ func (s *Server) TransferFile(conn net.Conn) error {
                        return err
                }
 
                        return err
                }
 

-               ffo, err := NewFlattenedFileObject(
-                       s.Config.FileRoot,
-                       fileTransfer.FilePath,
-                       fileTransfer.FileName,
-               )
+               var dataOffset int64
+               if fileTransfer.fileResumeData != nil {
+                       dataOffset = int64(binary.BigEndian.Uint32(fileTransfer.fileResumeData.ForkInfoList[0].DataSize[:]))
+               }
+
+               ffo, err := NewFlattenedFileObject(s.Config.FileRoot, fileTransfer.FilePath, fileTransfer.FileName, dataOffset)

                if err != nil {
                        return err
                }
 
                if err != nil {
                        return err
                }
 

-               s.Logger.Infow("File download started", "filePath", fullFilePath, "transactionRef", fileTransfer.ReferenceNumber, "RemoteAddr", conn.RemoteAddr().String())
+               s.Logger.Infow("File download started", "filePath", fullFilePath, "transactionRef", fileTransfer.ReferenceNumber)

 
 

-               // Start by sending flat file object to client
-               if _, err := conn.Write(ffo.BinaryMarshal()); err != nil {
-                       return err
+               if fileTransfer.options == nil {
+                       // Start by sending flat file object to client
+                       if _, err := conn.Write(ffo.BinaryMarshal()); err != nil {
+                               return err
+                       }

                }
 
                file, err := FS.Open(fullFilePath)
                }
 
                file, err := FS.Open(fullFilePath)


@@ -663,75 +720,68 @@ func (s *Server) TransferFile(conn net.Conn) error {
                }
 
                sendBuffer := make([]byte, 1048576)
                }
 
                sendBuffer := make([]byte, 1048576)

+               var totalSent int64

                for {
                        var bytesRead int
                for {
                        var bytesRead int

-                       if bytesRead, err = file.Read(sendBuffer); err == io.EOF {
+                       if bytesRead, err = file.ReadAt(sendBuffer, dataOffset+totalSent); err == io.EOF {
+                               if _, err := conn.Write(sendBuffer[:bytesRead]); err != nil {
+                                       return err
+                               }

                                break
                        }
                                break
                        }

+                       if err != nil {
+                               return err
+                       }
+                       totalSent += int64(bytesRead)

 
                        fileTransfer.BytesSent += bytesRead
 
 
                        fileTransfer.BytesSent += bytesRead
 

-                       delete(s.FileTransfers, transferRefNum)
-

                        if _, err := conn.Write(sendBuffer[:bytesRead]); err != nil {
                                return err
                        }
                }
        case FileUpload:
                        if _, err := conn.Write(sendBuffer[:bytesRead]); err != nil {
                                return err
                        }
                }
        case FileUpload:

-               if _, err := conn.Read(buf); err != nil {
-                       return err
-               }
+               destinationFile := s.Config.FileRoot + ReadFilePath(fileTransfer.FilePath) + "/" + string(fileTransfer.FileName)

 
 

-               ffo := ReadFlattenedFileObject(buf)
-               payloadLen := len(ffo.BinaryMarshal())
-               fileSize := int(binary.BigEndian.Uint32(ffo.FlatFileDataForkHeader.DataSize))
+               var file *os.File

 
 

-               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,
-               )
+               // A file upload has three possible cases:
+               // 1) Upload a new file
+               // 2) Resume a partially transferred file
+               // 3) Replace a fully uploaded file
+               // Unfortunately we have to infer which case applies by inspecting what is already on the file system

 
 

-               newFile, err := os.Create(destinationFile)
-               if err != nil {
-                       return err
+               // 1) Check for existing file:
+               _, err := os.Stat(destinationFile)
+               if err == nil {
+                       // If found, that means this upload is intended to replace the file
+                       if err = os.Remove(destinationFile); err != nil {
+                               return err
+                       }
+                       file, err = os.Create(destinationFile + incompleteFileSuffix)
+               }
+               if errors.Is(err, fs.ErrNotExist) {
+                       // If not found, open or create a new incomplete file
+                       file, err = os.OpenFile(destinationFile+incompleteFileSuffix, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0644)
+                       if err != nil {
+                               return err
+                       }

                }
 
                }
 

-               defer func() { _ = newFile.Close() }()
+               defer func() { _ = file.Close() }()

 
 

-               const buffSize = 1024
+               s.Logger.Infow("File upload started", "transactionRef", fileTransfer.ReferenceNumber, "dstFile", destinationFile)

 
 

-               if _, err := newFile.Write(buf[payloadLen:]); err != nil {
+               // TODO: replace io.Discard with a real file when ready to implement storing of resource fork data
+               if err := receiveFile(conn, file, io.Discard); err != nil {

                        return err
                }
                        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)
+               if err := os.Rename(destinationFile+".incomplete", destinationFile); err != nil {
+                       return err

                }
                }

+
+               s.Logger.Infow("File upload complete", "transactionRef", fileTransfer.ReferenceNumber, "dstFile", destinationFile)

        case FolderDownload:
                // Folder Download flow:
                // 1. Get filePath from the transfer
        case FolderDownload:
                // Folder Download flow:
                // 1. Get filePath from the transfer


@@ -749,7 +799,7 @@ func (s *Server) TransferFile(conn net.Conn) error {
                //                      [2]byte // Resume data size
                //                      []byte file resume data (see myField_FileResumeData)
                //
                //                      [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}
+               // 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
                //
                // When download is requested (case 2 or 3), server replies with:
                //                      [4]byte - file size


@@ -767,22 +817,28 @@ func (s *Server) TransferFile(conn net.Conn) error {
 
                basePathLen := len(fullFilePath)
 
 
                basePathLen := len(fullFilePath)
 

-               readBuffer := make([]byte, 1024)
+               s.Logger.Infow("Start folder download", "path", fullFilePath, "ReferenceNumber", fileTransfer.ReferenceNumber)

 
 

-               s.Logger.Infow("Start folder download", "path", fullFilePath, "ReferenceNumber", fileTransfer.ReferenceNumber, "RemoteAddr", conn.RemoteAddr())
+               nextAction := make([]byte, 2)
+               if _, err := io.ReadFull(conn, nextAction); err != nil {
+                       return err
+               }

 
                i := 0
 
                i := 0

-               _ = filepath.Walk(fullFilePath+"/", func(path string, info os.FileInfo, _ error) error {
+               err = filepath.Walk(fullFilePath+"/", func(path string, info os.FileInfo, err error) error {
+                       if err != nil {
+                               return err
+                       }

                        i += 1
                        i += 1

-                       subPath := path[basePathLen:]
+                       subPath := path[basePathLen+1:]

                        s.Logger.Infow("Sending fileheader", "i", i, "path", path, "fullFilePath", fullFilePath, "subPath", subPath, "IsDir", info.IsDir())
 
                        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
                        }
 
                        if i == 1 {
                                return nil
                        }
 

+                       fileHeader := NewFileHeader(subPath, info.IsDir())
+

                        // Send the file header to client
                        if _, err := conn.Write(fileHeader.Payload()); err != nil {
                                s.Logger.Errorf("error sending file header: %v", err)
                        // Send the file header to client
                        if _, err := conn.Write(fileHeader.Payload()); err != nil {
                                s.Logger.Errorf("error sending file header: %v", err)


@@ -790,12 +846,37 @@ func (s *Server) TransferFile(conn net.Conn) error {
                        }
 
                        // Read the client's Next Action request
                        }
 
                        // 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 {
+                       if _, err := io.ReadFull(conn, nextAction); err != nil {

                                return err
                        }
 
                                return err
                        }
 

-                       s.Logger.Infow("Client folder download action", "action", fmt.Sprintf("%X", readBuffer[0:2]))
+                       s.Logger.Infow("Client folder download action", "action", fmt.Sprintf("%X", nextAction[0:2]))
+
+                       var dataOffset int64
+
+                       switch nextAction[1] {
+                       case dlFldrActionResumeFile:
+                               // client asked to resume this file
+                               var frd FileResumeData
+                               // get size of resumeData
+                               if _, err := io.ReadFull(conn, nextAction); err != nil {
+                                       return err
+                               }
+
+                               resumeDataLen := binary.BigEndian.Uint16(nextAction)
+                               resumeDataBytes := make([]byte, resumeDataLen)
+                               if _, err := io.ReadFull(conn, resumeDataBytes); err != nil {
+                                       return err
+                               }
+
+                               if err := frd.UnmarshalBinary(resumeDataBytes); err != nil {
+                                       return err
+                               }
+                               dataOffset = int64(binary.BigEndian.Uint32(frd.ForkInfoList[0].DataSize[:]))
+                       case dlFldrActionNextFile:
+                               // client asked to skip this file
+                               return nil
+                       }

 
                        if info.IsDir() {
                                return nil
 
                        if info.IsDir() {
                                return nil


@@ -803,18 +884,13 @@ func (s *Server) TransferFile(conn net.Conn) error {
 
                        splitPath := strings.Split(path, "/")
 
 
                        splitPath := strings.Split(path, "/")
 

-                       ffo, err := NewFlattenedFileObject(
-                               strings.Join(splitPath[:len(splitPath)-1], "/"),
-                               nil,
-                               []byte(info.Name()),
-                       )
+                       ffo, err := NewFlattenedFileObject(strings.Join(splitPath[:len(splitPath)-1], "/"), nil, []byte(info.Name()), dataOffset)

                        if err != nil {
                                return err
                        }
                        s.Logger.Infow("File download started",
                                "fileName", info.Name(),
                                "transactionRef", fileTransfer.ReferenceNumber,
                        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()),
                        )
 
                                "TransferSize", fmt.Sprintf("%x", ffo.TransferSize()),
                        )
 


@@ -824,38 +900,52 @@ func (s *Server) TransferFile(conn net.Conn) error {
                                return err
                        }
 
                                return err
                        }
 

-                       // Send file bytes to client
+                       // Send ffo bytes to client

                        if _, err := conn.Write(ffo.BinaryMarshal()); err != nil {
                                s.Logger.Error(err)
                                return err
                        }
 
                        if _, err := conn.Write(ffo.BinaryMarshal()); err != nil {
                                s.Logger.Error(err)
                                return err
                        }
 

-                       file, err := os.Open(path)
+                       file, err := FS.Open(path)

                        if err != nil {
                                return err
                        }
 
                        if err != nil {
                                return err
                        }
 

+                       // // Copy N bytes from file to connection
+                       // _, err = io.CopyN(conn, file, int64(binary.BigEndian.Uint32(ffo.FlatFileDataForkHeader.DataSize[:])))
+                       // if err != nil {
+                       //      return err
+                       // }
+                       // file.Close()

                        sendBuffer := make([]byte, 1048576)
                        sendBuffer := make([]byte, 1048576)

-                       totalBytesSent := len(ffo.BinaryMarshal())
-
+                       var totalSent int64

                        for {
                        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)
+                               var bytesRead int
+                               if bytesRead, err = file.ReadAt(sendBuffer, dataOffset+totalSent); err == io.EOF {
+                                       if _, err := conn.Write(sendBuffer[:bytesRead]); err != nil {

                                                return err
                                        }
                                        break
                                }
                                                return err
                                        }
                                        break
                                }

+                               if err != nil {
+                                       panic(err)
+                               }
+                               totalSent += int64(bytesRead)

 
 

-                               sentBytes, readErr := conn.Write(sendBuffer[:bytesRead])
-                               totalBytesSent += sentBytes
-                               if readErr != nil {
+                               fileTransfer.BytesSent += bytesRead
+
+                               if _, err := conn.Write(sendBuffer[:bytesRead]); err != nil {

                                        return err
                                }
                        }
                                        return err
                                }
                        }

+
+                       // TODO: optionally send resource fork header and resource fork data
+
+                       // Read the client's Next Action request.  This is always 3, I think?
+                       if _, err := io.ReadFull(conn, nextAction); err != nil {
+                               return err
+                       }
+

                        return nil
                })
 
                        return nil
                })
 


@@ -867,7 +957,6 @@ func (s *Server) TransferFile(conn net.Conn) error {
                s.Logger.Infow(
                        "Folder upload started",
                        "transactionRef", fileTransfer.ReferenceNumber,
                s.Logger.Infow(
                        "Folder upload started",
                        "transactionRef", fileTransfer.ReferenceNumber,

-                       "RemoteAddr", conn.RemoteAddr().String(),

                        "dstPath", dstPath,
                        "TransferSize", fmt.Sprintf("%x", fileTransfer.TransferSize),
                        "FolderItemCount", fileTransfer.FolderItemCount,
                        "dstPath", dstPath,
                        "TransferSize", fmt.Sprintf("%x", fileTransfer.TransferSize),
                        "FolderItemCount", fileTransfer.FolderItemCount,


@@ -875,24 +964,23 @@ func (s *Server) TransferFile(conn net.Conn) error {
 
                // Check if the target folder exists.  If not, create it.
                if _, err := FS.Stat(dstPath); os.IsNotExist(err) {
 
                // Check if the target folder exists.  If not, create it.
                if _, err := FS.Stat(dstPath); os.IsNotExist(err) {

-                       s.Logger.Infow("Creating target path", "dstPath", dstPath)

                        if err := FS.Mkdir(dstPath, 0777); err != nil {
                        if err := FS.Mkdir(dstPath, 0777); err != nil {

-                               s.Logger.Error(err)
+                               return 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)
                // 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)
+               readBuffer := make([]byte, 1024)

 
 

-               for i := uint16(0); i < itemCount; i++ {
-                       if _, err := conn.Read(readBuffer); err != nil {
+               for i := 0; i < fileTransfer.ItemCount(); i++ {
+                       // TODO: fix potential short read with io.ReadFull
+                       _, err := conn.Read(readBuffer)
+                       if err != nil {

                                return err
                        }
                        fu := readFolderUpload(readBuffer)
                                return err
                        }
                        fu := readFolderUpload(readBuffer)


@@ -900,7 +988,6 @@ func (s *Server) TransferFile(conn net.Conn) error {
                        s.Logger.Infow(
                                "Folder upload continued",
                                "transactionRef", fmt.Sprintf("%x", fileTransfer.ReferenceNumber),
                        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[:]),
                                "FormattedPath", fu.FormattedPath(),
                                "IsFolder", fmt.Sprintf("%x", fu.IsFolder),
                                "PathItemCount", binary.BigEndian.Uint16(fu.PathItemCount[:]),


@@ -908,44 +995,104 @@ func (s *Server) TransferFile(conn net.Conn) error {
 
                        if fu.IsFolder == [2]byte{0, 1} {
                                if _, err := os.Stat(dstPath + "/" + fu.FormattedPath()); os.IsNotExist(err) {
 
                        if fu.IsFolder == [2]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 {
                                        if err := os.Mkdir(dstPath+"/"+fu.FormattedPath(), 0777); err != nil {

-                                               s.Logger.Error(err)
+                                               return err

                                        }
                                }
 
                                // Tell client to send next file
                                if _, err := conn.Write([]byte{0, dlFldrActionNextFile}); err != nil {
                                        }
                                }
 
                                // Tell client to send next file
                                if _, err := conn.Write([]byte{0, dlFldrActionNextFile}); err != nil {

-                                       s.Logger.Error(err)

                                        return err
                                }
                        } else {
                                        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 {
+                               nextAction := dlFldrActionSendFile
+
+                               // Check if we have the full file already.  If so, send dlFldrAction_NextFile to client to skip.
+                               _, err := os.Stat(dstPath + "/" + fu.FormattedPath())
+                               if err != nil && !errors.Is(err, fs.ErrNotExist) {
+                                       return err
+                               }
+                               if err == nil {
+                                       nextAction = dlFldrActionNextFile
+                               }
+
+                               //  Check if we have a partial file already.  If so, send dlFldrAction_ResumeFile to client to resume upload.
+                               inccompleteFile, err := os.Stat(dstPath + "/" + fu.FormattedPath() + incompleteFileSuffix)
+                               if err != nil && !errors.Is(err, fs.ErrNotExist) {

                                        return err
                                }
                                        return err
                                }

+                               if err == nil {
+                                       nextAction = dlFldrActionResumeFile
+                               }
+
+                               fmt.Printf("Next Action: %v\n", nextAction)

 
 

-                               if _, err := conn.Read(fileSize); err != nil {
-                                       fmt.Println("Error reading:", err.Error()) // TODO: handle
+                               if _, err := conn.Write([]byte{0, uint8(nextAction)}); err != nil {
+                                       return err

                                }
 
                                }
 

-                               s.Logger.Infow("Starting file transfer", "fileNum", i+1, "totalFiles", itemCount, "fileSize", fileSize)
+                               switch nextAction {
+                               case dlFldrActionNextFile:
+                                       continue
+                               case dlFldrActionResumeFile:
+                                       offset := make([]byte, 4)
+                                       binary.BigEndian.PutUint32(offset, uint32(inccompleteFile.Size()))
+
+                                       file, err := os.OpenFile(dstPath+"/"+fu.FormattedPath()+incompleteFileSuffix, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
+                                       if err != nil {
+                                               return err
+                                       }
+
+                                       fileResumeData := NewFileResumeData([]ForkInfoList{
+                                               *NewForkInfoList(offset),
+                                       })
+
+                                       b, _ := fileResumeData.BinaryMarshal()
+
+                                       bs := make([]byte, 2)
+                                       binary.BigEndian.PutUint16(bs, uint16(len(b)))
+
+                                       if _, err := conn.Write(append(bs, b...)); err != nil {
+                                               return err
+                                       }
+
+                                       if _, err := io.ReadFull(conn, fileSize); err != nil {
+                                               return err
+                                       }
+
+                                       if err := receiveFile(conn, file, ioutil.Discard); err != nil {
+                                               s.Logger.Error(err)
+                                       }
+
+                                       err = os.Rename(dstPath+"/"+fu.FormattedPath()+".incomplete", dstPath+"/"+fu.FormattedPath())
+                                       if err != nil {
+                                               return err
+                                       }
+
+                               case dlFldrActionSendFile:
+                                       if _, err := conn.Read(fileSize); err != nil {
+                                               return err
+                                       }
+
+                                       filePath := dstPath + "/" + fu.FormattedPath()
+                                       s.Logger.Infow("Starting file transfer", "path", filePath, "fileNum", i+1, "totalFiles", "zz", "fileSize", binary.BigEndian.Uint32(fileSize))
+
+                                       newFile, err := FS.Create(filePath + ".incomplete")
+                                       if err != nil {
+                                               return err
+                                       }

 
 

-                               if err := transferFile(conn, dstPath+"/"+fu.FormattedPath()); err != nil {
-                                       s.Logger.Error(err)
+                                       if err := receiveFile(conn, newFile, ioutil.Discard); err != nil {
+                                               s.Logger.Error(err)
+                                       }
+                                       _ = newFile.Close()
+                                       if err := os.Rename(filePath+".incomplete", filePath); err != nil {
+                                               return err
+                                       }

                                }
 
                                // Tell client to send next file
                                if _, err := conn.Write([]byte{0, dlFldrActionNextFile}); err != nil {
                                }
 
                                // 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
                                }
                        }
                                        return err
                                }
                        }


@@ -956,44 +1103,6 @@ func (s *Server) TransferFile(conn net.Conn) error {
        return nil
 }
 
        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.BinaryMarshal())
-       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)
-       }
-}
-
-

 // 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) {
 // 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) {