don't mutate configuration when updating http agent

lib/utils.js

@@ -88,17 +88,20 @@ utils.setHttpAgent = function setHttpAgent(
   bypassProxy = false,
   AwsConstructor
 ) {
-  config.httpOptions = _.merge(config.httpOptions, {});
-
-  if (bypassProxy) {
-    config.httpOptions.agent = new https.Agent({
+  const getNonProxyAgent = () =>
+    new https.Agent({
       keepAlive: true,
       rejectUnauthorized: true,
       maxSockets: 50
     });
-  }
 
-  config = _.omit(config, 'bypassProxy');
+  const newConfig = {
+    ...config,
+    httpOptions: {
+      ...config.httpOptions,
+      ...(bypassProxy ? { agent: getNonProxyAgent() } : {})
+    }
+  };
 
-  return new AwsConstructor(config);
+  return new AwsConstructor(_.omit(newConfig, 'bypassProxy'));
 };

package.json

@@ -2,7 +2,7 @@
   "dependencies": {
     "aws-sdk": "^2.327.0",
     "bluebird": "^3.5.0",
-    "lodash": "^4.17.11",
+    "lodash": "^4.17.15",
     "proxy-agent": "^3.0.3",
     "sinon-chai": "^3.3.0",
     "uuid": "^3.3.2"

test/unit/lib/utils.spec.js

@@ -70,6 +70,17 @@ describe('AWS Library utilities', function() {
     });
   });
 
+  it('should not mutate the passed in config when setting http agent', function() {
+    const awsMock = sinon.stub();
+    // bypassProxy shouldn't be passed to the AWS constructor
+    const config = { bypassProxy: 'a value' };
+    utils.setHttpAgent(config, true, awsMock);
+    expect(awsMock).to.have.been.calledWith({
+      httpOptions: { agent: sinon.match.any }
+    });
+    expect(config).to.deep.equal({ bypassProxy: 'a value' });
+  });
+
   it('should default to not setting up http keepalives', function() {
     const awsMock = sinon.stub();