Function createCustomToolHandler

src/tools/custom-tool-handler.ts:156–247

(toolConfig: ToolConfig)

 * @returns Handler function compatible with MCP server.registerTool
 */
export function createCustomToolHandler(toolConfig: ToolConfig) {
  // Build Zod schema shape for MCP registration
  const zodSchemaShape = buildZodSchemaFromParameters(toolConfig.parameters);
  // Wrap in z.object() for validation
  const zodSchema = z.object(zodSchemaShape);

  return async (args: any, extra: any) => {
    const startTime = Date.now();
    let success = true;
    let errorMessage: string | undefined;
    let paramValues: any[] = [];

    try {
      // 1. Validate arguments against Zod schema
      const validatedArgs = zodSchema.parse(args);

      // 2. Ensure source is connected (handles lazy connections)
      await ConnectorManager.ensureConnected(toolConfig.source);

      // 3. Get connector for the specified source
      const connector = ConnectorManager.getCurrentConnector(toolConfig.source);

      // 4. Build execute options from tool configuration
      const executeOptions = {
        readonly: toolConfig.readonly,
        maxRows: toolConfig.max_rows,
      };

      // 5. Check if SQL is allowed based on readonly mode
      const isReadonly = executeOptions.readonly === true;
      if (isReadonly && !isAllowedInReadonlyMode(toolConfig.statement, connector.id)) {
        errorMessage = createReadonlyViolationMessage(toolConfig.name, toolConfig.source, connector.id);
        success = false;
        return createToolErrorResponse(errorMessage, "READONLY_VIOLATION");
      }

      // 6. Map parameters to array format for SQL execution
      paramValues = mapArgumentsToArray(
        toolConfig.parameters,
        validatedArgs
      );

      // 7. Execute SQL with parameters
      const result = await connector.executeSQL(
        toolConfig.statement,
        executeOptions,
        paramValues
      );

      // 8. Build response data
      const responseData = {
        rows: result.rows,
        count: result.rowCount,
        source_id: toolConfig.source,
      };

      return createToolSuccessResponse(responseData);
    } catch (error) {