Refactor to guard

package.json

@@ -208,6 +208,7 @@
     "react-waypoint": "^10.3.0",
     "react-window": "^1.8.10",
     "reakit": "^1.3.11",
+    "redlock": "^5.0.0-beta.2",
     "reflect-metadata": "^0.2.2",
     "refractor": "^3.6.0",
     "request-filtering-agent": "^1.1.2",

server/emails/templates/DocumentPublishedOrUpdatedEmail.tsx

@@ -7,6 +7,7 @@ import HTMLHelper from "@server/models/helpers/HTMLHelper";
 import NotificationSettingsHelper from "@server/models/helpers/NotificationSettingsHelper";
 import SubscriptionHelper from "@server/models/helpers/SubscriptionHelper";
 import { can } from "@server/policies";
+import { CacheHelper } from "@server/utils/CacheHelper";
 import BaseEmail, { EmailMessageCategory, EmailProps } from "./BaseEmail";
 import Body from "./components/Body";
 import Button from "./components/Button";
@@ -68,21 +69,28 @@ export default class DocumentPublishedOrUpdatedEmail extends BaseEmail<
 
     let body;
     if (revisionId && team?.getPreference(TeamPreference.PreviewsInEmails)) {
-      // generate the diff html for the email
-      const revision = await Revision.findByPk(revisionId);
+      body = await CacheHelper.getDataOrSet<string>(
+        `diff:${revisionId}`,
+        async () => {
+          // generate the diff html for the email
+          const revision = await Revision.findByPk(revisionId);
 
-      if (revision) {
-        const before = await revision.before();
-        const content = await DocumentHelper.toEmailDiff(before, revision, {
-          includeTitle: false,
-          centered: false,
-          signedUrls: 4 * Day.seconds,
-          baseUrl: props.teamUrl,
-        });
+          if (revision) {
+            const before = await revision.before();
+            const content = await DocumentHelper.toEmailDiff(before, revision, {
+              includeTitle: false,
+              centered: false,
+              signedUrls: 4 * Day.seconds,
+              baseUrl: props.teamUrl,
+            });
 
-        // inline all css so that it works in as many email providers as possible.
-        body = content ? await HTMLHelper.inlineCSS(content) : undefined;
-      }
+            // inline all css so that it works in as many email providers as possible.
+            return content ? await HTMLHelper.inlineCSS(content) : undefined;
+          }
+          return;
+        },
+        30
+      );
     }
 
     return {

server/utils/CacheHelper.ts

@@ -1,6 +1,7 @@
 import { Day } from "@shared/utils/time";
 import Logger from "@server/logging/Logger";
 import Redis from "@server/storage/redis";
+import { MutexLock } from "./MutexLock";
 
 /**
  * A Helper class for server-side cache management
@@ -9,6 +10,54 @@ export class CacheHelper {
   // Default expiry time for cache data in seconds
   private static defaultDataExpiry = Day.seconds;
 
+  /**
+   * Given a key this method will attempt to get the data from cache store first
+   * If data is not found, it will call the callback to get the data and save it in cache
+   * using a distributed lock to prevent multiple writes.
+   *
+   * @param key Cache key
+   * @param callback Callback to get the data if not found in cache
+   * @param expiry Cache data expiry in seconds
+   */
+  public static async getDataOrSet<T>(
+    key: string,
+    callback: () => Promise<T | undefined>,
+    expiry?: number
+  ): Promise<T | undefined> {
+    let cache = await this.getData<T>(key);
+
+    if (cache) {
+      return cache;
+    }
+
+    // Nothing in the cache, acquire a lock to prevent multiple writes
+    let lock;
+    const lockKey = `lock:${key}`;
+    try {
+      try {
+        lock = await MutexLock.lock.acquire(
+          [lockKey],
+          MutexLock.defaultLockTimeout
+        );
+      } catch (err) {
+        Logger.error(`Could not acquire lock for ${key}`, err);
+      }
+      cache = await this.getData<T>(key);
+      if (cache) {
+        return cache;
+      }
+
+      // Get the data from the callback and save it in cache
+      const value = await callback();
+      if (value) {
+        await this.setData<T>(key, value, expiry);
+      }
+      return value;
+    } finally {
+      await lock?.release();
+    }
+  }
+
   /**
    * Given a key, gets the data from cache store
    *

server/utils/MutexLock.ts

@@ -0,0 +1,20 @@
+import Redlock from "redlock";
+import Redis from "@server/storage/redis";
+
+export class MutexLock {
+  // Default expiry time for qcuiring lock in milliseconds
+  public static defaultLockTimeout = 5000;
+
+  /**
+   * Returns the redlock instance
+   */
+  public static get lock(): Redlock {
+    this.redlock ??= new Redlock([Redis.defaultClient], {
+      retryJitter: 10,
+    });
+
+    return this.redlock;
+  }
+
+  private static redlock: Redlock;
+}

yarn.lock

@@ -4075,7 +4075,7 @@
     "@smithy/util-stream" "^3.3.1"
     tslib "^2.6.2"
 
-"@smithy/types@^3.3.0", "@smithy/types@^3.7.0", "@smithy/types@^3.7.1":
+"@smithy/types@^3.7.0", "@smithy/types@^3.7.1":
   version "3.7.1"
   resolved "https://registry.yarnpkg.com/@smithy/types/-/types-3.7.1.tgz#4af54c4e28351e9101996785a33f2fdbf93debe7"
   integrity sha512-XKLcLXZY7sUQgvvWyeaL/qwNPp6V3dWcUjqrQKjSb+tzYiCy340R/c64LV5j+Tnb2GhmunEX0eou+L+m2hJNYA==
@@ -11906,7 +11906,7 @@ node-abort-controller@^1.1.0:
   resolved "https://registry.yarnpkg.com/node-abort-controller/-/node-abort-controller-1.2.1.tgz#1eddb57eb8fea734198b11b28857596dc6165708"
   integrity "sha1-Ht21frj+pzQZixGyiFdZbcYWVwg= sha512-79PYeJuj6S9+yOHirR0JBLFOgjB6sQCir10uN6xRx25iD+ZD4ULqgRn3MwWBRaQGB0vEgReJzWwJo42T1R6YbQ=="
 
-node-abort-controller@^3.1.1:
+node-abort-controller@^3.0.1, node-abort-controller@^3.1.1:
   version "3.1.1"
   resolved "https://registry.yarnpkg.com/node-abort-controller/-/node-abort-controller-3.1.1.tgz#a94377e964a9a37ac3976d848cb5c765833b8548"
   integrity "sha1-qUN36WSpo3rDl22EjLXHZYM7hUg= sha512-AGK2yQKIjRuqnc6VkX2Xj5d+QW8xZ87pa1UK6yA6ouUyuxfHuMP6umE5QK7UmTeOAymo+Zx1Fxiuw9rVx8taHQ=="
@@ -13479,6 +13479,13 @@ redis@^3.0.0:
     redis-errors "^1.2.0"
     redis-parser "^3.0.0"
 
+redlock@^5.0.0-beta.2:
+  version "5.0.0-beta.2"
+  resolved "https://registry.yarnpkg.com/redlock/-/redlock-5.0.0-beta.2.tgz#a629c07e07d001c0fdd9f2efa614144c4416fe44"
+  integrity sha512-2RDWXg5jgRptDrB1w9O/JgSZC0j7y4SlaXnor93H/UJm/QyDiFgBKNtrh0TI6oCXqYSaSoXxFh6Sd3VtYfhRXw==
+  dependencies:
+    node-abort-controller "^3.0.1"
+
 redux@^4.2.0:
   version "4.2.0"
   resolved "https://registry.yarnpkg.com/redux/-/redux-4.2.0.tgz#46f10d6e29b6666df758780437651eeb2b969f13"