Swapped image size "Map" cache for adapter cache

refs https://github.com/TryGhost/Toolbox/issues/364

- The "new Map()" cache was a "hidden cache" that did not follow any specific pattern. Following the cache adapter pattern here makes it possible swapping out the cache for alternative implementations - e.g. Redis storage

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

@@ -0,0 +1,7 @@
+const Memory = require('./Memory');
+
+class ImageSizesCacheSyncInMemory extends Memory {
+
+}
+
+module.exports = ImageSizesCacheSyncInMemory;

ghost/core/core/server/lib/image/image-utils.js

@@ -4,12 +4,12 @@ const Gravatar = require('./gravatar');
 const ImageSize = require('./image-size');
 
 class ImageUtils {
-    constructor({config, urlUtils, settingsCache, storageUtils, storage, validator, request}) {
+    constructor({config, urlUtils, settingsCache, storageUtils, storage, validator, request, cacheStore}) {
         this.blogIcon = new BlogIcon({config, urlUtils, settingsCache, storageUtils});
         this.imageSize = new ImageSize({config, storage, storageUtils, validator, urlUtils, request});
         this.cachedImageSizeFromUrl = new CachedImageSizeFromUrl({
             getImageSizeFromUrl: this.imageSize.getImageSizeFromUrl.bind(this.imageSize),
-            cache: new Map()
+            cache: cacheStore
         });
         this.gravatar = new Gravatar({config, request});
     }

ghost/core/core/server/lib/image/index.js

@@ -7,4 +7,17 @@ const config = require('../../../shared/config');
 const settingsCache = require('../../../shared/settings-cache');
 const ImageUtils = require('./image-utils');
 
-module.exports = new ImageUtils({config, urlUtils, settingsCache, storageUtils, storage, validator, request});
+const adapterManager = require('../../services/adapter-manager');
+
+const cacheStore = adapterManager.getAdapter('cache:imageSizes');
+
+module.exports = new ImageUtils({
+    config,
+    urlUtils,
+    settingsCache,
+    storageUtils,
+    storage,
+    validator,
+    request,
+    cacheStore
+});

ghost/core/core/shared/config/defaults.json

@@ -27,7 +27,9 @@
         "cache": {
             "active": "Memory",
             "settings": "SettingsCacheSyncInMemory",
-            "SettingsCacheSyncInMemory": {}
+            "SettingsCacheSyncInMemory": {},
+            "imageSizes": "ImageSizesCacheSyncInMemory",
+            "ImageSizesCacheSyncInMemory": {}
         }
     },
     "storage": {

ghost/core/test/unit/server/lib/image/cached-image-size-from-url.test.js

@@ -2,7 +2,7 @@ const errors = require('@tryghost/errors');
 const should = require('should');
 const sinon = require('sinon');
 const CachedImageSizeFromUrl = require('../../../../../core/server/lib/image/cached-image-size-from-url');
-const InMemoryCache = require('../../../../../core/server/adapters/cache/Memory');
+const InMemoryCache = require('../../../../../core/server/adapters/cache/ImageSizesCacheSyncInMemory');
 
 describe('lib/image: image size cache', function () {
     let sizeOfStub;
@@ -64,7 +64,7 @@ describe('lib/image: image size cache', function () {
 
         sizeOfStub.rejects('error');
 
-        const cacheStore = new InMemoryCache()
+        const cacheStore = new InMemoryCache();
         const cachedImageSizeFromUrl = new CachedImageSizeFromUrl({
             getImageSizeFromUrl: sizeOfStub,
             cache: cacheStore