qwebchannel.js Example File

  /****************************************************************************
  **
  ** Copyright (C) 2016 The Qt Company Ltd.
  ** Copyright (C) 2014 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Milian Wolff <milian.wolff@kdab.com>
  ** Contact: https://www.qt.io/licensing/
  **
  ** This file is part of the QtWebChannel module of the Qt Toolkit.
  **
  ** $QT_BEGIN_LICENSE:BSD$
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  "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)
  {
      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;

      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)
      {
          for (var i in message.data) {
              var data = message.data[i];
              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 (var objectName in data) {
              var object = new QObject(objectName, data[objectName], channel);
          }
          // now unwrap properties, which might reference other registered objects
          for (var objectName in 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)
      {
          if (response instanceof Array) {
              // support list of objects
              var ret = new Array(response.length);
              for (var i = 0; i < response.length; ++i) {
                  ret[i] = object.unwrapQObject(response[i]);
              }
              return ret;
          }
          if (!response
              || !response["__QObject*__"]
              || response.id === undefined) {
              return response;
          }

          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
                  var propertyNames = [];
                  for (var propertyName in qObject) {
                      propertyNames.push(propertyName);
                  }
                  for (var idx in propertyNames) {
                      delete qObject[propertyNames[idx]];
                  }
              }
          });
          // here we are already initialized, and thus must directly unwrap the properties
          qObject.unwrapProperties();
          return qObject;
      }

      this.unwrapProperties = function()
      {
          for (var propertyIdx in 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);

                  if (!isPropertyNotifySignal && signalName !== "destroyed") {
                      // only required for "pure" signals, handled separately for properties in propertyUpdate
                      // also note that we always get notified about the destroyed signal
                      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;
                  }
                  object.__objectSignals__[signalIndex] = object.__objectSignals__[signalIndex] || [];
                  var idx = object.__objectSignals__[signalIndex].indexOf(callback);
                  if (idx === -1) {
                      console.error("Cannot find connection of signal " + signalName + " to " + callback.name);
                      return;
                  }
                  object.__objectSignals__[signalIndex].splice(idx, 1);
                  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 (var propertyIndex in propertyMap) {
              var propertyValue = propertyMap[propertyIndex];
              object.__propertyCache__[propertyIndex] = propertyValue;
          }

          for (var signalName in 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, signalArgs);
      }

      function addMethod(methodData)
      {
          var methodName = methodData[0];
          var methodIdx = methodData[1];
          object[methodName] = function() {
              var args = [];
              var callback;
              for (var i = 0; i < arguments.length; ++i) {
                  if (typeof arguments[i] === "function")
                      callback = arguments[i];
                  else
                      args.push(arguments[i]);
              }

              webChannel.exec({
                  "type": QWebChannelMessageTypes.invokeMethod,
                  "object": object.__id__,
                  "method": methodIdx,
                  "args": args
              }, function(response) {
                  if (response !== undefined) {
                      var result = object.unwrapQObject(response);
                      if (callback) {
                          (callback)(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;
                  webChannel.exec({
                      "type": QWebChannelMessageTypes.setProperty,
                      "object": object.__id__,
                      "property": propertyIndex,
                      "value": value
                  });
              }
          });

      }

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

      data.methods.forEach(addMethod);

      data.properties.forEach(bindGetterSetter);

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

      for (var name in data.enums) {
          object[name] = data.enums[name];
      }
  }

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