Prebid Core: Add readConfig functionality to clone the config instead of referencing it

src/config.js

@@ -16,7 +16,7 @@ import { isValidPriceConfig } from './cpmBucketManager.js';
 import find from 'core-js-pure/features/array/find.js';
 import includes from 'core-js-pure/features/array/includes.js';
 import Set from 'core-js-pure/features/set';
-import { mergeDeep } from './utils.js';
+import { mergeDeep, deepClone } from './utils.js';
 
 const from = require('core-js-pure/features/array/from.js');
 const utils = require('./utils.js');
@@ -315,6 +315,26 @@ export function newConfig() {
     return Object.assign({}, config);
   }
 
+  /*
+   * Returns the configuration object if called without parameters,
+   * or single configuration property if given a string matching a configuration
+   * property name.  Allows deep access e.g. getConfig('currency.adServerCurrency')
+   *
+   * If called with callback parameter, or a string and a callback parameter,
+   * subscribes to configuration updates. See `subscribe` function for usage.
+   *
+   * The object returned is a deepClone of the `config` property.
+   */
+  function readConfig(...args) {
+    if (args.length <= 1 && typeof args[0] !== 'function') {
+      const option = args[0];
+      const configClone = deepClone(_getConfig());
+      return option ? utils.deepAccess(configClone, option) : configClone;
+    }
+
+    return subscribe(...args);
+  }
+
   /*
    * Returns configuration object if called without parameters,
    * or single configuration property if given a string matching a configuration
@@ -629,6 +649,7 @@ export function newConfig() {
     getCurrentBidder,
     resetBidder,
     getConfig,
+    readConfig,
     setConfig,
     setDefaults,
     resetConfig,

src/prebid.js

@@ -897,6 +897,7 @@ $$PREBID_GLOBAL$$.markWinningBidAsUsed = function (markBidRequest) {
  * @alias module:pbjs.getConfig
  */
 $$PREBID_GLOBAL$$.getConfig = config.getConfig;
+$$PREBID_GLOBAL$$.readConfig = config.readConfig;
 
 /**
  * Set Prebid config options.

test/spec/config_spec.js

@@ -6,6 +6,7 @@ const utils = require('src/utils');
 
 let getConfig;
 let setConfig;
+let readConfig;
 let getBidderConfig;
 let setBidderConfig;
 let setDefaults;
@@ -17,6 +18,7 @@ describe('config API', function () {
     const config = newConfig();
     getConfig = config.getConfig;
     setConfig = config.setConfig;
+    readConfig = config.readConfig;
     getBidderConfig = config.getBidderConfig;
     setBidderConfig = config.setBidderConfig;
     setDefaults = config.setDefaults;
@@ -37,6 +39,67 @@ describe('config API', function () {
     expect(getConfig()).to.be.a('object');
   });
 
+  it('readConfig returns deepCopy of the internal config object', function () {
+    setConfig({ foo: {biz: 'bar'} });
+    const config1 = readConfig('foo');
+    config1.biz = 'buz';
+    const config2 = readConfig('foo');
+    expect(readConfig()).to.be.a('object');
+    expect(config1.biz).to.not.equal(config2.biz);
+  });
+
+  it('readConfig retrieves arbitrary configuration properties', function () {
+    setConfig({ baz: 'qux' });
+    expect(readConfig('baz')).to.equal('qux');
+  });
+
+  it('readConfig has subscribe functionality for adding listeners to config updates', function () {
+    const listener = sinon.spy();
+
+    readConfig(listener);
+
+    setConfig({ foo: 'bar' });
+
+    sinon.assert.calledOnce(listener);
+    sinon.assert.calledWith(listener, { foo: 'bar' });
+  });
+
+  it('readConfig subscribers can unsubscribe', function () {
+    const listener = sinon.spy();
+
+    const unsubscribe = getConfig(listener);
+
+    unsubscribe();
+
+    readConfig({ logging: true });
+
+    sinon.assert.notCalled(listener);
+  });
+
+  it('readConfig subscribers can subscribe to topics', function () {
+    const listener = sinon.spy();
+
+    readConfig('logging', listener);
+
+    setConfig({ logging: true, foo: 'bar' });
+
+    sinon.assert.calledOnce(listener);
+    sinon.assert.calledWithExactly(listener, { logging: true });
+  });
+
+  it('readConfig topic subscribers are only called when that topic is changed', function () {
+    const listener = sinon.spy();
+    const wildcard = sinon.spy();
+
+    readConfig('subject', listener);
+    readConfig(wildcard);
+
+    setConfig({ foo: 'bar' });
+
+    sinon.assert.notCalled(listener);
+    sinon.assert.calledOnce(wildcard);
+  });
+
   it('sets and gets arbitrary configuration properties', function () {
     setConfig({ baz: 'qux' });
     expect(getConfig('baz')).to.equal('qux');