[rbdr/mobius] / hotline / server.go

package hotline

import (
        "bufio"
        "bytes"
        "context"
        "crypto/rand"
        "encoding/binary"
        "errors"
        "fmt"
        "golang.org/x/text/encoding/charmap"
        "io"
        "log"
        "log/slog"
        "net"
        "strings"
        "sync"
        "time"
)

type contextKey string

var contextKeyReq = contextKey("req")

type requestCtx struct {
        remoteAddr string
}

// Converts bytes from Mac Roman encoding to UTF-8
var txtDecoder = charmap.Macintosh.NewDecoder()

// Converts bytes from UTF-8 to Mac Roman encoding
var txtEncoder = charmap.Macintosh.NewEncoder()

type Server struct {
        NetInterface string
        Port         int

        handlers map[TranType]HandlerFunc

        Config Config
        Logger *slog.Logger

        TrackerPassID [4]byte

        Stats Counter

        FS FileStore // Storage backend to use for File storage

        outbox chan Transaction

        Agreement io.ReadSeeker
        Banner    []byte

        FileTransferMgr FileTransferMgr
        ChatMgr         ChatManager
        ClientMgr       ClientManager
        AccountManager  AccountManager
        ThreadedNewsMgr ThreadedNewsMgr
        BanList         BanMgr

        MessageBoard io.ReadWriteSeeker
}

type Option = func(s *Server)

func WithConfig(config Config) func(s *Server) {
        return func(s *Server) {
                s.Config = config
        }
}

func WithLogger(logger *slog.Logger) func(s *Server) {
        return func(s *Server) {
                s.Logger = logger
        }
}

// WithPort optionally overrides the default TCP port.
func WithPort(port int) func(s *Server) {
        return func(s *Server) {
                s.Port = port
        }
}

// WithInterface optionally sets a specific interface to listen on.
func WithInterface(netInterface string) func(s *Server) {
        return func(s *Server) {
                s.NetInterface = netInterface
        }
}

type ServerConfig struct {
}

func NewServer(options ...Option) (*Server, error) {
        server := Server{
                handlers:        make(map[TranType]HandlerFunc),
                outbox:          make(chan Transaction),
                FS:              &OSFileStore{},
                ChatMgr:         NewMemChatManager(),
                ClientMgr:       NewMemClientMgr(),
                FileTransferMgr: NewMemFileTransferMgr(),
                Stats:           NewStats(),
        }

        for _, opt := range options {
                opt(&server)
        }

        // generate a new random passID for tracker registration
        _, err := rand.Read(server.TrackerPassID[:])
        if err != nil {
                return nil, err
        }

        return &server, nil
}

func (s *Server) CurrentStats() map[string]interface{} {
        return s.Stats.Values()
}

func (s *Server) ListenAndServe(ctx context.Context) error {
        go s.registerWithTrackers(ctx)
        go s.keepaliveHandler(ctx)
        go s.processOutbox()

        var wg sync.WaitGroup

        wg.Add(1)
        go func() {
                ln, err := net.Listen("tcp", fmt.Sprintf("%s:%v", s.NetInterface, s.Port))
                if err != nil {
                        log.Fatal(err)
                }

                log.Fatal(s.Serve(ctx, ln))
        }()

        wg.Add(1)
        go func() {
                ln, err := net.Listen("tcp", fmt.Sprintf("%s:%v", s.NetInterface, s.Port+1))
                if err != nil {
                        log.Fatal(err)
                }

                log.Fatal(s.ServeFileTransfers(ctx, ln))
        }()

        wg.Wait()

        return nil
}

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

                go func() {
                        defer func() { _ = conn.Close() }()

                        err = s.handleFileTransfer(
                                context.WithValue(ctx, contextKeyReq, requestCtx{remoteAddr: conn.RemoteAddr().String()}),
                                conn,
                        )

                        if err != nil {
                                s.Logger.Error("file transfer error", "reason", err)
                        }
                }()
        }
}

func (s *Server) sendTransaction(t Transaction) error {
        client := s.ClientMgr.Get(t.ClientID)

        if client == nil {
                return nil
        }

        _, err := io.Copy(client.Connection, &t)
        if err != nil {
                return fmt.Errorf("failed to send transaction to client %v: %v", t.ClientID, err)
        }

        return nil
}

func (s *Server) processOutbox() {
        for {
                t := <-s.outbox
                go func() {
                        if err := s.sendTransaction(t); err != nil {
                                s.Logger.Error("error sending transaction", "err", err)
                        }
                }()
        }
}

func (s *Server) Serve(ctx context.Context, ln net.Listener) error {
        for {
                select {
                case <-ctx.Done():
                        s.Logger.Info("Server shutting down")
                        return ctx.Err()
                default:
                        conn, err := ln.Accept()
                        if err != nil {
                                s.Logger.Error("Error accepting connection", "err", err)
                                continue
                        }

                        go func() {
                                connCtx := context.WithValue(ctx, contextKeyReq, requestCtx{
                                        remoteAddr: conn.RemoteAddr().String(),
                                })

                                s.Logger.Info("Connection established", "addr", conn.RemoteAddr())
                                defer conn.Close()

                                if err := s.handleNewConnection(connCtx, conn, conn.RemoteAddr().String()); err != nil {
                                        if err == io.EOF {
                                                s.Logger.Info("Client disconnected", "RemoteAddr", conn.RemoteAddr())
                                        } else {
                                                s.Logger.Error("Error serving request", "RemoteAddr", conn.RemoteAddr(), "err", err)
                                        }
                                }
                        }()
                }
        }
}

// time in seconds between tracker re-registration
const trackerUpdateFrequency = 300

// registerWithTrackers runs every trackerUpdateFrequency seconds to update the server's tracker entry on all configured
// trackers.
func (s *Server) registerWithTrackers(ctx context.Context) {
        ticker := time.NewTicker(trackerUpdateFrequency * time.Second)
        defer ticker.Stop()

        for {
                select {
                case <-ctx.Done():
                        return
                case <-ticker.C:
                        if s.Config.EnableTrackerRegistration {
                                tr := &TrackerRegistration{
                                        UserCount:   len(s.ClientMgr.List()),
                                        PassID:      s.TrackerPassID,
                                        Name:        s.Config.Name,
                                        Description: s.Config.Description,
                                }
                                binary.BigEndian.PutUint16(tr.Port[:], uint16(s.Port))

                                for _, t := range s.Config.Trackers {
                                        if err := register(&RealDialer{}, t, tr); err != nil {
                                                s.Logger.Error(fmt.Sprintf("Unable to register with tracker %v", t), "error", err)
                                        }
                                }
                        }
                }
        }

}

const (
        userIdleSeconds   = 300 // time in seconds before an inactive user is marked idle
        idleCheckInterval = 10  // time in seconds to check for idle users
)

// keepaliveHandler runs every idleCheckInterval seconds and increments a user's idle time by idleCheckInterval seconds.
// If the updated idle time exceeds userIdleSeconds and the user was not previously idle, we notify all connected clients
// that the user has gone idle.  For most clients, this turns the user grey in the user list.
func (s *Server) keepaliveHandler(ctx context.Context) {
        ticker := time.NewTicker(idleCheckInterval * time.Second)
        defer ticker.Stop()

        for {
                select {
                case <-ctx.Done():
                        return
                case <-ticker.C:
                        for _, c := range s.ClientMgr.List() {
                                c.mu.Lock()
                                c.IdleTime += idleCheckInterval

                                // Check if the user
                                if c.IdleTime > userIdleSeconds && !c.Flags.IsSet(UserFlagAway) {
                                        c.Flags.Set(UserFlagAway, 1)

                                        c.SendAll(
                                                TranNotifyChangeUser,
                                                NewField(FieldUserID, c.ID[:]),
                                                NewField(FieldUserFlags, c.Flags[:]),
                                                NewField(FieldUserName, c.UserName),
                                                NewField(FieldUserIconID, c.Icon),
                                        )
                                }
                                c.mu.Unlock()
                        }
                }
        }
}

func (s *Server) NewClientConn(conn io.ReadWriteCloser, remoteAddr string) *ClientConn {
        clientConn := &ClientConn{
                Icon:       []byte{0, 0}, // TODO: make array type
                Connection: conn,
                Server:     s,
                RemoteAddr: remoteAddr,

                ClientFileTransferMgr: NewClientFileTransferMgr(),
        }

        s.ClientMgr.Add(clientConn)

        return clientConn
}

func sendBanMessage(rwc io.Writer, message string) {
        t := NewTransaction(
                TranServerMsg,
                [2]byte{0, 0},
                NewField(FieldData, []byte(message)),
                NewField(FieldChatOptions, []byte{0, 0}),
        )
        _, _ = io.Copy(rwc, &t)
        time.Sleep(1 * time.Second)
}

// handleNewConnection takes a new net.Conn and performs the initial login sequence
func (s *Server) handleNewConnection(ctx context.Context, rwc io.ReadWriteCloser, remoteAddr string) error {
        defer dontPanic(s.Logger)

        if err := performHandshake(rwc); err != nil {
                return fmt.Errorf("perform handshake: %w", err)
        }

        // Check if remoteAddr is present in the ban list
        ipAddr := strings.Split(remoteAddr, ":")[0]
        if isBanned, banUntil := s.BanList.IsBanned(ipAddr); isBanned {
                // permaban
                if banUntil == nil {
                        sendBanMessage(rwc, "You are permanently banned on this server")
                        s.Logger.Debug("Disconnecting permanently banned IP", "remoteAddr", ipAddr)
                        return nil
                }

                // temporary ban
                if time.Now().Before(*banUntil) {
                        sendBanMessage(rwc, "You are temporarily banned on this server")
                        s.Logger.Debug("Disconnecting temporarily banned IP", "remoteAddr", ipAddr)
                        return nil
                }
        }

        // Create a new scanner for parsing incoming bytes into transaction tokens
        scanner := bufio.NewScanner(rwc)
        scanner.Split(transactionScanner)

        scanner.Scan()

        // Make a new []byte slice and copy the scanner bytes to it.  This is critical to avoid a data race as the
        // scanner re-uses the buffer for subsequent scans.
        buf := make([]byte, len(scanner.Bytes()))
        copy(buf, scanner.Bytes())

        var clientLogin Transaction
        if _, err := clientLogin.Write(buf); err != nil {
                return fmt.Errorf("error writing login transaction: %w", err)
        }

        c := s.NewClientConn(rwc, remoteAddr)
        defer c.Disconnect()

        encodedPassword := clientLogin.GetField(FieldUserPassword).Data
        c.Version = clientLogin.GetField(FieldVersion).Data

        login := clientLogin.GetField(FieldUserLogin).DecodeObfuscatedString()
        if login == "" {
                login = GuestAccount
        }

        c.Logger = s.Logger.With("ip", ipAddr, "login", login)

        // If authentication fails, send error reply and close connection
        if !c.Authenticate(login, encodedPassword) {
                t := c.NewErrReply(&clientLogin, "Incorrect login.")[0]

                _, err := io.Copy(rwc, &t)
                if err != nil {
                        return err
                }

                c.Logger.Info("Login failed", "clientVersion", fmt.Sprintf("%x", c.Version))

                return nil
        }

        if clientLogin.GetField(FieldUserIconID).Data != nil {
                c.Icon = clientLogin.GetField(FieldUserIconID).Data
        }

        c.Account = c.Server.AccountManager.Get(login)
        if c.Account == nil {
                return nil
        }

        if clientLogin.GetField(FieldUserName).Data != nil {
                if c.Authorize(AccessAnyName) {
                        c.UserName = clientLogin.GetField(FieldUserName).Data
                } else {
                        c.UserName = []byte(c.Account.Name)
                }
        }

        if c.Authorize(AccessDisconUser) {
                c.Flags.Set(UserFlagAdmin, 1)
        }

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

        // Accounts with AccessNoAgreement do not receive the server agreement on login.  The behavior is different between
        // client versions.  For 1.2.3 client, we do not send TranShowAgreement.  For other client versions, we send
        // TranShowAgreement but with the NoServerAgreement field set to 1.
        if c.Authorize(AccessNoAgreement) {
                // If client version is nil, then the client uses the 1.2.3 login behavior
                if c.Version != nil {
                        c.Server.outbox <- NewTransaction(TranShowAgreement, c.ID, NewField(FieldNoServerAgreement, []byte{1}))
                }
        } else {
                _, _ = c.Server.Agreement.Seek(0, 0)
                data, _ := io.ReadAll(c.Server.Agreement)

                c.Server.outbox <- NewTransaction(TranShowAgreement, c.ID, NewField(FieldData, data))
        }

        // If the client has provided a username as part of the login, we can infer that it is using the 1.2.3 login
        // flow and not the 1.5+ flow.
        if len(c.UserName) != 0 {
                // Add the client username to the logger.  For 1.5+ clients, we don't have this information yet as it comes as
                // part of TranAgreed
                c.Logger = c.Logger.With("name", string(c.UserName))
                c.Logger.Info("Login successful")

                // Notify other clients on the server that the new user has logged in.  For 1.5+ clients we don't have this
                // information yet, so we do it in TranAgreed instead
                for _, t := range c.NotifyOthers(
                        NewTransaction(
                                TranNotifyChangeUser, [2]byte{0, 0},
                                NewField(FieldUserName, c.UserName),
                                NewField(FieldUserID, c.ID[:]),
                                NewField(FieldUserIconID, c.Icon),
                                NewField(FieldUserFlags, c.Flags[:]),
                        ),
                ) {
                        c.Server.outbox <- t
                }
        }

        c.Server.Stats.Increment(StatConnectionCounter, StatCurrentlyConnected)
        defer c.Server.Stats.Decrement(StatCurrentlyConnected)

        if len(s.ClientMgr.List()) > c.Server.Stats.Get(StatConnectionPeak) {
                c.Server.Stats.Set(StatConnectionPeak, len(s.ClientMgr.List()))
        }

        // Scan for new transactions and handle them as they come in.
        for scanner.Scan() {
                // Copy the scanner bytes to a new slice to it to avoid a data race when the scanner re-uses the buffer.
                tmpBuf := make([]byte, len(scanner.Bytes()))
                copy(tmpBuf, scanner.Bytes())

                var t Transaction
                if _, err := t.Write(tmpBuf); err != nil {
                        return err
                }

                c.handleTransaction(t)
        }
        return nil
}

// handleFileTransfer receives a client net.Conn from the file transfer server, performs the requested transfer type, then closes the connection
func (s *Server) handleFileTransfer(ctx context.Context, rwc io.ReadWriter) error {
        defer dontPanic(s.Logger)

        // The first 16 bytes contain the file transfer.
        var t transfer
        if _, err := io.CopyN(&t, rwc, 16); err != nil {
                return fmt.Errorf("error reading file transfer: %w", err)
        }

        fileTransfer := s.FileTransferMgr.Get(t.ReferenceNumber)
        if fileTransfer == nil {
                return errors.New("invalid transaction ID")
        }

        defer func() {
                s.FileTransferMgr.Delete(t.ReferenceNumber)

                // Wait a few seconds before closing the connection: this is a workaround for problems
                // observed with Windows clients where the client must initiate close of the TCP connection before
                // the server does.  This is gross and seems unnecessary.  TODO: Revisit?
                time.Sleep(3 * time.Second)
        }()

        rLogger := s.Logger.With(
                "remoteAddr", ctx.Value(contextKeyReq).(requestCtx).remoteAddr,
                "login", fileTransfer.ClientConn.Account.Login,
                "Name", string(fileTransfer.ClientConn.UserName),
        )

        fullPath, err := ReadPath(s.Config.FileRoot, fileTransfer.FilePath, fileTransfer.FileName)
        if err != nil {
                return err
        }

        switch fileTransfer.Type {
        case BannerDownload:
                if _, err := io.Copy(rwc, bytes.NewBuffer(s.Banner)); err != nil {
                        return fmt.Errorf("error sending Banner: %w", err)
                }
        case FileDownload:
                s.Stats.Increment(StatDownloadCounter, StatDownloadsInProgress)
                defer func() {
                        s.Stats.Decrement(StatDownloadsInProgress)
                }()

                err = DownloadHandler(rwc, fullPath, fileTransfer, s.FS, rLogger, true)
                if err != nil {
                        return fmt.Errorf("file download: %w", err)
                }

        case FileUpload:
                s.Stats.Increment(StatUploadCounter, StatUploadsInProgress)
                defer func() {
                        s.Stats.Decrement(StatUploadsInProgress)
                }()

                err = UploadHandler(rwc, fullPath, fileTransfer, s.FS, rLogger, s.Config.PreserveResourceForks)
                if err != nil {
                        return fmt.Errorf("file upload error: %w", err)
                }

        case FolderDownload:
                s.Stats.Increment(StatDownloadCounter, StatDownloadsInProgress)
                defer func() {
                        s.Stats.Decrement(StatDownloadsInProgress)
                }()

                err = DownloadFolderHandler(rwc, fullPath, fileTransfer, s.FS, rLogger, s.Config.PreserveResourceForks)
                if err != nil {
                        return fmt.Errorf("file upload error: %w", err)
                }

        case FolderUpload:
                s.Stats.Increment(StatUploadCounter, StatUploadsInProgress)
                defer func() {
                        s.Stats.Decrement(StatUploadsInProgress)
                }()

                rLogger.Info(
                        "Folder upload started",
                        "dstPath", fullPath,
                        "TransferSize", binary.BigEndian.Uint32(fileTransfer.TransferSize),
                        "FolderItemCount", fileTransfer.FolderItemCount,
                )

                err = UploadFolderHandler(rwc, fullPath, fileTransfer, s.FS, rLogger, s.Config.PreserveResourceForks)
                if err != nil {
                        return fmt.Errorf("file upload error: %w", err)
                }
        }
        return nil
}