Override fetch for Altas App Services

CHANGELOG.md

@@ -4,7 +4,28 @@
 * `Realm.User.providerType` is deprecated, and will be remove in next major version. Use `Realm.User.identities` instead.
 
 ### Enhancements
-* None
+* Expose `Realm.App.Configuration.fetchOverride` to enable implementing a custom [`fetch`](https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch) function. ([#6159](https://github.com/realm/realm-js/issues/6159))
+
+```js
+const HTTP_METHOD: Record<number, string> = {
+  [0]: "GET",
+  [1]: "POST",
+  [2]: "PUT",
+  [3]: "PATCH",
+  [4]: "DELETE",
+};
+
+const customFetch = async (request: Request) => {
+  const { url, body, ...rest } = request;
+  if (typeof request.method == "number") {
+    rest.method = HTTP_METHOD[request.method];
+  }
+  const response = await fetch(url, rest); // `fetch` is assumed to be compliant with the Fetch API specification
+  return response;
+};
+
+let app = new Realm.App({ id: "my-app-id", fetchOverride: customFetch });
+```
 
 ### Fixed
 * Outside migration functions, it is not possible to change the value of a primary key. ([#6161](https://github.com/realm/realm-js/issues/6161), since v12.0.0)

integration-tests/tests/src/hooks/import-app-before.ts

@@ -32,6 +32,7 @@ export type AppConfigurationRelaxed = {
   timeout?: number;
   multiplexSessions?: boolean;
   baseFilePath?: string;
+  fetchOverride?: any;
 };
 
 export function importAppBefore(config: AppConfig | { config: AppConfig }, sdkConfig?: AppConfigurationRelaxed): void {

integration-tests/tests/src/node/custom-fetch.ts

@@ -0,0 +1,66 @@
+////////////////////////////////////////////////////////////////////////////
+//
+// Copyright 2022 Realm Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+////////////////////////////////////////////////////////////////////////////
+
+import { expect } from "chai";
+import { importAppBefore } from "../hooks";
+import { buildAppConfig } from "../utils/build-app-config";
+import fetch, { Request } from "node-fetch";
+import Realm from "realm";
+
+describe("custom fetch", () => {
+  let called = false;
+
+  const HTTP_METHOD: Record<number, string> = {
+    [0]: "GET",
+    [1]: "POST",
+    [2]: "PUT",
+    [3]: "PATCH",
+    [4]: "DELETE",
+  };
+
+  const customFetch = async (request: Request) => {
+    called = true;
+    const { url, body, ...rest } = request;
+    if (typeof request.method == "number") {
+      rest.method = HTTP_METHOD[request.method];
+    }
+    const response = await fetch(url, rest);
+    return response;
+  };
+
+  importAppBefore(buildAppConfig("with-anon").anonAuth(), { fetchOverride: customFetch });
+  afterEach(() => {
+    Realm.clearTestState();
+  });
+
+  it("custom fetch is called", async function (this: Mocha.Context & AppContext & RealmContext) {
+    let user;
+    called = false;
+    try {
+      expect(this.app).instanceOf(Realm.App);
+      const credentials = Realm.Credentials.anonymous();
+      user = await this.app.logIn(credentials);
+      expect(called).equals(true);
+      expect(user).instanceOf(Realm.User);
+      expect(user.deviceId).to.not.be.null;
+      expect(user.providerType).equals("anon-user");
+    } finally {
+      await user?.logOut();
+    }
+  });
+});

integration-tests/tests/src/node/index.ts

@@ -20,5 +20,6 @@
 
 import "./analytics";
 import "./clean-exit";
+import "./custom-fetch";
 import "./path";
 import "./sync-proxy";

integration-tests/tests/src/tests/sync/app.ts

@@ -21,9 +21,11 @@ import Realm, { AppConfiguration, BSON, MetadataMode } from "realm";
 
 import { importAppBefore } from "../../hooks";
 import { generatePartition } from "../../utils/generators";
-import { baseUrl } from "../../utils/import-app";
+import { baseUrl, Response } from "../../utils/import-app";
 import { select } from "../../utils/select";
 import { buildAppConfig } from "../../utils/build-app-config";
+import { Fetch, Request } from "@realm/network-transport";
+import { fetch } from "../../utils/fetch";
 
 const TestObjectSchema: Realm.ObjectSchema = {
   primaryKey: "_id",

packages/realm/realm-constants.json

@@ -1 +1 @@
-{"REALM_ANONYMIZED_BUNDLE_ID":"tkgif/+3l1e9wStGJp2TOngAK3UcQ2u7OM8ZYJU5JYo="}
+{"REALM_ANONYMIZED_BUNDLE_ID":"1RmJBlqbKuzyRiPm4AsdIIxe8xlRUntGcGFEwUnUh6A="}

packages/realm/src/app-services/App.ts

@@ -16,6 +16,7 @@
 //
 ////////////////////////////////////////////////////////////////////////////
 
+import { NetworkType, inject } from "src/platform/network";
 import {
   AnyUser,
   Credentials,
@@ -140,6 +141,13 @@ export type AppConfiguration = {
    * @since 12.2.0
    */
   metadata?: Metadata;
+
+  /**
+   * Specify a custom `fetch` implementation.
+   * @since 12.3.0
+   * @experimental This API is experimental and may change or be removed.
+   */
+  fetchOverride?: unknown;
 };
 
 /**
@@ -261,7 +269,8 @@ export class App<
   constructor(configOrId: AppConfiguration | string) {
     const config: AppConfiguration = typeof configOrId === "string" ? { id: configOrId } : configOrId;
     assert.object(config, "config");
-    const { id, baseUrl, app, timeout, multiplexSessions = true, baseFilePath, metadata } = config;
+    const { id, baseUrl, app, timeout, multiplexSessions = true, baseFilePath, metadata, fetchOverride } = config;
+
     assert.string(id, "id");
     if (timeout !== undefined) {
       assert.number(timeout, "timeout");
@@ -277,6 +286,10 @@ export class App<
       }
     }
 
+    if (fetchOverride) {
+      inject({ fetch: fetchOverride } as NetworkType);
+    }
+
     fs.ensureDirectoryForFile(fs.joinPaths(baseFilePath || fs.getDefaultDirectoryPath(), "mongodb-realm"));
     // TODO: This used getSharedApp in the legacy SDK, but it's failing AppTests
     this.internal = binding.App.getUncachedApp(

packages/realm/src/platform/network.ts

@@ -26,7 +26,7 @@ export type { FetchHeaders, Request };
 const debug = extendDebug("network");
 const transport = new DefaultNetworkTransport();
 
-type NetworkType = {
+export type NetworkType = {
   fetch(request: Request): Promise<FetchResponse>;
   fetch(request: binding.Request): Promise<FetchResponse>;
 };
@@ -60,5 +60,5 @@ export const network: NetworkType = {
 };
 
 export function inject(injected: NetworkType) {
-  Object.freeze(Object.assign(network, injected));
+  Object.assign(network, injected);
 }