Remove support for setting server.host to '0' (breaking)

src/core/server/http/http_config.test.ts

@@ -22,8 +22,8 @@ import { config, HttpConfig } from './http_config';
 import { CspConfig } from '../csp';
 import { ExternalUrlConfig } from '../external_url';
 
-const validHostnames = ['www.example.com', '8.8.8.8', '::1', 'localhost'];
-const invalidHostname = 'asdf$%^';
+const validHostnames = ['www.example.com', '8.8.8.8', '::1', 'localhost', '0.0.0.0'];
+const invalidHostnames = ['asdf$%^', '0'];
 
 jest.mock('os', () => {
   const original = jest.requireActual('os');
@@ -48,11 +48,10 @@ test('accepts valid hostnames', () => {
 });
 
 test('throws if invalid hostname', () => {
-  const httpSchema = config.schema;
-  const obj = {
-    host: invalidHostname,
-  };
-  expect(() => httpSchema.validate(obj)).toThrowErrorMatchingSnapshot();
+  for (const host of invalidHostnames) {
+    const httpSchema = config.schema;
+    expect(() => httpSchema.validate({ host })).toThrowErrorMatchingSnapshot();
+  }
 });
 
 describe('requestId', () => {
@@ -304,17 +303,17 @@ describe('with compression', () => {
 
   test('throws if invalid referrer whitelist', () => {
     const httpSchema = config.schema;
-    const invalidHostnames = {
+    const nonEmptyArray = {
       compression: {
-        referrerWhitelist: [invalidHostname],
+        referrerWhitelist: invalidHostnames,
       },
     };
     const emptyArray = {
       compression: {
         referrerWhitelist: [],
       },
     };
-    expect(() => httpSchema.validate(invalidHostnames)).toThrowErrorMatchingSnapshot();
+    expect(() => httpSchema.validate(nonEmptyArray)).toThrowErrorMatchingSnapshot();
     expect(() => httpSchema.validate(emptyArray)).toThrowErrorMatchingSnapshot();
   });
 

src/core/server/http/http_config.ts

@@ -73,6 +73,11 @@ export const config = {
       host: schema.string({
         defaultValue: 'localhost',
         hostname: true,
+        validate(value) {
+          if (value === '0') {
+            return 'value 0 is not a valid hostname';
+          }
+        },
       }),
       maxPayload: schema.byteSize({
         defaultValue: '1048576b',
@@ -195,13 +200,7 @@ export class HttpConfig {
     rawExternalUrlConfig: ExternalUrlConfig
   ) {
     this.autoListen = rawHttpConfig.autoListen;
-    // TODO: Consider dropping support for '0' in v8.0.0. This value is passed
-    // to hapi, which validates it. Prior to hapi v20, '0' was considered a
-    // valid host, however the validation logic internally in hapi was
-    // re-written for v20 and hapi no longer considers '0' a valid host. For
-    // details, see:
-    // https://github.com/elastic/kibana/issues/86716#issuecomment-749623781
-    this.host = rawHttpConfig.host === '0' ? '0.0.0.0' : rawHttpConfig.host;
+    this.host = rawHttpConfig.host;
     this.port = rawHttpConfig.port;
     this.cors = rawHttpConfig.cors;
     this.customResponseHeaders = Object.entries(rawHttpConfig.customResponseHeaders ?? {}).reduce(