App Hosting Emulator Prototype

schema/firebase-config.json

@@ -357,6 +357,18 @@
         "emulators": {
             "additionalProperties": false,
             "properties": {
+                "apphosting": {
+                    "additionalProperties": false,
+                    "properties": {
+                        "host": {
+                            "type": "string"
+                        },
+                        "port": {
+                            "type": "number"
+                        }
+                    },
+                    "type": "object"
+                },
                 "auth": {
                     "additionalProperties": false,
                     "properties": {

src/emulator/apphosting/index.ts

@@ -0,0 +1,48 @@
+import { EmulatorLogger } from "../emulatorLogger";
+import { EmulatorInfo, EmulatorInstance, Emulators } from "../types";
+import { start as apphostingStart } from "./serve";
+interface AppHostingEmulatorArgs {
+  options?: any;
+  port?: number;
+  host?: string;
+}
+
+/**
+ * An emulator instance for Firebase's App Hosting product. This class provides a simulated
+ * environment for testing App Hosting features locally.
+ */
+export class AppHostingEmulator implements EmulatorInstance {
+  private logger = EmulatorLogger.forEmulator(Emulators.APPHOSTING);
+  constructor(private args: AppHostingEmulatorArgs) {}
+
+  async start(): Promise<void> {
+    this.args.options.host = this.args.host;
+    this.args.options.port = this.args.port;
+
+    this.logger.logLabeled("INFO", Emulators.APPHOSTING, "starting apphosting emulator");
+    const { port } = await apphostingStart(this.args.options);
+    this.logger.logLabeled("INFO", Emulators.APPHOSTING, `serving on port ${port}`);
+  }
+
+  connect(): Promise<void> {
+    this.logger.logLabeled("INFO", Emulators.APPHOSTING, "connecting apphosting emulator");
+    return Promise.resolve();
+  }
+
+  stop(): Promise<void> {
+    this.logger.logLabeled("INFO", Emulators.APPHOSTING, "stopping apphosting emulator");
+    return Promise.resolve();
+  }
+
+  getInfo(): EmulatorInfo {
+    return {
+      name: Emulators.APPHOSTING,
+      host: this.args.host!,
+      port: this.args.port!,
+    };
+  }
+
+  getName(): Emulators {
+    return Emulators.APPHOSTING;
+  }
+}

src/emulator/apphosting/serve.spec.ts

@@ -0,0 +1,33 @@
+import * as portUtils from "../portUtils";
+import * as sinon from "sinon";
+import * as spawn from "../../init/spawn";
+import { expect } from "chai";
+import * as serve from "./serve";
+
+describe("serve", () => {
+  let checkListenableStub: sinon.SinonStub;
+  let wrapSpawnStub: sinon.SinonStub;
+
+  beforeEach(() => {
+    checkListenableStub = sinon.stub(portUtils, "checkListenable");
+    wrapSpawnStub = sinon.stub(spawn, "wrapSpawn");
+  });
+
+  afterEach(() => {
+    checkListenableStub.restore();
+    wrapSpawnStub.restore();
+  });
+
+  describe("start", () => {
+    it("should only select an available port to serve", async () => {
+      checkListenableStub.onFirstCall().returns(false);
+      checkListenableStub.onSecondCall().returns(false);
+      checkListenableStub.onThirdCall().returns(true);
+
+      wrapSpawnStub.returns(Promise.resolve());
+
+      const res = await serve.start({ host: "127.0.0.1", port: 5000 });
+      expect(res.port).to.equal(5002);
+    });
+  });
+});

src/emulator/apphosting/serve.ts

@@ -0,0 +1,38 @@
+/**
+ * Start the App Hosting server.
+ * @param options the Firebase CLI options.
+ */
+import { isIPv4 } from "net";
+import { checkListenable } from "../portUtils";
+import { wrapSpawn } from "../../init/spawn";
+
+/**
+ * Spins up a project locally by running the project's dev command.
+ */
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+export async function start(options: any): Promise<{ port: number }> {
+  let port = options.port;
+  while (!(await availablePort(options.host, port))) {
+    port += 1;
+  }
+
+  serve(options, port);
+
+  return { port };
+}
+
+function availablePort(host: string, port: number): Promise<boolean> {
+  return checkListenable({
+    address: host,
+    port,
+    family: isIPv4(host) ? "IPv4" : "IPv6",
+  });
+}
+
+/**
+ * Exported for unit testing
+ */
+export async function serve(options: any, port: string) {
+  // TODO: update to support other package managers and frameworks other than NextJS
+  await wrapSpawn("npm", ["run", "dev", "--", "-H", options.host, "-p", port], process.cwd());
+}

src/emulator/constants.ts

@@ -7,6 +7,7 @@ export const DEFAULT_PORTS: { [s in Emulators]: number } = {
   hosting: 5000,
   functions: 5001,
   extensions: 5001, // The Extensions Emulator runs on the same port as the Functions Emulator
+  apphosting: 5002,
   firestore: 8080,
   pubsub: 8085,
   database: 9000,
@@ -22,6 +23,7 @@ export const FIND_AVAILBLE_PORT_BY_DEFAULT: Record<Emulators, boolean> = {
   hub: true,
   logging: true,
   hosting: true,
+  apphosting: true,
   functions: false,
   firestore: false,
   database: false,
@@ -39,6 +41,7 @@ export const EMULATOR_DESCRIPTION: Record<Emulators, string> = {
   hub: "emulator hub",
   logging: "Logging Emulator",
   hosting: "Hosting Emulator",
+  apphosting: "App Hosting Emulator",
   functions: "Functions Emulator",
   firestore: "Firestore Emulator",
   database: "Database Emulator",

src/emulator/controller.ts

@@ -58,6 +58,7 @@ import { PubsubEmulator } from "./pubsubEmulator";
 import { StorageEmulator } from "./storage";
 import { readFirebaseJson } from "../dataconnect/fileUtils";
 import { TasksEmulator } from "./tasksEmulator";
+import { AppHostingEmulator } from "./apphosting";
 
 const START_LOGGING_EMULATOR = utils.envOverride(
   "START_LOGGING_EMULATOR",
@@ -886,6 +887,25 @@ export async function startAll(
     await startEmulator(hostingEmulator);
   }
 
+  /**
+   * Similar to the Hosting emulator, the App Hosting emulator should also
+   * start after the other emulators. This is because the service running on
+   * app hosting emulator may depend on other emulators (i.e auth, firestore,
+   * storage, etc).
+   */
+  if (experiments.isEnabled("emulatorapphosting")) {
+    if (listenForEmulator.apphosting) {
+      const apphostingAddr = legacyGetFirstAddr(Emulators.APPHOSTING);
+      const apphostingEmulator = new AppHostingEmulator({
+        host: apphostingAddr.host,
+        port: apphostingAddr.port,
+        options,
+      });
+
+      await startEmulator(apphostingEmulator);
+    }
+  }
+
   if (listenForEmulator.logging) {
     const loggingAddr = legacyGetFirstAddr(Emulators.LOGGING);
     const loggingEmulator = new LoggingEmulator({

src/emulator/portUtils.ts

@@ -209,6 +209,8 @@ const EMULATOR_CAN_LISTEN_ON_PRIMARY_ONLY: Record<PortName, boolean> = {
 
   // Only one hostname possible in .server mode, can switch to middleware later.
   hosting: true,
+
+  apphosting: true,
 };
 
 export interface EmulatorListenConfig {

src/emulator/registry.ts

@@ -79,6 +79,12 @@ export class EmulatorRegistry {
       // Hosting is next because it can trigger functions.
       hosting: 2,
 
+      /** App Hosting should be shut down next. Users should not be interacting
+       * with their app while its being shut down as the app may using the
+       * background trigger emulators below.
+       */
+      apphosting: 2.1,
+
       // All background trigger emulators are equal here, so we choose
       // an order for consistency.
       database: 3.0,

src/emulator/types.ts

@@ -1,5 +1,6 @@
 import { ChildProcess } from "child_process";
 import { EventEmitter } from "events";
+import * as experiments from "../experiments";
 
 export enum Emulators {
   AUTH = "auth",
@@ -8,6 +9,7 @@ export enum Emulators {
   FIRESTORE = "firestore",
   DATABASE = "database",
   HOSTING = "hosting",
+  APPHOSTING = "apphosting",
   PUBSUB = "pubsub",
   UI = "ui",
   LOGGING = "logging",
@@ -48,6 +50,7 @@ export const ALL_SERVICE_EMULATORS = [
   Emulators.FIRESTORE,
   Emulators.DATABASE,
   Emulators.HOSTING,
+  ...(experiments.isEnabled("emulatorapphosting") ? [Emulators.APPHOSTING] : []),
   Emulators.PUBSUB,
   Emulators.STORAGE,
   Emulators.EVENTARC,

src/experiments.ts

@@ -78,6 +78,10 @@ export const ALL_EXPERIMENTS = experiments({
   emulatoruisnapshot: {
     shortDescription: "Load pre-release versions of the emulator UI",
   },
+  emulatorapphosting: {
+    shortDescription: "App Hosting emulator",
+    public: false,
+  },
 
   // Hosting experiments
   webframeworks: {

src/firebaseConfig.ts

@@ -203,6 +203,10 @@ export type EmulatorsConfig = {
     host?: string;
     port?: number;
   };
+  apphosting?: {
+    host?: string;
+    port?: number;
+  };
   pubsub?: {
     host?: string;
     port?: number;