Use a utility to wrap response.body in an async iterator

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

@@ -31,6 +31,7 @@ import {
   ProviderType,
   PushClient,
   assert,
+  asyncIteratorFromResponse,
   binding,
   cleanArguments,
   createFactory,
@@ -314,8 +315,7 @@ export class User<
     assert(response.ok, () => `Request failed: ${response.statusText} (${response.status})`);
     assert(response.body, "Expected a body in the response");
 
-    throw new Error("ReadableStream is not yet implementing AsyncIterable");
-    // return response.body;
+    return asyncIteratorFromResponse(response);
   }
 
   /**

packages/realm/src/async-iterator-from-response.ts

@@ -0,0 +1,53 @@
+////////////////////////////////////////////////////////////////////////////
+//
+// Copyright 2024 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 { Response } from "@realm/fetch";
+
+/** @internal */
+export function asyncIteratorFromResponse({ body }: Response): AsyncIterable<Uint8Array> {
+  if (typeof body !== "object" || body === null) {
+    throw new Error("Expected a non-null object");
+  } else if (Symbol.asyncIterator in body) {
+    return body as AsyncIterable<Uint8Array>;
+  } else if ("getReader" in body) {
+    return {
+      [Symbol.asyncIterator]() {
+        const reader = body.getReader();
+        return {
+          async next() {
+            const { done, value } = await reader.read();
+            if (done) {
+              // TODO: Simply return the result once https://github.com/microsoft/TypeScript-DOM-lib-generator/pull/1676 is merged and released
+              return { done, value: undefined };
+            } else if (value instanceof Uint8Array) {
+              return { done, value };
+            } else {
+              throw new Error("Expected value to be Uint8Array");
+            }
+          },
+          async return() {
+            await reader.cancel();
+            return { done: true, value: null };
+          },
+        };
+      },
+    };
+  } else {
+    throw new Error("Expected an AsyncIterable or a ReadableStream");
+  }
+}

packages/realm/src/internal.ts

@@ -39,6 +39,8 @@ export * from "./assert";
 /** @internal */
 export * from "./ranges";
 /** @internal */
+export * from "./async-iterator-from-response";
+/** @internal */
 export * from "./Listeners";
 /** @internal */
 export * from "./JSONCacheMap";