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extensions/chromium/telemetry.js

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+/*
+Copyright 2016 Mozilla Foundation
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+/* eslint strict: ["error", "function"] */
+
+(function () {
+  "use strict";
+  // This module sends the browser and extension version to a server, to
+  // determine whether it is safe to drop support for old Chrome versions in
+  // future extension updates.
+  //
+  // The source code for the server is available at:
+  // https://github.com/Rob--W/pdfjs-telemetry
+  var LOG_URL = "https://pdfjs.robwu.nl/logpdfjs";
+
+  // The minimum time to wait before sending a ping, so that we don't send too
+  // many requests even if the user restarts their browser very often.
+  // We want one ping a day, so a minimum delay of 12 hours should be OK.
+  var MINIMUM_TIME_BETWEEN_PING = 12 * 36e5;
+
+  if (chrome.extension.inIncognitoContext) {
+    // The extension uses incognito split mode, so there are two background
+    // pages. Only send telemetry when not in incognito mode.
+    return;
+  }
+
+  if (chrome.runtime.id !== "oemmndcbldboiebfnladdacbdfmadadm") {
+    // Only send telemetry for the official PDF.js extension.
+    console.warn("Disabled telemetry because this is not an official build.");
+    return;
+  }
+
+  // The localStorage API is unavailable in service workers. We store data in
+  // chrome.storage.local and use this "localStorage" object to enable
+  // synchronous access in the logic.
+  const localStorage = {
+    telemetryLastTime: 0,
+    telemetryDeduplicationId: "",
+    telemetryLastVersion: "",
+  };
+
+  chrome.alarms.onAlarm.addListener(alarm => {
+    if (alarm.name === "maybeSendPing") {
+      maybeSendPing();
+    }
+  });
+  chrome.storage.session.get({ didPingCheck: false }, async items => {
+    if (items?.didPingCheck) {
+      return;
+    }
+    maybeSendPing();
+    await chrome.alarms.clear("maybeSendPing");
+    await chrome.alarms.create("maybeSendPing", { periodInMinutes: 60 });
+    chrome.storage.session.set({ didPingCheck: true });
+  });
+
+  function updateLocalStorage(key, value) {
+    localStorage[key] = value;
+    // Note: We mirror the data in localStorage because the following is async.
+    chrome.storage.local.set({ [key]: value });
+  }
+
+  function maybeSendPing() {
+    getLoggingPref(function (didOptOut) {
+      if (didOptOut) {
+        // Respect the user's decision to not send statistics.
+        return;
+      }
+      if (!navigator.onLine) {
+        // No network available; Wait until the next scheduled ping opportunity.
+        // Even if onLine is true, the server may still be unreachable. But
+        // because it is impossible to tell whether a request failed due to the
+        // inability to connect, or a deliberate connection termination by the
+        // server, we don't validate the response and assume that the request
+        // succeeded. This ensures that the server cannot ask the client to
+        // send more pings.
+        return;
+      }
+      doSendPing();
+    });
+  }
+
+  function doSendPing() {
+    chrome.storage.local.get(localStorage, items => {
+      Object.assign(localStorage, items);
+
+      var lastTime = parseInt(localStorage.telemetryLastTime) || 0;
+      var wasUpdated = didUpdateSinceLastCheck();
+      if (!wasUpdated && Date.now() - lastTime < MINIMUM_TIME_BETWEEN_PING) {
+        return;
+      }
+      updateLocalStorage("telemetryLastTime", Date.now());
+
+      var deduplication_id = getDeduplicationId(wasUpdated);
+      var extension_version = chrome.runtime.getManifest().version;
+      fetch(LOG_URL, {
+        method: "POST",
+        headers: new Headers({
+          "Deduplication-Id": deduplication_id,
+          "Extension-Version": extension_version,
+        }),
+        // Set mode=cors so that the above custom headers are included in the
+        // request.
+        mode: "cors",
+        // Omits credentials such as cookies in the requests, which guarantees
+        // that the server cannot track the client via HTTP cookies.
+        credentials: "omit",
+        cache: "no-store",
+      });
+    });
+  }
+
+  /**
+   * Generate a 40-bit hexadecimal string (=10 letters, 1.1E12 possibilities).
+   * This is used by the server to discard duplicate entries of the same browser
+   * version when the log data is aggregated.
+   */
+  function getDeduplicationId(wasUpdated) {
+    var id = localStorage.telemetryDeduplicationId;
+    // The ID is only used to deduplicate reports for the same browser version,
+    // so it is OK to change the ID if the browser is updated. By changing the
+    // ID, the server cannot track users for a long period even if it wants to.
+    if (!id || !/^[0-9a-f]{10}$/.test(id) || wasUpdated) {
+      id = "";
+      var buf = new Uint8Array(5);
+      crypto.getRandomValues(buf);
+      for (const c of buf) {
+        id += (c >>> 4).toString(16) + (c & 0xf).toString(16);
+      }
+      updateLocalStorage("telemetryDeduplicationId", id);
+    }
+    return id;
+  }
+
+  /**
+   * Returns whether the browser has received a major update since the last call
+   * to this function.
+   */
+  function didUpdateSinceLastCheck() {
+    var chromeVersion = /Chrome\/(\d+)\./.exec(navigator.userAgent);
+    chromeVersion = chromeVersion && chromeVersion[1];
+    if (!chromeVersion || localStorage.telemetryLastVersion === chromeVersion) {
+      return false;
+    }
+    updateLocalStorage("telemetryLastVersion", chromeVersion);
+    return true;
+  }
+
+  /**
+   * Get the value of the telemetry preference. The callback is invoked with a
+   * boolean if a preference is found, and with the undefined value otherwise.
+   */
+  function getLoggingPref(callback) {
+    // Try to look up the preference in the storage, in the following order:
+    var areas = ["sync", "local", "managed"];
+
+    next();
+    function next(result) {
+      var storageAreaName = areas.shift();
+      if (typeof result === "boolean" || !storageAreaName) {
+        callback(result);
+        return;
+      }
+
+      if (!chrome.storage[storageAreaName]) {
+        next();
+        return;
+      }
+
+      chrome.storage[storageAreaName].get("disableTelemetry", function (items) {
+        next(items && items.disableTelemetry);
+      });
+    }
+  }
+})();