Observe fixed response headers

Prediction

The response content can stay small while fields tell a recipient how the representation should be handled or constrained. HEAD should retain relevant metadata without returning the text content.

Controlled observation

Compare a download preset with a security preset, then request the security preset with HEAD. The Worker exposes only these reviewed teaching fields to the HTTPClarity origin through its CORS response contract.

Explanation

Response fields are metadata and control information, not decorations on the body. Content-Disposition suggests presentation or download handling; Content-Security-Policy and X-Frame-Options constrain selected browser behaviors. A real deployment needs a policy designed for its own content and threat model.

HTTP/1.1 200 OK
Content-Type: text/plain; charset=utf-8
Content-Disposition: attachment; filename="httpclarity-demo.txt"
X-Lab-Preset: download

Fixed download response-field preset.

'curl' '--include' '--request' 'GET' 'https://lab.httpclarity.com/v1/headers/download'

const response = await fetch("https://lab.httpclarity.com/v1/headers/download", {
  "method": "GET"
});
console.log(response.status, await response.text());

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