feat(ai): Add prefer_in_cloud option for inference mode

.changeset/feat-prefer-in-cloud.md

@@ -0,0 +1,10 @@
+---
+"@firebase/ai": minor
+"firebase": minor
+---
+
+feat: Add `prefer_in_cloud` option for inference mode
+
+This change introduces a new `InferenceMode` option, `prefer_in_cloud`. When this mode is selected, the SDK will attempt to use the cloud backend first. If the cloud call fails with a network-related error, it will fall back to the on-device model if available.
+
+This also includes a refactoring of the logic for dispatching requests to either the on-device or cloud backends to improve clarity and remove duplication.

common/api-review/ai.api.md

@@ -727,6 +727,7 @@ export const InferenceMode: {
     readonly PREFER_ON_DEVICE: "prefer_on_device";
     readonly ONLY_ON_DEVICE: "only_on_device";
     readonly ONLY_IN_CLOUD: "only_in_cloud";
+    readonly PREFER_IN_CLOUD: "prefer_in_cloud";
 };
 
 // @public

docs-devsite/ai.md

@@ -631,6 +631,7 @@ InferenceMode: {
     readonly PREFER_ON_DEVICE: "prefer_on_device";
     readonly ONLY_ON_DEVICE: "only_on_device";
     readonly ONLY_IN_CLOUD: "only_in_cloud";
+    readonly PREFER_IN_CLOUD: "prefer_in_cloud";
 }
 ```
 

packages/ai/src/methods/count-tokens.test.ts

@@ -196,24 +196,16 @@ describe('countTokens()', () => {
       );
     });
   });
-  it('on-device', async () => {
-    const chromeAdapter = fakeChromeAdapter;
-    const isAvailableStub = stub(chromeAdapter, 'isAvailable').resolves(true);
-    const mockResponse = getMockResponse(
-      'vertexAI',
-      'unary-success-total-tokens.json'
-    );
-    const countTokensStub = stub(chromeAdapter, 'countTokens').resolves(
-      mockResponse as Response
+  it('throws if mode is ONLY_ON_DEVICE', async () => {
+    const chromeAdapter = new ChromeAdapterImpl(
+      // @ts-expect-error
+      undefined,
+      InferenceMode.ONLY_ON_DEVICE
     );
-    const result = await countTokens(
-      fakeApiSettings,
-      'model',
-      fakeRequestParams,
-      chromeAdapter
+    await expect(
+      countTokens(fakeApiSettings, 'model', fakeRequestParams, chromeAdapter)
+    ).to.be.rejectedWith(
+      /countTokens\(\) is not supported for on-device models/
     );
-    expect(result.totalTokens).eq(6);
-    expect(isAvailableStub).to.be.called;
-    expect(countTokensStub).to.be.calledWith(fakeRequestParams);
   });
 });

packages/ai/src/methods/count-tokens.ts

@@ -15,16 +15,20 @@
  * limitations under the License.
  */
 
+import { AIError } from '../errors';
 import {
   CountTokensRequest,
   CountTokensResponse,
-  RequestOptions
+  InferenceMode,
+  RequestOptions,
+  AIErrorCode
 } from '../types';
 import { Task, makeRequest } from '../requests/request';
 import { ApiSettings } from '../types/internal';
 import * as GoogleAIMapper from '../googleai-mappers';
 import { BackendType } from '../public-types';
 import { ChromeAdapter } from '../types/chrome-adapter';
+import { ChromeAdapterImpl } from './chrome-adapter';
 
 export async function countTokensOnCloud(
   apiSettings: ApiSettings,
@@ -57,9 +61,13 @@ export async function countTokens(
   chromeAdapter?: ChromeAdapter,
   requestOptions?: RequestOptions
 ): Promise<CountTokensResponse> {
-  if (chromeAdapter && (await chromeAdapter.isAvailable(params))) {
-    return (await chromeAdapter.countTokens(params)).json();
+  if (
+    (chromeAdapter as ChromeAdapterImpl)?.mode === InferenceMode.ONLY_ON_DEVICE
+  ) {
+    throw new AIError(
+      AIErrorCode.UNSUPPORTED,
+      'countTokens() is not supported for on-device models.'
+    );
   }
-
   return countTokensOnCloud(apiSettings, model, params, requestOptions);
 }

packages/ai/src/methods/generate-content.ts

@@ -29,6 +29,7 @@ import { ApiSettings } from '../types/internal';
 import * as GoogleAIMapper from '../googleai-mappers';
 import { BackendType } from '../public-types';
 import { ChromeAdapter } from '../types/chrome-adapter';
+import { callCloudOrDevice } from '../requests/hybrid-helpers';
 
 async function generateContentStreamOnCloud(
   apiSettings: ApiSettings,
@@ -56,17 +57,13 @@ export async function generateContentStream(
   chromeAdapter?: ChromeAdapter,
   requestOptions?: RequestOptions
 ): Promise<GenerateContentStreamResult> {
-  let response;
-  if (chromeAdapter && (await chromeAdapter.isAvailable(params))) {
-    response = await chromeAdapter.generateContentStream(params);
-  } else {
-    response = await generateContentStreamOnCloud(
-      apiSettings,
-      model,
-      params,
-      requestOptions
-    );
-  }
+  const response = await callCloudOrDevice(
+    params,
+    chromeAdapter,
+    () => chromeAdapter!.generateContentStream(params),
+    () =>
+      generateContentStreamOnCloud(apiSettings, model, params, requestOptions)
+  );
   return processStream(response, apiSettings); // TODO: Map streaming responses
 }
 
@@ -96,17 +93,12 @@ export async function generateContent(
   chromeAdapter?: ChromeAdapter,
   requestOptions?: RequestOptions
 ): Promise<GenerateContentResult> {
-  let response;
-  if (chromeAdapter && (await chromeAdapter.isAvailable(params))) {
-    response = await chromeAdapter.generateContent(params);
-  } else {
-    response = await generateContentOnCloud(
-      apiSettings,
-      model,
-      params,
-      requestOptions
-    );
-  }
+  const response = await callCloudOrDevice(
+    params,
+    chromeAdapter,
+    () => chromeAdapter!.generateContent(params),
+    () => generateContentOnCloud(apiSettings, model, params, requestOptions)
+  );
   const generateContentResponse = await processGenerateContentResponse(
     response,
     apiSettings