fix: 🐛 prenormalize findAll responses in application adapter

Ember Data fetch-manager will throw an error if an array resposne is an
empty object before it reaches the serializer.  Thus we need to
intercept the response in the adapter and "prenormalize" it to contain
an empty items array `{items: []}`.

addons/api/addon/adapters/application.js

@@ -6,6 +6,37 @@ import { dasherize } from '@ember/string';
 import { pluralize } from 'ember-inflector';
 import { isArray } from '@ember/array';
 
+/**
+ * Returns false if the payload is an empty object, true otherwise.
+ * Taken from Ember Data fetch-manager.
+ * @param {object} adapterPayload
+ * @return {boolean}
+ */
+function payloadIsNotBlank(adapterPayload) {
+  if (Array.isArray(adapterPayload)) {
+    return true;
+  } else {
+    return Object.keys(adapterPayload || {}).length !== 0;
+  }
+}
+
+/**
+ * If the resonse is not empty, returns the response.  Otherwise, returns
+ * a new payload containing an empty `items` array, as expected by
+ * the serializer.
+ *
+ * Normally this would be performed 100% inside the serializer.
+ * However, the fetch manager, which we cannot easily override, glues the
+ * adapter and serializers together.  Before it forwards a response from the
+ * adapter on to the serializer, it checks for an "empty" response.  If the
+ * response is empty, fetch manager throws and error and never forwards it on.
+ * @param {object} response
+ * @return {object}
+ */
+function prenormalizeArrayResponse(response) {
+  return payloadIsNotBlank(response) ? response : {items: []};
+}
+
 export default class ApplicationAdapter extends RESTAdapter {
   // =attributes
 
@@ -36,6 +67,26 @@ export default class ApplicationAdapter extends RESTAdapter {
     return dasherize(pluralize(type));
   }
 
+  /**
+   * Intercepts "empty" responses and adds an empty `items` array.
+   * @override
+   * @method findAll
+   * @return {Promise} promise
+   */
+  findAll() {
+    return super.findAll(...arguments).then(prenormalizeArrayResponse);
+  }
+
+  /**
+   * Intercepts "empty" responses and adds an empty `items` array.
+   * @override
+   * @method query
+   * @return {Promise} promise
+   */
+  query() {
+    return super.query(...arguments).then(prenormalizeArrayResponse);
+  }
+
   /**
    * Overrides default ajax method by rewritting PUT requests as PATCH.
    * PATCH is the request method used by our API for updates.

addons/api/package.json

@@ -35,6 +35,7 @@
     "ember-cli-dependency-checker": "^3.2.0",
     "ember-cli-eslint": "^5.1.0",
     "ember-cli-inject-live-reload": "^2.0.2",
+    "ember-cli-mirage": "^1.1.7",
     "ember-cli-sri": "^2.1.1",
     "ember-cli-template-lint": "^1.0.0-beta.3",
     "ember-cli-uglify": "^3.0.0",

addons/api/tests/dummy/mirage/config.js

@@ -0,0 +1,26 @@
+export default function() {
+
+  // These comments are here to help you get started. Feel free to delete them.
+
+  /*
+    Config (with defaults).
+
+    Note: these only affect routes defined *after* them!
+  */
+
+  // this.urlPrefix = '';    // make this `http://localhost:8080`, for example, if your API is on a different server
+  // this.namespace = '';    // make this `/api`, for example, if your API is namespaced
+  // this.timing = 400;      // delay for each request, automatically set to 0 during testing
+
+  /*
+    Shorthand cheatsheet:
+
+    this.get('/posts');
+    this.post('/posts');
+    this.get('/posts/:id');
+    this.put('/posts/:id'); // or this.patch
+    this.del('/posts/:id');
+
+    https://www.ember-cli-mirage.com/docs/route-handlers/shorthands
+  */
+}

addons/api/tests/dummy/mirage/scenarios/default.js

@@ -0,0 +1,9 @@
+export default function(/* server */) {
+
+  /*
+    Seed your development database using your factories.
+    This data will not be loaded in your tests.
+  */
+
+  // server.createList('post', 10);
+}

addons/api/tests/dummy/mirage/serializers/application.js

@@ -0,0 +1,4 @@
+import { JSONAPISerializer } from 'ember-cli-mirage';
+
+export default JSONAPISerializer.extend({
+});

addons/api/tests/unit/adapters/application-test.js

@@ -3,9 +3,12 @@ import { setupTest } from 'ember-qunit';
 import config from 'ember-get-config';
 import RESTAdapter from '@ember-data/adapter/rest';
 import { InvalidError } from '@ember-data/adapter/error';
+import setupMirage from 'ember-cli-mirage/test-support/setup-mirage';
+import { Response } from 'miragejs';
 
 module('Unit | Adapter | application', function (hooks) {
   setupTest(hooks);
+  setupMirage(hooks);
 
   test('its namespace is equal to the configured namespace', function (assert) {
     assert.expect(2);
@@ -24,12 +27,23 @@ module('Unit | Adapter | application', function (hooks) {
     assert.expect(1);
     const adapter = this.owner.lookup('adapter:application');
     // TODO this is icky, should be changed to a spy or stub
+    const originalAjax = RESTAdapter.prototype.ajax;
     RESTAdapter.prototype.ajax = (url, type) => {
       assert.equal(type, 'PATCH');
+      RESTAdapter.prototype.ajax = originalAjax;
     };
     adapter.ajax('/', 'PUT');
   });
 
+  test('it prenormalizes "empty" responses into a form that the fetch-manager will not reject', async function (assert) {
+    assert.expect(1);
+    const adapter = this.owner.lookup('adapter:project');
+    const store = this.owner.lookup('service:store');
+    this.server.get('/v1/projects', () => new Response({}));
+    const prenormalized = await adapter.findAll(store, {modelName: 'project'}, null, []);
+    assert.deepEqual(prenormalized, {items: []});
+  });
+
   test('it correctly identifies 400 responses as invalid', function (assert) {
     assert.expect(2);
     const adapter = this.owner.lookup('adapter:application');

yarn.lock

@@ -7330,6 +7330,21 @@ ember-cli-mirage@^1.1.6:
     lodash-es "^4.17.11"
     miragejs "^0.1.31"
 
+ember-cli-mirage@^1.1.7:
+  version "1.1.7"
+  resolved "https://registry.yarnpkg.com/ember-cli-mirage/-/ember-cli-mirage-1.1.7.tgz#846ec8e5199b15fa670da30dfa1708a8ee11e9dc"
+  integrity sha512-4kVLXXvgHYlv30ChM47U4xYnUtphIoEj+BQwXX0QT7pvD3KQxYnmfZSwlevSEVUy2UhbsBUPw6merENb+dIQ0A==
+  dependencies:
+    broccoli-file-creator "^2.1.1"
+    broccoli-funnel "^3.0.2"
+    broccoli-merge-trees "^4.2.0"
+    ember-auto-import "^1.2.19"
+    ember-cli-babel "^7.5.0"
+    ember-get-config "^0.2.2"
+    ember-inflector "^2.0.0 || ^3.0.0"
+    lodash-es "^4.17.11"
+    miragejs "^0.1.31"
+
 ember-cli-normalize-entity-name@^1.0.0:
   version "1.0.0"
   resolved "https://registry.yarnpkg.com/ember-cli-normalize-entity-name/-/ember-cli-normalize-entity-name-1.0.0.tgz#0b14f7bcbc599aa117b5fddc81e4fd03c4bad5b7"