feat(core): Parse Multimodal MCP Tool responses (#5529)

Co-authored-by: Luccas Paroni <luccasparoni@google.com>
This commit is contained in:
Luccas Paroni
2025-08-05 16:19:47 -03:00
committed by GitHub
parent b465145229
commit 2778c7d851
4 changed files with 580 additions and 56 deletions

View File

@@ -131,8 +131,11 @@ describe('DiscoveredMCPTool', () => {
success: true,
details: 'executed',
};
const mockFunctionResponseContent: Part[] = [
{ text: JSON.stringify(mockToolSuccessResultObject) },
const mockFunctionResponseContent = [
{
type: 'text',
text: JSON.stringify(mockToolSuccessResultObject),
},
];
const mockMcpToolResponseParts: Part[] = [
{
@@ -149,11 +152,13 @@ describe('DiscoveredMCPTool', () => {
expect(mockCallTool).toHaveBeenCalledWith([
{ name: serverToolName, args: params },
]);
expect(toolResult.llmContent).toEqual(mockMcpToolResponseParts);
const stringifiedResponseContent = JSON.stringify(
mockToolSuccessResultObject,
);
expect(toolResult.llmContent).toEqual([
{ text: stringifiedResponseContent },
]);
expect(toolResult.returnDisplay).toBe(stringifiedResponseContent);
});
@@ -170,6 +175,9 @@ describe('DiscoveredMCPTool', () => {
mockCallTool.mockResolvedValue(mockMcpToolResponsePartsEmpty);
const toolResult: ToolResult = await tool.execute(params);
expect(toolResult.returnDisplay).toBe('```json\n[]\n```');
expect(toolResult.llmContent).toEqual([
{ text: '[Error: Could not parse tool response]' },
]);
});
it('should propagate rejection if mcpTool.callTool rejects', async () => {
@@ -186,6 +194,361 @@ describe('DiscoveredMCPTool', () => {
await expect(tool.execute(params)).rejects.toThrow(expectedError);
});
it('should handle a simple text response correctly', async () => {
const tool = new DiscoveredMCPTool(
mockCallableToolInstance,
serverName,
serverToolName,
baseDescription,
inputSchema,
);
const params = { query: 'test' };
const successMessage = 'This is a success message.';
// Simulate the response from the GenAI SDK, which wraps the MCP
// response in a functionResponse Part.
const sdkResponse: Part[] = [
{
functionResponse: {
name: serverToolName,
response: {
// The `content` array contains MCP ContentBlocks.
content: [{ type: 'text', text: successMessage }],
},
},
},
];
mockCallTool.mockResolvedValue(sdkResponse);
const toolResult = await tool.execute(params);
// 1. Assert that the llmContent sent to the scheduler is a clean Part array.
expect(toolResult.llmContent).toEqual([{ text: successMessage }]);
// 2. Assert that the display output is the simple text message.
expect(toolResult.returnDisplay).toBe(successMessage);
// 3. Verify that the underlying callTool was made correctly.
expect(mockCallTool).toHaveBeenCalledWith([
{ name: serverToolName, args: params },
]);
});
it('should handle an AudioBlock response', async () => {
const tool = new DiscoveredMCPTool(
mockCallableToolInstance,
serverName,
serverToolName,
baseDescription,
inputSchema,
);
const params = { action: 'play' };
const sdkResponse: Part[] = [
{
functionResponse: {
name: serverToolName,
response: {
content: [
{
type: 'audio',
data: 'BASE64_AUDIO_DATA',
mimeType: 'audio/mp3',
},
],
},
},
},
];
mockCallTool.mockResolvedValue(sdkResponse);
const toolResult = await tool.execute(params);
expect(toolResult.llmContent).toEqual([
{
text: `[Tool '${serverToolName}' provided the following audio data with mime-type: audio/mp3]`,
},
{
inlineData: {
mimeType: 'audio/mp3',
data: 'BASE64_AUDIO_DATA',
},
},
]);
expect(toolResult.returnDisplay).toBe('[Audio: audio/mp3]');
});
it('should handle a ResourceLinkBlock response', async () => {
const tool = new DiscoveredMCPTool(
mockCallableToolInstance,
serverName,
serverToolName,
baseDescription,
inputSchema,
);
const params = { resource: 'get' };
const sdkResponse: Part[] = [
{
functionResponse: {
name: serverToolName,
response: {
content: [
{
type: 'resource_link',
uri: 'file:///path/to/thing',
name: 'resource-name',
title: 'My Resource',
},
],
},
},
},
];
mockCallTool.mockResolvedValue(sdkResponse);
const toolResult = await tool.execute(params);
expect(toolResult.llmContent).toEqual([
{
text: 'Resource Link: My Resource at file:///path/to/thing',
},
]);
expect(toolResult.returnDisplay).toBe(
'[Link to My Resource: file:///path/to/thing]',
);
});
it('should handle an embedded text ResourceBlock response', async () => {
const tool = new DiscoveredMCPTool(
mockCallableToolInstance,
serverName,
serverToolName,
baseDescription,
inputSchema,
);
const params = { resource: 'get' };
const sdkResponse: Part[] = [
{
functionResponse: {
name: serverToolName,
response: {
content: [
{
type: 'resource',
resource: {
uri: 'file:///path/to/text.txt',
text: 'This is the text content.',
mimeType: 'text/plain',
},
},
],
},
},
},
];
mockCallTool.mockResolvedValue(sdkResponse);
const toolResult = await tool.execute(params);
expect(toolResult.llmContent).toEqual([
{ text: 'This is the text content.' },
]);
expect(toolResult.returnDisplay).toBe('This is the text content.');
});
it('should handle an embedded binary ResourceBlock response', async () => {
const tool = new DiscoveredMCPTool(
mockCallableToolInstance,
serverName,
serverToolName,
baseDescription,
inputSchema,
);
const params = { resource: 'get' };
const sdkResponse: Part[] = [
{
functionResponse: {
name: serverToolName,
response: {
content: [
{
type: 'resource',
resource: {
uri: 'file:///path/to/data.bin',
blob: 'BASE64_BINARY_DATA',
mimeType: 'application/octet-stream',
},
},
],
},
},
},
];
mockCallTool.mockResolvedValue(sdkResponse);
const toolResult = await tool.execute(params);
expect(toolResult.llmContent).toEqual([
{
text: `[Tool '${serverToolName}' provided the following embedded resource with mime-type: application/octet-stream]`,
},
{
inlineData: {
mimeType: 'application/octet-stream',
data: 'BASE64_BINARY_DATA',
},
},
]);
expect(toolResult.returnDisplay).toBe(
'[Embedded Resource: application/octet-stream]',
);
});
it('should handle a mix of content block types', async () => {
const tool = new DiscoveredMCPTool(
mockCallableToolInstance,
serverName,
serverToolName,
baseDescription,
inputSchema,
);
const params = { action: 'complex' };
const sdkResponse: Part[] = [
{
functionResponse: {
name: serverToolName,
response: {
content: [
{ type: 'text', text: 'First part.' },
{
type: 'image',
data: 'BASE64_IMAGE_DATA',
mimeType: 'image/jpeg',
},
{ type: 'text', text: 'Second part.' },
],
},
},
},
];
mockCallTool.mockResolvedValue(sdkResponse);
const toolResult = await tool.execute(params);
expect(toolResult.llmContent).toEqual([
{ text: 'First part.' },
{
text: `[Tool '${serverToolName}' provided the following image data with mime-type: image/jpeg]`,
},
{
inlineData: {
mimeType: 'image/jpeg',
data: 'BASE64_IMAGE_DATA',
},
},
{ text: 'Second part.' },
]);
expect(toolResult.returnDisplay).toBe(
'First part.\n[Image: image/jpeg]\nSecond part.',
);
});
it('should ignore unknown content block types', async () => {
const tool = new DiscoveredMCPTool(
mockCallableToolInstance,
serverName,
serverToolName,
baseDescription,
inputSchema,
);
const params = { action: 'test' };
const sdkResponse: Part[] = [
{
functionResponse: {
name: serverToolName,
response: {
content: [
{ type: 'text', text: 'Valid part.' },
{ type: 'future_block', data: 'some-data' },
],
},
},
},
];
mockCallTool.mockResolvedValue(sdkResponse);
const toolResult = await tool.execute(params);
expect(toolResult.llmContent).toEqual([{ text: 'Valid part.' }]);
expect(toolResult.returnDisplay).toBe(
'Valid part.\n[Unknown content type: future_block]',
);
});
it('should handle a complex mix of content block types', async () => {
const tool = new DiscoveredMCPTool(
mockCallableToolInstance,
serverName,
serverToolName,
baseDescription,
inputSchema,
);
const params = { action: 'super-complex' };
const sdkResponse: Part[] = [
{
functionResponse: {
name: serverToolName,
response: {
content: [
{ type: 'text', text: 'Here is a resource.' },
{
type: 'resource_link',
uri: 'file:///path/to/resource',
name: 'resource-name',
title: 'My Resource',
},
{
type: 'resource',
resource: {
uri: 'file:///path/to/text.txt',
text: 'Embedded text content.',
mimeType: 'text/plain',
},
},
{
type: 'image',
data: 'BASE64_IMAGE_DATA',
mimeType: 'image/jpeg',
},
],
},
},
},
];
mockCallTool.mockResolvedValue(sdkResponse);
const toolResult = await tool.execute(params);
expect(toolResult.llmContent).toEqual([
{ text: 'Here is a resource.' },
{
text: 'Resource Link: My Resource at file:///path/to/resource',
},
{ text: 'Embedded text content.' },
{
text: `[Tool '${serverToolName}' provided the following image data with mime-type: image/jpeg]`,
},
{
inlineData: {
mimeType: 'image/jpeg',
data: 'BASE64_IMAGE_DATA',
},
},
]);
expect(toolResult.returnDisplay).toBe(
'Here is a resource.\n[Link to My Resource: file:///path/to/resource]\nEmbedded text content.\n[Image: image/jpeg]',
);
});
});
describe('shouldConfirmExecute', () => {

View File

@@ -22,6 +22,40 @@ import {
type ToolParams = Record<string, unknown>;
// Discriminated union for MCP Content Blocks to ensure type safety.
type McpTextBlock = {
type: 'text';
text: string;
};
type McpMediaBlock = {
type: 'image' | 'audio';
mimeType: string;
data: string;
};
type McpResourceBlock = {
type: 'resource';
resource: {
text?: string;
blob?: string;
mimeType?: string;
};
};
type McpResourceLinkBlock = {
type: 'resource_link';
uri: string;
title?: string;
name?: string;
};
type McpContentBlock =
| McpTextBlock
| McpMediaBlock
| McpResourceBlock
| McpResourceLinkBlock;
export class DiscoveredMCPTool extends BaseTool<ToolParams, ToolResult> {
private static readonly allowlist: Set<string> = new Set();
@@ -114,70 +148,145 @@ export class DiscoveredMCPTool extends BaseTool<ToolParams, ToolResult> {
},
];
const responseParts: Part[] = await this.mcpTool.callTool(functionCalls);
const rawResponseParts = await this.mcpTool.callTool(functionCalls);
const transformedParts = transformMcpContentToParts(rawResponseParts);
return {
llmContent: responseParts,
returnDisplay: getStringifiedResultForDisplay(responseParts),
llmContent: transformedParts,
returnDisplay: getStringifiedResultForDisplay(rawResponseParts),
};
}
}
/**
* Processes an array of `Part` objects, primarily from a tool's execution result,
* to generate a user-friendly string representation, typically for display in a CLI.
*
* The `result` array can contain various types of `Part` objects:
* 1. `FunctionResponse` parts:
* - If the `response.content` of a `FunctionResponse` is an array consisting solely
* of `TextPart` objects, their text content is concatenated into a single string.
* This is to present simple textual outputs directly.
* - If `response.content` is an array but contains other types of `Part` objects (or a mix),
* the `content` array itself is preserved. This handles structured data like JSON objects or arrays
* returned by a tool.
* - If `response.content` is not an array or is missing, the entire `functionResponse`
* object is preserved.
* 2. Other `Part` types (e.g., `TextPart` directly in the `result` array):
* - These are preserved as is.
*
* All processed parts are then collected into an array, which is JSON.stringify-ed
* with indentation and wrapped in a markdown JSON code block.
*/
function getStringifiedResultForDisplay(result: Part[]) {
if (!result || result.length === 0) {
return '```json\n[]\n```';
function transformTextBlock(block: McpTextBlock): Part {
return { text: block.text };
}
function transformImageAudioBlock(
block: McpMediaBlock,
toolName: string,
): Part[] {
return [
{
text: `[Tool '${toolName}' provided the following ${
block.type
} data with mime-type: ${block.mimeType}]`,
},
{
inlineData: {
mimeType: block.mimeType,
data: block.data,
},
},
];
}
function transformResourceBlock(
block: McpResourceBlock,
toolName: string,
): Part | Part[] | null {
const resource = block.resource;
if (resource?.text) {
return { text: resource.text };
}
if (resource?.blob) {
const mimeType = resource.mimeType || 'application/octet-stream';
return [
{
text: `[Tool '${toolName}' provided the following embedded resource with mime-type: ${mimeType}]`,
},
{
inlineData: {
mimeType,
data: resource.blob,
},
},
];
}
return null;
}
const processFunctionResponse = (part: Part) => {
if (part.functionResponse) {
const responseContent = part.functionResponse.response?.content;
if (responseContent && Array.isArray(responseContent)) {
// Check if all parts in responseContent are simple TextParts
const allTextParts = responseContent.every(
(p: Part) => p.text !== undefined,
);
if (allTextParts) {
return responseContent.map((p: Part) => p.text).join('');
}
// If not all simple text parts, return the array of these content parts for JSON stringification
return responseContent;
}
// If no content, or not an array, or not a functionResponse, stringify the whole functionResponse part for inspection
return part.functionResponse;
}
return part; // Fallback for unexpected structure or non-FunctionResponsePart
function transformResourceLinkBlock(block: McpResourceLinkBlock): Part {
return {
text: `Resource Link: ${block.title || block.name} at ${block.uri}`,
};
}
const processedResults =
result.length === 1
? processFunctionResponse(result[0])
: result.map(processFunctionResponse);
if (typeof processedResults === 'string') {
return processedResults;
/**
* Transforms the raw MCP content blocks from the SDK response into a
* standard GenAI Part array.
* @param sdkResponse The raw Part[] array from `mcpTool.callTool()`.
* @returns A clean Part[] array ready for the scheduler.
*/
function transformMcpContentToParts(sdkResponse: Part[]): Part[] {
const funcResponse = sdkResponse?.[0]?.functionResponse;
const mcpContent = funcResponse?.response?.content as McpContentBlock[];
const toolName = funcResponse?.name || 'unknown tool';
if (!Array.isArray(mcpContent)) {
return [{ text: '[Error: Could not parse tool response]' }];
}
return '```json\n' + JSON.stringify(processedResults, null, 2) + '\n```';
const transformed = mcpContent.flatMap(
(block: McpContentBlock): Part | Part[] | null => {
switch (block.type) {
case 'text':
return transformTextBlock(block);
case 'image':
case 'audio':
return transformImageAudioBlock(block, toolName);
case 'resource':
return transformResourceBlock(block, toolName);
case 'resource_link':
return transformResourceLinkBlock(block);
default:
return null;
}
},
);
return transformed.filter((part): part is Part => part !== null);
}
/**
* Processes the raw response from the MCP tool to generate a clean,
* human-readable string for display in the CLI. It summarizes non-text
* content and presents text directly.
*
* @param rawResponse The raw Part[] array from the GenAI SDK.
* @returns A formatted string representing the tool's output.
*/
function getStringifiedResultForDisplay(rawResponse: Part[]): string {
const mcpContent = rawResponse?.[0]?.functionResponse?.response
?.content as McpContentBlock[];
if (!Array.isArray(mcpContent)) {
return '```json\n' + JSON.stringify(rawResponse, null, 2) + '\n```';
}
const displayParts = mcpContent.map((block: McpContentBlock): string => {
switch (block.type) {
case 'text':
return block.text;
case 'image':
return `[Image: ${block.mimeType}]`;
case 'audio':
return `[Audio: ${block.mimeType}]`;
case 'resource_link':
return `[Link to ${block.title || block.name}: ${block.uri}]`;
case 'resource':
if (block.resource?.text) {
return block.resource.text;
}
return `[Embedded Resource: ${
block.resource?.mimeType || 'unknown type'
}]`;
default:
return `[Unknown content type: ${(block as { type: string }).type}]`;
}
});
return displayParts.join('\n');
}
/** Visible for testing */