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feat(rtc): add LocalParticipant.send_bytes - #858
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Expose the FFI's existing one-shot byte stream send (StreamSendBytesRequest) in Python, mirroring send_text / send_file. Because the whole payload is known up front, short payloads go out as a single inline packet and larger ones are deflate-compressed when every recipient supports data streams v2 — something the incremental stream_bytes writer can't do. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
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Summary
Introduces a new
LocalParticipant.send_bytes(data, *, topic, name, mime_type, destination_identities, attributes, stream_id, compress)method, the byte-stream analogue ofsend_textand the in-memory analogue ofsend_file.The FFI already implements this (
StreamSendBytesRequest, handled bylivekit-data-stream'ssend_bytes); it just wasn't exposed in Python. Because the whole payload is known up front, it means the Rust side can:Neither is possible through the incremental
stream_byteswriter, which always sends header + chunk(s) + trailer uncompressed. That makessend_bytesthe right primitive for small, frequent messages.Background info
This is being added now because I did some benchmarking and still noticed quite a bit of rtc data channel congestion even with rpc v2, data stream v2, and transcription deduplication. After digging in, it looks like the cause was the
RoomSessionTransportfromlivekit-agents- it sends quite a fewlk.agent.sessionevents, each as its ownstream_bytesstream.Measured against a JS client (client protocol 3, with transcription deduplication enabled), one agent turn produced ~92 such streams, each 3 packets. Switching that call to
send_bytescut the client's per-turn data channel traffic from ~52 KB / 354 messages to ~37 KB / 170 messages (−29% bytes, −52% messages). On constrained mobile network links, that decrease in bytes results in decreased queue pressure in front of RPCs and transcriptions, which is a big reason why data streams v2 were introduced in the first place.Testing
test_send_bytes_small(hello-world round trip +ByteStreamInfoassertions). It fails on the current release (AttributeError) and passes with this change, alongsidetest_send_text_smallandtest_send_file_round_trip.ruff check/ruff format --check(pinned 0.15.4) clean;mypy -p livekit.rtcadds no new errors.