refs #6415 better workaround for possible empty visits

We will now always wait 800ms after a first tracking request was issued.
This should give enough time to create a visitor before any other request
is executed. Ideally we will resolve this issue on the server side as
this problem can occur using other SDKs as well and for some servers or
sometimes the 800ms might be not long enough.

1 files changed, 58 insertions, 29 deletions

diff --git a/js/piwik.js b/js/piwik.js
index ac49858073..47cea39920 100644
--- a/js/piwik.js
+++ b/js/piwik.js
@@ -2267,10 +2267,10 @@ if (typeof Piwik !== 'object') {
                 trackedContentImpressions = [],
                 isTrackOnlyVisibleContentEnabled = false,
 
-                // Guard to prevent empty visits see #6415. If there is a new visitor and there are 2 tracking requests
-                // at nearly same time (eg trackPageView and trackContentImpression) 2 visits will be created as both
-                // visitors are basically at the same time.
-                contentImpressionTrackingDelayInMs = 650,
+                // Guard to prevent empty visits see #6415. If there is a new visitor and the first 2 (or 3 or 4)
+                // tracking requests are at nearly same time (eg trackPageView and trackContentImpression) 2 or more
+                // visits will be created
+                timeNextTrackingRequestCanBeExecutedImmediately = false,
 
                 // Guard against installing the link tracker more than once per Tracker instance
                 linkTrackingInstalled = false,
@@ -2467,20 +2467,59 @@ if (typeof Piwik !== 'object') {
                 }
             }
 
+            function setExpireDateTime(delay) {
+
+                var now  = new Date();
+                var time = now.getTime() + delay;
+
+                if (!expireDateTime || time > expireDateTime) {
+                    expireDateTime = time;
+                }
+            }
+
+            function makeSureThereIsAGapAfterFirstTrackingRequestToPreventMultipleVisitorCreation(callback)
+            {
+                var now     = new Date();
+                var timeNow = now.getTime();
+
+                if (timeNextTrackingRequestCanBeExecutedImmediately && timeNow < timeNextTrackingRequestCanBeExecutedImmediately) {
+                    // we are in the time frame shortly after the first request. we have to delay this request a bit to make sure
+                    // a visitor has been created meanwhile.
+
+                    var timeToWait = timeNextTrackingRequestCanBeExecutedImmediately - timeNow;
+
+                    setTimeout(callback, timeToWait);
+                    setExpireDateTime(timeToWait + 50); // set timeout is not necessarily executed at timeToWait so delay a bit more
+                    timeNextTrackingRequestCanBeExecutedImmediately += 50; // delay next tracking request by further 50ms to next execute them at same time
+
+                    return;
+                }
+
+                if (timeNextTrackingRequestCanBeExecutedImmediately === false) {
+                    // it is the first request, we want to execute this one directly and delay all the next one(s) within a delay.
+                    // All requests after this delay can be executed as usual again
+                    var delayInMs = 800;
+                    timeNextTrackingRequestCanBeExecutedImmediately = timeNow + delayInMs;
+                }
+
+                callback();
+            }
+
             /*
              * Send request
              */
             function sendRequest(request, delay, callback) {
-                var now = new Date();
 
                 if (!configDoNotTrack && request) {
-                    if (configRequestMethod === 'POST') {
-                        sendXmlHttpRequest(request, callback);
-                    } else {
-                        getImage(request, callback);
-                    }
+                    makeSureThereIsAGapAfterFirstTrackingRequestToPreventMultipleVisitorCreation(function () {
+                        if (configRequestMethod === 'POST') {
+                            sendXmlHttpRequest(request, callback);
+                        } else {
+                            getImage(request, callback);
+                        }
 
-                    expireDateTime = now.getTime() + delay;
+                        setExpireDateTime(delay);
+                    });
                 }
             }
 
@@ -2502,12 +2541,12 @@ if (typeof Piwik !== 'object') {
                     return;
                 }
 
-                var now  = new Date();
                 var bulk = '{"requests":["?' + requests.join('","?') + '"]}';
 
-                sendXmlHttpRequest(bulk, null, false);
-
-                expireDateTime = now.getTime() + delay;
+                makeSureThereIsAGapAfterFirstTrackingRequestToPreventMultipleVisitorCreation(function () {
+                    sendXmlHttpRequest(bulk, null, false);
+                    setExpireDateTime(delay);
+                });
             }
 
             /*
@@ -3384,9 +3423,6 @@ if (typeof Piwik !== 'object') {
                         return;
                     }
 
-                    var now = new Date();
-                    expireDateTime = now.getTime() + configTrackerPause;
-
                     var contentBlock = content.findParentContentNode(targetNode);
 
                     var interactedElement;
@@ -3398,10 +3434,11 @@ if (typeof Piwik !== 'object') {
                     }
 
                     if (!isNodeAuthorizedToTriggerInteraction(contentBlock, interactedElement)) {
-                        expireDateTime = now.getTime();
                         return;
                     }
 
+                    setExpireDateTime(configTrackerPause);
+
                     if (query.isLinkElement(targetNode) &&
                         query.hasNodeAttributeWithValue(targetNode, 'href') &&
                         query.hasNodeAttributeWithValue(targetNode, content.CONTENT_TARGET_ATTR)) {
@@ -3427,7 +3464,6 @@ if (typeof Piwik !== 'object') {
                     var block = content.buildContentBlock(contentBlock);
 
                     if (!block) {
-                        expireDateTime = now.getTime();
                         return;
                     }
 
@@ -4769,11 +4805,7 @@ if (typeof Piwik !== 'object') {
                             var contentNodes = content.findContentNodes();
                             var requests     = getContentImpressionsRequestsFromNodes(contentNodes);
 
-                            setTimeout(function () {
-                                sendBulkRequest(requests, configTrackerPause);
-                            }, contentImpressionTrackingDelayInMs);
-
-                            contentImpressionTrackingDelayInMs = 0;
+                            sendBulkRequest(requests, configTrackerPause);
                         });
                     });
                 },
@@ -4833,10 +4865,7 @@ if (typeof Piwik !== 'object') {
                             var contentNodes = content.findContentNodes();
                             var requests     = getCurrentlyVisibleContentImpressionsRequestsIfNotTrackedYet(contentNodes);
 
-                            setTimeout(function () {
-                                sendBulkRequest(requests, configTrackerPause);
-                            }, contentImpressionTrackingDelayInMs);
-                            contentImpressionTrackingDelayInMs = 0;
+                            sendBulkRequest(requests, configTrackerPause);
                         });
                     });
                 },