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

packages/@n8n/nodes-langchain/utils/output_parsers/N8nItemListOutputParser.ts

@@ -0,0 +1,55 @@
+import { BaseOutputParser, OutputParserException } from '@langchain/core/output_parsers';
+
+export class N8nItemListOutputParser extends BaseOutputParser<string[]> {
+	lc_namespace = ['n8n-nodes-langchain', 'output_parsers', 'list_items'];
+
+	private numberOfItems: number = 3;
+
+	private separator: string;
+
+	constructor(options: { numberOfItems?: number; separator?: string }) {
+		super();
+		if (options.numberOfItems && options.numberOfItems > 0) {
+			this.numberOfItems = options.numberOfItems;
+		}
+		this.separator = options.separator ?? '\\n';
+		if (this.separator === '\\n') {
+			this.separator = '\n';
+		}
+	}
+
+	async parse(text: string): Promise<string[]> {
+		const response = text
+			.split(this.separator)
+			.map((item) => item.trim())
+			.filter((item) => item);
+
+		if (this.numberOfItems && response.length < this.numberOfItems) {
+			// Only error if to few items got returned, if there are to many we can autofix it
+			throw new OutputParserException(
+				`Wrong number of items returned. Expected ${this.numberOfItems} items but got ${response.length} items instead.`,
+			);
+		}
+
+		return response.slice(0, this.numberOfItems);
+	}
+
+	getFormatInstructions(): string {
+		const instructions = `Your response should be a list of ${
+			this.numberOfItems ? this.numberOfItems + ' ' : ''
+		}items separated by`;
+
+		const numberOfExamples = this.numberOfItems;
+
+		const examples: string[] = [];
+		for (let i = 1; i <= numberOfExamples; i++) {
+			examples.push(`item${i}`);
+		}
+
+		return `${instructions} "${this.separator}" (for example: "${examples.join(this.separator)}")`;
+	}
+
+	getSchema() {
+		return;
+	}
+}