Add recordSuccessMetric utility

Summary: Wraps a future and records the success rate. This will be stored along with the sessionId and the userId, so we can drill down and get the success rate at different levels.

Reviewed By: passy

Differential Revision: D13635049

fbshipit-source-id: 4e0e6bdc0f9b76b08cf37c5d9fe87909f7338534

src/server.js

@@ -17,6 +17,7 @@ import {Single} from 'rsocket-flowable';
 import Client from './Client.js';
 import type {UninitializedClient} from './UninitializedClient';
 import {RecurringError} from './utils/errors';
+import {recordSuccessMetric} from './utils/metrics';
 
 const EventEmitter = (require('events'): any);
 const invariant = require('invariant');
@@ -177,8 +178,15 @@ export default class Server extends EventEmitter {
           const {csr, destination} = json;
           return new Single(subscriber => {
             subscriber.onSubscribe();
-            this.certificateProvider
-              .processCertificateSigningRequest(csr, clientData.os, destination)
+            recordSuccessMetric(
+              this.certificateProvider.processCertificateSigningRequest(
+                csr,
+                clientData.os,
+                destination,
+              ),
+              'processCertificateSigningRequest',
+              this.logger,
+            )
               .then(result => {
                 subscriber.onComplete({
                   data: JSON.stringify({
@@ -190,20 +198,10 @@ export default class Server extends EventEmitter {
                   client,
                   deviceId: result.deviceId,
                 });
-                this.logger.track(
-                  'success-rate',
-                  'processCertificateSigningRequest',
-                  1,
-                );
               })
               .catch(e => {
                 subscriber.onError(e);
                 this.emit('client-setup-error', {client, error: e});
-                this.logger.track(
-                  'success-rate',
-                  'processCertificateSigningRequest',
-                  0,
-                );
               });
           });
         }

src/utils/__tests__/metrics.node.js

@@ -0,0 +1,58 @@
+/**
+ * Copyright 2018-present Facebook.
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ * @format
+ */
+import {recordSuccessMetric} from '../metrics';
+import type Logger from '../../fb-stubs/Logger';
+
+//$FlowFixMe pretend logger is the right type
+const logger: Logger = {
+  track: jest.fn(),
+};
+
+beforeAll(() => {
+  logger.track.mockClear();
+});
+
+test('Wrapping a successful promise preserves result and logs correctly', () => {
+  const successPromise = Promise.resolve('Yay!');
+  const wrappedPromise = recordSuccessMetric(
+    successPromise,
+    'test metric',
+    logger,
+  );
+  return wrappedPromise
+    .then(wrappedValue => {
+      expect(wrappedValue).toBe('Yay!');
+    })
+    .then(() => {
+      expect(logger.track).toHaveBeenCalledWith(
+        'success-rate',
+        'test metric',
+        1,
+      );
+    });
+});
+
+test('Wrapping a rejected promise preserves result and logs correctly', () => {
+  const successPromise = Promise.reject('Oh no!');
+  const wrappedPromise = recordSuccessMetric(
+    successPromise,
+    'test metric',
+    logger,
+  );
+  expect.assertions(2); // Make sure to fail if catch block isn't visited
+  return wrappedPromise
+    .catch(wrappedValue => {
+      expect(wrappedValue).toBe('Oh no!');
+    })
+    .then(() => {
+      expect(logger.track).toHaveBeenCalledWith(
+        'success-rate',
+        'test metric',
+        0,
+      );
+    });
+});

src/utils/metrics.js

@@ -0,0 +1,30 @@
+/**
+ * Copyright 2018-present Facebook.
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ * @format
+ */
+
+import type Logger from '../fb-stubs/Logger';
+
+/*
+ * Wraps a Promise, preserving it's functionality but logging the success or
+ failure state of it, with a given name, based on whether it's fulfilled or
+ rejected.
+ */
+export function recordSuccessMetric(
+  promise: Promise<*>,
+  name: string,
+  logger: Logger,
+): Promise<*> {
+  return promise.then(
+    fulfilledValue => {
+      logger.track('success-rate', name, 1);
+      return fulfilledValue;
+    },
+    rejectionReason => {
+      logger.track('success-rate', name, 0);
+      return Promise.reject(rejectionReason);
+    },
+  );
+}