Fix #3265 - pbs cookie sync race condition (#3393)

* Fix #3265 - pbs cookie sync race condition

* add/update jsdoc comments

Author: jsnellbaker

modules/prebidServerBidAdapter/index.js

@@ -150,7 +150,7 @@ function queueSync(bidderCodes, gdprConsent) {
     (response) => {
       try {
         response = JSON.parse(response);
-        response.bidder_status.forEach(bidder => doBidderSync(bidder.usersync.type, bidder.usersync.url, bidder.bidder));
+        doAllSyncs(response.bidder_status);
       } catch (e) {
         utils.logError(e);
       }
@@ -162,24 +162,40 @@ function queueSync(bidderCodes, gdprConsent) {
     });
 }
 
+function doAllSyncs(bidders) {
+  if (bidders.length === 0) {
+    return;
+  }
+
+  const thisSync = bidders.pop();
+  if (thisSync.no_cookie) {
+    doBidderSync(thisSync.usersync.type, thisSync.usersync.url, thisSync.bidder, doAllSyncs.bind(null, bidders));
+  } else {
+    doAllSyncs(bidders);
+  }
+}
+
 /**
  * Run a cookie sync for the given type, url, and bidder
  *
  * @param {string} type the type of sync, "image", "redirect", "iframe"
  * @param {string} url the url to sync
  * @param {string} bidder name of bidder doing sync for
+ * @param {function} done an exit callback; to signify this pixel has either: finished rendering or something went wrong
  */
-function doBidderSync(type, url, bidder) {
+function doBidderSync(type, url, bidder, done) {
   if (!url) {
     utils.logError(`No sync url for bidder "${bidder}": ${url}`);
+    done();
   } else if (type === 'image' || type === 'redirect') {
     utils.logMessage(`Invoking image pixel user sync for bidder: "${bidder}"`);
-    utils.triggerPixel(url);
+    utils.triggerPixel(url, done);
   } else if (type == 'iframe') {
     utils.logMessage(`Invoking iframe user sync for bidder: "${bidder}"`);
-    utils.insertUserSyncIframe(url);
+    utils.insertUserSyncIframe(url, done);
   } else {
     utils.logError(`User sync type "${type}" not supported for bidder: "${bidder}"`);
+    done();
   }
 }
 

src/utils.js

@@ -568,8 +568,17 @@ exports.insertElement = function(elm, doc, target) {
   } catch (e) {}
 };
 
-exports.triggerPixel = function (url) {
+/**
+ * Inserts an image pixel with the specified `url` for cookie sync
+ * @param {string} url URL string of the image pixel to load
+ * @param  {function} [done] an optional exit callback, used when this usersync pixel is added during an async process
+ */
+exports.triggerPixel = function (url, done) {
   const img = new Image();
+  if (done && exports.isFn(done)) {
+    img.addEventListener('load', done);
+    img.addEventListener('error', done);
+  }
   img.src = url;
 };
 
@@ -615,12 +624,17 @@ exports.insertHtmlIntoIframe = function(htmlCode) {
  * Inserts empty iframe with the specified `url` for cookie sync
  * @param  {string} url URL to be requested
  * @param  {string} encodeUri boolean if URL should be encoded before inserted. Defaults to true
+ * @param  {function} [done] an optional exit callback, used when this usersync pixel is added during an async process
  */
-exports.insertUserSyncIframe = function(url) {
+exports.insertUserSyncIframe = function(url, done) {
   let iframeHtml = exports.createTrackPixelIframeHtml(url, false, 'allow-scripts allow-same-origin');
   let div = document.createElement('div');
   div.innerHTML = iframeHtml;
   let iframe = div.firstChild;
+  if (done && exports.isFn(done)) {
+    iframe.addEventListener('load', done);
+    iframe.addEventListener('error', done);
+  }
   exports.insertElement(iframe);
 };