fix(OpenAI Node): Limit chat history to context window when using memory (#13137)

packages/@n8n/nodes-langchain/nodes/vendors/OpenAi/actions/assistant/message.operation.ts

@@ -22,7 +22,7 @@ import { promptTypeOptions } from '@utils/descriptions';
 import { getConnectedTools } from '@utils/helpers';
 import { getTracingConfig } from '@utils/tracing';
 
-import { formatToOpenAIAssistantTool } from '../../helpers/utils';
+import { formatToOpenAIAssistantTool, getChatMessages } from '../../helpers/utils';
 import { assistantRLC } from '../descriptions';
 
 const properties: INodeProperties[] = [
@@ -252,7 +252,7 @@ export async function execute(this: IExecuteFunctions, i: number): Promise<INode
 	};
 	let thread: OpenAIClient.Beta.Threads.Thread;
 	if (memory) {
-		const chatMessages = await memory.chatHistory.getMessages();
+		const chatMessages = await getChatMessages(memory);
 
 		// Construct a new thread from the chat history to map the memory
 		if (chatMessages.length) {

packages/@n8n/nodes-langchain/nodes/vendors/OpenAi/helpers/utils.ts

@@ -1,5 +1,7 @@
+import type { BaseMessage } from '@langchain/core/messages';
 import type { StructuredTool } from '@langchain/core/tools';
 import type { OpenAIClient } from '@langchain/openai';
+import type { BufferWindowMemory } from 'langchain/memory';
 import { zodToJsonSchema } from 'zod-to-json-schema';
 
 // Copied from langchain(`langchain/src/tools/convert_to_openai.ts`)
@@ -43,3 +45,7 @@ export function formatToOpenAIAssistantTool(tool: StructuredTool): OpenAIClient.
 		},
 	};
 }
+
+export async function getChatMessages(memory: BufferWindowMemory): Promise<BaseMessage[]> {
+	return (await memory.loadMemoryVariables({}))[memory.memoryKey] as BaseMessage[];
+}

packages/@n8n/nodes-langchain/nodes/vendors/OpenAi/test/utils.test.ts

@@ -0,0 +1,46 @@
+import { AIMessage, HumanMessage } from '@langchain/core/messages';
+import { BufferWindowMemory } from 'langchain/memory';
+
+import { getChatMessages } from '../helpers/utils';
+
+describe('OpenAI message history', () => {
+	it('should only get a limited number of messages', async () => {
+		const memory = new BufferWindowMemory({
+			returnMessages: true,
+			k: 2,
+		});
+		expect(await getChatMessages(memory)).toEqual([]);
+
+		await memory.saveContext(
+			[new HumanMessage({ content: 'human 1' })],
+			[new AIMessage({ content: 'ai 1' })],
+		);
+		// `k` means turns, but `getChatMessages` returns messages, so a Human and an AI message.
+		expect((await getChatMessages(memory)).length).toEqual(2);
+
+		await memory.saveContext(
+			[new HumanMessage({ content: 'human 2' })],
+			[new AIMessage({ content: 'ai 2' })],
+		);
+		expect((await getChatMessages(memory)).length).toEqual(4);
+		expect((await getChatMessages(memory)).map((msg) => msg.content)).toEqual([
+			'human 1',
+			'ai 1',
+			'human 2',
+			'ai 2',
+		]);
+
+		// We expect this to be trimmed...
+		await memory.saveContext(
+			[new HumanMessage({ content: 'human 3' })],
+			[new AIMessage({ content: 'ai 3' })],
+		);
+		expect((await getChatMessages(memory)).length).toEqual(4);
+		expect((await getChatMessages(memory)).map((msg) => msg.content)).toEqual([
+			'human 2',
+			'ai 2',
+			'human 3',
+			'ai 3',
+		]);
+	});
+});