How do I redirect a user when an external API calls a webhook in NextJS

Question

I'm using NextJS with the pages router. I have a form where a user can start a process that takes ~30 seconds. The processing is done by an external API that I have no control over. The external API calls a webhook when the processing is completed. I want to redirect the user from the form page to a results page showcasing the results.

I have a database where I'm storing the user id along with the corresponding process id and it can be retrieved in the webhook handler.

import { NextApiRequest, NextApiResponse } from "next";

export default async function handler(
    req: NextApiRequest,
    res: NextApiResponse
) {
    const query = req.query;
    const user_id = query.user_id;
    const generation_id = query.generation_id;
    const original_image = query.original_image;
    const webhookData = req.body;
    console.log("Received webhook:", webhookData);
    res.status(200).end();
}

The workflow works as:

• User 1 clicks a button on form page
• Process starts in background in an external API
• Process completes
• My webhook handler is called along with the user's ID

How do I redirect User 1 to the results page from here?

I'm using the Replicate API to generate images from an SDXL model.

I tried sending a redirect response in the webhook handler

import { NextApiRequest, NextApiResponse } from "next";

export default async function handler(
    req: NextApiRequest,
    res: NextApiResponse
) {
    const query = req.query;
    const user_id = query.user_id;
    const generation_id = query.generation_id;
    const original_image = query.original_image;
    const webhookData = req.body;
    console.log("Received webhook:", webhookData);
    res.redirect("/results");
}

but that response obviously went to the external API, not the user who clicked the button.

Answer 1

If I understand correctly you are using the predictions.create to create the prediction and then add a webhook url.

Webhooks are meant to be used as a separate operation from the current user session, its not linked to your user current session. What you can do with the webhook for example, is to send an email to the user with the results.

But If I am correct, then the API will respond the prediction ID immediately, which you can use to call the replicate API for status.

From the docs: In the case of success, output will be an object containing the output of the model. Any files will be represented as HTTPS URLs.

I will add the link to the replicate docs: https://replicate.com/docs/reference/http#predictions.get