Added optional in-memory TTL cache

refs https://github.com/TryGhost/Toolbox/issues/515

- We don't have a good way to test TTL caches without setting up Redis in the environment
- Adding in-memory cache adapter with TTL allows to run tests on CI without having to install Redis
- Also, TTL in memory cache can be a great substitution for Redis-based caches on instances that
have a lot of spare RAM and don't need to use Redis necessarily
- MemoryTTL cache accepts two parameters "TTL" and "max"
- TTL - is time in milliseconds to hold the value for in cache
- max - is the maximum amount of items to keep in the cache

- To use MemoryTTL cache specify following config in the cache section:
```
    "adapters": {
        "cache": {
            "imageSizes": {
                "adapter": "MemoryTTL",
                "ttl": 3600
            }
        }
    }
```
- Above config would apply MemoryTTL cache to imageSizes feature with TTL fo 3600 ms

ghost/adapter-cache-memory-ttl/.eslintrc.js

@@ -0,0 +1,6 @@
+module.exports = {
+    plugins: ['ghost'],
+    extends: [
+        'plugin:ghost/node'
+    ]
+};

ghost/adapter-cache-memory-ttl/README.md

@@ -0,0 +1,23 @@
+# Adapter Cache Memory Ttl
+
+Cache adapter with in-memory storage with TTL functionality
+
+
+## Usage
+
+
+## Develop
+
+This is a monorepo package.
+
+Follow the instructions for the top-level repo.
+1. `git clone` this repo & `cd` into it as usual
+2. Run `yarn` to install top-level dependencies.
+
+
+
+## Test
+
+- `yarn lint` run just eslint
+- `yarn test` run lint and tests
+

ghost/adapter-cache-memory-ttl/index.js

@@ -0,0 +1 @@
+module.exports = require('./lib/adapter-cache-memory-ttl');

ghost/adapter-cache-memory-ttl/lib/adapter-cache-memory-ttl.js

@@ -0,0 +1,54 @@
+const TTLCache = require('@isaacs/ttlcache');
+const Base = require('@tryghost/adapter-base-cache');
+
+/**
+ * Cache adapter compatible wrapper around TTLCache
+ * Distinct features of this cache adapter:
+ * - it is in-memory only
+ * - it supports time-to-live (TTL)
+ * - it supports a max number of items
+ */
+class MemoryTTL extends Base {
+    #cache;
+
+    /**
+     *
+     * @param {Object} [deps]
+     * @param {Number} [deps.max] - The max number of items to keep in the cache.
+     * @param {Number} [deps.ttl] - The max time in ms to store items
+     */
+    constructor({max = Infinity, ttl = Infinity} = {}) {
+        super();
+
+        this.#cache = new TTLCache({max, ttl});
+    }
+
+    get(key) {
+        return this.#cache.get(key);
+    }
+
+    /**
+     *
+     * @param {String} key
+     * @param {*} value
+     * @param {Object} [options]
+     * @param {Number} [options.ttl]
+    */
+    set(key, value, {ttl} = {}) {
+        this.#cache.set(key, value, {ttl});
+    }
+
+    reset() {
+        this.#cache.clear();
+    }
+
+    /**
+     * Helper method to assist "getAll" type of operations
+     * @returns {Array<String>} all keys present in the cache
+     */
+    keys() {
+        return [...this.#cache.keys()];
+    }
+}
+
+module.exports = MemoryTTL;

ghost/adapter-cache-memory-ttl/package.json

@@ -0,0 +1,28 @@
+{
+    "name": "@tryghost/adapter-cache-memory-ttl",
+    "version": "0.0.0",
+    "repository": "https://github.com/TryGhost/Ghost/tree/main/packages/adapter-cache-memory-ttl",
+    "author": "Ghost Foundation",
+    "private": true,
+    "main": "index.js",
+    "scripts": {
+        "dev": "echo \"Implement me!\"",
+        "test:unit": "NODE_ENV=testing c8 --all --check-coverage --reporter text --reporter cobertura mocha './test/**/*.test.js'",
+        "test": "yarn test:unit",
+        "lint:code": "eslint *.js lib/ --ext .js --cache",
+        "lint": "yarn lint:code && yarn lint:test",
+        "lint:test": "eslint -c test/.eslintrc.js test/ --ext .js --cache"
+    },
+    "files": [
+        "index.js",
+        "lib"
+    ],
+    "devDependencies": {
+        "c8": "7.13.0",
+        "mocha": "10.2.0",
+        "sinon": "15.0.1"
+    },
+    "dependencies": {
+        "@isaacs/ttlcache": "1.2.1"
+    }
+}

ghost/adapter-cache-memory-ttl/test/.eslintrc.js

@@ -0,0 +1,6 @@
+module.exports = {
+    plugins: ['ghost'],
+    extends: [
+        'plugin:ghost/test'
+    ]
+};

ghost/adapter-cache-memory-ttl/test/adapter-cache-memory-ttl.test.js

@@ -0,0 +1,100 @@
+const assert = require('assert');
+const MemoryTTLCache = require('../index');
+
+const sleep = ms => (
+    new Promise((resolve) => {
+        setTimeout(resolve, ms);
+    })
+);
+
+describe('Cache Adapter In Memory with Time To Live', function () {
+    it('Can initialize a cache instance', function () {
+        const cache = new MemoryTTLCache();
+        assert.ok(cache);
+    });
+
+    describe('get', function () {
+        it('Can get a value from the cache', async function () {
+            const cache = new MemoryTTLCache({});
+            cache.set('a', 'b');
+            assert.equal(cache.get('a'), 'b', 'should get the value from the cache');
+
+            await sleep(100);
+
+            assert.equal(cache.get('a'), 'b', 'should get the value from the cache after some time');
+        });
+
+        it('Can get a value from the cache before TTL kicks in', async function () {
+            const cache = new MemoryTTLCache({ttl: 150});
+            cache.set('a', 'b');
+            assert.equal(cache.get('a'), 'b', 'should get the value from the cache');
+
+            await sleep(100);
+
+            assert.equal(cache.get('a'), 'b', 'should get the value from the cache before TTL time');
+
+            // NOTE: 100 + 100 = 200, which is more than 150 TTL
+            await sleep(100);
+
+            assert.equal(cache.get('a'), undefined, 'should NOT get the value from the cache after TTL time');
+        });
+    });
+
+    describe('set', function () {
+        it('Can set a value in the cache', async function () {
+            const cache = new MemoryTTLCache({ttl: 150});
+
+            cache.set('a', 'b');
+
+            assert.equal(cache.get('a'), 'b', 'should get the value from the cache');
+
+            await sleep(100);
+
+            assert.equal(cache.get('a'), 'b', 'should get the value from the cache after time < TTL');
+
+            await sleep(100);
+
+            assert.equal(cache.get('a'), undefined, 'should NOT get the value from the cache after TTL time');
+        });
+
+        it('Can override TTL time', async function () {
+            const cache = new MemoryTTLCache({ttl: 150});
+
+            cache.set('a', 'b', {ttl: 99});
+
+            assert.equal(cache.get('a'), 'b', 'should get the value from the cache');
+
+            await sleep(100);
+
+            assert.equal(cache.get('a'), undefined, 'should NOT get the value from the cache after TTL time');
+        });
+    });
+
+    describe('reset', function () {
+        it('Can reset the cache', async function () {
+            const cache = new MemoryTTLCache({ttl: 150});
+
+            cache.set('a', 'b');
+            cache.set('c', 'd');
+
+            assert.equal(cache.get('a'), 'b', 'should get the value from the cache');
+            assert.equal(cache.get('c'), 'd', 'should get the value from the cache');
+
+            cache.reset();
+
+            assert.equal(cache.get('a'), undefined, 'should NOT get the value from the cache after reset');
+            assert.equal(cache.get('c'), undefined, 'should NOT get the value from the cache after reset');
+        });
+    });
+
+    describe('keys', function () {
+        it('Can get all keys from the cache', async function () {
+            const cache = new MemoryTTLCache({ttl: 200});
+
+            cache.set('a', 'b');
+            cache.set('c', 'd');
+
+            assert.deepEqual(cache.keys(), ['a', 'c'], 'should get all keys from the cache');
+        });
+    });
+});

ghost/core/core/server/adapters/cache/MemoryTTL.js

@@ -0,0 +1,3 @@
+const TTLMemoryCache = require('@tryghost/adapter-cache-memory-ttl');
+
+module.exports = TTLMemoryCache;

yarn.lock

@@ -2830,6 +2830,11 @@
   resolved "https://registry.yarnpkg.com/@humanwhocodes/object-schema/-/object-schema-1.2.1.tgz#b520529ec21d8e5945a1851dfd1c32e94e39ff45"
   integrity sha512-ZnQMnLV4e7hDlUvw8H+U8ASL02SS2Gn6+9Ac3wGGLIe7+je2AeAOxPY+izIPJDfFDb7eDjev0Us8MO1iFRN8hA==
 
+"@isaacs/ttlcache@1.2.1":
+  version "1.2.1"
+  resolved "https://registry.yarnpkg.com/@isaacs/ttlcache/-/ttlcache-1.2.1.tgz#07f54e31ee2dde9f0d2608fe3707f358596825e2"
+  integrity sha512-6hUKl0TcmeenJXitePBS/vPn1l/C8+sO4vvSmRh/hW4CeBm+QselPM6AyiM7WON6jApouCJGUfHYbaNObcMFrQ==
+
 "@istanbuljs/load-nyc-config@^1.0.0":
   version "1.1.0"
   resolved "https://registry.yarnpkg.com/@istanbuljs/load-nyc-config/-/load-nyc-config-1.1.0.tgz#fd3db1d59ecf7cf121e80650bb86712f9b55eced"