feat: Add error handling for inMemoryCache

api-server/server/models/donation.js

@@ -1,6 +1,7 @@
 import { Observable } from 'rx';
 import debug from 'debug';
 
+import { reportError } from '../middlewares/error-reporter';
 import InMemoryCache from '../utils/in-memory-cache';
 
 const log = debug('fcc:boot:donate');
@@ -9,7 +10,7 @@ const fiveMinutes = 1000 * 60 * 5;
 export default function(Donation) {
   let activeDonationUpdateInterval = null;
   const activeDonationCountCacheTTL = fiveMinutes;
-  const activeDonationCountCache = InMemoryCache(0);
+  const activeDonationCountCache = InMemoryCache(0, reportError);
   const activeDonationsQuery$ = () =>
     Donation.find$({
       // eslint-disable-next-line no-undefined
@@ -23,25 +24,50 @@ export default function(Donation) {
   }
 
   process.on('exit', cleanUp);
+
   Donation.on('dataSourceAttached', () => {
     Donation.find$ = Observable.fromNodeCallback(Donation.find.bind(Donation));
     Donation.findOne$ = Observable.fromNodeCallback(
       Donation.findOne.bind(Donation)
     );
-    activeDonationsQuery$().subscribe(count => {
-      log('activeDonator count: %d', count);
-      return activeDonationCountCache.update(() => count);
-    });
 
+    seedTheCache()
+      .then(setupCacheUpdateInterval)
+      .catch(err => {
+        const errMsg = `Error caught seeding the cache: ${err.message}`;
+        err.message = errMsg;
+        reportError(err);
+      });
+  });
+
+  function seedTheCache() {
+    return new Promise((resolve, reject) =>
+      Observable.defer(activeDonationsQuery$).subscribe(count => {
+        log('activeDonator count: %d', count);
+        activeDonationCountCache.update(() => count);
+        return resolve();
+      }, reject)
+    );
+  }
+
+  function setupCacheUpdateInterval() {
     activeDonationUpdateInterval = setInterval(
       () =>
-        activeDonationsQuery$().subscribe(count => {
-          log('activeDonator count: %d', count);
-          return activeDonationCountCache.update(() => count);
-        }),
+        Observable.defer(activeDonationsQuery$).subscribe(
+          count => {
+            log('activeDonator count: %d', count);
+            return activeDonationCountCache.update(() => count);
+          },
+          err => {
+            const errMsg = `Error caught updating the cache: ${err.message}`;
+            err.message = errMsg;
+            reportError(err);
+          }
+        ),
       activeDonationCountCacheTTL
     );
-  });
+    return null;
+  }
 
   function getCurrentActiveDonationCount$() {
     return Observable.of(activeDonationCountCache.get());

api-server/server/utils/in-memory-cache.js

@@ -2,21 +2,32 @@ function isPromiseLike(thing) {
   return !!thing && typeof thing.then === 'function';
 }
 
-function InMemoryCache(initialValue) {
+function InMemoryCache(initialValue, reportError) {
+  if (typeof reportError !== 'function') {
+    throw new Error(
+      'No reportError function specified for this in-memory-cache'
+    );
+  }
   const cacheKey = Symbol('cacheKey');
   const cache = new Map();
-
-  if (typeof initialValue !== 'undefined') {
-    cache.set(cacheKey, initialValue);
-  }
+  cache.set(cacheKey, initialValue);
 
   return {
     get() {
       const value = cache.get(cacheKey);
       return typeof value !== 'undefined' ? value : null;
     },
+
     async update(fn) {
-      const maybePromisedValue = fn();
+      let maybePromisedValue;
+      try {
+        maybePromisedValue = fn();
+      } catch (e) {
+        const errMsg = `InMemoryCache > update > caught: ${e.message}`;
+        e.message = errMsg;
+        reportError(e);
+        return null;
+      }
       if (isPromiseLike(maybePromisedValue)) {
         return maybePromisedValue.then(value => cache.set(cacheKey, value));
       } else {
@@ -25,6 +36,7 @@ function InMemoryCache(initialValue) {
         return null;
       }
     },
+
     clear() {
       return cache.delete(cacheKey);
     }

api-server/server/utils/in-memory-cache.test.js

@@ -1,33 +1,40 @@
-/* global describe expect it beforeEach */
+/* global describe expect it */
 import inMemoryCache from './in-memory-cache';
+import sinon from 'sinon';
 
 describe('InMemoryCache', () => {
+  let reportErrorStub;
   const theAnswer = 42;
   const before = 'before';
   const after = 'after';
   const emptyCacheValue = null;
 
-  describe('get', () => {
-    it('returns null for an empty cache', () => {
-      const cache = inMemoryCache();
-      expect(cache.get()).toBe(emptyCacheValue);
-    });
+  beforeEach(() => {
+    reportErrorStub = sinon.spy();
+  });
 
+  it('throws if no report function is passed as a second argument', () => {
+    expect(() => inMemoryCache(null)).toThrowError(
+      'No reportError function specified for this in-memory-cache'
+    );
+  });
+
+  describe('get', () => {
     it('returns an initial value', () => {
-      const cache = inMemoryCache(theAnswer);
+      const cache = inMemoryCache(theAnswer, reportErrorStub);
       expect(cache.get()).toBe(theAnswer);
     });
   });
 
   describe('update', () => {
     it('updates the cached value', () => {
-      const cache = inMemoryCache(before);
+      const cache = inMemoryCache(before, reportErrorStub);
       cache.update(() => after);
       expect(cache.get()).toBe(after);
     });
 
     it('can handle promises correctly', done => {
-      const cache = inMemoryCache(before);
+      const cache = inMemoryCache(before, reportErrorStub);
       cache.update(() => new Promise(resolve => resolve(after)));
       // because async
       setImmediate(() => {
@@ -35,12 +42,25 @@ describe('InMemoryCache', () => {
         done();
       });
     });
+
+    it('reports errors thrown from the update function', () => {
+      const reportErrorStub = sinon.spy();
+      const cache = inMemoryCache(before, reportErrorStub);
+
+      const updateError = new Error('An update error');
+      const updateThatThrows = () => {
+        throw updateError;
+      };
+
+      cache.update(updateThatThrows);
+      expect(reportErrorStub.calledWith(updateError)).toBe(true);
+    });
   });
 
   describe('clear', () => {
     it('clears the  cache', () => {
       expect.assertions(2);
-      const cache = inMemoryCache(theAnswer);
+      const cache = inMemoryCache(theAnswer, reportErrorStub);
       expect(cache.get()).toBe(theAnswer);
       cache.clear();
       expect(cache.get()).toBe(emptyCacheValue);