echo-policy-nested.html

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<!DOCTYPE html>

<body>

<script>

// This document will contain an iframe which will either host echo-policy.py,

// or will host another copy of this document, with the nesting level reduced

// by one. This way, an arbitrary nesting depth can be achieved, with the

// final inner-most frame reporting back the advertised required policy.

// The 'id' URL parameter will be passed to the nested document.

// The 'level' URL paramater will be reduced by 1 and passed to the nested

// document if it was at least 1. (If it was 0, then echo-policy.py will be

// nested instead, and the level parameter will not be passed.)

// This document is served with a Document Policy header that should satisfy

// any requests that include a required policy for the

// 'lossless-images-max-bpp' feature.

const params = new URLSearchParams(window.location.search);

const id = params.get('id');

const level = params.get('level');

const iframe = document.createElement('iframe');

var hostname;

if (level >= 1) {

  params.set('level',level-1);

  hostname = document.location.pathname + "?" + params.toString();

} else {

  params.delete('level');

  hostname = "/document-policy/echo-policy.py?" + params.toString();

iframe.src = hostname;

document.body.appendChild(iframe);

</script>