Avoid big strings on the stack

[mirror_novnc.git] / core / websock.js

/*
 * Websock: high-performance binary WebSockets
 * Copyright (C) 2012 Joel Martin
 * Licensed under MPL 2.0 (see LICENSE.txt)
 *
 * Websock is similar to the standard WebSocket object but with extra
 * buffer handling.
 *
 * Websock has built-in receive queue buffering; the message event
 * does not contain actual data but is simply a notification that
 * there is new data available. Several rQ* methods are available to
 * read binary data off of the receive queue.
 */

import * as Log from './util/logging.js';

export default function Websock() {
    "use strict";

    this._websocket = null;  // WebSocket object

    this._rQi = 0;           // Receive queue index
    this._rQlen = 0;         // Next write position in the receive queue
    this._rQbufferSize = 1024 * 1024 * 4; // Receive queue buffer size (4 MiB)
    this._rQmax = this._rQbufferSize / 8;
    // called in init: this._rQ = new Uint8Array(this._rQbufferSize);
    this._rQ = null; // Receive queue

    this._sQbufferSize = 1024 * 10;  // 10 KiB
    // called in init: this._sQ = new Uint8Array(this._sQbufferSize);
    this._sQlen = 0;
    this._sQ = null;  // Send queue

    this._eventHandlers = {
        'message': function () {},
        'open': function () {},
        'close': function () {},
        'error': function () {}
    };
}

// this has performance issues in some versions Chromium, and
// doesn't gain a tremendous amount of performance increase in Firefox
// at the moment.  It may be valuable to turn it on in the future.
const ENABLE_COPYWITHIN = false;

const MAX_RQ_GROW_SIZE = 40 * 1024 * 1024;  // 40 MiB

Websock.prototype = {
    // Getters and Setters
    get_sQ: function () {
        return this._sQ;
    },

    get_rQ: function () {
        return this._rQ;
    },

    get_rQi: function () {
        return this._rQi;
    },

    set_rQi: function (val) {
        this._rQi = val;
    },

    // Receive Queue
    rQlen: function () {
        return this._rQlen - this._rQi;
    },

    rQpeek8: function () {
        return this._rQ[this._rQi];
    },

    rQshift8: function () {
        return this._rQ[this._rQi++];
    },

    rQskip8: function () {
        this._rQi++;
    },

    rQskipBytes: function (num) {
        this._rQi += num;
    },

    // TODO(directxman12): test performance with these vs a DataView
    rQshift16: function () {
        return (this._rQ[this._rQi++] << 8) +
               this._rQ[this._rQi++];
    },

    rQshift32: function () {
        return (this._rQ[this._rQi++] << 24) +
               (this._rQ[this._rQi++] << 16) +
               (this._rQ[this._rQi++] << 8) +
               this._rQ[this._rQi++];
    },

    rQshiftStr: function (len) {
        if (typeof(len) === 'undefined') { len = this.rQlen(); }
        const arr = this.rQshiftBytes(len);
        let str = "";
        // Handle large arrays in steps to avoid long strings on the stack
        for (let i = 0; i < len; i += 4096) {
            let part = arr.slice(i, i + Math.min(4096, len));
            str = str.concat(String.fromCharCode.apply(null, part));
        }
        return str;
    },

    rQshiftBytes: function (len) {
        if (typeof(len) === 'undefined') { len = this.rQlen(); }
        this._rQi += len;
        return new Uint8Array(this._rQ.buffer, this._rQi - len, len);
    },

    rQshiftTo: function (target, len) {
        if (len === undefined) { len = this.rQlen(); }
        // TODO: make this just use set with views when using a ArrayBuffer to store the rQ
        target.set(new Uint8Array(this._rQ.buffer, this._rQi, len));
        this._rQi += len;
    },

    rQwhole: function () {
        return new Uint8Array(this._rQ.buffer, 0, this._rQlen);
    },

    rQslice: function (start, end) {
        if (end) {
            return new Uint8Array(this._rQ.buffer, this._rQi + start, end - start);
        } else {
            return new Uint8Array(this._rQ.buffer, this._rQi + start, this._rQlen - this._rQi - start);
        }
    },

    // Check to see if we must wait for 'num' bytes (default to FBU.bytes)
    // to be available in the receive queue. Return true if we need to
    // wait (and possibly print a debug message), otherwise false.
    rQwait: function (msg, num, goback) {
        const rQlen = this._rQlen - this._rQi; // Skip rQlen() function call
        if (rQlen < num) {
            if (goback) {
                if (this._rQi < goback) {
                    throw new Error("rQwait cannot backup " + goback + " bytes");
                }
                this._rQi -= goback;
            }
            return true; // true means need more data
        }
        return false;
    },

    // Send Queue

    flush: function () {
        if (this._sQlen > 0 && this._websocket.readyState === WebSocket.OPEN) {
            this._websocket.send(this._encode_message());
            this._sQlen = 0;
        }
    },

    send: function (arr) {
        this._sQ.set(arr, this._sQlen);
        this._sQlen += arr.length;
        this.flush();
    },

    send_string: function (str) {
        this.send(str.split('').map(function (chr) {
            return chr.charCodeAt(0);
        }));
    },

    // Event Handlers
    off: function (evt) {
        this._eventHandlers[evt] = function () {};
    },

    on: function (evt, handler) {
        this._eventHandlers[evt] = handler;
    },

    _allocate_buffers: function () {
        this._rQ = new Uint8Array(this._rQbufferSize);
        this._sQ = new Uint8Array(this._sQbufferSize);
    },

    init: function () {
        this._allocate_buffers();
        this._rQi = 0;
        this._websocket = null;
    },

    open: function (uri, protocols) {
        this.init();

        this._websocket = new WebSocket(uri, protocols);
        this._websocket.binaryType = 'arraybuffer';

        this._websocket.onmessage = this._recv_message.bind(this);
        this._websocket.onopen = (function () {
            Log.Debug('>> WebSock.onopen');
            if (this._websocket.protocol) {
                Log.Info("Server choose sub-protocol: " + this._websocket.protocol);
            }

            this._eventHandlers.open();
            Log.Debug("<< WebSock.onopen");
        }).bind(this);
        this._websocket.onclose = (function (e) {
            Log.Debug(">> WebSock.onclose");
            this._eventHandlers.close(e);
            Log.Debug("<< WebSock.onclose");
        }).bind(this);
        this._websocket.onerror = (function (e) {
            Log.Debug(">> WebSock.onerror: " + e);
            this._eventHandlers.error(e);
            Log.Debug("<< WebSock.onerror: " + e);
        }).bind(this);
    },

    close: function () {
        if (this._websocket) {
            if ((this._websocket.readyState === WebSocket.OPEN) ||
                    (this._websocket.readyState === WebSocket.CONNECTING)) {
                Log.Info("Closing WebSocket connection");
                this._websocket.close();
            }

            this._websocket.onmessage = function (e) { return; };
        }
    },

    // private methods
    _encode_message: function () {
        // Put in a binary arraybuffer
        // according to the spec, you can send ArrayBufferViews with the send method
        return new Uint8Array(this._sQ.buffer, 0, this._sQlen);
    },

    _expand_compact_rQ: function (min_fit) {
        const resizeNeeded = min_fit || this._rQlen - this._rQi > this._rQbufferSize / 2;
        if (resizeNeeded) {
            if (!min_fit) {
                // just double the size if we need to do compaction
                this._rQbufferSize *= 2;
            } else {
                // otherwise, make sure we satisy rQlen - rQi + min_fit < rQbufferSize / 8
                this._rQbufferSize = (this._rQlen - this._rQi + min_fit) * 8;
            }
        }

        // we don't want to grow unboundedly
        if (this._rQbufferSize > MAX_RQ_GROW_SIZE) {
            this._rQbufferSize = MAX_RQ_GROW_SIZE;
            if (this._rQbufferSize - this._rQlen - this._rQi < min_fit) {
                throw new Error("Receive Queue buffer exceeded " + MAX_RQ_GROW_SIZE + " bytes, and the new message could not fit");
            }
        }

        if (resizeNeeded) {
            const old_rQbuffer = this._rQ.buffer;
            this._rQmax = this._rQbufferSize / 8;
            this._rQ = new Uint8Array(this._rQbufferSize);
            this._rQ.set(new Uint8Array(old_rQbuffer, this._rQi));
        } else {
            if (ENABLE_COPYWITHIN) {
                this._rQ.copyWithin(0, this._rQi);
            } else {
                this._rQ.set(new Uint8Array(this._rQ.buffer, this._rQi));
            }
        }

        this._rQlen = this._rQlen - this._rQi;
        this._rQi = 0;
    },

    _decode_message: function (data) {
        // push arraybuffer values onto the end
        const u8 = new Uint8Array(data);
        if (u8.length > this._rQbufferSize - this._rQlen) {
            this._expand_compact_rQ(u8.length);
        }
        this._rQ.set(u8, this._rQlen);
        this._rQlen += u8.length;
    },

    _recv_message: function (e) {
        this._decode_message(e.data);
        if (this.rQlen() > 0) {
            this._eventHandlers.message();
            // Compact the receive queue
            if (this._rQlen == this._rQi) {
                this._rQlen = 0;
                this._rQi = 0;
            } else if (this._rQlen > this._rQmax) {
                this._expand_compact_rQ();
            }
        } else {
            Log.Debug("Ignoring empty message");
        }
    }
};