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I built a nextjs app, it is an image generation platform with AI, I want to limit signed in users to only send one image generation request at a time, so I don't want them to open the dashboard from multiple tabs and send simultaneous requests, how can I implement that?

To prevent users from sending multiple image generation requests simultaneously, you can implement a combination of client-side and server-side checks. Here's a suggested approach:

Client-side: Use localStorage or sessionStorage to store a flag indicating whether a request is in progress.

Server-side: Implement a rate-limiting middleware to limit requests per user.

Step 1: Client-side flag

In your Next.js app, you can use localStorage or sessionStorage to store a flag when a user initiates an image generation request. This flag will help you determine if there's already a request in progress.

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// When the user submits a request
function handleRequestSubmission() {
  // Check if there's already a request in progress
  if (localStorage.getItem('requestInProgress') === 'true') {
    alert('You already have an image generation request in progress. Please wait until it completes.');
    return;
  }

  // Set the flag and send the request
  localStorage.setItem('requestInProgress', 'true');
  sendImageGenerationRequest();
}

// When the request is completed
function onRequestCompleted() {
  localStorage.removeItem('requestInProgress');
}
Step 2: Server-side rate limiting

To ensure users can't bypass the client-side restrictions by sending requests directly to the API, you should implement rate limiting on the server-side. You can use a package like express-rate-limit to limit requests per user.

Install the package: npm install express-rate-limit

Set up rate limiting in your API:

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const rateLimit = require('express-rate-limit');

// Create a rate limiter with custom options
const imageGenerationLimiter = rateLimit({
  windowMs: 60 * 1000, // 1 minute window
  max: 1, // Limit each user to 1 request per windowMs
  message: 'You can only send one image generation request at a time. Please wait.',
});

// Apply the rate limiter to your API route
app.post('/api/generate-image', imageGenerationLimiter, async (req, res) => {
  // Your image generation logic here
});
This approach combines both client-side and server-side checks to ensure that users can only send one image generation request at a time. Remember to adjust the rate limiting settings according to your desired limits and infrastructure capacity.