Handle reporting by background script for thread safety

Reporting by content scripts can cause race conditions and
duplicate reports when multiple tabs are loaded concurrently.

Author: cburkert

app/scripts/background.js

@@ -1,3 +1,5 @@
+import { sendReport } from "./study.js";
+
 browser.storage.sync.get("ghrOn").then((res) => {
   if (typeof res.ghrOn == "undefined") {
     browser.storage.sync.set({
@@ -26,3 +28,25 @@ browser.runtime.onInstalled.addListener(async ({ reason, temporary }) => {
       break;
   }
 });
+
+
+// Synchronise reporting in background script to avoid
+// duplicate reporting by parallel active content scripts
+var reportRunning = false;
+function manageReporting(message, sender, respond) {
+  if (message.type != "sendReport") {
+    return; // message not for us
+  }
+  if (reportRunning) {
+    return; // already triggered by another sender
+  }
+  reportRunning = true;
+  sendReport()
+  .then(() => respond("done"))
+  .catch((err) => respond(err))
+  .finally(() => {
+    reportRunning = false;
+  });
+  return true; // make caller wait for async response
+}
+browser.runtime.onMessage.addListener(manageReporting);

app/scripts/redact.js

@@ -1,5 +1,5 @@
 import { DateTime } from "luxon";
-import { updateStudyData, sendReport, updateViewCount } from "./study.js";
+import { updateStudyData, updateViewCount } from "./study.js";
 import { toFuzzyDate } from "./fuzzydate.js";
 import { createPopper } from '@popperjs/core';
 
@@ -657,11 +657,15 @@ function calcDistanceToClosestSibling(el) {
     // - log view for study (if opted in)
     logViewLoad();
 
-    // - send study report if participanting and necessary
+    // - send study report if participating and necessary
+    // The actual sending is done by the background script to be
+    // thread-safe for parallel content script runs
     browser.storage.local.get("studyOptIn")
     .then((res) => {
       if (res.studyOptIn) {
-        return sendReport();
+        return browser.runtime.sendMessage(
+          { type: "sendReport" }
+        );
       }
     })
     .catch(error => console.error(error));