refactor: Extract mask token function from npm datasource to utils (#3040)

Helps with https://github.com/renovatebot/renovate/pull/3039  

lib/config/decrypt.js

 const is = require('@sindresorhus/is');
 const crypto = require('crypto');
-const { maskToken } = require('../datasource/npm');
+const { maskToken } = require('../util/mask');
 
 module.exports = {
   decryptConfig,

lib/datasource/npm/get.js

@@ -8,9 +8,8 @@ const parse = require('github-url-from-git');
 const { isBase64 } = require('validator');
 
 const hostRules = require('../../util/host-rules');
-
+const { maskToken } = require('../../util/mask');
 const { getNpmrc } = require('./npmrc');
-const { maskToken } = require('./mask');
 
 module.exports = {
   getDependency,

lib/datasource/npm/index.js

 const { resetMemCache, resetCache } = require('./get');
 const { getPreset } = require('./presets');
 const { getPkgReleases } = require('./releases');
-const { maskToken } = require('./mask');
 const { setNpmrc } = require('./npmrc');
 
 module.exports = {
-  maskToken,
   setNpmrc,
   getPreset,
   getPkgReleases,

lib/datasource/npm/mask.js

-module.exports = {
-  maskToken,
-};
-
-// istanbul ignore next
-function maskToken(token) {
-  // istanbul ignore if
-  if (!token) {
-    return token;
-  }
-  return `${token.substring(0, 2)}${new Array(token.length - 3).join(
-    '*'
-  )}${token.slice(-2)}`;
-}

lib/platform/github/gh-got-wrapper.js

@@ -3,6 +3,7 @@ const ghGot = require('gh-got');
 const delay = require('delay');
 const parseLinkHeader = require('parse-link-header');
 const hostRules = require('../../util/host-rules');
+const { maskToken } = require('../../util/mask');
 
 let cache = {};
 let stats = {};
@@ -196,16 +197,6 @@ async function get(path, options, retries = 5) {
   }
 }
 
-// istanbul ignore next
-function maskToken(token) {
-  if (!token) {
-    return token;
-  }
-  return `${token.substring(0, 2)}${new Array(token.length - 3).join(
-    '*'
-  )}${token.slice(-2)}`;
-}
-
 const helpers = ['get', 'post', 'put', 'patch', 'head', 'delete'];
 
 for (const x of helpers) {

lib/util/mask.js

+function maskToken(str) {
+  return str
+    ? [
+        str.substring(0, 2),
+        new Array(str.length - 3).join('*'),
+        str.slice(-2),
+      ].join('')
+    : str;
+}
+
+module.exports = {
+  maskToken,
+};

test/util/mask.spec.js

+const { maskToken } = require('../../lib/util/mask');
+
+describe('util/mask', () => {
+  describe('.maskToken', () => {
+    it('returns value if passed value is falsy', () => {
+      expect(maskToken('')).toEqual('');
+    });
+
+    it('hides value content', () => {
+      expect(maskToken('123456789')).toEqual('12*****89');
+    });
+  });
+});