Using navigator.permissions.query for Local Network Access in Chrome

Local network access in Chrome has undergone significant changes with the introduction of stricter security policies. Managing permissions effectively is now vital for anyone building web applications that require interactions with local devices or private networks. This blog post delves into the navigator.permissions.query API and explains how to use it to check and manage Chrome’s local-network-access permissions for your applications.

Why Does Chrome Restrict Local Network Access?

Chrome introduced local-network-access restrictions to mitigate vulnerabilities caused by unsecured local network requests. These policies protect users from potential abuses like DNS rebinding attacks, where attackers can inject malicious scripts to target devices on a user’s network.

To adapt to these changes, Chrome requires explicit permission from users before allowing web apps to access local network endpoints. The navigator.permissions.query API empowers developers to programmatically check the permission status, respond appropriately, and guide users through enabling permissions.

Introduction to navigator.permissions.query

What Is It?

The navigator.permissions.query API is a browser API that allows developers to query the current state of permissions for specific browser features, such as geolocation, notifications, or local network access. For local network access, the permission name is local-network-access.

Why Use It?

By leveraging this API, you can:

Detect whether the user has granted, denied, or not yet been prompted for the local-network-access permission.
Offer custom UI or messaging based on the user’s permission state.
Improve user experience by guiding them through granting permissions in a seamless way.

Implementation: Checking Local Network Permissions with Code

Let’s dive into how to use navigator.permissions.query to check the status of local network access.

Step 1: Query the Permission

The first step is querying the permission state. Use the following code:

navigator.permissions.query({ name: "local-network-access" })
  .then(result => {
    console.log(`LNA Permission State: ${result.state}`);
    if (result.state === "granted") {
      console.log("Local Network Access Permission granted. Proceed with API requests.");
    } else if (result.state === "prompt") {
      console.log("Permission is in prompt state. A user action may be required.");
    } else if (result.state === "denied") {
      console.log("Permission denied. Provide additional context or instructions for the user.");
    }
  })
  .catch(error => {
    console.error("Failed to query the permission:", error);
  });

What to Expect?

granted: The browser will allow requests to local networks.
prompt: The user will be prompted to grant or deny the permission.
denied: The browser will block local network requests.

Adding Fallbacks for Denied or Prompt States

When users deny the permission or are yet to be prompted, it’s important to provide clear guidance. Below is an extended implementation:

function checkLocalNetworkAccessPermission() {
  navigator.permissions.query({ name: "local-network-access" })
    .then(result => {
      document.querySelector(".permission-status").innerText = `Permission State: ${result.state}`;
      
      switch (result.state) {
        case "granted":
          authorizeLocalRequests();
          break;

        case "prompt":
          showUserGuide("Allow access to local networks via the browser prompt.");
          break;

        case "denied":
          showFallbackUI("Access denied. Please allow local network access in Chrome settings.");
          break;
      }
    })
    .catch(error => {
      console.error("Permission query error:", error);
    });
}

function authorizeLocalRequests() {
  console.log("You can now make requests to local network endpoints.");
  // Add your local network API logic here
}

function showUserGuide(message) {
  console.log(message);
  // Display visual guide to inform the user (optional).
}

function showFallbackUI(message) {
  console.log(message);
  // Optionally render fallback content or UI.
}

checkLocalNetworkAccessPermission();

This snippet guides users through various permission states and handles each gracefully.

Best Practices for Local Network Permissions

1. Always Provide Context

Explain why your application needs local network access. Use simple but precise messaging to assure users that their security won’t be compromised.

2. Handle Errors Gracefully

The permission query might fail due to browser bugs or restrictions. Always handle these errors in your code to avoid a broken user experience.

try {
  // Permission handling code here
} catch (error) {
  console.error("Unexpected error querying permission:", error.message);
}

3. Preempt Permission States

If the state is prompt, inform users what to expect. Show UI context, such as instructions to click "Allow."

4. Respect Privacy

Avoid nagging users to grant permissions repeatedly if they’ve denied them. Focus on providing alternative experiences or additional explanations instead.

Conclusion: Empowering Applications with Permissions

Chrome’s restrictions on local network access improve security for users but require developers to adapt their applications to remain functional. The navigator.permissions.query API is a powerful tool to help navigate these new restrictions. By checking permissions programmatically, you can guide users through permission flows, fallback gracefully in denied cases, and ultimately ensure smooth local network interactions.

By implementing best practices and understanding how permission states impact the user experience, developers can design robust and secure applications that thrive even under Chrome’s enhanced security measures.