examples/datafusion-ffi-example/python/tests/_test_physical_extension_codec.py

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from __future__ import annotations

import pyarrow as pa
from datafusion import ExecutionPlan, SessionContext
from datafusion_ffi_example import MyPhysicalExtensionCodec


def _setup_session_with_codec() -> tuple[SessionContext, MyPhysicalExtensionCodec]:
    base = SessionContext()
    batch = pa.RecordBatch.from_arrays(
        [pa.array([-1, -2, -3])],
        names=["a"],
    )
    base.register_record_batches("t", [[batch]])
    codec = MyPhysicalExtensionCodec()
    ctx = base.with_physical_extension_codec(codec)
    return ctx, codec


def test_ffi_physical_codec_install_and_export():
    ctx, _codec = _setup_session_with_codec()
    capsule = ctx.__datafusion_physical_extension_codec__()
    assert capsule is not None


def test_ffi_physical_codec_consulted_on_udf_encode():
    """Serializing through ctx.physical_codec() routes try_encode_udf to
    the user-installed FFI codec.

    Mirror of the logical-side dispatch test: verifies
    `PyExecutionPlan.to_bytes -> session.physical_codec ->
    PythonPhysicalCodec -> FFI_PhysicalExtensionCodec -> user impl`
    forwards correctly. Does not test Python-UDF-specific dispatch —
    PythonPhysicalCodec currently delegates all UDF encoding to its
    inner codec unconditionally.
    """
    ctx, codec = _setup_session_with_codec()
    df = ctx.sql("SELECT abs(a) AS x FROM t")
    plan = df.execution_plan()

    before = codec.encode_udf_calls()
    _ = plan.to_bytes(ctx)
    after = codec.encode_udf_calls()

    assert after > before, (
        f"Expected user FFI codec encode_udf to fire, before={before} after={after}"
    )


def test_ffi_physical_codec_roundtrip():
    """A plan referencing an FFI-imported UDF round-trips via the
    user-supplied physical codec. On decode, the receiver resolves the
    UDF from the function registry; `try_decode_udf` only fires when a
    codec inlines the UDF body, which the counting codec does not."""
    ctx, _codec = _setup_session_with_codec()
    df = ctx.sql("SELECT abs(a) AS x FROM t")
    original = df.execution_plan()
    blob = original.to_bytes(ctx)

    restored = ExecutionPlan.from_bytes(ctx, blob)
    assert str(original) == str(restored)


def test_ffi_physical_codec_composes_with_later_install():
    """Codecs compose: a second install appends to the chain instead
    of replacing the first codec. The second codec here (default-backed
    export from a fresh session) encodes UDFs by name without writing
    bytes, which the chain treats as "no opinion" — so the user codec
    installed first is still consulted. Under replace semantics its
    counter stays at zero."""
    ctx, codec = _setup_session_with_codec()
    ctx = ctx.with_physical_extension_codec(
        SessionContext().__datafusion_physical_extension_codec__()
    )

    df = ctx.sql("SELECT abs(a) AS x FROM t")
    original = df.execution_plan()

    before = codec.encode_udf_calls()
    blob = original.to_bytes(ctx)
    assert codec.encode_udf_calls() > before

    restored = ExecutionPlan.from_bytes(ctx, blob)
    assert str(original) == str(restored)