fix: Add support for IPv6 loopback and all IPv4 addresses (#14)

frontend/packages/common-frontend/src/ConnectionState.ts

@@ -122,10 +122,24 @@ export class ConnectionStateStore {
   }
 }
 
+export const isLocalhost = (hostname: string) => {
+  if (hostname === 'localhost') {
+    return true;
+  }
+  if (hostname === '[::1]') {
+    return true;
+  }
+  if (hostname.match(/^127\.\d+\.\d+\.\d+$/)) {
+    return true;
+  }
+
+  return false;
+};
+
 const $wnd = window as any;
 if (!$wnd.Vaadin?.connectionState) {
   let online;
-  if (window.location.hostname === 'localhost' || window.location.hostname === '127.0.0.1') {
+  if (isLocalhost(window.location.hostname)) {
     // We do not know if we are online or not as we cannot trust navigator.onLine which checks availability of a network connection. Better to assume online so localhost apps can work
     online = true;
   } else {

frontend/packages/common-frontend/test/ConnectionState.test.ts

@@ -1,6 +1,6 @@
 import { assert, expect } from '@open-wc/testing';
 import sinon from 'sinon';
-import { ConnectionState, ConnectionStateStore } from '../src';
+import { ConnectionState, ConnectionStateStore, isLocalhost } from '../src';
 
 describe('ConnectionStateStore', () => {
   it('should call state change listeners when transitioning between states', () => {
@@ -157,4 +157,17 @@ describe('ConnectionStateStore', () => {
       navigatorStub.restore();
     }
   });
+  it('should know which hosts are localhost', async () => {
+    expect(isLocalhost("localhost")).to.be.true;
+    expect(isLocalhost("127.0.0.1")).to.be.true;
+    expect(isLocalhost("127.0.0.2")).to.be.true;
+    expect(isLocalhost("127.1.2.3")).to.be.true;
+    expect(isLocalhost("[::1]")).to.be.true;
+    expect(isLocalhost("::1")).to.be.false;
+    expect(isLocalhost("127.0.0.1.com")).to.be.false;
+    expect(isLocalhost("foo127.0.0.1")).to.be.false;
+    expect(isLocalhost("localhost.com")).to.be.false;
+    expect(isLocalhost("my.localhost")).to.be.false;
+  });
+
 });