Bound bi-stream handler concurrency at accept site#477
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A peer could open unbounded bi-streams and exhaust memory before the inner `agent.limits().sync` check inside `serve_sync` ever fired. Move the try_acquire up to `spawn_bipayload_handler`, before `tokio::spawn`, and write `MaxConcurrencyReached` on the stream when no permits remain. The duplicate check inside `serve_sync` is removed: keeping both would consume two permits per sync from the same 3-permit pool.
somtochiama
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May 13, 2026
| // adding a parallel counter. Acquiring before `tokio::spawn` | ||
| // prevents an unbounded peer from exhausting tasks/memory just | ||
| // by opening streams. | ||
| let permit = match agent.limits().sync.clone().try_acquire_owned() { |
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Maybe we'd want to make this configurable? Right now we have it set to three and there's no way to tune it.
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A peer could open unbounded bi-streams and exhaust memory before the inner
agent.limits().synccheck insideserve_syncever fired. Move the try_acquire up tospawn_bipayload_handler, beforetokio::spawn, and writeMaxConcurrencyReachedon the stream when no permits remain.The duplicate check inside
serve_syncis removed: keeping both would consume two permits per sync from the same 3-permit pool.