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fix(core): binary content handling in parallel function responses #17058

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fix(core): binary content handling in parallel function responses #17058

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b276128
fix(core): ensure single part response for Gemini 2.x in parallel turns
jw409 Jan 8, 2026
dc64eb7
fix(core): enforce strict 1:1 function response mapping by nesting bi…
jw409 Jan 8, 2026
0e4cf4e
fix(core): use accurate message when binary content is omitted
jw409 Jan 20, 2026
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7 changes: 3 additions & 4 deletions packages/core/src/utils/generateContentResponseUtilities.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -158,7 +158,7 @@ describe('generateContentResponseUtilities', () => {
]);
});

it('should handle llmContent with fileData for Gemini 3 model (should be siblings)', () => {
it('should handle llmContent with fileData for Gemini 3 model (should be nested)', () => {
const llmContent: Part = {
fileData: { mimeType: 'application/pdf', fileUri: 'gs://...' },
};
Expand All @@ -174,9 +174,9 @@ describe('generateContentResponseUtilities', () => {
name: toolName,
id: callId,
response: { output: 'Binary content provided (1 item(s)).' },
parts: [llmContent],
},
},
llmContent,
]);
});

Expand All @@ -202,7 +202,7 @@ describe('generateContentResponseUtilities', () => {
]);
});

it('should handle llmContent with fileData for non-Gemini 3 models', () => {
it('should handle llmContent with fileData for non-Gemini 3 models (should omit siblings)', () => {
const llmContent: Part = {
fileData: { mimeType: 'application/pdf', fileUri: 'gs://...' },
};
Expand All @@ -220,7 +220,6 @@ describe('generateContentResponseUtilities', () => {
response: { output: 'Binary content provided (1 item(s)).' },
},
},
llmContent,
]);
});

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21 changes: 12 additions & 9 deletions packages/core/src/utils/generateContentResponseUtilities.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -97,17 +97,18 @@ export function convertToFunctionResponse(
};

const isMultimodalFRSupported = supportsMultimodalFunctionResponse(model);
const siblingParts: Part[] = [...fileDataParts];
const siblingParts: Part[] = [];

if (inlineDataParts.length > 0) {
if (isMultimodalFRSupported) {
// Nest inlineData if supported by the model
if (isMultimodalFRSupported) {
const binaryParts = [...fileDataParts, ...inlineDataParts];
if (binaryParts.length > 0) {
// Nest all binary content if supported by the model
(part.functionResponse as unknown as { parts: Part[] }).parts =
inlineDataParts;
} else {
// Otherwise treat as siblings
siblingParts.push(...inlineDataParts);
binaryParts;
}
} else {
// Otherwise treat as siblings (which will be dropped below)
siblingParts.push(...fileDataParts, ...inlineDataParts);
}

// Add descriptive text if the response object is empty but we have binary content
Expand All @@ -122,7 +123,9 @@ export function convertToFunctionResponse(
}

if (siblingParts.length > 0) {
return [part, ...siblingParts];
debugLogger.warn(
`Model ${model} does not support multimodal function responses. Sibling parts will be omitted to prevent API errors in parallel function calling.`,
);
}
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@gemini-code-assist gemini-code-assist bot Jan 20, 2026

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high

This logic correctly warns and drops sibling parts for non-multimodal models. However, there's a related issue: the code at lines 115-123 has already added a descriptive text like output: 'Binary content provided (...)' to the response. This message becomes misleading because the binary content is now being dropped. The model will be told binary content is provided when it has actually been omitted.

To fix this, we should clear this misleading message from the response object when we drop the parts and there was no original text content. This will also require updating the test 'should handle llmContent with fileData for non-Gemini 3 models (should omit siblings)' to expect response: {}.

Suggested change
if (siblingParts.length > 0) {
return [part, ...siblingParts];
debugLogger.warn(
`Model ${model} does not support multimodal function responses. Sibling parts will be omitted to prevent API errors in parallel function calling.`,
);
}
if (siblingParts.length > 0) {
debugLogger.warn(
`Model ${model} does not support multimodal function responses. Sibling parts will be omitted to prevent API errors in parallel function calling.`,
);
// If there was no original text, the response object may contain a misleading
// "Binary content provided" message from the dropped parts. Clear it.
if (textParts.length === 0) {
part.functionResponse!.response = {};
}
}


return [part];
Expand Down