forwardImageAsync awaited response.arrayBuffer(), so the whole image sat in
server memory before anything was sent to the client. A media board asks for
dozens of posters and backdrops at once, so that is dozens of full images held
simultaneously - and a client that gives up midway still cost a complete
server-side download.
Forwarding response.body instead lets backpressure reach upstream. Measured
with 30 concurrent 2 MiB images and deliberately slow clients, one fresh
process per arm because the allocator does not return freed spans:
buffered +116.0 MiB, +117.8 MiB peak RSS
streamed +74.2 MiB, +78.8 MiB peak RSS
-36% peak RSS on that load, and it scales with concurrency times image size.
Content-Length is now forwarded too, so clients still get a progress bar.
Thomas Camlong
cf240addea