fix(ai): remove error logging in sendMessageStream()

Removes error logging in `sendMessageStream()`. These errors are
catchable by the user, so there is no need to log them.
This removes the anti-pattern of throwing a `SILENT_ERROR` to skip
promise chains.

This fix is important for when we add [AbortSignal](
#8890). Since aborting a
request raises an `AbortError`, every time a request is aborted, there
will be an error logged to the console, which is undesirable for the
user.

Author: dlarocque

.changeset/dull-rabbits-fix.md

@@ -0,0 +1,5 @@
+---
+'@firebase/ai': patch
+---
+
+Removed error logging in `ChatSession.sendMessageStream()`, since these errors are catchable.

packages/ai/src/methods/chat-session.test.ts

@@ -20,7 +20,7 @@ import { match, restore, stub, useFakeTimers } from 'sinon';
 import sinonChai from 'sinon-chai';
 import chaiAsPromised from 'chai-as-promised';
 import * as generateContentMethods from './generate-content';
-import { Content, GenerateContentStreamResult, InferenceMode } from '../types';
+import { Content, InferenceMode } from '../types';
 import { ChatSession } from './chat-session';
 import { ApiSettings } from '../types/internal';
 import { VertexAIBackend } from '../backend';
@@ -136,31 +136,5 @@ describe('ChatSession', () => {
       expect(consoleStub).to.not.be.called;
       clock.restore();
     });
-    it('downstream sendPromise errors should log but not throw', async () => {
-      const clock = useFakeTimers();
-      const consoleStub = stub(console, 'error');
-      // make response undefined so that response.candidates errors
-      const generateContentStreamStub = stub(
-        generateContentMethods,
-        'generateContentStream'
-      ).resolves({} as unknown as GenerateContentStreamResult);
-      const chatSession = new ChatSession(
-        fakeApiSettings,
-        'a-model',
-        fakeChromeAdapter
-      );
-      await chatSession.sendMessageStream('hello');
-      expect(generateContentStreamStub).to.be.calledWith(
-        fakeApiSettings,
-        'a-model',
-        match.any
-      );
-      await clock.runAllAsync();
-      expect(consoleStub.args[0][1].toString()).to.include(
-        // Firefox has different wording when a property is undefined
-        'undefined'
-      );
-      clock.restore();
-    });
   });
 });

packages/ai/src/methods/chat-session.ts

@@ -32,11 +32,6 @@ import { ApiSettings } from '../types/internal';
 import { logger } from '../logger';
 import { ChromeAdapter } from '../types/chrome-adapter';
 
-/**
- * Do not log a message for this error.
- */
-const SILENT_ERROR = 'SILENT_ERROR';
-
 /**
  * ChatSession class that enables sending chat messages and stores
  * history of sent and received messages so far.
@@ -153,14 +148,9 @@ export class ChatSession {
       this.requestOptions
     );
 
-    // Add onto the chain.
-    this._sendPromise = this._sendPromise
-      .then(() => streamPromise)
-      // This must be handled to avoid unhandled rejection, but jump
-      // to the final catch block with a label to not log this error.
-      .catch(_ignored => {
-        throw new Error(SILENT_ERROR);
-      })
+    // This promise is not returned to the user, but is used to chain promise sequences that
+    // update the history and handle errors.
+    const historyUpdatePromise = streamPromise
       .then(streamResult => streamResult.response)
       .then(response => {
         if (response.candidates && response.candidates.length > 0) {
@@ -180,16 +170,14 @@ export class ChatSession {
           }
         }
       })
-      .catch(e => {
-        // Errors in streamPromise are already catchable by the user as
-        // streamPromise is returned.
-        // Avoid duplicating the error message in logs.
-        if (e.message !== SILENT_ERROR) {
-          // Users do not have access to _sendPromise to catch errors
-          // downstream from streamPromise, so they should not throw.
-          logger.error(e);
-        }
+      .catch(() => {
+        // Suppress unhandled rejection error. The user is responsible for handling the error
+        // on the returned streamPromise.
       });
+
+    // Chain the history update to the serialization promise.
+    this._sendPromise = historyUpdatePromise;
+
     return streamPromise;
   }
 }