feat(storage): Add getDownloadUrl method to the Storage API

src/storage/index.ts

@@ -20,11 +20,31 @@
  * @packageDocumentation
  */
 
-import { App, getApp } from '../app';
-import { FirebaseApp } from '../app/firebase-app';
-import { Storage } from './storage';
+import { File } from "@google-cloud/storage";
+import { App, getApp } from "../app";
+import { FirebaseApp } from "../app/firebase-app";
+import { Storage } from "./storage";
+import { FirebaseError } from "../utils/error";
 
-export { Storage } from './storage';
+export { Storage } from "./storage";
+
+interface FirebaseMetadata {
+  name: string;
+  bucket: string;
+  generation: string;
+  metageneration: string;
+  contentType: string;
+  timeCreated: string;
+  updated: string;
+  storageClass: string;
+  size: string;
+  md5Hash: string;
+  contentEncoding: string;
+  contentDisposition: string;
+  crc32c: string;
+  etag: string;
+  downloadTokens?: string;
+}
 
 /**
  * Gets the {@link Storage} service for the default app or a given app.
@@ -46,10 +66,64 @@ export { Storage } from './storage';
  * ```
  */
 export function getStorage(app?: App): Storage {
-  if (typeof app === 'undefined') {
+  if (typeof app === "undefined") {
     app = getApp();
   }
 
   const firebaseApp: FirebaseApp = app as FirebaseApp;
-  return firebaseApp.getOrInitService('storage', (app) => new Storage(app));
+  return firebaseApp.getOrInitService("storage", (app) => new Storage(app));
+}
+/**
+ * Gets metadata from Firebase backend instead of GCS
+ * @returns {FirebaseMetadata}
+ */
+function getFirebaseMetadata(
+  endpoint: string,
+  file: File
+): Promise<FirebaseMetadata> {
+  // Build any custom headers based on the defined interceptors on the parent
+  // storage object and this object
+  const uri = `${endpoint}/b/${file.bucket.name}/o/${encodeURIComponent(
+    file.name
+  )}`;
+
+  return new Promise((resolve, reject) => {
+    file.storage.makeAuthenticatedRequest(
+      {
+        method: "GET",
+        uri,
+      },
+      (err, body) => {
+        if (err) {
+          reject(err);
+        } else {
+          resolve(body);
+        }
+      }
+    );
+  });
+}
+
+/**
+ * Gets the download URL for a given file. Will throw a `FirebaseError` if there are no download tokens available.
+ * @returns {Promise<string>}
+ */
+
+export async function getDownloadUrl(file: File) {
+  const endpoint =
+    (process.env.STORAGE_EMULATOR_HOST ||
+      process.env.STORAGE_HOST_OVERRIDE ||
+      "https://firebasestorage.googleapis.com") + "/v0";
+  const { downloadTokens } = await getFirebaseMetadata(endpoint, file);
+  if (!downloadTokens) {
+    throw new FirebaseError({
+      code: "storage/no-download-token",
+      message:
+        "No download token available. Please create one in the Firebase Console.",
+    });
+  }
+  const [token] = downloadTokens.split(",");
+  return `${endpoint}/b/${file.bucket.name}/o/${encodeURIComponent(
+    file.name
+  )}?alt=media&token=${token}`;
 }

src/storage/storage.ts

@@ -17,8 +17,8 @@
 
 import { App } from '../app';
 import { FirebaseError } from '../utils/error';
-import { FirebaseStorageClient, FirebaseStorageBucket } from './cloud-extensions';
 import { ServiceAccountCredential, isApplicationDefault } from '../app/credential-internal';
+import { Bucket, Storage as StorageClient} from '@google-cloud/storage';
 
 import * as utils from '../utils/index';
 import * as validator from '../utils/validator';
@@ -31,7 +31,7 @@ import * as validator from '../utils/validator';
 export class Storage {
 
   private readonly appInternal: App;
-  private readonly storageClient: FirebaseStorageClient;
+  private readonly storageClient: StorageClient;
 
   /**
    * @param app - The app for this Storage service.
@@ -60,10 +60,9 @@ export class Storage {
       process.env.STORAGE_EMULATOR_HOST = `http://${process.env.FIREBASE_STORAGE_EMULATOR_HOST}`;
     }
 
-    let storage: typeof FirebaseStorageClient;
+    let storage: typeof StorageClient;
     try {
-      require('@google-cloud/storage').Storage;
-      storage = FirebaseStorageClient;
+      storage = require('@google-cloud/storage').Storage;
     } catch (err) {
       throw new FirebaseError({
         code: 'storage/missing-dependencies',
@@ -107,7 +106,7 @@ export class Storage {
    * @returns A {@link https://cloud.google.com/nodejs/docs/reference/storage/latest/Bucket | Bucket}
    * instance as defined in the `@google-cloud/storage` package.
    */
-  public bucket(name?: string): FirebaseStorageBucket {
+  public bucket(name?: string): Bucket {
     const bucketName = (typeof name !== 'undefined')
       ? name :  this.appInternal.options.storageBucket;
     if (validator.isNonEmptyString(bucketName)) {
@@ -120,7 +119,6 @@ export class Storage {
                 'explicitly when calling the getBucket() method.',
     });
   }
-
   /**
    * Optional app whose `Storage` service to
    * return. If not provided, the default `Storage` service will be returned.