Backlog rfcs/backlog/rfc-bun-arraybuffersink.md

Bun.ArrayBufferSink — streaming buffer builder for SSR

Bun.ArrayBufferSink lets you accumulate bytes from many writes into a single ArrayBuffer or stream them out, with fewer intermediate allocations than Uint8Ar…

Summary

Bun.ArrayBufferSink lets you accumulate bytes from many writes into a single ArrayBuffer or stream them out, with fewer intermediate allocations than Uint8Array concatenation.

Why backlog

Current SSR uses renderToReadableStream from React and pipes through to Response. No measured benefit yet — we don't have profiling that says the stream path is allocation-bound.

Trigger to promote to draft

  • SSR profiling (e.g. heap snapshots under load) shows the stream → Response path is GC-bound, OR
  • An HTML compressor / minifier plugin wants a write-sink it can flush incrementally.

Bun-unique classification

Bun-only — Node has no equivalent streaming buffer builder. Buffer.concat is eager; writable streams are higher-level.

Open questions when promoted

  • Does this replace ReadableStream end-to-end, or only the inner accumulation buffer behind a stream wrapper?
  • Edge adapter (no Bun) needs a fallback path — likely Uint8Array concat with a worse allocation profile.