Convert CoreMessage to useChat Message for Persisting User Chats

[sullyo]

Feature Description

It would be great to have a utility function or method to convert a CoreMessage (server-side format) to the format used by useChat messages for easier loading and persisting of user chats.

Currently, we can convert messages to CoreMessage on the server-side, but there's no direct way to convert them back to the format used by useChat. This creates complexity when a user has tool calls, closes the chat, and returns later, as all messages need to be loaded again. A straightforward utility would streamline this process, especially for reloading conversations.

Right now custom logic is required to load and display past messages in useChat when a user resumes a chat session.

Use Case

Save chat messages for the user.
Load all user messages, including tool calls, on returning to a chat session.

Additional context

No response

[yamz8]

any updates here?

[ingara]

@sullyo have you already implemented this logic on your end? If so, would you be open to sharing it? We’re at a point where we’ll need to develop something similar soon.

[danielzohar]

Here's a simple implementation:

import { CoreMessage, generateId, Message } from "ai";

function createMessage(role: "user" | "assistant", content: string): Message {
  const res: Message = {
    id: generateId(),
    role,
    content,
    createdAt: new Date(),
  };
  return res;
}

/**
 * Converts CoreMessages to Messages
 * Should be provided by the `ai` package in the future
 * @see https:/vercel/ai/issues/3161
 */
export function convertToMessages(coreMessages: CoreMessage[]): Message[] {
  return coreMessages.flatMap((m) => {
    if (m.role !== "user" && m.role !== "assistant") return [];
    if (m.content === null) return [];

    if (typeof m.content === "string") {
      return [createMessage(m.role, m.content)];
    }

    const res = [];
    for (const c of m.content) {
      if (c.type === "text") {
        res.push(createMessage(m.role, c.text));
      }
    }
    return res;
  });
}

[jeremyphilemon]

Hey @sullyo, thanks for the feature request – this sounds like a great utility function to include!

We just implemented this in the chatbot template here and definitely can see it useful for restoring conversations from history

@ingara would love for you to try it out and share feedback with us before we add it to the sdk