Cloudflare ESI worker / TypeError: Body has already been used - cloudflare

Question

I'm trying to use a CloudFlare worker to manage my backend ESI fragments but i get an error:
Uncaught (in promise) TypeError: Body has already been used. It can only be used once. Use tee() first if you need to read it twice.
Uncaught (in response) TypeError: Body has already been used. It can only be used once. Use tee() first if you need to read it twice.
I don't find where the body has already been used
The process is:
get a response with the parts
Transform the body by replacing parts fragments with sub Backend calls (streamTransformBody function)
return the response
addEventListener("fetch", event => {
event.respondWith(handleRequest(event.request))
});
const esiHeaders = {
"user-agent": "cloudflare"
}
async function handleRequest(request) {
// get cookies from the request
if(cookie = request.headers.get("Cookie")) {
esiHeaders["Cookie"] = cookie
console.log(cookie)
}
// Clone the request so that it's no longer immutable
newRequest = new Request(request)
// remove cookie from request
newRequest.headers.delete('Cookie')
// Add header to get <esi>
newRequest.headers.set("Surrogate-Capability", "abc=ESI/1.0")
console.log(newRequest.url);
const response = await fetch(newRequest);
let contentType = response.headers.get('content-type')
if (!contentType || !contentType.startsWith("text/")) {
return response
}
// Clone the response so that it's no longer immutable
const newResponse = new Response(response.body, response);
let { readable, writable } = new TransformStream()
streamTransformBody(newResponse.body, writable)
newResponse.headers.append('x-workers-hello', 'Hello from
Cloudflare Workers');
return newResponse;
}
async function streamTransformBody(readable, writable) {
const startTag = "<".charCodeAt(0);
const endTag = ">".charCodeAt(0);
let reader = readable.getReader();
let writer = writable.getWriter();
let templateChunks = null;
while (true) {
let { done, value } = await reader.read();
if (done) break;
while (value.byteLength > 0) {
if (templateChunks) {
let end = value.indexOf(endTag);
if (end === -1) {
templateChunks.push(value);
break;
} else {
templateChunks.push(value.subarray(0, end));
await writer.write(await translate(templateChunks));
templateChunks = null;
value = value.subarray(end + 1);
}
}
let start = value.indexOf(startTag);
if (start === -1) {
await writer.write(value);
break;
} else {
await writer.write(value.subarray(0, start));
value = value.subarray(start + 1);
templateChunks = [];
}
}
}
await writer.close();
}
async function translate(chunks) {
const decoder = new TextDecoder();
let templateKey = chunks.reduce(
(accumulator, chunk) =>
accumulator + decoder.decode(chunk, { stream: true }),
""
);
templateKey += decoder.decode();
return handleTemplate(new TextEncoder(), templateKey);
}
async function handleTemplate(encoder, templateKey) {
const linkRegex = /(esi:include.*src="(.*?)".*\/)/gm
let result = linkRegex.exec(templateKey);
let esi
if (!result) {
return encoder.encode(`<${templateKey}>`);
}
if (result[2]) {
esi = await subRequests(result[2]);
}
return encoder.encode(
`${esi}`
);
}
async function subRequests(target){
target = esiHost + target
const init = {
method: 'GET',
headers: esiHeaders
}
let response = await fetch(target, init)
if (!response.ok) {
return ''
}
let text = await response.text()
return '<!--esi-->' + text + '<!--/esi-->'
}