"Faster Delivery for Faster Connections: The Role of Downlink in HTTP"

• Server Response
  With this information, the server can adjust the content it sends back to the user. For example, the server might send high-resolution images for users with fast connections and lower-resolution ones for users with slower connections.

• Client Hint
  The Downlink header is a way for the browser to tell the server about the user's estimated internet download speed. This speed is indicated in Megabits per second (Mbps).

Technical details

• The Downlink header value is rounded to the nearest 25 kilobits per second (kbps) to prevent uniquely identifying a user's connection (fingerprinting).

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Scenario
A website displays product images. The server can use the Downlink value to deliver different sized images based on the user's connection speed.

Pseudo-code (server-side)

// Assuming a templating language

if (request.headers.has('Downlink')) {
  let downlinkSpeed = parseInt(request.headers.get('Downlink'));

  if (downlinkSpeed > 100) { // High speed connection (arbitrary threshold)
    // Serve high-resolution image
    image_url = "/images/product_high_res.jpg";
  } else {
    // Serve low-resolution image
    image_url = "/images/product_low_res.jpg";
  }
} else {
  // Default image (optional)
  image_url = "/images/product_default.jpg";
}

// Use the image_url variable in your HTML template
<img src="{{ image_url }}">

This is a simplified example, but it demonstrates how the server can check for the Downlink header and adjust content delivery accordingly.

• The Downlink value might not always be available, so you'd likely want to have a default behavior.
• This is pseudo-code, the actual implementation will vary depending on your server-side language and framework.

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1. User-Agent Header
   The browser sends a "User-Agent" header that identifies the browser and its version. While not as precise as Downlink, you can use patterns in the User-Agent string to make educated guesses about the user's device and potentially their internet speed. This approach is less accurate and might become obsolete as browsers become more standardized.

2. JavaScript Detection
   You can write client-side JavaScript code to estimate the user's internet speed. Libraries like Perceived Bandwidth Estimation [invalid URL removed] can help with this. This approach requires user interaction and might not be suitable for all situations.

3. Server-side Throttling
   Your server can send the content initially and then throttle the download speed based on pre-defined settings. This is less dynamic but ensures a consistent user experience.

4. Content Negotiation
   The server can send multiple versions of the content with varying quality levels. The browser can then request the most suitable version based on its capabilities. This requires creating and managing different content versions but avoids relying on client hints.

The best approach depends on your specific needs and priorities. Consider factors like:

• Development Effort
  How much effort are you willing to invest in implementing the solution?
• User Experience
  Do you want a completely seamless experience or are you comfortable with some initial loading time?
• Accuracy
  How important is it to have a precise measurement of the user's internet speed?