Hongsheng Liuandhsliu_ustc
44c8d1c449
Signed-off-by: Hongsheng Liu <liuhongsheng4@huawei.com> Co-authored-by: hsliu_ustc <hsliu_ustc@noreply.gitcode.com>
110 lines
3.7 KiB
Markdown
110 lines
3.7 KiB
Markdown
# OpenPI Robot Policy WebSocket API
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Use `WS /v1/realtime/robot/openpi` for low-latency robot-policy inference with
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OpenPI-compatible clients. A persistent WebSocket carries observations to the
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loaded policy model and returns action arrays.
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Despite the `/realtime` prefix, this endpoint does not use the OpenAI Realtime
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event schema. It uses binary MessagePack frames with NumPy extensions.
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## Availability
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The endpoint is available only when the loaded diffusion policy configuration
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contains `policy_server_config`. The server sends that model-specific
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configuration to the client as the first binary frame.
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For example, DreamZero declares:
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```yaml
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policy_server_config:
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image_resolution: [180, 320]
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n_external_cameras: 2
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needs_wrist_camera: true
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needs_stereo_camera: false
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needs_session_id: true
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action_space: joint_position
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```
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Without this configuration, the WebSocket returns `Robot policy not available`
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and closes.
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## DreamZero Quick Start
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Start the bundled DreamZero deployment:
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```bash
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vllm serve GEAR-Dreams/DreamZero-DROID --omni --port 8091 \
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--served-model-name dreamzero-droid \
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--deploy-config vllm_omni/deploy/dreamzero_tp1_cfg2.yaml \
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--enforce-eager --disable-log-stats
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```
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Install the optional client dependencies, download the sample camera inputs,
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and run the client:
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```bash
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pip install openpi-client websockets opencv-python
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hf download YangshenDeng/vllm-omni-dreamzero-assets \
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--repo-type dataset \
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--local-dir outputs/dreamzero/assets
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python examples/online_serving/dreamzero/openpi_client.py \
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--host 127.0.0.1 \
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--port 8091 \
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--video-dir outputs/dreamzero/assets
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```
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## Protocol
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The connection is request-response after an initial server handshake:
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```text
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connect
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<- msgpack(policy_server_config)
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infer
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-> msgpack({"endpoint": "infer", "session_id": "...", ...observation})
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<- msgpack(ndarray | dict[str, ndarray])
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reset
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-> msgpack({"endpoint": "reset"})
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<- msgpack({"status": "reset successful"})
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```
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If `endpoint` is omitted, the server treats the message as `infer`. Each
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inference message produces one action response after the engine request
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completes; action tokens or intermediate tensors are not streamed.
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NumPy arrays use the marker format implemented by `openpi-client`. The server
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also accepts the legacy vLLM NumPy marker representation on input. JSON text
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frames are not observation messages.
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## Sessions and Reset
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- The API layer's current-session and first-call counters are scoped to each
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WebSocket connection.
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- `session_id` identifies model-side state across observations on that
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connection. If omitted, it defaults to `default`.
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- The first inference for a session is sent to the model with `reset=true`.
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- Changing `session_id`, or sending the `reset` command, causes the next
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inference to start with `reset=true`.
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- The policy pipeline owns observation transforms and persistent model state,
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normally keyed by `session_id`; the API layer forwards the raw observation
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dictionary.
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## Limits and Errors
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- Maximum inbound payload size is 64 MiB.
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- The server closes an idle connection after 30 seconds.
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- Invalid binary input returns a MessagePack
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`{"type":"error","message":"Invalid request payload"}` response.
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- Inference failures return a generic `Internal inference error` without
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exposing an internal traceback.
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- Unsupported NumPy object, structured, and complex dtypes are rejected.
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Observation keys, camera layout, state tensors, and action shapes are defined
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by the loaded policy rather than by this transport. Read the handshake before
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constructing observations. See the [DreamZero example](https://github.com/vllm-project/vllm-omni/tree/main/examples/online_serving/dreamzero)
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for a complete OpenPI client and DROID simulation loop.
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