[Bugfix][Frontend] Accept the msgpack-numpy package's numpy markers on the OpenPI endpoint

tests/entrypoints/openai_api/test_openpi_connection.py

@@ -68,7 +68,7 @@ def test_pack_and_unpack_round_trip_numpy_values():
     assert decoded["nested"][0]["done"] == np.bool_(True)
 
 
-def test_unpack_accepts_msgpack_numpy_marker_dicts():
+def test_unpack_accepts_vllm_native_marker_dicts():
     action = np.asarray([[1.0, 2.0]], dtype=np.float32)
     payload = {
         b"actions": {
@@ -88,6 +88,58 @@ def test_unpack_accepts_msgpack_numpy_marker_dicts():
     np.testing.assert_allclose(decoded[b"actions"], np.asarray([[1.0, 0.0]], dtype=np.float32))
 
 
+def test_unpack_accepts_msgpack_numpy_marker_dicts():
+    action = np.asarray([[1.0, 2.0]], dtype=np.float32)
+    payload = {
+        b"actions": {
+            b"nd": True,
+            b"type": action.dtype.str,
+            b"kind": b"",
+            b"shape": action.shape,
+            b"data": action.tobytes(),
+        }
+    }
+
+    decoded = openpi_connection._unpack_numpy(payload)
+
+    np.testing.assert_allclose(decoded[b"actions"], action)
+    assert decoded[b"actions"].dtype == np.float32
+
+
+def test_unpack_rejects_msgpack_numpy_structured_array_markers():
+    values = np.zeros(2, dtype=[("a", "<i4"), ("b", "<f4")])
+    payload = {
+        b"nd": True,
+        b"type": values.dtype.descr,
+        b"kind": b"V",
+        b"shape": values.shape,
+        b"data": values.tobytes(),
+    }
+
+    with pytest.raises(ValueError, match="Unsupported dtype"):
+        openpi_connection._unpack_numpy(payload)
+
+
+def test_unpack_msgpack_numpy_packed_observation():
+    msgpack_numpy = pytest.importorskip("msgpack_numpy")
+    obs = {
+        "observation/exterior_image_0_left": np.zeros((180, 320, 3), dtype=np.uint8),
+        "observation/joint_position": np.arange(7, dtype=np.float32),
+    }
+
+    decoded = openpi_connection._unpack(msgpack_numpy.packb(obs))
+
+    np.testing.assert_array_equal(
+        decoded["observation/exterior_image_0_left"],
+        obs["observation/exterior_image_0_left"],
+    )
+    np.testing.assert_allclose(
+        decoded["observation/joint_position"],
+        obs["observation/joint_position"],
+    )
+    assert decoded["observation/joint_position"].dtype == np.float32
+
+
 def test_unpack_accepts_openpi_client_ndarray_markers():
     image = np.arange(6, dtype=np.uint8).reshape(2, 3)
     payload = {

vllm_omni/entrypoints/openpi/connection.py

@@ -17,6 +17,13 @@
 vLLM-native markers:
     ndarray -> {nd: true, type, kind, shape, data}
     scalar  -> {nd: false, type, kind, data}
+
+`kind` is required on the `nd` markers because it is what separates them from a
+plain user mapping, but its value is dialect-specific: the vLLM-native markers
+carry the dtype kind character while the `msgpack-numpy` package leaves it empty
+for plain dtypes and sets "V" for structured ones. Both spellings are accepted.
+Scalars packed by `msgpack-numpy` omit `kind` entirely and are therefore left as
+mappings.
 """
 
 from __future__ import annotations
@@ -83,9 +90,14 @@ def _decode_vllm_numpy_marker(obj: dict[Any, Any]) -> Any:
     if nd is _MISSING or dtype is _MISSING or kind is _MISSING or data is _MISSING:
         return _MISSING
 
-    dtype_obj = np.dtype(_decode_marker_text(dtype))
     kind_text = _decode_marker_text(kind)
-    if dtype_obj.kind != kind_text:
+    # Structured markers carry a dtype descriptor list in `type`, so reject them
+    # before `np.dtype()` sees something it cannot parse.
+    if kind_text == "V":
+        raise ValueError("Unsupported dtype: structured arrays")
+
+    dtype_obj = np.dtype(_decode_marker_text(dtype))
+    if kind_text not in ("", dtype_obj.kind):
         raise ValueError(f"NumPy dtype marker kind mismatch: {dtype_obj.kind!r} != {kind_text!r}")
     if dtype_obj.kind in ("V", "O", "c"):
         raise ValueError(f"Unsupported dtype: {dtype_obj}")