🧩 fix: additionalProperties Handling and Ref Resolution in Zod Schemas (#8381)

* fix: false flagging object as empty object when it has `additionalProperties` field

* 🔧 fix: Implement $ref resolution in JSON Schema handling

* 🔧 fix: Resolve JSON Schema references before conversion to Zod

* chore: move zod logic packages/api

api/server/services/MCP.js

@@ -2,16 +2,17 @@ const { z } = require('zod');
 const { tool } = require('@langchain/core/tools');
 const { logger } = require('@librechat/data-schemas');
 const { Time, CacheKeys, StepTypes } = require('librechat-data-provider');
-const { sendEvent, normalizeServerName, MCPOAuthHandler } = require('@librechat/api');
 const { Constants: AgentConstants, Providers, GraphEvents } = require('@librechat/agents');
+const { Constants, ContentTypes, isAssistantsEndpoint } = require('librechat-data-provider');
 const {
-  Constants,
+  sendEvent,
-  ContentTypes,
+  MCPOAuthHandler,
-  isAssistantsEndpoint,
+  normalizeServerName,
+  resolveJsonSchemaRefs,
   convertJsonSchemaToZod,
-} = require('librechat-data-provider');
+} = require('@librechat/api');
-const { getMCPManager, getFlowStateManager } = require('~/config');
 const { findToken, createToken, updateToken } = require('~/models');
+const { getMCPManager, getFlowStateManager } = require('~/config');
 const { getCachedTools } = require('./Config');
 const { getLogStores } = require('~/cache');
 
@@ -113,7 +114,8 @@ async function createMCPTool({ req, res, toolKey, provider: _provider }) {
   /** @type {LCTool} */
   const { description, parameters } = toolDefinition;
   const isGoogle = _provider === Providers.VERTEXAI || _provider === Providers.GOOGLE;
-  let schema = convertJsonSchemaToZod(parameters, {
+  const resolvedJsonSchema = resolveJsonSchemaRefs(parameters);
+  let schema = convertJsonSchemaToZod(resolvedJsonSchema, {
     allowEmptyObject: !isGoogle,
     transformOneOfAnyOf: true,
   });

api/typedefs.js

@@ -1074,7 +1074,7 @@
 
 /**
  * @exports JsonSchemaType
- * @typedef {import('librechat-data-provider').JsonSchemaType} JsonSchemaType
+ * @typedef {import('@librechat/api').JsonSchemaType} JsonSchemaType
  * @memberof typedefs
  */
 

packages/api/src/index.ts

@@ -2,6 +2,7 @@
 export * from './mcp/manager';
 export * from './mcp/oauth';
 export * from './mcp/auth';
+export * from './mcp/zod';
 /* Utilities */
 export * from './mcp/utils';
 export * from './utils';

packages/api/src/mcp/manager.ts

@@ -1,11 +1,12 @@
 import { logger } from '@librechat/data-schemas';
 import { CallToolResultSchema, ErrorCode, McpError } from '@modelcontextprotocol/sdk/types.js';
-import type { RequestOptions } from '@modelcontextprotocol/sdk/shared/protocol.js';
 import type { OAuthClientInformation } from '@modelcontextprotocol/sdk/shared/auth.js';
-import type { JsonSchemaType, TUser } from 'librechat-data-provider';
+import type { RequestOptions } from '@modelcontextprotocol/sdk/shared/protocol.js';
 import type { TokenMethods } from '@librechat/data-schemas';
-import type { FlowStateManager } from '~/flow/manager';
+import type { TUser } from 'librechat-data-provider';
 import type { MCPOAuthTokens, MCPOAuthFlowMetadata } from './oauth/types';
+import type { FlowStateManager } from '~/flow/manager';
+import type { JsonSchemaType } from '~/types/zod';
 import type { FlowMetadata } from '~/flow/types';
 import type * as t from './types';
 import { CONSTANTS, isSystemUserId } from './enum';
@@ -892,7 +893,7 @@ export class MCPManager {
         this.updateUserLastActivity(userId);
       }
       this.checkIdleConnections();
-      return formatToolContent(result, provider);
+      return formatToolContent(result as t.MCPToolCallResponse, provider);
     } catch (error) {
       // Log with context and re-throw or handle as needed
       logger.error(`${logPrefix}[${toolName}] Tool call failed`, error);

packages/api/src/mcp/types/index.ts

@@ -7,8 +7,9 @@ import {
   WebSocketOptionsSchema,
   StreamableHTTPOptionsSchema,
 } from 'librechat-data-provider';
-import type { JsonSchemaType, TPlugin } from 'librechat-data-provider';
 import type * as t from '@modelcontextprotocol/sdk/types.js';
+import type { TPlugin } from 'librechat-data-provider';
+import type { JsonSchemaType } from '~/types/zod';
 
 export type StdioOptions = z.infer<typeof StdioOptionsSchema>;
 export type WebSocketOptions = z.infer<typeof WebSocketOptionsSchema>;

packages/api/src/mcp/zod.spec.ts

@@ -1,8 +1,8 @@
 /* eslint-disable @typescript-eslint/no-explicit-any */
 // zod.spec.ts
 import { z } from 'zod';
-import { convertJsonSchemaToZod } from './zod';
+import type { JsonSchemaType } from '~/types';
-import type { JsonSchemaType } from './zod';
+import { resolveJsonSchemaRefs, convertJsonSchemaToZod } from './zod';
 
 describe('convertJsonSchemaToZod', () => {
   describe('primitive types', () => {
@@ -1083,4 +1083,403 @@ describe('convertJsonSchemaToZod', () => {
       expect(() => zodSchema?.parse(true)).toThrow();
     });
   });
+
+  describe('additionalProperties with anyOf/oneOf and allowEmptyObject', () => {
+    it('should handle anyOf with object containing only additionalProperties when allowEmptyObject is false', () => {
+      const schema: JsonSchemaType & { anyOf?: any } = {
+        type: 'object',
+        properties: {
+          filter: {
+            description: 'Filter field',
+            anyOf: [
+              {
+                type: 'object',
+                additionalProperties: {
+                  type: 'object',
+                  properties: {
+                    _icontains: { type: 'string' },
+                  },
+                },
+              },
+              {
+                type: 'null',
+              },
+            ],
+          } as JsonSchemaType & { anyOf?: any },
+        },
+      };
+
+      const zodSchema = convertJsonSchemaToZod(schema, {
+        allowEmptyObject: false,
+        transformOneOfAnyOf: true,
+      });
+
+      expect(zodSchema).toBeDefined();
+
+      const testData = {
+        filter: {
+          title: {
+            _icontains: 'Pirate',
+          },
+        },
+      };
+
+      const result = zodSchema?.parse(testData);
+      expect(result).toEqual(testData);
+      expect(result?.filter).toBeDefined();
+      expect(result?.filter?.title?._icontains).toBe('Pirate');
+    });
+
+    it('should not treat objects with additionalProperties as empty', () => {
+      const schema: JsonSchemaType = {
+        type: 'object',
+        additionalProperties: {
+          type: 'string',
+        },
+      };
+
+      const zodSchemaWithoutAllow = convertJsonSchemaToZod(schema, {
+        allowEmptyObject: false,
+      });
+
+      // Should not return undefined because it has additionalProperties
+      expect(zodSchemaWithoutAllow).toBeDefined();
+
+      const testData = {
+        customField: 'value',
+      };
+
+      expect(zodSchemaWithoutAllow?.parse(testData)).toEqual(testData);
+    });
+
+    it('should handle oneOf with object containing only additionalProperties', () => {
+      const schema: JsonSchemaType & { oneOf?: any } = {
+        type: 'object',
+        properties: {},
+        oneOf: [
+          {
+            type: 'object',
+            additionalProperties: true,
+          },
+          {
+            type: 'object',
+            properties: {
+              specificField: { type: 'string' },
+            },
+          },
+        ],
+      };
+
+      const zodSchema = convertJsonSchemaToZod(schema, {
+        allowEmptyObject: false,
+        transformOneOfAnyOf: true,
+      });
+
+      expect(zodSchema).toBeDefined();
+
+      // Test with additional properties
+      const testData1 = {
+        randomField: 'value',
+        anotherField: 123,
+      };
+
+      expect(zodSchema?.parse(testData1)).toEqual(testData1);
+
+      // Test with specific field
+      const testData2 = {
+        specificField: 'test',
+      };
+
+      expect(zodSchema?.parse(testData2)).toEqual(testData2);
+    });
+
+    it('should handle complex nested schema with $ref-like structure', () => {
+      const schema: JsonSchemaType & { anyOf?: any } = {
+        type: 'object',
+        properties: {
+          query: {
+            type: 'object',
+            properties: {
+              filter: {
+                description: 'Filter conditions',
+                anyOf: [
+                  {
+                    // This simulates a resolved $ref
+                    anyOf: [
+                      {
+                        type: 'object',
+                        properties: {
+                          _or: {
+                            type: 'array',
+                            items: { type: 'object' },
+                          },
+                        },
+                        required: ['_or'],
+                      },
+                      {
+                        type: 'object',
+                        additionalProperties: {
+                          anyOf: [
+                            {
+                              type: 'object',
+                              properties: {
+                                _icontains: { type: 'string' },
+                                _eq: { type: 'string' },
+                              },
+                            },
+                          ],
+                        },
+                      },
+                    ],
+                  },
+                  {
+                    type: 'null',
+                  },
+                ],
+              } as JsonSchemaType & { anyOf?: any },
+            },
+          },
+        },
+      };
+
+      const zodSchema = convertJsonSchemaToZod(schema, {
+        allowEmptyObject: false,
+        transformOneOfAnyOf: true,
+      });
+
+      expect(zodSchema).toBeDefined();
+
+      const testData = {
+        query: {
+          filter: {
+            title: {
+              _icontains: 'Pirate',
+            },
+          },
+        },
+      };
+
+      const result = zodSchema?.parse(testData);
+      expect(result).toEqual(testData);
+      expect(result?.query?.filter?.title?._icontains).toBe('Pirate');
+    });
+  });
+
+  describe('$ref resolution with resolveJsonSchemaRefs', () => {
+    it('should handle schemas with $ref references when resolved', () => {
+      const schemaWithRefs = {
+        type: 'object' as const,
+        properties: {
+          collection: {
+            type: 'string' as const,
+          },
+          query: {
+            type: 'object' as const,
+            properties: {
+              filter: {
+                anyOf: [{ $ref: '#/$defs/__schema0' }, { type: 'null' as const }],
+              },
+            },
+          },
+        },
+        required: ['collection', 'query'],
+        $defs: {
+          __schema0: {
+            anyOf: [
+              {
+                type: 'object' as const,
+                properties: {
+                  _or: {
+                    type: 'array' as const,
+                    items: { $ref: '#/$defs/__schema0' },
+                  },
+                },
+                required: ['_or'],
+              },
+              {
+                type: 'object' as const,
+                additionalProperties: {
+                  anyOf: [
+                    {
+                      type: 'object' as const,
+                      properties: {
+                        _eq: {
+                          anyOf: [
+                            { type: 'string' as const },
+                            { type: 'number' as const },
+                            { type: 'null' as const },
+                          ],
+                        },
+                      },
+                    },
+                  ],
+                },
+              },
+            ],
+          },
+        },
+      };
+
+      // First test without resolving refs - should not work properly
+      const zodSchemaUnresolved = convertJsonSchemaToZod(schemaWithRefs as any, {
+        allowEmptyObject: true,
+        transformOneOfAnyOf: true,
+      });
+
+      const testData = {
+        collection: 'posts',
+        query: {
+          filter: {
+            status: {
+              _eq: 'draft',
+            },
+          },
+        },
+      };
+
+      // Without resolving refs, the filter field won't work correctly
+      const resultUnresolved = zodSchemaUnresolved?.parse(testData);
+      expect(resultUnresolved?.query?.filter).toEqual({});
+
+      // Now resolve refs first
+      const resolvedSchema = resolveJsonSchemaRefs(schemaWithRefs);
+
+      // Verify refs were resolved
+      expect(resolvedSchema.properties?.query?.properties?.filter?.anyOf?.[0]).not.toHaveProperty(
+        '$ref',
+      );
+      expect(resolvedSchema.properties?.query?.properties?.filter?.anyOf?.[0]).toHaveProperty(
+        'anyOf',
+      );
+
+      const zodSchemaResolved = convertJsonSchemaToZod(resolvedSchema as any, {
+        allowEmptyObject: true,
+        transformOneOfAnyOf: true,
+      });
+
+      // With resolved refs, it should work correctly
+      const resultResolved = zodSchemaResolved?.parse(testData);
+      expect(resultResolved).toEqual(testData);
+      expect(resultResolved?.query?.filter?.status?._eq).toBe('draft');
+    });
+
+    it('should handle circular $ref references without infinite loops', () => {
+      const schemaWithCircularRefs = {
+        type: 'object' as const,
+        properties: {
+          node: { $ref: '#/$defs/TreeNode' },
+        },
+        $defs: {
+          TreeNode: {
+            type: 'object' as const,
+            properties: {
+              value: { type: 'string' as const },
+              children: {
+                type: 'array' as const,
+                items: { $ref: '#/$defs/TreeNode' },
+              },
+            },
+          },
+        },
+      };
+
+      // Should not throw or hang
+      const resolved = resolveJsonSchemaRefs(schemaWithCircularRefs);
+      expect(resolved).toBeDefined();
+
+      // The circular reference should be broken with a simple object schema
+      const zodSchema = convertJsonSchemaToZod(resolved as any, {
+        allowEmptyObject: true,
+        transformOneOfAnyOf: true,
+      });
+
+      expect(zodSchema).toBeDefined();
+
+      const testData = {
+        node: {
+          value: 'root',
+          children: [
+            {
+              value: 'child1',
+              children: [],
+            },
+          ],
+        },
+      };
+
+      expect(() => zodSchema?.parse(testData)).not.toThrow();
+    });
+
+    it('should handle various edge cases safely', () => {
+      // Test with null/undefined
+      expect(resolveJsonSchemaRefs(null as any)).toBeNull();
+      expect(resolveJsonSchemaRefs(undefined as any)).toBeUndefined();
+
+      // Test with non-object primitives
+      expect(resolveJsonSchemaRefs('string' as any)).toBe('string');
+      expect(resolveJsonSchemaRefs(42 as any)).toBe(42);
+      expect(resolveJsonSchemaRefs(true as any)).toBe(true);
+
+      // Test with arrays
+      const arrayInput = [{ type: 'string' }, { $ref: '#/def' }];
+      const arrayResult = resolveJsonSchemaRefs(arrayInput as any);
+      expect(Array.isArray(arrayResult)).toBe(true);
+      expect(arrayResult).toHaveLength(2);
+
+      // Test with schema that has no refs
+      const noRefSchema = {
+        type: 'object' as const,
+        properties: {
+          name: { type: 'string' as const },
+          nested: {
+            type: 'object' as const,
+            properties: {
+              value: { type: 'number' as const },
+            },
+          },
+        },
+      };
+
+      const resolvedNoRef = resolveJsonSchemaRefs(noRefSchema);
+      expect(resolvedNoRef).toEqual(noRefSchema);
+
+      // Test with invalid ref (non-existent)
+      const invalidRefSchema = {
+        type: 'object' as const,
+        properties: {
+          item: { $ref: '#/$defs/nonExistent' },
+        },
+        $defs: {
+          other: { type: 'string' as const },
+        },
+      };
+
+      const resolvedInvalid = resolveJsonSchemaRefs(invalidRefSchema);
+      // Invalid refs should be preserved as-is
+      expect(resolvedInvalid.properties?.item?.$ref).toBe('#/$defs/nonExistent');
+
+      // Test with empty object
+      expect(resolveJsonSchemaRefs({})).toEqual({});
+
+      // Test with schema containing special JSON Schema keywords
+      const schemaWithKeywords = {
+        type: 'object' as const,
+        properties: {
+          value: {
+            type: 'string' as const,
+            minLength: 5,
+            maxLength: 10,
+            pattern: '^[A-Z]',
+          },
+        },
+        additionalProperties: false,
+        minProperties: 1,
+      };
+
+      const resolvedKeywords = resolveJsonSchemaRefs(schemaWithKeywords);
+      expect(resolvedKeywords).toEqual(schemaWithKeywords);
+      expect(resolvedKeywords.properties?.value?.minLength).toBe(5);
+      expect(resolvedKeywords.additionalProperties).toBe(false);
+    });
+  });
 });

packages/api/src/mcp/zod.ts

@@ -1,30 +1,16 @@
 import { z } from 'zod';
-
+import type { JsonSchemaType, ConvertJsonSchemaToZodOptions } from '~/types';
-export type JsonSchemaType = {
-  type: 'string' | 'number' | 'boolean' | 'array' | 'object';
-  enum?: string[];
-  items?: JsonSchemaType;
-  properties?: Record<string, JsonSchemaType>;
-  required?: string[];
-  description?: string;
-  additionalProperties?: boolean | JsonSchemaType;
-};
 
 function isEmptyObjectSchema(jsonSchema?: JsonSchemaType): boolean {
   return (
     jsonSchema != null &&
     typeof jsonSchema === 'object' &&
     jsonSchema.type === 'object' &&
-    (jsonSchema.properties == null || Object.keys(jsonSchema.properties).length === 0)
+    (jsonSchema.properties == null || Object.keys(jsonSchema.properties).length === 0) &&
+    !jsonSchema.additionalProperties // Don't treat objects with additionalProperties as empty
   );
 }
 
-type ConvertJsonSchemaToZodOptions = {
-  allowEmptyObject?: boolean;
-  dropFields?: string[];
-  transformOneOfAnyOf?: boolean;
-};
-
 function dropSchemaFields(
   schema: JsonSchemaType | undefined,
   fields: string[],
@@ -98,6 +84,10 @@ function convertToZodUnion(
           return convertJsonSchemaToZod(objSchema, options);
         }
 
+        return convertJsonSchemaToZod(objSchema, options);
+      } else if (!subSchema.type && subSchema.additionalProperties) {
+        // It's likely an object schema with additionalProperties
+        const objSchema = { ...subSchema, type: 'object' } as JsonSchemaType;
         return convertJsonSchemaToZod(objSchema, options);
       } else if (!subSchema.type && subSchema.items) {
         // It's likely an array schema
@@ -182,6 +172,82 @@ function convertToZodUnion(
   return zodSchemas[0];
 }
 
+/**
+ * Helper function to resolve $ref references
+ * @param schema - The schema to resolve
+ * @param definitions - The definitions to use
+ * @param visited - The set of visited references
+ * @returns The resolved schema
+ */
+export function resolveJsonSchemaRefs<T extends Record<string, unknown>>(
+  schema: T,
+  definitions?: Record<string, unknown>,
+  visited = new Set<string>(),
+): T {
+  // Handle null, undefined, or non-object values first
+  if (!schema || typeof schema !== 'object') {
+    return schema;
+  }
+
+  // If no definitions provided, try to extract from schema.$defs or schema.definitions
+  if (!definitions) {
+    definitions = (schema.$defs || schema.definitions) as Record<string, unknown>;
+  }
+
+  // Handle arrays
+  if (Array.isArray(schema)) {
+    return schema.map((item) => resolveJsonSchemaRefs(item, definitions, visited)) as unknown as T;
+  }
+
+  // Handle objects
+  const result: Record<string, unknown> = {};
+
+  for (const [key, value] of Object.entries(schema)) {
+    // Skip $defs/definitions at root level to avoid infinite recursion
+    if ((key === '$defs' || key === 'definitions') && !visited.size) {
+      result[key] = value;
+      continue;
+    }
+
+    // Handle $ref
+    if (key === '$ref' && typeof value === 'string') {
+      // Prevent circular references
+      if (visited.has(value)) {
+        // Return a simple schema to break the cycle
+        return { type: 'object' } as unknown as T;
+      }
+
+      // Extract the reference path
+      const refPath = value.replace(/^#\/(\$defs|definitions)\//, '');
+      const resolved = definitions?.[refPath];
+
+      if (resolved) {
+        visited.add(value);
+        const resolvedSchema = resolveJsonSchemaRefs(
+          resolved as Record<string, unknown>,
+          definitions,
+          visited,
+        );
+        visited.delete(value);
+
+        // Merge the resolved schema into the result
+        Object.assign(result, resolvedSchema);
+      } else {
+        // If we can't resolve the reference, keep it as is
+        result[key] = value;
+      }
+    } else if (value && typeof value === 'object') {
+      // Recursively resolve nested objects/arrays
+      result[key] = resolveJsonSchemaRefs(value as Record<string, unknown>, definitions, visited);
+    } else {
+      // Copy primitive values as is
+      result[key] = value;
+    }
+  }
+
+  return result as T;
+}
+
 export function convertJsonSchemaToZod(
   schema: JsonSchemaType & Record<string, unknown>,
   options: ConvertJsonSchemaToZodOptions = {},

packages/api/src/types/index.ts

@@ -4,3 +4,4 @@ export * from './google';
 export * from './mistral';
 export * from './openai';
 export * from './run';
+export * from './zod';

packages/api/src/types/zod.ts

@@ -0,0 +1,15 @@
+export type JsonSchemaType = {
+  type: 'string' | 'number' | 'boolean' | 'array' | 'object';
+  enum?: string[];
+  items?: JsonSchemaType;
+  properties?: Record<string, JsonSchemaType>;
+  required?: string[];
+  description?: string;
+  additionalProperties?: boolean | JsonSchemaType;
+};
+
+export type ConvertJsonSchemaToZodOptions = {
+  allowEmptyObject?: boolean;
+  dropFields?: string[];
+  transformOneOfAnyOf?: boolean;
+};

packages/data-provider/src/index.ts

@@ -8,7 +8,6 @@ export * from './artifacts';
 /* schema helpers  */
 export * from './parsers';
 export * from './ocr';
-export * from './zod';
 /* custom/dynamic configurations  */
 export * from './generate';
 export * from './models';