refactor(calculateDurationMs): move this method to common utils

lib/connection/apm.js

@@ -1,7 +1,7 @@
 'use strict';
 const KillCursor = require('../connection/commands').KillCursor;
 const GetMore = require('../connection/commands').GetMore;
-const process = require('process');
+const calculateDurationInMs = require('../utils').calculateDurationInMs;
 
 /** Commands that we want to redact because of the sensitive nature of their contents */
 const SENSITIVE_COMMANDS = new Set([
@@ -18,11 +18,6 @@ const SENSITIVE_COMMANDS = new Set([
 
 // helper methods
 const extractCommandName = command => Object.keys(command)[0];
-const calculateDurationInMs = started => {
-  const hrtime = process.hrtime(started);
-  return (hrtime[0] * 1e9 + hrtime[1]) / 1e6;
-};
-
 const namespace = command => command.ns;
 const databaseName = command => command.ns.split('.')[0];
 const collectionName = command => command.ns.split('.')[1];

lib/utils.js

@@ -2,13 +2,28 @@
 
 const crypto = require('crypto');
 
+/**
+ * Generate a UUIDv4
+ */
 const uuidV4 = () => {
   const result = crypto.randomBytes(16);
   result[6] = (result[6] & 0x0f) | 0x40;
   result[8] = (result[8] & 0x3f) | 0x80;
   return result;
 };
 
+/**
+ * Returns the duration calculated from two high resolution timers in milliseconds
+ *
+ * @param {Object} started A high resolution timestamp created from `process.hrtime()`
+ * @returns {Number} The duration in milliseconds
+ */
+const calculateDurationInMs = started => {
+  const hrtime = process.hrtime(started);
+  return (hrtime[0] * 1e9 + hrtime[1]) / 1e6;
+};
+
 module.exports = {
-  uuidV4: uuidV4
+  uuidV4,
+  calculateDurationInMs
 };