PubSubManager

This object allows to take advantage of the pattern "publish/subscribe" applied to the discovery of nodes with the DAB. Note: the underlying technology requires a supported browser; please see HTML 5 Server-Sent Events for an updated list.

A subscription can be made with the same set of constraints of a DAB discover. Basing on the "publish/subscribe" pattern, once a subscription is subscribed to the PubSubManager, the DAB ("publisher") performs cyclically a discover with the specified constraints and options and the API client ("subscriber") is updated when there are some changes on the result set. The updates are sent until the subscription expires or it is canceled.

 // this function is called when there are some changes
                         var onUpdates = function(resultSet, timeRange){

                            // retrieves the paginator
                            var resultSet = resultSet.paginator;

                            // prints the result set
                            document.writeln("- Result set -"); 
                            document.writeln("start:"+resultSet.start+"<br>");
                            // ... other prints  
                            document.writeln('<br><br>');

                            // the current paginator page (the first of the result set)    
                            var page = paginator.page();
    
                            // prints page nodes
                            while(page.hasNext()){
  
                                // retrieves the next page node
                                var node = page.next();
 
                                // retrieves the node report
                                var report = node.report();
      
                                // document.writeln(JSON.stringify(report,null,4));
                                document.writeln(report.title+'<br>');
                            }

                            document.writeln('<br>');
                        };

                        // this function is called when the subscription expires
                        // here the subscription is renewed and submitted again
                        var onExpiration = function(event){
         
                            subscription = subscription.renew();
    
                            pubSub.subscribe(subscription, onUpdates, onExpiration, onConnectionError, false);
                        };

                        // this function is called in case of connection errors
                        var onConnectionError = function(error){

                            var msg = '';
                            switch(error){
                            case 'TOO_MANY_CONNECTIONS':
                                msg = 'There too many subscriptions at the moment, please wait a while for a free slot...';
                                break;
                            case 'CONNECTION_LOST':
                                msg = 'The connection with the server is lost, please try again later'; 
                                break;
                            case 'SUBSCRIPTION_REJECTED':
                                msg = 'A subscription with the specified label and client identifier already exists';
                                break;       
                            }

                            document.writeln('<b>---</b>');
                            document.writeln('<b>'+msg+'</b>');
                            document.writeln('<b>---</b>');
                        };

                        // creates the DAB object
                        var dab = GIAPI.DAB(GIAPI.demo.api);
          
                        // get the PubSubManager from the DAB
                        var pubSub = dab.pubSubManager();

                        // creates some constraints
                        var constraints = {         
                            "where": {
                                "south": -10,
                                "west": -20,
                                "north": 10,
                                "east": 20
                            },
      
                            "when": {
                                "from" : "2000-01-01",
                                "to": "2013-01-01"
                            },

                            "what": ["water"]   
                        };

                        // creates an ID which identifies this API client
                        var clientID = 'example-client-ID';

                        // creates a random label
                        var subscriptionLabel = 'label-'+GIAPI.random();

                        // creates a subscription with the above constraints and client id
                        var subscription = GIAPI.Subscription(subscriptionLabel, constraints, clientID);

                        // subscribes the subscription to the PubSubManager
                        pubSub.subscribe(subscription, onUpdates, onExpiration, onConnectionError);