Get the http response size

Hi Cloudflare Team,

we are using r2 in an worker with sample code from here:

we plan to use send the response metrics to workers analytics engine.

const cache = caches.default
            const cacheKey = new Request(url.toString(), {
                headers: request.headers, method: 'GET' // Make HEAD requests cacheable
            let response = await cache.match(cacheKey)

but for the response from cache, it seemed we cannot easily find the content-length header or is there any other way to find the size of this response from cache?

thanks in advance