Retry requests to /api endpoint

Handle requests to the /api endpoint that fail with network errors in
the same way as failed requests to the /app endpoint by retrying the
request with exponential backoff until it succeeds.

Otherwise, if the request fails then `store.(Annotation|Search)Resource`
are not populated and code that tries to make API requests fails.

h/static/scripts/store.js

@@ -2,6 +2,8 @@
 
 var angular = require('angular');
 
+var retryUtil = require('./retry-util');
+
 function prependTransform(defaults, transform) {
   // We can't guarantee that the default transformation is an array
   var result = angular.isArray(defaults) ? defaults.slice(0) : [defaults];
@@ -57,10 +59,14 @@ function encodeUriQuery(val) {
 // then proceed to parse as a delimiter in the query string. To avoid this
 // problem we use a very conservative encoder, found above.
 function serializeParams(params) {
-  if (!params) return '';
+  if (!params) {
+    return '';
+  }
   var parts = [];
   forEachSorted(params, function(value, key) {
-    if (value === null || typeof value === 'undefined') return;
+    if (value === null || typeof value === 'undefined') {
+      return;
+    }
     if (angular.isArray(value)) {
       angular.forEach(value, function(v, k) {
         parts.push(encodeUriQuery(key)  + '=' + encodeUriQuery(serializeValue(v)));
@@ -99,10 +105,9 @@ function store($http, $resource, settings) {
   };
 
   // We call the API root and it gives back the actions it provides.
-  instance.$resolved = false;
-  instance.$promise = $http.get(settings.apiUrl)
-    .finally(function () { instance.$resolved = true; })
-    .then(function (response) {
+  instance.$promise = retryUtil.retryPromiseOperation(function () {
+    return $http.get(settings.apiUrl);
+  }).then(function (response) {
     var links = response.data.links;
 
     // N.B. in both cases below we explicitly override the default `get`

h/static/scripts/test/store-test.js

 'use strict';
 
-var inject = angular.mock.inject;
-var module = angular.mock.module;
+var angular = require('angular');
+var proxyquire = require('proxyquire');
+
+var util = require('./util');
 
 describe('store', function () {
   var $httpBackend = null;
@@ -10,12 +12,19 @@ describe('store', function () {
 
   before(function () {
     angular.module('h', ['ngResource'])
-    .service('store', require('../store'));
+    .service('store', proxyquire('../store', util.noCallThru({
+      angular: angular,
+      './retry-util': {
+        retryPromiseOperation: function (fn) {
+          return fn();
+        },
+      },
+    })));
   });
 
-  beforeEach(module('h'));
+  beforeEach(angular.mock.module('h'));
 
-  beforeEach(module(function ($provide) {
+  beforeEach(angular.mock.module(function ($provide) {
     sandbox = sinon.sandbox.create();
     $provide.value('settings', {apiUrl: 'http://example.com/api'});
   }));
@@ -26,7 +35,7 @@ describe('store', function () {
     sandbox.restore();
   });
 
-  beforeEach(inject(function ($q, _$httpBackend_, _store_) {
+  beforeEach(angular.mock.inject(function ($q, _$httpBackend_, _store_) {
     $httpBackend = _$httpBackend_;
     store = _store_;
 
@@ -50,8 +59,8 @@ describe('store', function () {
   }));
 
   it('reads the operations from the backend', function () {
-    assert.isFunction(store.AnnotationResource, 'expected store.AnnotationResource to be a function')
-    assert.isFunction(store.SearchResource, 'expected store.SearchResource to be a function')
+    assert.isFunction(store.AnnotationResource);
+    assert.isFunction(store.SearchResource);
   });
 
   it('saves a new annotation', function () {