add message truncation utility for gen_ai byte limits

Author: naaa760

packages/core/src/utils/ai/messageTruncation.ts

@@ -0,0 +1,37 @@
+export function getByteSize(str: string): number {
+  return new TextEncoder().encode(str).length;
+}
+
+export function truncateMessagesByBytes(messages: unknown[], maxBytes: number): unknown[] {
+  if (!Array.isArray(messages) || messages.length === 0) {
+    return messages;
+  }
+
+  const messagesJson = JSON.stringify(messages);
+  const totalBytes = getByteSize(messagesJson);
+
+  if (totalBytes <= maxBytes) {
+    return messages;
+  }
+
+  let truncatedMessages = [...messages];
+
+  while (truncatedMessages.length > 0) {
+    const truncatedJson = JSON.stringify(truncatedMessages);
+    const truncatedBytes = getByteSize(truncatedJson);
+
+    if (truncatedBytes <= maxBytes) {
+      break;
+    }
+
+    truncatedMessages.shift();
+  }
+
+  return truncatedMessages;
+}
+
+export const DEFAULT_GEN_AI_MESSAGES_BYTE_LIMIT = 100000;
+
+export function truncateGenAiMessages(messages: unknown[]): unknown[] {
+  return truncateMessagesByBytes(messages, DEFAULT_GEN_AI_MESSAGES_BYTE_LIMIT);
+}