# Pub Sub System - Publish and Subscribe System The Pub-Sub-System is a basic Publish and Subscribe System. A Pub-Sub System consists of 3 Main Elements: * Publishers * Subscribers * Broker Whereas Publishers publishes data on a given Topic, Subscribers receives updates of the data of a subscribed Topic. Topics are used as a Base to share data. For instance, if a Sensor publishes its value on the Topic `Room1.Temperature` every subscribtion which subscribes to `Room1` or `Room1.Temperature` will receive the updated Value. By unsubscribing, a Subscriber doesn't receive Updates anymore. Thereby, the Publish-and-Subscribe mechanism ensure, a loose coupleing between the Elements and scalability. Summarized Attributes of a Pub-Sub-System * A Publisher doesn't know its subscribers * A Subscriber doesn't kown the Publisher(s) * Different Publishers are able to Publish data on the same Topic * Broker are responsible for sharing data and subscriptions etc. --- ## Description of the Implementation The Basic Pub-Sub-System which is based on a Binary Tree-Model. For Instance, there are Publishers for the following Topics: * `Root.Topic1` * `Root.Topic2` * `Root.Topic2.Part1` * `Root.Topic2.Part2` * `Root.Topic2.Part3` Thereby the **Tree** is build up like that. ``` (Root) / \ / \ (Topic1) (Topic2) / | \ / | \ (Part1) | (Part2) | (Part3) ``` Data of Topics are shared only to its '*Super-Topics*' and '*Child-Topics*' (see the Examples) ### Example 1 - Publishing data on `Root/Topic2` If a Publisher of the Topic `Root.Topic2` publishes an update, the Subscribe of the following Topics receives an update. * `Root` * `Root.Topic2` * `Root.Topic2.Part1` * `Root.Topic2.Part2` * `Root.Topic2.Part3` Thereby each element gets the new Data in the following format: > **Example-Data:** `{ Part1 : 1, Part2 : 'test', Part3 : 1.337 }` is published on the Topic `Root/Topic2` | Topic | Received Data of the Subscription in ***JSON-Notation***| | ---- | ---- | | `Root` | `{ Topic1: 'someData', Topic2 : { Part1 : 1, Part2 : 'test', Part3 : [1.337, 1.338] } }` | | `Root.Topic2` | `{ Part1 : 1, Part2 : 'test', Part3 : 1.337 }` | | `Root.Topic2.Part1` | `1` | | `Root.Topic2.Part2` | `'test'` | | `Root.Topic2.Part3` | `[1.337, 1.338]` | | `Root.Topic2.Part3.0` | `1.337` | | `Root.Topic2.Part3.1` | `1.338` | > Subscriber of the Topic `Root.Topic1` doesn't receive Updates. ### Example 2 - Publishing data on `Root.Topic2.Part3` If a Publisher of the Topic `Root.Topic2.Part3` publishes an update, the Subscribe of the following Topics receives an update. * `Root` * `Root.Topic2` * `Root.Topic2.Part3` Thereby each element gets the new Data in the following format: > **Example-Data:** `[1234, 1.338]` is published on the Topic `Root.Topic2.Part3` | Topic | Received Data of the Subscription in ***JSON-Notation***| | ---- | ---- | | `Root` | `{ Topic1: 'someData', Topic2 : { Part1 : 1, Part2 : 'test', Part3 : [1234, 1.338] } }` | | `Root.Topic2` | `{ Part1 : 1, Part2 : 'test', Part3 : [1234, 1.338] }` | | `Root.Topic2.Part3` | `[1234, 1.338]` | | `Root.Topic2.Part3.0` | `1234` | | `Root.Topic2.Part3.1` | `1.338` No Update will be Pusblished, cause the value didn't change | > Subscriber of the Topic `Root.Topic1`, `Root.Topic2.Part1`, `Root.Topic2.Part3.1` and `Root.Topic2.Part2` doesn't receive Updates, cause their values didn't change. --- ## Technical Implementation The Pub-Sub-System is build up with a Base-Node-Container. This Container is responsible to create (if necessary) new Topics on which a Subscription could be subscribe or data could be published. Based on all available Subscriptions published Data send to the corresponding Subscriptions. * No multiple Pub-Sub-Systems at a Time, otherwise an exception is thrown. * **Subscribers must unsubscribe** if the should not listening any more. For Instance pause/deactivate or dispose an specific Object. (use the `unregister` function of a Subscribtion) * Subscriptions could be activated again by calling `register` * Subscriptions are automatically active. --- ## Observables Observables allow a simple integration of attributes of an object. Therefore the `IObserveable` interface is used. ### Example - Integrate an Observable To use an Observable the following code must be used, where as `TYPE` describes the data type like `number`, `string`, etc. ```typescript @inject(PUBSUB.TYPES.Observable) public attributeName: PUBSUB.Observable; ``` Furthermore the Class containing the observable attribute **must** implement the **`IContainsObservables`-Interface**, as presented in the example below: ```typescript /** Import the Pub-Sub-System (Path must be adapted) */ import * as PUBSUB from 'Pub-Sub-System/assembly/manual-assembly'; /** Define a Class containing an observable @see attribute_01 */ @injectable() class TestClass implements IContainsObservables { /** Values of the IOnlineValues - Interface */ path: string = ''; offeredTopics: Map> ; /** * Defining the Attribute which should be integrated into the Publish * and Subscribe System. The value should be a 'number' * * @type {PUBSUB.Observer} * @memberof TestClass */ @inject(PUBSUB.TYPES.Observable) public attribute_01: PUBSUB.Observable; /** * Creates an instance of TestClass. * @memberof TestClass */ constructor() { /** Set a Values - That must be done during the construction */ this.path = ''; this.offeredTopics = new Map>(); } } ``` ### Working with Observables By default oberserables publish their content on an automatically generated Topic. This topic could be adapted and read with the `path` - attibute of an Observable. ```typescript ``` #### Subscribing to Changes To subscribe to changes of an obserable simply use the metho `subscribe`. You can determine whether the subscription should receive the information `async` (Putting task on the next Tick of the Nodejs / JavaScript Eventloop) or `sync` (immediately). The Following Parameters are used: | Param | Type | Default | Description | | --- | --- | --- | --- | | func | [subscriptionCallback](#subscriptionCallback) | | Function which is called when new Datas are pushed | | [mode] | `'sync'` \ `'immediate'` | `'sync'`| Mode of the Subscription | **Returns**: ISubscription - The corresponding Subscription whereas the subscriptionCallback is defined as: | Param | Type | Description | | --- | --- | --- | | content | any | The new Data | | [topic] | string | The Topic on which the Data where from | | [timeStamp] | number | The timeStamp on which the data where changed | **Returns** - void ##### Example ```typescript /** Simplified Construction of the Object */ const _test = new TestClass(); /** Subscribe to changes of the attribute */ _test.attribute_01.subscribe((_num, _topic) => { console.log('subscription on', _topic, '. Value changed to:', _num); }, 'sync'); /** Change the Value of the observable => Subscription will be triggered */ _test.attribute_01.value = 1337; ``` #### Changing Values and reading values The value of an observable could be changed with the `value` attribute of an observable ```typescript /** Simplified Construction of the Object */ const _test = new TestClass(); /** Change the Value of the observable => Subscription will be triggered */ _test.attribute_01.value = 1337; /** Reading a Value */ const _aVar = _test.attribute_01.value; ``` ### Sample Application ```typescript import { Builder } from '../../mod-Assembly-Builder/src/Container-Builder.FileLoader'; import { DESCRIPTION, PubSubSystem } from '../assembly/manual-assembly'; Builder.instance.addElements(DESCRIPTION.PROVIDED_CLASSES) Builder.instance.addActivationHandler(DESCRIPTION.ACTIVATIONHANDLERS); Builder.load(); Builder.on('loaded', () => { // Create a Publish and Subscribe System const _pubSub = Builder.instance.container.get(DESCRIPTION.TYPES.PubSubSystem); // Create a Subscription on the topic: "test.topic" const _sub = _pubSub.createSubscription('test.topic', (_data, _topic, _timestamp) => { console.log('received with inform', _data); }); // Create a Publisher and Publish "1" on a Subtopic _pubSub.createPublisher('test.topic.child').publishData(1); _pubSub.createPublisher('test.topic').publishData(2); // Change the Subscription Mode. _sub.options.mode = ['direct']; // The following Subscription will be now ignored _pubSub.createPublisher('test.topic.child').publishData(3); _pubSub.createPublisher('test.topic').publishData(4); }); ``` Results in the Output ``` Changing Value to 1337 Calling Subscription of root._id8ebg4qDkQjjx the 0'th time. Value changed to: 1337 Adding Setter Changing Value to 133123 In Setter of the attribute_01 Calling Subscription of root._id8ebg4qDkQjjx the 1'th time. Value changed to: 100 Reading after setter 100 Changing Path Changing Value to 1337 In Setter of the attribute_01 In Setter of the attribute_01 Calling Subscription of root._test.attribute_01 the 2'th time. Value changed to: 100 create Link with Pub-Sub-System plublish 1336 on _test.attribute_01 In Setter of the attribute_01 Calling Subscription of root._test.attribute_01 the 3'th time. Value changed to: 1336 plublish 1336 on _test.attribute_01 Calling Subscription of root._test.attribute_01 the 4'th time. Value changed to: 1336 ```