return tool result directly (#52)

Author: Pederzh

src/adapters/langchain_adapter.ts

@@ -2,10 +2,7 @@ import type { JSONSchema } from '@dmitryrechkin/json-schema-to-zod'
 import type { StructuredToolInterface } from '@langchain/core/tools'
 import type {
   CallToolResult,
-  EmbeddedResource,
-  ImageContent,
   Tool as MCPTool,
-  TextContent,
 } from '@modelcontextprotocol/sdk/types.js'
 import type { ZodTypeAny } from 'zod'
 import type { BaseConnector } from '../connectors/base.js'
@@ -26,49 +23,6 @@ function schemaToZod(schema: unknown): ZodTypeAny {
   }
 }
 
-function parseMcpToolResult(toolResult: CallToolResult): string {
-  if (toolResult.isError) {
-    throw new Error(`Tool execution failed: ${toolResult.content}`)
-  }
-  if (!toolResult.content || toolResult.content.length === 0) {
-    throw new Error('Tool execution returned no content')
-  }
-
-  let decoded = ''
-  for (const item of toolResult.content) {
-    switch (item.type) {
-      case 'text': {
-        decoded += (item as TextContent).text
-        break
-      }
-      case 'image': {
-        decoded += (item as ImageContent).data
-        break
-      }
-      case 'resource': {
-        const res = (item as EmbeddedResource).resource
-        if (res?.text !== undefined) {
-          decoded += res.text
-        }
-        else if (res?.blob !== undefined) {
-          // eslint-disable-next-line node/prefer-global/buffer
-          decoded += res.blob instanceof Uint8Array || res.blob instanceof Buffer
-            // eslint-disable-next-line node/prefer-global/buffer
-            ? Buffer.from(res.blob).toString('base64')
-            : String(res.blob)
-        }
-        else {
-          throw new Error(`Unexpected resource type: ${res?.type}`)
-        }
-        break
-      }
-      default:
-        throw new Error(`Unexpected content type: ${(item as any).type}`)
-    }
-  }
-  return decoded
-}
-
 export class LangChainAdapter extends BaseAdapter<StructuredToolInterface> {
   constructor(disallowedTools: string[] = []) {
     super(disallowedTools)
@@ -99,7 +53,7 @@ export class LangChainAdapter extends BaseAdapter<StructuredToolInterface> {
         logger.debug(`MCP tool \"${mcpTool.name}\" received input: ${JSON.stringify(input)}`)
         try {
           const result: CallToolResult = await connector.callTool(mcpTool.name, input)
-          return parseMcpToolResult(result)
+          return JSON.stringify(result)
         }
         catch (err: any) {
           logger.error(`Error executing MCP tool: ${err.message}`)