[Gemini Connector] Throw tool validation error on MALFORMED_FUNCTION_CALL finish reason when processing Gemini Stream (#227110)

SrdjanLL · SrdjanLL · commit f70b0e4a0938 · 2025-07-09T16:19:57.000+01:00
Closes: #227096 ## Summary Throw tool validation error on `MALFORMED_FUNCTION_CALL` finish reason - Update the error-throwing finish reasons when processing vertex stream - Enrich the error message with finish message so it's captured in the trace for easier troubleshooting. ### Testing - The bug was caught when the API was throwing the error below during the Obs AI Assistant evaluation: ```bash ERROR ChatCompletionError: Cannot read properties of undefined (reading 'parts') at Object.next (throw_serialized_chat_completion_errors.ts:29:17) at ``` - Reproduced in the debug mode and found the root cause: <img width="1657" alt="image" src="https://github.com/user-attachments/assets/073469dc-fc48-4f09-9aaf-2b5cfd85edfb" /> - Fixed and ensured this gets captured in a trace: - [trace example prior to this change](https://35-187-109-62.sslip.io/projects/UHJvamVjdDoxMQ==/traces/76ab1b0405dcf157f7ca5e74f5cbcca8?selected): <img width="1222" alt="image" src="https://github.com/user-attachments/assets/71be8d73-78a8-4bd6-86d4-f772600ade76" /> - [new trace example](https://35-187-109-62.sslip.io/projects/UHJvamVjdDoxMQ==/traces/2dadbbfa9e132f4de71da255fe157f95?selected): <img width="1222" alt="image" src="https://github.com/user-attachments/assets/1d0738d8-4c6e-4d55-8dae-769f1ebcffac" /> (cherry picked from commit 92cce95) # Conflicts: # x-pack/platform/plugins/shared/inference/server/chat_complete/adapters/gemini/process_vertex_stream.ts
diff --git a/x-pack/platform/plugins/shared/inference/server/chat_complete/adapters/gemini/process_vertex_stream.ts b/x-pack/platform/plugins/shared/inference/server/chat_complete/adapters/gemini/process_vertex_stream.ts
@@ -13,11 +13,45 @@ import {
 } from '@kbn/inference-common';
 import { generateFakeToolCallId } from '../../../../common';
 import type { GenerateContentResponseChunk } from './types';
+import { createToolValidationError } from '../../errors';
 
 export function processVertexStream() {
   return (source: Observable<GenerateContentResponseChunk>) =>
     new Observable<ChatCompletionChunkEvent | ChatCompletionTokenCountEvent>((subscriber) => {
       function handleNext(value: GenerateContentResponseChunk) {
+        const finishReason = value.candidates?.[0].finishReason as string | undefined;
+
+        function emitTokenCountIfApplicable() {
+          // 'usageMetadata' can be present as an empty object on chunks
+          // only the last chunk will have its fields populated
+          if (value.usageMetadata?.totalTokenCount) {
+            subscriber.next({
+              type: ChatCompletionEventType.ChatCompletionTokenCount,
+              tokens: {
+                prompt: value.usageMetadata.promptTokenCount,
+                completion: value.usageMetadata.candidatesTokenCount,
+                cached: value.usageMetadata.cachedContentTokenCount,
+                total: value.usageMetadata.totalTokenCount,
+              },
+            });
+          }
+        }
+
+        if (finishReason === 'UNEXPECTED_TOOL_CALL' || finishReason === 'MALFORMED_FUNCTION_CALL') {
+          const finishMessage = value.candidates?.[0].finishMessage;
+          const validationErrorMessage = finishMessage
+            ? `${finishReason} - ${finishMessage}`
+            : finishReason;
+          emitTokenCountIfApplicable();
+          subscriber.error(
+            createToolValidationError(validationErrorMessage, {
+              errorsText: finishMessage,
+              toolCalls: [],
+            })
+          );
+          return;
+        }
+
         const contentPart = value.candidates?.[0].content.parts[0];
         const completion = contentPart?.text;
         const toolCall = contentPart?.functionCall;
