This is how my file stitching logic works, and it's actually pretty fast (some reported 2mbps-30mbps depending if the DC had those keys locally cached), it's just incrementally more expensive for each 2mb increase in file size. https://github.com/judge2020/cloudflare-file-hosting/tree/dd... But it might be a little much for this to be a first-party solution.

Thanks for the tip. By the way, line 84 introduces some unneeded serialization; you could get some more speed there by fetching the bits in parallel.