Observe compression negotiation

Prediction

The server can select gzip when acceptable and identity otherwise, while Vary: Accept-Encoding tells caches which request field affected selection.

Controlled observation

Choose identity or gzip and use the generated cURL example to inspect the response fields. The Lab deliberately does not calculate or display compressed transfer bytes.

Explanation

Content-Encoding describes coding applied to the representation. Browser APIs normally expose decoded content, so displayed text length is not wire transfer size.

Cloudflare edge boundary

Cloudflare normally replaces the request’s visible Accept-Encoding field before it reaches a Worker and exposes the client value separately when available. This exercise therefore supports only the two generated presets. It is not an oracle for arbitrary quality-value combinations.

When the original field is available, the handler honors q=0 and returns 406 Not Acceptable if both identity and gzip are forbidden. The response also uses Cache-Control: no-transform so an intermediary does not silently turn the identity demonstration into a different content coding.

HTTP/1.1 200 OK
Content-Type: text/plain; charset=utf-8
Vary: Accept-Encoding
X-Lab-Content-Coding: identity

HTTP clarity makes negotiated representations observable. …

'curl' '--include' '--compressed' '--request' 'GET' '--header' 'Accept-Encoding: identity' 'https://lab.httpclarity.com/v1/compression'

// Browser Fetch cannot reproduce this wire-level request.
// Use the cURL or PHP example instead.

<?php
$options = ['http' => [
    'method' => 'GET',
    'ignore_errors' => true,
    'header' => 'Accept-Encoding: identity',
]];
$context = stream_context_create($options);
$body = file_get_contents('https://lab.httpclarity.com/v1/compression', false, $context);
var_dump($http_response_header, $body);