MeshCentral/public/novnc/core/rfb.js

/*
 * noVNC: HTML5 VNC client
 * Copyright (C) 2018 The noVNC Authors
 * Licensed under MPL 2.0 (see LICENSE.txt)
 *
 * See README.md for usage and integration instructions.
 *
 */

import * as Log from './util/logging.js';
import { decodeUTF8 } from './util/strings.js';
import { dragThreshold } from './util/browser.js';
import EventTargetMixin from './util/eventtarget.js';
import Display from "./display.js";
import Keyboard from "./input/keyboard.js";
import Mouse from "./input/mouse.js";
import Cursor from "./util/cursor.js";
import Websock from "./websock.js";
import DES from "./des.js";
import KeyTable from "./input/keysym.js";
import XtScancode from "./input/xtscancodes.js";
import { encodings } from "./encodings.js";
import "./util/polyfill.js";

import RawDecoder from "./decoders/raw.js";
import CopyRectDecoder from "./decoders/copyrect.js";
import RREDecoder from "./decoders/rre.js";
import HextileDecoder from "./decoders/hextile.js";
import TightDecoder from "./decoders/tight.js";
import TightPNGDecoder from "./decoders/tightpng.js";

// How many seconds to wait for a disconnect to finish
const DISCONNECT_TIMEOUT = 3;
const DEFAULT_BACKGROUND = 'rgb(40, 40, 40)';

export default class RFB extends EventTargetMixin {
    constructor(target, url, options) {
        if (!target) {
            throw new Error("Must specify target");
        }
        if (!url) {
            throw new Error("Must specify URL");
        }

        super();

        this._target = target;
        this._url = url;

        // Connection details
        options = options || {};
        this._rfb_credentials = options.credentials || {};
        this._shared = 'shared' in options ? !!options.shared : true;
        this._repeaterID = options.repeaterID || '';
        this._showDotCursor = options.showDotCursor || false;

        // Internal state
        this._rfb_connection_state = '';
        this._rfb_init_state = '';
        this._rfb_auth_scheme = -1;
        this._rfb_clean_disconnect = true;

        // Server capabilities
        this._rfb_version = 0;
        this._rfb_max_version = 3.8;
        this._rfb_tightvnc = false;
        this._rfb_xvp_ver = 0;

        this._fb_width = 0;
        this._fb_height = 0;

        this._fb_name = "";

        this._capabilities = { power: false };

        this._supportsFence = false;

        this._supportsContinuousUpdates = false;
        this._enabledContinuousUpdates = false;

        this._supportsSetDesktopSize = false;
        this._screen_id = 0;
        this._screen_flags = 0;

        this._qemuExtKeyEventSupported = false;

        // Internal objects
        this._sock = null;              // Websock object
        this._display = null;           // Display object
        this._flushing = false;         // Display flushing state
        this._keyboard = null;          // Keyboard input handler object
        this._mouse = null;             // Mouse input handler object

        // Timers
        this._disconnTimer = null;      // disconnection timer
        this._resizeTimeout = null;     // resize rate limiting

        // Decoder states
        this._decoders = {};

        this._FBU = {
            rects: 0,
            x: 0,
            y: 0,
            width: 0,
            height: 0,
            encoding: null,
        };

        // Mouse state
        this._mouse_buttonMask = 0;
        this._mouse_arr = [];
        this._viewportDragging = false;
        this._viewportDragPos = {};
        this._viewportHasMoved = false;

        // Bound event handlers
        this._eventHandlers = {
            focusCanvas: this._focusCanvas.bind(this),
            windowResize: this._windowResize.bind(this),
        };

        // main setup
        Log.Debug(">> RFB.constructor");

        // Create DOM elements
        this._screen = document.createElement('div');
        this._screen.style.display = 'flex';
        this._screen.style.width = '100%';
        this._screen.style.height = '100%';
        this._screen.style.overflow = 'auto';
        this._screen.style.background = DEFAULT_BACKGROUND;
        this._canvas = document.createElement('canvas');
        this._canvas.style.margin = 'auto';
        // Some browsers add an outline on focus
        this._canvas.style.outline = 'none';
        // IE miscalculates width without this :(
        this._canvas.style.flexShrink = '0';
        this._canvas.width = 0;
        this._canvas.height = 0;
        this._canvas.tabIndex = -1;
        this._screen.appendChild(this._canvas);

        // Cursor
        this._cursor = new Cursor();

        // XXX: TightVNC 2.8.11 sends no cursor at all until Windows changes
        // it. Result: no cursor at all until a window border or an edit field
        // is hit blindly. But there are also VNC servers that draw the cursor
        // in the framebuffer and don't send the empty local cursor. There is
        // no way to satisfy both sides.
        //
        // The spec is unclear on this "initial cursor" issue. Many other
        // viewers (TigerVNC, RealVNC, Remmina) display an arrow as the
        // initial cursor instead.
        this._cursorImage = RFB.cursors.none;

        // populate decoder array with objects
        this._decoders[encodings.encodingRaw] = new RawDecoder();
        this._decoders[encodings.encodingCopyRect] = new CopyRectDecoder();
        this._decoders[encodings.encodingRRE] = new RREDecoder();
        this._decoders[encodings.encodingHextile] = new HextileDecoder();
        this._decoders[encodings.encodingTight] = new TightDecoder();
        this._decoders[encodings.encodingTightPNG] = new TightPNGDecoder();

        // NB: nothing that needs explicit teardown should be done
        // before this point, since this can throw an exception
        try {
            this._display = new Display(this._canvas);
        } catch (exc) {
            Log.Error("Display exception: " + exc);
            throw exc;
        }
        this._display.onflush = this._onFlush.bind(this);
        this._display.clear();

        this._keyboard = new Keyboard(this._canvas);
        this._keyboard.onkeyevent = this._handleKeyEvent.bind(this);

        this._mouse = new Mouse(this._canvas);
        this._mouse.onmousebutton = this._handleMouseButton.bind(this);
        this._mouse.onmousemove = this._handleMouseMove.bind(this);

        this._sock = new Websock();
        this._sock.on('message', () => {
            this._handle_message();
        });
        this._sock.on('open', () => {
            if ((this._rfb_connection_state === 'connecting') &&
                (this._rfb_init_state === '')) {
                this._rfb_init_state = 'ProtocolVersion';
                Log.Debug("Starting VNC handshake");
            } else {
                this._fail("Unexpected server connection while " +
                           this._rfb_connection_state);
            }
        });
        this._sock.on('close', (e) => {
            Log.Debug("WebSocket on-close event");
            let msg = "";
            if (e.code) {
                msg = "(code: " + e.code;
                if (e.reason) {
                    msg += ", reason: " + e.reason;
                }
                msg += ")";
            }
            switch (this._rfb_connection_state) {
                case 'connecting':
                    this._fail("Connection closed " + msg);
                    break;
                case 'connected':
                    // Handle disconnects that were initiated server-side
                    this._updateConnectionState('disconnecting');
                    this._updateConnectionState('disconnected');
                    break;
                case 'disconnecting':
                    // Normal disconnection path
                    this._updateConnectionState('disconnected');
                    break;
                case 'disconnected':
                    this._fail("Unexpected server disconnect " +
                               "when already disconnected " + msg);
                    break;
                default:
                    this._fail("Unexpected server disconnect before connecting " +
                               msg);
                    break;
            }
            this._sock.off('close');
        });
        this._sock.on('error', e => Log.Warn("WebSocket on-error event"));

        // Slight delay of the actual connection so that the caller has
        // time to set up callbacks
        setTimeout(this._updateConnectionState.bind(this, 'connecting'));

        Log.Debug("<< RFB.constructor");

        // ===== PROPERTIES =====

        this.dragViewport = false;
        this.focusOnClick = true;

        this._viewOnly = false;
        this._clipViewport = false;
        this._scaleViewport = false;
        this._resizeSession = false;
    }

    // ===== PROPERTIES =====

    get viewOnly() { return this._viewOnly; }
    set viewOnly(viewOnly) {
        this._viewOnly = viewOnly;

        if (this._rfb_connection_state === "connecting" ||
            this._rfb_connection_state === "connected") {
            if (viewOnly) {
                this._keyboard.ungrab();
                this._mouse.ungrab();
            } else {
                this._keyboard.grab();
                this._mouse.grab();
            }
        }
    }

    get capabilities() { return this._capabilities; }

    get touchButton() { return this._mouse.touchButton; }
    set touchButton(button) { this._mouse.touchButton = button; }

    get clipViewport() { return this._clipViewport; }
    set clipViewport(viewport) {
        this._clipViewport = viewport;
        this._updateClip();
    }

    get scaleViewport() { return this._scaleViewport; }
    set scaleViewport(scale) {
        this._scaleViewport = scale;
        // Scaling trumps clipping, so we may need to adjust
        // clipping when enabling or disabling scaling
        if (scale && this._clipViewport) {
            this._updateClip();
        }
        this._updateScale();
        if (!scale && this._clipViewport) {
            this._updateClip();
        }
    }

    get resizeSession() { return this._resizeSession; }
    set resizeSession(resize) {
        this._resizeSession = resize;
        if (resize) {
            this._requestRemoteResize();
        }
    }

    get showDotCursor() { return this._showDotCursor; }
    set showDotCursor(show) {
        this._showDotCursor = show;
        this._refreshCursor();
    }

    get background() { return this._screen.style.background; }
    set background(cssValue) { this._screen.style.background = cssValue; }

    // ===== PUBLIC METHODS =====

    disconnect() {
        this._updateConnectionState('disconnecting');
        this._sock.off('error');
        this._sock.off('message');
        this._sock.off('open');
    }

    sendCredentials(creds) {
        this._rfb_credentials = creds;
        setTimeout(this._init_msg.bind(this), 0);
    }

    sendCtrlAltDel() {
        if (this._rfb_connection_state !== 'connected' || this._viewOnly) { return; }
        Log.Info("Sending Ctrl-Alt-Del");

        this.sendKey(KeyTable.XK_Control_L, "ControlLeft", true);
        this.sendKey(KeyTable.XK_Alt_L, "AltLeft", true);
        this.sendKey(KeyTable.XK_Delete, "Delete", true);
        this.sendKey(KeyTable.XK_Delete, "Delete", false);
        this.sendKey(KeyTable.XK_Alt_L, "AltLeft", false);
        this.sendKey(KeyTable.XK_Control_L, "ControlLeft", false);
    }

    machineShutdown() {
        this._xvpOp(1, 2);
    }

    machineReboot() {
        this._xvpOp(1, 3);
    }

    machineReset() {
        this._xvpOp(1, 4);
    }

    // Send a key press. If 'down' is not specified then send a down key
    // followed by an up key.
    sendKey(keysym, code, down) {
        if (this._rfb_connection_state !== 'connected' || this._viewOnly) { return; }

        if (down === undefined) {
            this.sendKey(keysym, code, true);
            this.sendKey(keysym, code, false);
            return;
        }

        const scancode = XtScancode[code];

        if (this._qemuExtKeyEventSupported && scancode) {
            // 0 is NoSymbol
            keysym = keysym || 0;

            Log.Info("Sending key (" + (down ? "down" : "up") + "): keysym " + keysym + ", scancode " + scancode);

            RFB.messages.QEMUExtendedKeyEvent(this._sock, keysym, down, scancode);
        } else {
            if (!keysym) {
                return;
            }
            Log.Info("Sending keysym (" + (down ? "down" : "up") + "): " + keysym);
            RFB.messages.keyEvent(this._sock, keysym, down ? 1 : 0);
        }
    }

    focus() {
        this._canvas.focus();
    }

    blur() {
        this._canvas.blur();
    }

    clipboardPasteFrom(text) {
        if (this._rfb_connection_state !== 'connected' || this._viewOnly) { return; }
        RFB.messages.clientCutText(this._sock, text);
    }

    // ===== PRIVATE METHODS =====

    _connect() {
        Log.Debug(">> RFB.connect");

        Log.Info("connecting to " + this._url);

        try {
            // WebSocket.onopen transitions to the RFB init states
            this._sock.open(this._url, ['binary']);
        } catch (e) {
            if (e.name === 'SyntaxError') {
                this._fail("Invalid host or port (" + e + ")");
            } else {
                this._fail("Error when opening socket (" + e + ")");
            }
        }

        // Make our elements part of the page
        this._target.appendChild(this._screen);

        this._cursor.attach(this._canvas);
        this._refreshCursor();

        // Monitor size changes of the screen
        // FIXME: Use ResizeObserver, or hidden overflow
        window.addEventListener('resize', this._eventHandlers.windowResize);

        // Always grab focus on some kind of click event
        this._canvas.addEventListener("mousedown", this._eventHandlers.focusCanvas);
        this._canvas.addEventListener("touchstart", this._eventHandlers.focusCanvas);

        Log.Debug("<< RFB.connect");
    }

    _disconnect() {
        Log.Debug(">> RFB.disconnect");
        this._cursor.detach();
        this._canvas.removeEventListener("mousedown", this._eventHandlers.focusCanvas);
        this._canvas.removeEventListener("touchstart", this._eventHandlers.focusCanvas);
        window.removeEventListener('resize', this._eventHandlers.windowResize);
        this._keyboard.ungrab();
        this._mouse.ungrab();
        this._sock.close();
        try {
            this._target.removeChild(this._screen);
        } catch (e) {
            if (e.name === 'NotFoundError') {
                // Some cases where the initial connection fails
                // can disconnect before the _screen is created
            } else {
                throw e;
            }
        }
        clearTimeout(this._resizeTimeout);
        Log.Debug("<< RFB.disconnect");
    }

    _focusCanvas(event) {
        // Respect earlier handlers' request to not do side-effects
        if (event.defaultPrevented) {
            return;
        }

        if (!this.focusOnClick) {
            return;
        }

        this.focus();
    }

    _windowResize(event) {
        // If the window resized then our screen element might have
        // as well. Update the viewport dimensions.
        window.requestAnimationFrame(() => {
            this._updateClip();
            this._updateScale();
        });

        if (this._resizeSession) {
            // Request changing the resolution of the remote display to
            // the size of the local browser viewport.

            // In order to not send multiple requests before the browser-resize
            // is finished we wait 0.5 seconds before sending the request.
            clearTimeout(this._resizeTimeout);
            this._resizeTimeout = setTimeout(this._requestRemoteResize.bind(this), 500);
        }
    }

    // Update state of clipping in Display object, and make sure the
    // configured viewport matches the current screen size
    _updateClip() {
        const cur_clip = this._display.clipViewport;
        let new_clip = this._clipViewport;

        if (this._scaleViewport) {
            // Disable viewport clipping if we are scaling
            new_clip = false;
        }

        if (cur_clip !== new_clip) {
            this._display.clipViewport = new_clip;
        }

        if (new_clip) {
            // When clipping is enabled, the screen is limited to
            // the size of the container.
            const size = this._screenSize();
            this._display.viewportChangeSize(size.w, size.h);
            this._fixScrollbars();
        }
    }

    _updateScale() {
        if (!this._scaleViewport) {
            this._display.scale = 1.0;
        } else {
            const size = this._screenSize();
            this._display.autoscale(size.w, size.h);
        }
        this._fixScrollbars();
    }

    // Requests a change of remote desktop size. This message is an extension
    // and may only be sent if we have received an ExtendedDesktopSize message
    _requestRemoteResize() {
        clearTimeout(this._resizeTimeout);
        this._resizeTimeout = null;

        if (!this._resizeSession || this._viewOnly ||
            !this._supportsSetDesktopSize) {
            return;
        }

        const size = this._screenSize();
        RFB.messages.setDesktopSize(this._sock,
                                    Math.floor(size.w), Math.floor(size.h),
                                    this._screen_id, this._screen_flags);

        Log.Debug('Requested new desktop size: ' +
                   size.w + 'x' + size.h);
    }

    // Gets the the size of the available screen
    _screenSize() {
        let r = this._screen.getBoundingClientRect();
        return { w: r.width, h: r.height };
    }

    _fixScrollbars() {
        // This is a hack because Chrome screws up the calculation
        // for when scrollbars are needed. So to fix it we temporarily
        // toggle them off and on.
        const orig = this._screen.style.overflow;
        this._screen.style.overflow = 'hidden';
        // Force Chrome to recalculate the layout by asking for
        // an element's dimensions
        this._screen.getBoundingClientRect();
        this._screen.style.overflow = orig;
    }

    /*
     * Connection states:
     *   connecting
     *   connected
     *   disconnecting
     *   disconnected - permanent state
     */
    _updateConnectionState(state) {
        const oldstate = this._rfb_connection_state;

        if (state === oldstate) {
            Log.Debug("Already in state '" + state + "', ignoring");
            return;
        }

        // The 'disconnected' state is permanent for each RFB object
        if (oldstate === 'disconnected') {
            Log.Error("Tried changing state of a disconnected RFB object");
            return;
        }

        // Ensure proper transitions before doing anything
        switch (state) {
            case 'connected':
                if (oldstate !== 'connecting') {
                    Log.Error("Bad transition to connected state, " +
                               "previous connection state: " + oldstate);
                    return;
                }
                break;

            case 'disconnected':
                if (oldstate !== 'disconnecting') {
                    Log.Error("Bad transition to disconnected state, " +
                               "previous connection state: " + oldstate);
                    return;
                }
                break;

            case 'connecting':
                if (oldstate !== '') {
                    Log.Error("Bad transition to connecting state, " +
                               "previous connection state: " + oldstate);
                    return;
                }
                break;

            case 'disconnecting':
                if (oldstate !== 'connected' && oldstate !== 'connecting') {
                    Log.Error("Bad transition to disconnecting state, " +
                               "previous connection state: " + oldstate);
                    return;
                }
                break;

            default:
                Log.Error("Unknown connection state: " + state);
                return;
        }

        // State change actions

        this._rfb_connection_state = state;

        Log.Debug("New state '" + state + "', was '" + oldstate + "'.");

        if (this._disconnTimer && state !== 'disconnecting') {
            Log.Debug("Clearing disconnect timer");
            clearTimeout(this._disconnTimer);
            this._disconnTimer = null;

            // make sure we don't get a double event
            this._sock.off('close');
        }

        switch (state) {
            case 'connecting':
                this._connect();
                break;

            case 'connected':
                this.dispatchEvent(new CustomEvent("connect", { detail: {} }));
                break;

            case 'disconnecting':
                this._disconnect();

                this._disconnTimer = setTimeout(() => {
                    Log.Error("Disconnection timed out.");
                    this._updateConnectionState('disconnected');
                }, DISCONNECT_TIMEOUT * 1000);
                break;

            case 'disconnected':
                this.dispatchEvent(new CustomEvent(
                    "disconnect", { detail:
                                    { clean: this._rfb_clean_disconnect } }));
                break;
        }
    }

    /* Print errors and disconnect
     *
     * The parameter 'details' is used for information that
     * should be logged but not sent to the user interface.
     */
    _fail(details) {
        switch (this._rfb_connection_state) {
            case 'disconnecting':
                Log.Error("Failed when disconnecting: " + details);
                break;
            case 'connected':
                Log.Error("Failed while connected: " + details);
                break;
            case 'connecting':
                Log.Error("Failed when connecting: " + details);
                break;
            default:
                Log.Error("RFB failure: " + details);
                break;
        }
        this._rfb_clean_disconnect = false; //This is sent to the UI

        // Transition to disconnected without waiting for socket to close
        this._updateConnectionState('disconnecting');
        this._updateConnectionState('disconnected');

        return false;
    }

    _setCapability(cap, val) {
        this._capabilities[cap] = val;
        this.dispatchEvent(new CustomEvent("capabilities",
                                           { detail: { capabilities: this._capabilities } }));
    }

    _handle_message() {
        if (this._sock.rQlen === 0) {
            Log.Warn("handle_message called on an empty receive queue");
            return;
        }

        switch (this._rfb_connection_state) {
            case 'disconnected':
                Log.Error("Got data while disconnected");
                break;
            case 'connected':
                while (true) {
                    if (this._flushing) {
                        break;
                    }
                    if (!this._normal_msg()) {
                        break;
                    }
                    if (this._sock.rQlen === 0) {
                        break;
                    }
                }
                break;
            default:
                this._init_msg();
                break;
        }
    }

    _handleKeyEvent(keysym, code, down) {
        this.sendKey(keysym, code, down);
    }

    _handleMouseButton(x, y, down, bmask) {
        if (down) {
            this._mouse_buttonMask |= bmask;
        } else {
            this._mouse_buttonMask &= ~bmask;
        }

        if (this.dragViewport) {
            if (down && !this._viewportDragging) {
                this._viewportDragging = true;
                this._viewportDragPos = {'x': x, 'y': y};
                this._viewportHasMoved = false;

                // Skip sending mouse events
                return;
            } else {
                this._viewportDragging = false;

                // If we actually performed a drag then we are done
                // here and should not send any mouse events
                if (this._viewportHasMoved) {
                    return;
                }

                // Otherwise we treat this as a mouse click event.
                // Send the button down event here, as the button up
                // event is sent at the end of this function.
                RFB.messages.pointerEvent(this._sock,
                                          this._display.absX(x),
                                          this._display.absY(y),
                                          bmask);
            }
        }

        if (this._viewOnly) { return; } // View only, skip mouse events

        if (this._rfb_connection_state !== 'connected') { return; }
        RFB.messages.pointerEvent(this._sock, this._display.absX(x), this._display.absY(y), this._mouse_buttonMask);
    }

    _handleMouseMove(x, y) {
        if (this._viewportDragging) {
            const deltaX = this._viewportDragPos.x - x;
            const deltaY = this._viewportDragPos.y - y;

            if (this._viewportHasMoved || (Math.abs(deltaX) > dragThreshold ||
                                           Math.abs(deltaY) > dragThreshold)) {
                this._viewportHasMoved = true;

                this._viewportDragPos = {'x': x, 'y': y};
                this._display.viewportChangePos(deltaX, deltaY);
            }

            // Skip sending mouse events
            return;
        }

        if (this._viewOnly) { return; } // View only, skip mouse events

        if (this._rfb_connection_state !== 'connected') { return; }
        RFB.messages.pointerEvent(this._sock, this._display.absX(x), this._display.absY(y), this._mouse_buttonMask);
    }

    // Message Handlers

    _negotiate_protocol_version() {
        if (this._sock.rQwait("version", 12)) {
            return false;
        }

        const sversion = this._sock.rQshiftStr(12).substr(4, 7);
        Log.Info("Server ProtocolVersion: " + sversion);
        let is_repeater = 0;
        switch (sversion) {
            case "000.000":  // UltraVNC repeater
                is_repeater = 1;
                break;
            case "003.003":
            case "003.006":  // UltraVNC
            case "003.889":  // Apple Remote Desktop
                this._rfb_version = 3.3;
                break;
            case "003.007":
                this._rfb_version = 3.7;
                break;
            case "003.008":
            case "004.000":  // Intel AMT KVM
            case "004.001":  // RealVNC 4.6
            case "005.000":  // RealVNC 5.3
                this._rfb_version = 3.8;
                break;
            default:
                return this._fail("Invalid server version " + sversion);
        }

        if (is_repeater) {
            let repeaterID = "ID:" + this._repeaterID;
            while (repeaterID.length < 250) {
                repeaterID += "\0";
            }
            this._sock.send_string(repeaterID);
            return true;
        }

        if (this._rfb_version > this._rfb_max_version) {
            this._rfb_version = this._rfb_max_version;
        }

        const cversion = "00" + parseInt(this._rfb_version, 10) +
                       ".00" + ((this._rfb_version * 10) % 10);
        this._sock.send_string("RFB " + cversion + "\n");
        Log.Debug('Sent ProtocolVersion: ' + cversion);

        this._rfb_init_state = 'Security';
    }

    _negotiate_security() {
        // Polyfill since IE and PhantomJS doesn't have
        // TypedArray.includes()
        function includes(item, array) {
            for (let i = 0; i < array.length; i++) {
                if (array[i] === item) {
                    return true;
                }
            }
            return false;
        }

        if (this._rfb_version >= 3.7) {
            // Server sends supported list, client decides
            const num_types = this._sock.rQshift8();
            if (this._sock.rQwait("security type", num_types, 1)) { return false; }

            if (num_types === 0) {
                this._rfb_init_state = "SecurityReason";
                this._security_context = "no security types";
                this._security_status = 1;
                return this._init_msg();
            }

            const types = this._sock.rQshiftBytes(num_types);
            Log.Debug("Server security types: " + types);

            // Look for each auth in preferred order
            if (includes(1, types)) {
                this._rfb_auth_scheme = 1; // None
            } else if (includes(22, types)) {
                this._rfb_auth_scheme = 22; // XVP
            } else if (includes(16, types)) {
                this._rfb_auth_scheme = 16; // Tight
            } else if (includes(2, types)) {
                this._rfb_auth_scheme = 2; // VNC Auth
            } else {
                return this._fail("Unsupported security types (types: " + types + ")");
            }

            this._sock.send([this._rfb_auth_scheme]);
        } else {
            // Server decides
            if (this._sock.rQwait("security scheme", 4)) { return false; }
            this._rfb_auth_scheme = this._sock.rQshift32();

            if (this._rfb_auth_scheme == 0) {
                this._rfb_init_state = "SecurityReason";
                this._security_context = "authentication scheme";
                this._security_status = 1;
                return this._init_msg();
            }
        }

        this._rfb_init_state = 'Authentication';
        Log.Debug('Authenticating using scheme: ' + this._rfb_auth_scheme);

        return this._init_msg(); // jump to authentication
    }

    _handle_security_reason() {
        if (this._sock.rQwait("reason length", 4)) {
            return false;
        }
        const strlen = this._sock.rQshift32();
        let reason = "";

        if (strlen > 0) {
            if (this._sock.rQwait("reason", strlen, 4)) { return false; }
            reason = this._sock.rQshiftStr(strlen);
        }

        if (reason !== "") {
            this.dispatchEvent(new CustomEvent(
                "securityfailure",
                { detail: { status: this._security_status,
                            reason: reason } }));

            return this._fail("Security negotiation failed on " +
                              this._security_context +
                              " (reason: " + reason + ")");
        } else {
            this.dispatchEvent(new CustomEvent(
                "securityfailure",
                { detail: { status: this._security_status } }));

            return this._fail("Security negotiation failed on " +
                              this._security_context);
        }
    }

    // authentication
    _negotiate_xvp_auth() {
        if (!this._rfb_credentials.username ||
            !this._rfb_credentials.password ||
            !this._rfb_credentials.target) {
            this.dispatchEvent(new CustomEvent(
                "credentialsrequired",
                { detail: { types: ["username", "password", "target"] } }));
            return false;
        }

        const xvp_auth_str = String.fromCharCode(this._rfb_credentials.username.length) +
                           String.fromCharCode(this._rfb_credentials.target.length) +
                           this._rfb_credentials.username +
                           this._rfb_credentials.target;
        this._sock.send_string(xvp_auth_str);
        this._rfb_auth_scheme = 2;
        return this._negotiate_authentication();
    }

    _negotiate_std_vnc_auth() {
        if (this._sock.rQwait("auth challenge", 16)) { return false; }

        if (!this._rfb_credentials.password) {
            this.dispatchEvent(new CustomEvent(
                "credentialsrequired",
                { detail: { types: ["password"] } }));
            return false;
        }

        // TODO(directxman12): make genDES not require an Array
        const challenge = Array.prototype.slice.call(this._sock.rQshiftBytes(16));
        const response = RFB.genDES(this._rfb_credentials.password, challenge);
        this._sock.send(response);
        this._rfb_init_state = "SecurityResult";
        return true;
    }

    _negotiate_tight_tunnels(numTunnels) {
        const clientSupportedTunnelTypes = {
            0: { vendor: 'TGHT', signature: 'NOTUNNEL' }
        };
        const serverSupportedTunnelTypes = {};
        // receive tunnel capabilities
        for (let i = 0; i < numTunnels; i++) {
            const cap_code = this._sock.rQshift32();
            const cap_vendor = this._sock.rQshiftStr(4);
            const cap_signature = this._sock.rQshiftStr(8);
            serverSupportedTunnelTypes[cap_code] = { vendor: cap_vendor, signature: cap_signature };
        }

        Log.Debug("Server Tight tunnel types: " + serverSupportedTunnelTypes);

        // Siemens touch panels have a VNC server that supports NOTUNNEL,
        // but forgets to advertise it. Try to detect such servers by
        // looking for their custom tunnel type.
        if (serverSupportedTunnelTypes[1] &&
            (serverSupportedTunnelTypes[1].vendor === "SICR") &&
            (serverSupportedTunnelTypes[1].signature === "SCHANNEL")) {
            Log.Debug("Detected Siemens server. Assuming NOTUNNEL support.");
            serverSupportedTunnelTypes[0] = { vendor: 'TGHT', signature: 'NOTUNNEL' };
        }

        // choose the notunnel type
        if (serverSupportedTunnelTypes[0]) {
            if (serverSupportedTunnelTypes[0].vendor != clientSupportedTunnelTypes[0].vendor ||
                serverSupportedTunnelTypes[0].signature != clientSupportedTunnelTypes[0].signature) {
                return this._fail("Client's tunnel type had the incorrect " +
                                  "vendor or signature");
            }
            Log.Debug("Selected tunnel type: " + clientSupportedTunnelTypes[0]);
            this._sock.send([0, 0, 0, 0]);  // use NOTUNNEL
            return false; // wait until we receive the sub auth count to continue
        } else {
            return this._fail("Server wanted tunnels, but doesn't support " +
                              "the notunnel type");
        }
    }

    _negotiate_tight_auth() {
        if (!this._rfb_tightvnc) {  // first pass, do the tunnel negotiation
            if (this._sock.rQwait("num tunnels", 4)) { return false; }
            const numTunnels = this._sock.rQshift32();
            if (numTunnels > 0 && this._sock.rQwait("tunnel capabilities", 16 * numTunnels, 4)) { return false; }

            this._rfb_tightvnc = true;

            if (numTunnels > 0) {
                this._negotiate_tight_tunnels(numTunnels);
                return false;  // wait until we receive the sub auth to continue
            }
        }

        // second pass, do the sub-auth negotiation
        if (this._sock.rQwait("sub auth count", 4)) { return false; }
        const subAuthCount = this._sock.rQshift32();
        if (subAuthCount === 0) {  // empty sub-auth list received means 'no auth' subtype selected
            this._rfb_init_state = 'SecurityResult';
            return true;
        }

        if (this._sock.rQwait("sub auth capabilities", 16 * subAuthCount, 4)) { return false; }

        const clientSupportedTypes = {
            'STDVNOAUTH__': 1,
            'STDVVNCAUTH_': 2
        };

        const serverSupportedTypes = [];

        for (let i = 0; i < subAuthCount; i++) {
            this._sock.rQshift32(); // capNum
            const capabilities = this._sock.rQshiftStr(12);
            serverSupportedTypes.push(capabilities);
        }

        Log.Debug("Server Tight authentication types: " + serverSupportedTypes);

        for (let authType in clientSupportedTypes) {
            if (serverSupportedTypes.indexOf(authType) != -1) {
                this._sock.send([0, 0, 0, clientSupportedTypes[authType]]);
                Log.Debug("Selected authentication type: " + authType);

                switch (authType) {
                    case 'STDVNOAUTH__':  // no auth
                        this._rfb_init_state = 'SecurityResult';
                        return true;
                    case 'STDVVNCAUTH_': // VNC auth
                        this._rfb_auth_scheme = 2;
                        return this._init_msg();
                    default:
                        return this._fail("Unsupported tiny auth scheme " +
                                          "(scheme: " + authType + ")");
                }
            }
        }

        return this._fail("No supported sub-auth types!");
    }

    _negotiate_authentication() {
        switch (this._rfb_auth_scheme) {
            case 1:  // no auth
                if (this._rfb_version >= 3.8) {
                    this._rfb_init_state = 'SecurityResult';
                    return true;
                }
                this._rfb_init_state = 'ClientInitialisation';
                return this._init_msg();

            case 22:  // XVP auth
                return this._negotiate_xvp_auth();

            case 2:  // VNC authentication
                return this._negotiate_std_vnc_auth();

            case 16:  // TightVNC Security Type
                return this._negotiate_tight_auth();

            default:
                return this._fail("Unsupported auth scheme (scheme: " +
                                  this._rfb_auth_scheme + ")");
        }
    }

    _handle_security_result() {
        if (this._sock.rQwait('VNC auth response ', 4)) { return false; }

        const status = this._sock.rQshift32();

        if (status === 0) { // OK
            this._rfb_init_state = 'ClientInitialisation';
            Log.Debug('Authentication OK');
            return this._init_msg();
        } else {
            if (this._rfb_version >= 3.8) {
                this._rfb_init_state = "SecurityReason";
                this._security_context = "security result";
                this._security_status = status;
                return this._init_msg();
            } else {
                this.dispatchEvent(new CustomEvent(
                    "securityfailure",
                    { detail: { status: status } }));

                return this._fail("Security handshake failed");
            }
        }
    }

    _negotiate_server_init() {
        if (this._sock.rQwait("server initialization", 24)) { return false; }

        /* Screen size */
        const width = this._sock.rQshift16();
        const height = this._sock.rQshift16();

        /* PIXEL_FORMAT */
        const bpp         = this._sock.rQshift8();
        const depth       = this._sock.rQshift8();
        const big_endian  = this._sock.rQshift8();
        const true_color  = this._sock.rQshift8();

        const red_max     = this._sock.rQshift16();
        const green_max   = this._sock.rQshift16();
        const blue_max    = this._sock.rQshift16();
        const red_shift   = this._sock.rQshift8();
        const green_shift = this._sock.rQshift8();
        const blue_shift  = this._sock.rQshift8();
        this._sock.rQskipBytes(3);  // padding

        // NB(directxman12): we don't want to call any callbacks or print messages until
        //                   *after* we're past the point where we could backtrack

        /* Connection name/title */
        const name_length = this._sock.rQshift32();
        if (this._sock.rQwait('server init name', name_length, 24)) { return false; }
        this._fb_name = decodeUTF8(this._sock.rQshiftStr(name_length));

        if (this._rfb_tightvnc) {
            if (this._sock.rQwait('TightVNC extended server init header', 8, 24 + name_length)) { return false; }
            // In TightVNC mode, ServerInit message is extended
            const numServerMessages = this._sock.rQshift16();
            const numClientMessages = this._sock.rQshift16();
            const numEncodings = this._sock.rQshift16();
            this._sock.rQskipBytes(2);  // padding

            const totalMessagesLength = (numServerMessages + numClientMessages + numEncodings) * 16;
            if (this._sock.rQwait('TightVNC extended server init header', totalMessagesLength, 32 + name_length)) { return false; }

            // we don't actually do anything with the capability information that TIGHT sends,
            // so we just skip the all of this.

            // TIGHT server message capabilities
            this._sock.rQskipBytes(16 * numServerMessages);

            // TIGHT client message capabilities
            this._sock.rQskipBytes(16 * numClientMessages);

            // TIGHT encoding capabilities
            this._sock.rQskipBytes(16 * numEncodings);
        }

        // NB(directxman12): these are down here so that we don't run them multiple times
        //                   if we backtrack
        Log.Info("Screen: " + width + "x" + height +
                  ", bpp: " + bpp + ", depth: " + depth +
                  ", big_endian: " + big_endian +
                  ", true_color: " + true_color +
                  ", red_max: " + red_max +
                  ", green_max: " + green_max +
                  ", blue_max: " + blue_max +
                  ", red_shift: " + red_shift +
                  ", green_shift: " + green_shift +
                  ", blue_shift: " + blue_shift);

        if (big_endian !== 0) {
            Log.Warn("Server native endian is not little endian");
        }

        if (red_shift !== 16) {
            Log.Warn("Server native red-shift is not 16");
        }

        if (blue_shift !== 0) {
            Log.Warn("Server native blue-shift is not 0");
        }

        // we're past the point where we could backtrack, so it's safe to call this
        this.dispatchEvent(new CustomEvent(
            "desktopname",
            { detail: { name: this._fb_name } }));

        this._resize(width, height);

        if (!this._viewOnly) { this._keyboard.grab(); }
        if (!this._viewOnly) { this._mouse.grab(); }

        this._fb_depth = 24;

        if (this._fb_name === "Intel(r) AMT KVM") {
            Log.Warn("Intel AMT KVM only supports 8/16 bit depths. Using low color mode.");
            this._fb_depth = 8;
        }

        RFB.messages.pixelFormat(this._sock, this._fb_depth, true);
        this._sendEncodings();
        RFB.messages.fbUpdateRequest(this._sock, false, 0, 0, this._fb_width, this._fb_height);

        this._updateConnectionState('connected');
        return true;
    }

    _sendEncodings() {
        const encs = [];

        // In preference order
        encs.push(encodings.encodingCopyRect);
        // Only supported with full depth support
        if (this._fb_depth == 24) {
            encs.push(encodings.encodingTight);
            encs.push(encodings.encodingTightPNG);
            encs.push(encodings.encodingHextile);
            encs.push(encodings.encodingRRE);
        }
        encs.push(encodings.encodingRaw);

        // Psuedo-encoding settings
        encs.push(encodings.pseudoEncodingQualityLevel0 + 6);
        encs.push(encodings.pseudoEncodingCompressLevel0 + 2);

        encs.push(encodings.pseudoEncodingDesktopSize);
        encs.push(encodings.pseudoEncodingLastRect);
        encs.push(encodings.pseudoEncodingQEMUExtendedKeyEvent);
        encs.push(encodings.pseudoEncodingExtendedDesktopSize);
        encs.push(encodings.pseudoEncodingXvp);
        encs.push(encodings.pseudoEncodingFence);
        encs.push(encodings.pseudoEncodingContinuousUpdates);

        if (this._fb_depth == 24) {
            encs.push(encodings.pseudoEncodingCursor);
        }

        RFB.messages.clientEncodings(this._sock, encs);
    }

    /* RFB protocol initialization states:
     *   ProtocolVersion
     *   Security
     *   Authentication
     *   SecurityResult
     *   ClientInitialization - not triggered by server message
     *   ServerInitialization
     */
    _init_msg() {
        switch (this._rfb_init_state) {
            case 'ProtocolVersion':
                return this._negotiate_protocol_version();

            case 'Security':
                return this._negotiate_security();

            case 'Authentication':
                return this._negotiate_authentication();

            case 'SecurityResult':
                return this._handle_security_result();

            case 'SecurityReason':
                return this._handle_security_reason();

            case 'ClientInitialisation':
                this._sock.send([this._shared ? 1 : 0]); // ClientInitialisation
                this._rfb_init_state = 'ServerInitialisation';
                return true;

            case 'ServerInitialisation':
                return this._negotiate_server_init();

            default:
                return this._fail("Unknown init state (state: " +
                                  this._rfb_init_state + ")");
        }
    }

    _handle_set_colour_map_msg() {
        Log.Debug("SetColorMapEntries");

        return this._fail("Unexpected SetColorMapEntries message");
    }

    _handle_server_cut_text() {
        Log.Debug("ServerCutText");

        if (this._sock.rQwait("ServerCutText header", 7, 1)) { return false; }
        this._sock.rQskipBytes(3);  // Padding
        const length = this._sock.rQshift32();
        if (this._sock.rQwait("ServerCutText", length, 8)) { return false; }

        const text = this._sock.rQshiftStr(length);

        if (this._viewOnly) { return true; }

        this.dispatchEvent(new CustomEvent(
            "clipboard",
            { detail: { text: text } }));

        return true;
    }

    _handle_server_fence_msg() {
        if (this._sock.rQwait("ServerFence header", 8, 1)) { return false; }
        this._sock.rQskipBytes(3); // Padding
        let flags = this._sock.rQshift32();
        let length = this._sock.rQshift8();

        if (this._sock.rQwait("ServerFence payload", length, 9)) { return false; }

        if (length > 64) {
            Log.Warn("Bad payload length (" + length + ") in fence response");
            length = 64;
        }

        const payload = this._sock.rQshiftStr(length);

        this._supportsFence = true;

        /*
         * Fence flags
         *
         *  (1<<0)  - BlockBefore
         *  (1<<1)  - BlockAfter
         *  (1<<2)  - SyncNext
         *  (1<<31) - Request
         */

        if (!(flags & (1<<31))) {
            return this._fail("Unexpected fence response");
        }

        // Filter out unsupported flags
        // FIXME: support syncNext
        flags &= (1<<0) | (1<<1);

        // BlockBefore and BlockAfter are automatically handled by
        // the fact that we process each incoming message
        // synchronuosly.
        RFB.messages.clientFence(this._sock, flags, payload);

        return true;
    }

    _handle_xvp_msg() {
        if (this._sock.rQwait("XVP version and message", 3, 1)) { return false; }
        this._sock.rQskipBytes(1);  // Padding
        const xvp_ver = this._sock.rQshift8();
        const xvp_msg = this._sock.rQshift8();

        switch (xvp_msg) {
            case 0:  // XVP_FAIL
                Log.Error("XVP Operation Failed");
                break;
            case 1:  // XVP_INIT
                this._rfb_xvp_ver = xvp_ver;
                Log.Info("XVP extensions enabled (version " + this._rfb_xvp_ver + ")");
                this._setCapability("power", true);
                break;
            default:
                this._fail("Illegal server XVP message (msg: " + xvp_msg + ")");
                break;
        }

        return true;
    }

    _normal_msg() {
        let msg_type;
        if (this._FBU.rects > 0) {
            msg_type = 0;
        } else {
            msg_type = this._sock.rQshift8();
        }

        let first, ret;
        switch (msg_type) {
            case 0:  // FramebufferUpdate
                ret = this._framebufferUpdate();
                if (ret && !this._enabledContinuousUpdates) {
                    RFB.messages.fbUpdateRequest(this._sock, true, 0, 0,
                                                 this._fb_width, this._fb_height);
                }
                return ret;

            case 1:  // SetColorMapEntries
                return this._handle_set_colour_map_msg();

            case 2:  // Bell
                Log.Debug("Bell");
                this.dispatchEvent(new CustomEvent(
                    "bell",
                    { detail: {} }));
                return true;

            case 3:  // ServerCutText
                return this._handle_server_cut_text();

            case 150: // EndOfContinuousUpdates
                first = !this._supportsContinuousUpdates;
                this._supportsContinuousUpdates = true;
                this._enabledContinuousUpdates = false;
                if (first) {
                    this._enabledContinuousUpdates = true;
                    this._updateContinuousUpdates();
                    Log.Info("Enabling continuous updates.");
                } else {
                    // FIXME: We need to send a framebufferupdaterequest here
                    // if we add support for turning off continuous updates
                }
                return true;

            case 248: // ServerFence
                return this._handle_server_fence_msg();

            case 250:  // XVP
                return this._handle_xvp_msg();

            default:
                this._fail("Unexpected server message (type " + msg_type + ")");
                Log.Debug("sock.rQslice(0, 30): " + this._sock.rQslice(0, 30));
                return true;
        }
    }

    _onFlush() {
        this._flushing = false;
        // Resume processing
        if (this._sock.rQlen > 0) {
            this._handle_message();
        }
    }

    _framebufferUpdate() {
        if (this._FBU.rects === 0) {
            if (this._sock.rQwait("FBU header", 3, 1)) { return false; }
            this._sock.rQskipBytes(1);  // Padding
            this._FBU.rects = this._sock.rQshift16();

            // Make sure the previous frame is fully rendered first
            // to avoid building up an excessive queue
            if (this._display.pending()) {
                this._flushing = true;
                this._display.flush();
                return false;
            }
        }

        while (this._FBU.rects > 0) {
            if (this._FBU.encoding === null) {
                if (this._sock.rQwait("rect header", 12)) { return false; }
                /* New FramebufferUpdate */

                const hdr = this._sock.rQshiftBytes(12);
                this._FBU.x        = (hdr[0] << 8) + hdr[1];
                this._FBU.y        = (hdr[2] << 8) + hdr[3];
                this._FBU.width    = (hdr[4] << 8) + hdr[5];
                this._FBU.height   = (hdr[6] << 8) + hdr[7];
                this._FBU.encoding = parseInt((hdr[8] << 24) + (hdr[9] << 16) +
                                              (hdr[10] << 8) + hdr[11], 10);
            }

            if (!this._handleRect()) {
                return false;
            }

            this._FBU.rects--;
            this._FBU.encoding = null;
        }

        this._display.flip();

        return true;  // We finished this FBU
    }

    _handleRect() {
        switch (this._FBU.encoding) {
            case encodings.pseudoEncodingLastRect:
                this._FBU.rects = 1; // Will be decreased when we return
                return true;

            case encodings.pseudoEncodingCursor:
                return this._handleCursor();

            case encodings.pseudoEncodingQEMUExtendedKeyEvent:
                // Old Safari doesn't support creating keyboard events
                try {
                    const keyboardEvent = document.createEvent("keyboardEvent");
                    if (keyboardEvent.code !== undefined) {
                        this._qemuExtKeyEventSupported = true;
                    }
                } catch (err) {
                    // Do nothing
                }
                return true;

            case encodings.pseudoEncodingDesktopSize:
                this._resize(this._FBU.width, this._FBU.height);
                return true;

            case encodings.pseudoEncodingExtendedDesktopSize:
                return this._handleExtendedDesktopSize();

            default:
                return this._handleDataRect();
        }
    }

    _handleCursor() {
        const hotx = this._FBU.x;  // hotspot-x
        const hoty = this._FBU.y;  // hotspot-y
        const w = this._FBU.width;
        const h = this._FBU.height;

        const pixelslength = w * h * 4;
        const masklength = Math.ceil(w / 8) * h;

        let bytes = pixelslength + masklength;
        if (this._sock.rQwait("cursor encoding", bytes)) {
            return false;
        }

        // Decode from BGRX pixels + bit mask to RGBA
        const pixels = this._sock.rQshiftBytes(pixelslength);
        const mask = this._sock.rQshiftBytes(masklength);
        let rgba = new Uint8Array(w * h * 4);

        let pix_idx = 0;
        for (let y = 0; y < h; y++) {
            for (let x = 0; x < w; x++) {
                let mask_idx = y * Math.ceil(w / 8) + Math.floor(x / 8);
                let alpha = (mask[mask_idx] << (x % 8)) & 0x80 ? 255 : 0;
                rgba[pix_idx    ] = pixels[pix_idx + 2];
                rgba[pix_idx + 1] = pixels[pix_idx + 1];
                rgba[pix_idx + 2] = pixels[pix_idx];
                rgba[pix_idx + 3] = alpha;
                pix_idx += 4;
            }
        }

        this._updateCursor(rgba, hotx, hoty, w, h);

        return true;
    }

    _handleExtendedDesktopSize() {
        if (this._sock.rQwait("ExtendedDesktopSize", 4)) {
            return false;
        }

        const number_of_screens = this._sock.rQpeek8();

        let bytes = 4 + (number_of_screens * 16);
        if (this._sock.rQwait("ExtendedDesktopSize", bytes)) {
            return false;
        }

        const firstUpdate = !this._supportsSetDesktopSize;
        this._supportsSetDesktopSize = true;

        // Normally we only apply the current resize mode after a
        // window resize event. However there is no such trigger on the
        // initial connect. And we don't know if the server supports
        // resizing until we've gotten here.
        if (firstUpdate) {
            this._requestRemoteResize();
        }

        this._sock.rQskipBytes(1);  // number-of-screens
        this._sock.rQskipBytes(3);  // padding

        for (let i = 0; i < number_of_screens; i += 1) {
            // Save the id and flags of the first screen
            if (i === 0) {
                this._screen_id = this._sock.rQshiftBytes(4);    // id
                this._sock.rQskipBytes(2);                       // x-position
                this._sock.rQskipBytes(2);                       // y-position
                this._sock.rQskipBytes(2);                       // width
                this._sock.rQskipBytes(2);                       // height
                this._screen_flags = this._sock.rQshiftBytes(4); // flags
            } else {
                this._sock.rQskipBytes(16);
            }
        }

        /*
         * The x-position indicates the reason for the change:
         *
         *  0 - server resized on its own
         *  1 - this client requested the resize
         *  2 - another client requested the resize
         */

        // We need to handle errors when we requested the resize.
        if (this._FBU.x === 1 && this._FBU.y !== 0) {
            let msg = "";
            // The y-position indicates the status code from the server
            switch (this._FBU.y) {
                case 1:
                    msg = "Resize is administratively prohibited";
                    break;
                case 2:
                    msg = "Out of resources";
                    break;
                case 3:
                    msg = "Invalid screen layout";
                    break;
                default:
                    msg = "Unknown reason";
                    break;
            }
            Log.Warn("Server did not accept the resize request: "
                     + msg);
        } else {
            this._resize(this._FBU.width, this._FBU.height);
        }

        return true;
    }

    _handleDataRect() {
        let decoder = this._decoders[this._FBU.encoding];
        if (!decoder) {
            this._fail("Unsupported encoding (encoding: " +
                       this._FBU.encoding + ")");
            return false;
        }

        try {
            return decoder.decodeRect(this._FBU.x, this._FBU.y,
                                      this._FBU.width, this._FBU.height,
                                      this._sock, this._display,
                                      this._fb_depth);
        } catch (err) {
            this._fail("Error decoding rect: " + err);
            return false;
        }
    }

    _updateContinuousUpdates() {
        if (!this._enabledContinuousUpdates) { return; }

        RFB.messages.enableContinuousUpdates(this._sock, true, 0, 0,
                                             this._fb_width, this._fb_height);
    }

    _resize(width, height) {
        this._fb_width = width;
        this._fb_height = height;

        this._display.resize(this._fb_width, this._fb_height);

        // Adjust the visible viewport based on the new dimensions
        this._updateClip();
        this._updateScale();

        this._updateContinuousUpdates();
    }

    _xvpOp(ver, op) {
        if (this._rfb_xvp_ver < ver) { return; }
        Log.Info("Sending XVP operation " + op + " (version " + ver + ")");
        RFB.messages.xvpOp(this._sock, ver, op);
    }

    _updateCursor(rgba, hotx, hoty, w, h) {
        this._cursorImage = {
            rgbaPixels: rgba,
            hotx: hotx, hoty: hoty, w: w, h: h,
        };
        this._refreshCursor();
    }

    _shouldShowDotCursor() {
        // Called when this._cursorImage is updated
        if (!this._showDotCursor) {
            // User does not want to see the dot, so...
            return false;
        }

        // The dot should not be shown if the cursor is already visible,
        // i.e. contains at least one not-fully-transparent pixel.
        // So iterate through all alpha bytes in rgba and stop at the
        // first non-zero.
        for (let i = 3; i < this._cursorImage.rgbaPixels.length; i += 4) {
            if (this._cursorImage.rgbaPixels[i]) {
                return false;
            }
        }

        // At this point, we know that the cursor is fully transparent, and
        // the user wants to see the dot instead of this.
        return true;
    }

    _refreshCursor() {
        const image = this._shouldShowDotCursor() ? RFB.cursors.dot : this._cursorImage;
        this._cursor.change(image.rgbaPixels,
                            image.hotx, image.hoty,
                            image.w, image.h
        );
    }

    static genDES(password, challenge) {
        const passwordChars = password.split('').map(c => c.charCodeAt(0));
        return (new DES(passwordChars)).encrypt(challenge);
    }
}

// Class Methods
RFB.messages = {
    keyEvent(sock, keysym, down) {
        const buff = sock._sQ;
        const offset = sock._sQlen;

        buff[offset] = 4;  // msg-type
        buff[offset + 1] = down;

        buff[offset + 2] = 0;
        buff[offset + 3] = 0;

        buff[offset + 4] = (keysym >> 24);
        buff[offset + 5] = (keysym >> 16);
        buff[offset + 6] = (keysym >> 8);
        buff[offset + 7] = keysym;

        sock._sQlen += 8;
        sock.flush();
    },

    QEMUExtendedKeyEvent(sock, keysym, down, keycode) {
        function getRFBkeycode(xt_scancode) {
            const upperByte = (keycode >> 8);
            const lowerByte = (keycode & 0x00ff);
            if (upperByte === 0xe0 && lowerByte < 0x7f) {
                return lowerByte | 0x80;
            }
            return xt_scancode;
        }

        const buff = sock._sQ;
        const offset = sock._sQlen;

        buff[offset] = 255; // msg-type
        buff[offset + 1] = 0; // sub msg-type

        buff[offset + 2] = (down >> 8);
        buff[offset + 3] = down;

        buff[offset + 4] = (keysym >> 24);
        buff[offset + 5] = (keysym >> 16);
        buff[offset + 6] = (keysym >> 8);
        buff[offset + 7] = keysym;

        const RFBkeycode = getRFBkeycode(keycode);

        buff[offset + 8] = (RFBkeycode >> 24);
        buff[offset + 9] = (RFBkeycode >> 16);
        buff[offset + 10] = (RFBkeycode >> 8);
        buff[offset + 11] = RFBkeycode;

        sock._sQlen += 12;
        sock.flush();
    },

    pointerEvent(sock, x, y, mask) {
        const buff = sock._sQ;
        const offset = sock._sQlen;

        buff[offset] = 5; // msg-type

        buff[offset + 1] = mask;

        buff[offset + 2] = x >> 8;
        buff[offset + 3] = x;

        buff[offset + 4] = y >> 8;
        buff[offset + 5] = y;

        sock._sQlen += 6;
        sock.flush();
    },

    // TODO(directxman12): make this unicode compatible?
    clientCutText(sock, text) {
        const buff = sock._sQ;
        const offset = sock._sQlen;

        buff[offset] = 6; // msg-type

        buff[offset + 1] = 0; // padding
        buff[offset + 2] = 0; // padding
        buff[offset + 3] = 0; // padding

        let length = text.length;

        buff[offset + 4] = length >> 24;
        buff[offset + 5] = length >> 16;
        buff[offset + 6] = length >> 8;
        buff[offset + 7] = length;

        sock._sQlen += 8;

        // We have to keep track of from where in the text we begin creating the
        // buffer for the flush in the next iteration.
        let textOffset = 0;

        let remaining = length;
        while (remaining > 0) {

            let flushSize = Math.min(remaining, (sock._sQbufferSize - sock._sQlen));
            for (let i = 0; i < flushSize; i++) {
                buff[sock._sQlen + i] =  text.charCodeAt(textOffset + i);
            }

            sock._sQlen += flushSize;
            sock.flush();

            remaining -= flushSize;
            textOffset += flushSize;
        }
    },

    setDesktopSize(sock, width, height, id, flags) {
        const buff = sock._sQ;
        const offset = sock._sQlen;

        buff[offset] = 251;              // msg-type
        buff[offset + 1] = 0;            // padding
        buff[offset + 2] = width >> 8;   // width
        buff[offset + 3] = width;
        buff[offset + 4] = height >> 8;  // height
        buff[offset + 5] = height;

        buff[offset + 6] = 1;            // number-of-screens
        buff[offset + 7] = 0;            // padding

        // screen array
        buff[offset + 8] = id >> 24;     // id
        buff[offset + 9] = id >> 16;
        buff[offset + 10] = id >> 8;
        buff[offset + 11] = id;
        buff[offset + 12] = 0;           // x-position
        buff[offset + 13] = 0;
        buff[offset + 14] = 0;           // y-position
        buff[offset + 15] = 0;
        buff[offset + 16] = width >> 8;  // width
        buff[offset + 17] = width;
        buff[offset + 18] = height >> 8; // height
        buff[offset + 19] = height;
        buff[offset + 20] = flags >> 24; // flags
        buff[offset + 21] = flags >> 16;
        buff[offset + 22] = flags >> 8;
        buff[offset + 23] = flags;

        sock._sQlen += 24;
        sock.flush();
    },

    clientFence(sock, flags, payload) {
        const buff = sock._sQ;
        const offset = sock._sQlen;

        buff[offset] = 248; // msg-type

        buff[offset + 1] = 0; // padding
        buff[offset + 2] = 0; // padding
        buff[offset + 3] = 0; // padding

        buff[offset + 4] = flags >> 24; // flags
        buff[offset + 5] = flags >> 16;
        buff[offset + 6] = flags >> 8;
        buff[offset + 7] = flags;

        const n = payload.length;

        buff[offset + 8] = n; // length

        for (let i = 0; i < n; i++) {
            buff[offset + 9 + i] = payload.charCodeAt(i);
        }

        sock._sQlen += 9 + n;
        sock.flush();
    },

    enableContinuousUpdates(sock, enable, x, y, width, height) {
        const buff = sock._sQ;
        const offset = sock._sQlen;

        buff[offset] = 150;             // msg-type
        buff[offset + 1] = enable;      // enable-flag

        buff[offset + 2] = x >> 8;      // x
        buff[offset + 3] = x;
        buff[offset + 4] = y >> 8;      // y
        buff[offset + 5] = y;
        buff[offset + 6] = width >> 8;  // width
        buff[offset + 7] = width;
        buff[offset + 8] = height >> 8; // height
        buff[offset + 9] = height;

        sock._sQlen += 10;
        sock.flush();
    },

    pixelFormat(sock, depth, true_color) {
        const buff = sock._sQ;
        const offset = sock._sQlen;

        let bpp;

        if (depth > 16) {
            bpp = 32;
        } else if (depth > 8) {
            bpp = 16;
        } else {
            bpp = 8;
        }

        const bits = Math.floor(depth/3);

        buff[offset] = 0;  // msg-type

        buff[offset + 1] = 0; // padding
        buff[offset + 2] = 0; // padding
        buff[offset + 3] = 0; // padding

        buff[offset + 4] = bpp;                 // bits-per-pixel
        buff[offset + 5] = depth;               // depth
        buff[offset + 6] = 0;                   // little-endian
        buff[offset + 7] = true_color ? 1 : 0;  // true-color

        buff[offset + 8] = 0;    // red-max
        buff[offset + 9] = (1 << bits) - 1;  // red-max

        buff[offset + 10] = 0;   // green-max
        buff[offset + 11] = (1 << bits) - 1; // green-max

        buff[offset + 12] = 0;   // blue-max
        buff[offset + 13] = (1 << bits) - 1; // blue-max

        buff[offset + 14] = bits * 2; // red-shift
        buff[offset + 15] = bits * 1; // green-shift
        buff[offset + 16] = bits * 0; // blue-shift

        buff[offset + 17] = 0;   // padding
        buff[offset + 18] = 0;   // padding
        buff[offset + 19] = 0;   // padding

        sock._sQlen += 20;
        sock.flush();
    },

    clientEncodings(sock, encodings) {
        const buff = sock._sQ;
        const offset = sock._sQlen;

        buff[offset] = 2; // msg-type
        buff[offset + 1] = 0; // padding

        buff[offset + 2] = encodings.length >> 8;
        buff[offset + 3] = encodings.length;

        let j = offset + 4;
        for (let i = 0; i < encodings.length; i++) {
            const enc = encodings[i];
            buff[j] = enc >> 24;
            buff[j + 1] = enc >> 16;
            buff[j + 2] = enc >> 8;
            buff[j + 3] = enc;

            j += 4;
        }

        sock._sQlen += j - offset;
        sock.flush();
    },

    fbUpdateRequest(sock, incremental, x, y, w, h) {
        const buff = sock._sQ;
        const offset = sock._sQlen;

        if (typeof(x) === "undefined") { x = 0; }
        if (typeof(y) === "undefined") { y = 0; }

        buff[offset] = 3;  // msg-type
        buff[offset + 1] = incremental ? 1 : 0;

        buff[offset + 2] = (x >> 8) & 0xFF;
        buff[offset + 3] = x & 0xFF;

        buff[offset + 4] = (y >> 8) & 0xFF;
        buff[offset + 5] = y & 0xFF;

        buff[offset + 6] = (w >> 8) & 0xFF;
        buff[offset + 7] = w & 0xFF;

        buff[offset + 8] = (h >> 8) & 0xFF;
        buff[offset + 9] = h & 0xFF;

        sock._sQlen += 10;
        sock.flush();
    },

    xvpOp(sock, ver, op) {
        const buff = sock._sQ;
        const offset = sock._sQlen;

        buff[offset] = 250; // msg-type
        buff[offset + 1] = 0; // padding

        buff[offset + 2] = ver;
        buff[offset + 3] = op;

        sock._sQlen += 4;
        sock.flush();
    }
};

RFB.cursors = {
    none: {
        rgbaPixels: new Uint8Array(),
        w: 0, h: 0,
        hotx: 0, hoty: 0,
    },

    dot: {
        /* eslint-disable indent */
        rgbaPixels: new Uint8Array([
            255, 255, 255, 255,   0,   0,   0, 255, 255, 255, 255, 255,
              0,   0,   0, 255,   0,   0,   0,   0,   0,   0,  0,  255,
            255, 255, 255, 255,   0,   0,   0, 255, 255, 255, 255, 255,
        ]),
        /* eslint-enable indent */
        w: 3, h: 3,
        hotx: 1, hoty: 1,
    }
};