fix(Token Splitter Node): Prevent tiktoken blocking on repetitive content (#16769)

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

@@ -258,3 +258,50 @@ export function unwrapNestedOutput(output: Record<string, unknown>): Record<stri
 export function nodeNameToToolName(node: INode): string {
 	return node.name.replace(/[\s.?!=+#@&*()[\]{}:;,<>\/\\'"^%$]/g, '_').replace(/_+/g, '_');
 }
+
+/**
+ * Detects if a text contains a character that repeats sequentially for a specified threshold.
+ * This is used to prevent performance issues with tiktoken on highly repetitive content.
+ * @param text The text to check
+ * @param threshold The minimum number of sequential repeats to detect (default: 1000)
+ * @returns true if a character repeats sequentially for at least the threshold amount
+ */
+export function hasLongSequentialRepeat(text: string, threshold = 1000): boolean {
+	try {
+		// Validate inputs
+		if (
+			text === null ||
+			typeof text !== 'string' ||
+			text.length === 0 ||
+			threshold <= 0 ||
+			text.length < threshold
+		) {
+			return false;
+		}
+		// Use string iterator to avoid creating array copy (memory efficient)
+		const iterator = text[Symbol.iterator]();
+		let prev = iterator.next();
+
+		if (prev.done) {
+			return false;
+		}
+
+		let count = 1;
+		for (const char of iterator) {
+			if (char === prev.value) {
+				count++;
+				if (count >= threshold) {
+					return true;
+				}
+			} else {
+				count = 1;
+				prev = { value: char, done: false };
+			}
+		}
+
+		return false;
+	} catch (error) {
+		// On any error, return false to allow normal processing
+		return false;
+	}
+}