feat(Structured Output Parser Node): Refactor Output Parsers and Improve Error Handling (#11148)

packages/@n8n/nodes-langchain/utils/output_parsers/N8nOutputFixingParser.ts

@@ -0,0 +1,95 @@
+import type { Callbacks } from '@langchain/core/callbacks/manager';
+import type { BaseLanguageModel } from '@langchain/core/language_models/base';
+import type { AIMessage } from '@langchain/core/messages';
+import { BaseOutputParser } from '@langchain/core/output_parsers';
+import type { IExecuteFunctions } from 'n8n-workflow';
+import { NodeConnectionType } from 'n8n-workflow';
+
+import type { N8nStructuredOutputParser } from './N8nStructuredOutputParser';
+import { NAIVE_FIX_PROMPT } from './prompt';
+import { logAiEvent } from '../helpers';
+
+export class N8nOutputFixingParser extends BaseOutputParser {
+	private context: IExecuteFunctions;
+
+	private model: BaseLanguageModel;
+
+	private outputParser: N8nStructuredOutputParser;
+
+	lc_namespace = ['langchain', 'output_parsers', 'fix'];
+
+	constructor(
+		context: IExecuteFunctions,
+		model: BaseLanguageModel,
+		outputParser: N8nStructuredOutputParser,
+	) {
+		super();
+		this.context = context;
+		this.model = model;
+		this.outputParser = outputParser;
+	}
+
+	getRetryChain() {
+		return NAIVE_FIX_PROMPT.pipe(this.model);
+	}
+
+	/**
+	 * Attempts to parse the completion string using the output parser.
+	 * If the initial parse fails, it tries to fix the output using a retry chain.
+	 * @param completion The string to be parsed
+	 * @returns The parsed response
+	 * @throws Error if both parsing attempts fail
+	 */
+	async parse(completion: string, callbacks?: Callbacks) {
+		const { index } = this.context.addInputData(NodeConnectionType.AiOutputParser, [
+			[{ json: { action: 'parse', text: completion } }],
+		]);
+
+		try {
+			// First attempt to parse the completion
+			const response = await this.outputParser.parse(completion, callbacks, (e) => e);
+			void logAiEvent(this.context, 'ai-output-parsed', { text: completion, response });
+
+			this.context.addOutputData(NodeConnectionType.AiOutputParser, index, [
+				[{ json: { action: 'parse', response } }],
+			]);
+
+			return response;
+		} catch (error) {
+			try {
+				// Second attempt: use retry chain to fix the output
+				const result = (await this.getRetryChain().invoke({
+					completion,
+					error,
+					instructions: this.getFormatInstructions(),
+				})) as AIMessage;
+
+				const resultText = result.content.toString();
+				const parsed = await this.outputParser.parse(resultText, callbacks);
+
+				// Add the successfully parsed output to the context
+				this.context.addOutputData(NodeConnectionType.AiOutputParser, index, [
+					[{ json: { action: 'parse', response: parsed } }],
+				]);
+
+				return parsed;
+			} catch (autoParseError) {
+				// If both attempts fail, add the error to the output and throw
+				this.context.addOutputData(NodeConnectionType.AiOutputParser, index, autoParseError);
+				throw autoParseError;
+			}
+		}
+	}
+
+	/**
+	 * Method to get the format instructions for the parser.
+	 * @returns The format instructions for the parser.
+	 */
+	getFormatInstructions() {
+		return this.outputParser.getFormatInstructions();
+	}
+
+	getSchema() {
+		return this.outputParser.schema;
+	}
+}