qwebchannel.js

// Copyright (C) 2016 The Qt Company Ltd.
// Copyright (C) 2016 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Milian Wolff <milian.wolff@kdab.com>
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only

"use strict";

var QWebChannelMessageTypes = {
    signal: 1,
    propertyUpdate: 2,
    init: 3,
    idle: 4,
    debug: 5,
    invokeMethod: 6,
    connectToSignal: 7,
    disconnectFromSignal: 8,
    setProperty: 9,
    response: 10,
};

var QWebChannel = function(transport, initCallback, converters)
{
    if (typeof transport !== "object" || typeof transport.send !== "function") {
        console.error("The QWebChannel expects a transport object with a send function and onmessage callback property." +
                      " Given is: transport: " + typeof(transport) + ", transport.send: " + typeof(transport.send));
        return;
    }

    var channel = this;
    this.transport = transport;

    var converterRegistry =
    {
        Date : function(response) {
            if (typeof response === "string"
                && response.match(
                        /^-?\d+-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(?:\.\d*)?([-+\u2212](\d{2}):(\d{2})|Z)?$/)) {
                var date = new Date(response);
                if (!isNaN(date))
                    return date;
            }
            return undefined; // Return undefined if current converter is not applicable
        }
    };

    this.usedConverters = [];

    this.addConverter = function(converter)
    {
        if (typeof converter === "string") {
            if (converterRegistry.hasOwnProperty(converter))
                this.usedConverters.push(converterRegistry[converter]);
            else
                console.error("Converter '" + converter + "' not found");
        } else if (typeof converter === "function") {
            this.usedConverters.push(converter);
        } else {
            console.error("Invalid converter object type " + typeof converter);
        }
    }

    if (Array.isArray(converters)) {
        for (const converter of converters)
            this.addConverter(converter);
    } else if (converters !== undefined) {
        this.addConverter(converters);
    }

    this.send = function(data)
    {
        if (typeof(data) !== "string") {
            data = JSON.stringify(data);
        }
        channel.transport.send(data);
    }

    this.transport.onmessage = function(message)
    {
        var data = message.data;
        if (typeof data === "string") {
            data = JSON.parse(data);
        }
        switch (data.type) {
            case QWebChannelMessageTypes.signal:
                channel.handleSignal(data);
                break;
            case QWebChannelMessageTypes.response:
                channel.handleResponse(data);
                break;
            case QWebChannelMessageTypes.propertyUpdate:
                channel.handlePropertyUpdate(data);
                break;
            default:
                console.error("invalid message received:", message.data);
                break;
        }
    }

    this.execCallbacks = {};
    this.execId = 0;
    this.exec = function(data, callback)
    {
        if (!callback) {
            // if no callback is given, send directly
            channel.send(data);
            return;
        }
        if (channel.execId === Number.MAX_VALUE) {
            // wrap
            channel.execId = Number.MIN_VALUE;
        }
        if (data.hasOwnProperty("id")) {
            console.error("Cannot exec message with property id: " + JSON.stringify(data));
            return;
        }
        data.id = channel.execId++;
        channel.execCallbacks[data.id] = callback;
        channel.send(data);
    };

    this.objects = {};

    this.handleSignal = function(message)
    {
        var object = channel.objects[message.object];
        if (object) {
            object.signalEmitted(message.signal, message.args);
        } else {
            console.warn("Unhandled signal: " + message.object + "::" + message.signal);
        }
    }

    this.handleResponse = function(message)
    {
        if (!message.hasOwnProperty("id")) {
            console.error("Invalid response message received: ", JSON.stringify(message));
            return;
        }
        channel.execCallbacks[message.id](message.data);
        delete channel.execCallbacks[message.id];
    }

    this.handlePropertyUpdate = function(message)
    {
        message.data.forEach(data => {
            var object = channel.objects[data.object];
            if (object) {
                object.propertyUpdate(data.signals, data.properties);
            } else {
                console.warn("Unhandled property update: " + data.object + "::" + data.signal);
            }
        });
        channel.exec({type: QWebChannelMessageTypes.idle});
    }

    this.debug = function(message)
    {
        channel.send({type: QWebChannelMessageTypes.debug, data: message});
    };

    channel.exec({type: QWebChannelMessageTypes.init}, function(data) {
        for (const objectName of Object.keys(data)) {
            new QObject(objectName, data[objectName], channel);
        }

        // now unwrap properties, which might reference other registered objects
        for (const objectName of Object.keys(channel.objects)) {
            channel.objects[objectName].unwrapProperties();
        }

        if (initCallback) {
            initCallback(channel);
        }
        channel.exec({type: QWebChannelMessageTypes.idle});
    });
};

function QObject(name, data, webChannel)
{
    this.__id__ = name;
    webChannel.objects[name] = this;

    // List of callbacks that get invoked upon signal emission
    this.__objectSignals__ = {};

    // Cache of all properties, updated when a notify signal is emitted
    this.__propertyCache__ = {};

    var object = this;

    // ----------------------------------------------------------------------

    this.unwrapQObject = function(response)
    {
        for (const converter of webChannel.usedConverters) {
            var result = converter(response);
            if (result !== undefined)
                return result;
        }

        if (response instanceof Array) {
            // support list of objects
            return response.map(qobj => object.unwrapQObject(qobj))
        }
        if (!(response instanceof Object))
            return response;

        if (!response["__QObject*__"] || response.id === undefined) {
            var jObj = {};
            for (const propName of Object.keys(response)) {
                jObj[propName] = object.unwrapQObject(response[propName]);
            }
            return jObj;
        }

        var objectId = response.id;
        if (webChannel.objects[objectId])
            return webChannel.objects[objectId];

        if (!response.data) {
            console.error("Cannot unwrap unknown QObject " + objectId + " without data.");
            return;
        }

        var qObject = new QObject( objectId, response.data, webChannel );
        qObject.destroyed.connect(function() {
            if (webChannel.objects[objectId] === qObject) {
                delete webChannel.objects[objectId];
                // reset the now deleted QObject to an empty {} object
                // just assigning {} though would not have the desired effect, but the
                // below also ensures all external references will see the empty map
                // NOTE: this detour is necessary to workaround QTBUG-40021
                Object.keys(qObject).forEach(name => delete qObject[name]);
            }
        });
        // here we are already initialized, and thus must directly unwrap the properties
        qObject.unwrapProperties();
        return qObject;
    }

    this.unwrapProperties = function()
    {
        for (const propertyIdx of Object.keys(object.__propertyCache__)) {
            object.__propertyCache__[propertyIdx] = object.unwrapQObject(object.__propertyCache__[propertyIdx]);
        }
    }

    function addSignal(signalData, isPropertyNotifySignal)
    {
        var signalName = signalData[0];
        var signalIndex = signalData[1];
        object[signalName] = {
            connect: function(callback) {
                if (typeof(callback) !== "function") {
                    console.error("Bad callback given to connect to signal " + signalName);
                    return;
                }

                object.__objectSignals__[signalIndex] = object.__objectSignals__[signalIndex] || [];
                object.__objectSignals__[signalIndex].push(callback);

                // only required for "pure" signals, handled separately for properties in propertyUpdate
                if (isPropertyNotifySignal)
                    return;

                // also note that we always get notified about the destroyed signal
                if (signalName === "destroyed" || signalName === "destroyed()" || signalName === "destroyed(QObject*)")
                    return;

                // and otherwise we only need to be connected only once
                if (object.__objectSignals__[signalIndex].length == 1) {
                    webChannel.exec({
                        type: QWebChannelMessageTypes.connectToSignal,
                        object: object.__id__,
                        signal: signalIndex
                    });
                }
            },
            disconnect: function(callback) {
                if (typeof(callback) !== "function") {
                    console.error("Bad callback given to disconnect from signal " + signalName);
                    return;
                }
                // This makes a new list. This is important because it won't interfere with
                // signal processing if a disconnection happens while emittig a signal
                object.__objectSignals__[signalIndex] = (object.__objectSignals__[signalIndex] || []).filter(function(c) {
                  return c != callback;
                });
                if (!isPropertyNotifySignal && object.__objectSignals__[signalIndex].length === 0) {
                    // only required for "pure" signals, handled separately for properties in propertyUpdate
                    webChannel.exec({
                        type: QWebChannelMessageTypes.disconnectFromSignal,
                        object: object.__id__,
                        signal: signalIndex
                    });
                }
            }
        };
    }

    /**
     * Invokes all callbacks for the given signalname. Also works for property notify callbacks.
     */
    function invokeSignalCallbacks(signalName, signalArgs)
    {
        var connections = object.__objectSignals__[signalName];
        if (connections) {
            connections.forEach(function(callback) {
                callback.apply(callback, signalArgs);
            });
        }
    }

    this.propertyUpdate = function(signals, propertyMap)
    {
        // update property cache
        for (const propertyIndex of Object.keys(propertyMap)) {
            var propertyValue = propertyMap[propertyIndex];
            object.__propertyCache__[propertyIndex] = this.unwrapQObject(propertyValue);
        }

        for (const signalName of Object.keys(signals)) {
            // Invoke all callbacks, as signalEmitted() does not. This ensures the
            // property cache is updated before the callbacks are invoked.
            invokeSignalCallbacks(signalName, signals[signalName]);
        }
    }

    this.signalEmitted = function(signalName, signalArgs)
    {
        invokeSignalCallbacks(signalName, this.unwrapQObject(signalArgs));
    }

    function addMethod(methodData)
    {
        var methodName = methodData[0];
        var methodIdx = methodData[1];

        // Fully specified methods are invoked by id, others by name for host-side overload resolution
        var invokedMethod = methodName[methodName.length - 1] === ')' ? methodIdx : methodName

        object[methodName] = function() {
            var args = [];
            var callback;
            var errCallback;
            for (var i = 0; i < arguments.length; ++i) {
                var argument = arguments[i];
                if (typeof argument === "function")
                    callback = argument;
                else
                    args.push(argument);
            }

            var result;
            // during test, webChannel.exec synchronously calls the callback
            // therefore, the promise must be constucted before calling
            // webChannel.exec to ensure the callback is set up
            if (!callback && (typeof(Promise) === 'function')) {
              result = new Promise(function(resolve, reject) {
                callback = resolve;
                errCallback = reject;
              });
            }

            webChannel.exec({
                "type": QWebChannelMessageTypes.invokeMethod,
                "object": object.__id__,
                "method": invokedMethod,
                "args": args
            }, function(response) {
                if (response !== undefined) {
                    var result = object.unwrapQObject(response);
                    if (callback) {
                        (callback)(result);
                    }
                } else if (errCallback) {
                  (errCallback)();
                }
            });

            return result;
        };
    }

    function bindGetterSetter(propertyInfo)
    {
        var propertyIndex = propertyInfo[0];
        var propertyName = propertyInfo[1];
        var notifySignalData = propertyInfo[2];
        // initialize property cache with current value
        // NOTE: if this is an object, it is not directly unwrapped as it might
        // reference other QObject that we do not know yet
        object.__propertyCache__[propertyIndex] = propertyInfo[3];

        if (notifySignalData) {
            if (notifySignalData[0] === 1) {
                // signal name is optimized away, reconstruct the actual name
                notifySignalData[0] = propertyName + "Changed";
            }
            addSignal(notifySignalData, true);
        }

        Object.defineProperty(object, propertyName, {
            configurable: true,
            get: function () {
                var propertyValue = object.__propertyCache__[propertyIndex];
                if (propertyValue === undefined) {
                    // This shouldn't happen
                    console.warn("Undefined value in property cache for property \"" + propertyName + "\" in object " + object.__id__);
                }

                return propertyValue;
            },
            set: function(value) {
                if (value === undefined) {
                    console.warn("Property setter for " + propertyName + " called with undefined value!");
                    return;
                }
                object.__propertyCache__[propertyIndex] = value;
                var valueToSend = value;
                webChannel.exec({
                    "type": QWebChannelMessageTypes.setProperty,
                    "object": object.__id__,
                    "property": propertyIndex,
                    "value": valueToSend
                });
            }
        });

    }

    // ----------------------------------------------------------------------

    data.methods.forEach(addMethod);

    data.properties.forEach(bindGetterSetter);

    data.signals.forEach(function(signal) { addSignal(signal, false); });

    Object.assign(object, data.enums);
}

QObject.prototype.toJSON = function() {
    if (this.__id__ === undefined) return {};
    return {
        id: this.__id__,
        "__QObject*__": true
    };
};

//required for use with nodejs
if (typeof module === 'object') {
    module.exports = {
        QWebChannel: QWebChannel
    };
}