datafusion_ffi/

table_provider.rs

// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

use std::any::Any;
use std::ffi::c_void;
use std::sync::Arc;

use abi_stable::StableAbi;
use abi_stable::std_types::{ROption, RResult, RVec};
use arrow::datatypes::SchemaRef;
use async_ffi::{FfiFuture, FutureExt};
use async_trait::async_trait;
use datafusion_catalog::{Session, TableProvider};
use datafusion_common::error::{DataFusionError, Result};
use datafusion_execution::TaskContext;
use datafusion_expr::dml::InsertOp;
use datafusion_expr::{Expr, TableProviderFilterPushDown, TableType};
use datafusion_physical_plan::ExecutionPlan;
use datafusion_proto::logical_plan::from_proto::parse_exprs;
use datafusion_proto::logical_plan::to_proto::serialize_exprs;
use datafusion_proto::logical_plan::{
    DefaultLogicalExtensionCodec, LogicalExtensionCodec,
};
use datafusion_proto::protobuf::LogicalExprList;
use prost::Message;
use tokio::runtime::Handle;

use super::execution_plan::FFI_ExecutionPlan;
use super::insert_op::FFI_InsertOp;
use crate::arrow_wrappers::WrappedSchema;
use crate::execution::FFI_TaskContextProvider;
use crate::proto::logical_extension_codec::FFI_LogicalExtensionCodec;
use crate::session::{FFI_SessionRef, ForeignSession};
use crate::table_source::{FFI_TableProviderFilterPushDown, FFI_TableType};
use crate::util::FFIResult;
use crate::{df_result, rresult_return};

/// A stable struct for sharing [`TableProvider`] across FFI boundaries.
///
/// # Struct Layout
///
/// The following description applies to all structs provided in this crate.
///
/// Each of the exposed structs in this crate is provided with a variant prefixed
/// with `Foreign`. This variant is designed to be used by the consumer of the
/// foreign code. The `Foreign` structs should _never_ access the `private_data`
/// fields. Instead they should only access the data returned through the function
/// calls defined on the `FFI_` structs. The second purpose of the `Foreign`
/// structs is to contain additional data that may be needed by the traits that
/// are implemented on them. Some of these traits require borrowing data which
/// can be far more convenient to be locally stored.
///
/// For example, we have a struct `FFI_TableProvider` to give access to the
/// `TableProvider` functions like `table_type()` and `scan()`. If we write a
/// library that wishes to expose it's `TableProvider`, then we can access the
/// private data that contains the Arc reference to the `TableProvider` via
/// `FFI_TableProvider`. This data is local to the library.
///
/// If we have a program that accesses a `TableProvider` via FFI, then it
/// will use `ForeignTableProvider`. When using `ForeignTableProvider` we **must**
/// not attempt to access the `private_data` field in `FFI_TableProvider`. If a
/// user is testing locally, you may be able to successfully access this field, but
/// it will only work if you are building against the exact same version of
/// `DataFusion` for both libraries **and** the same compiler. It will not work
/// in general.
///
/// It is worth noting that which library is the `local` and which is `foreign`
/// depends on which interface we are considering. For example, suppose we have a
/// Python library called `my_provider` that exposes a `TableProvider` called
/// `MyProvider` via `FFI_TableProvider`. Within the library `my_provider` we can
/// access the `private_data` via `FFI_TableProvider`. We connect this to
/// `datafusion-python`, where we access it as a `ForeignTableProvider`. Now when
/// we call `scan()` on this interface, we have to pass it a `FFI_SessionConfig`.
/// The `SessionConfig` is local to `datafusion-python` and **not** `my_provider`.
/// It is important to be careful when expanding these functions to be certain which
/// side of the interface each object refers to.
#[repr(C)]
#[derive(Debug, StableAbi)]
pub struct FFI_TableProvider {
    /// Return the table schema
    schema: unsafe extern "C" fn(provider: &Self) -> WrappedSchema,

    /// Perform a scan on the table. See [`TableProvider`] for detailed usage information.
    ///
    /// # Arguments
    ///
    /// * `provider` - the table provider
    /// * `session` - session
    /// * `projections` - if specified, only a subset of the columns are returned
    /// * `filters_serialized` - filters to apply to the scan, which are a
    ///   [`LogicalExprList`] protobuf message serialized into bytes to pass
    ///   across the FFI boundary.
    /// * `limit` - if specified, limit the number of rows returned
    scan: unsafe extern "C" fn(
        provider: &Self,
        session: FFI_SessionRef,
        projections: ROption<RVec<usize>>,
        filters_serialized: RVec<u8>,
        limit: ROption<usize>,
    ) -> FfiFuture<FFIResult<FFI_ExecutionPlan>>,

    /// Return the type of table. See [`TableType`] for options.
    table_type: unsafe extern "C" fn(provider: &Self) -> FFI_TableType,

    /// Based upon the input filters, identify which are supported. The filters
    /// are a [`LogicalExprList`] protobuf message serialized into bytes to pass
    /// across the FFI boundary.
    supports_filters_pushdown: Option<
        unsafe extern "C" fn(
            provider: &FFI_TableProvider,
            filters_serialized: RVec<u8>,
        ) -> FFIResult<RVec<FFI_TableProviderFilterPushDown>>,
    >,

    insert_into: unsafe extern "C" fn(
        provider: &Self,
        session: FFI_SessionRef,
        input: &FFI_ExecutionPlan,
        insert_op: FFI_InsertOp,
    ) -> FfiFuture<FFIResult<FFI_ExecutionPlan>>,

    pub logical_codec: FFI_LogicalExtensionCodec,

    /// Used to create a clone on the provider of the execution plan. This should
    /// only need to be called by the receiver of the plan.
    clone: unsafe extern "C" fn(plan: &Self) -> Self,

    /// Release the memory of the private data when it is no longer being used.
    release: unsafe extern "C" fn(arg: &mut Self),

    /// Return the major DataFusion version number of this provider.
    pub version: unsafe extern "C" fn() -> u64,

    /// Internal data. This is only to be accessed by the provider of the plan.
    /// A [`ForeignTableProvider`] should never attempt to access this data.
    private_data: *mut c_void,

    /// Utility to identify when FFI objects are accessed locally through
    /// the foreign interface. See [`crate::get_library_marker_id`] and
    /// the crate's `README.md` for more information.
    pub library_marker_id: extern "C" fn() -> usize,
}

unsafe impl Send for FFI_TableProvider {}
unsafe impl Sync for FFI_TableProvider {}

struct ProviderPrivateData {
    provider: Arc<dyn TableProvider + Send>,
    runtime: Option<Handle>,
}

impl FFI_TableProvider {
    fn inner(&self) -> &Arc<dyn TableProvider + Send> {
        let private_data = self.private_data as *const ProviderPrivateData;
        unsafe { &(*private_data).provider }
    }

    fn runtime(&self) -> &Option<Handle> {
        let private_data = self.private_data as *const ProviderPrivateData;
        unsafe { &(*private_data).runtime }
    }
}

unsafe extern "C" fn schema_fn_wrapper(provider: &FFI_TableProvider) -> WrappedSchema {
    provider.inner().schema().into()
}

unsafe extern "C" fn table_type_fn_wrapper(
    provider: &FFI_TableProvider,
) -> FFI_TableType {
    provider.inner().table_type().into()
}

fn supports_filters_pushdown_internal(
    provider: &Arc<dyn TableProvider + Send>,
    filters_serialized: &[u8],
    task_ctx: &Arc<TaskContext>,
    codec: &dyn LogicalExtensionCodec,
) -> Result<RVec<FFI_TableProviderFilterPushDown>> {
    let filters = match filters_serialized.is_empty() {
        true => vec![],
        false => {
            let proto_filters = LogicalExprList::decode(filters_serialized)
                .map_err(|e| DataFusionError::Plan(e.to_string()))?;

            parse_exprs(proto_filters.expr.iter(), task_ctx.as_ref(), codec)?
        }
    };
    let filters_borrowed: Vec<&Expr> = filters.iter().collect();

    let results: RVec<_> = provider
        .supports_filters_pushdown(&filters_borrowed)?
        .iter()
        .map(|v| v.into())
        .collect();

    Ok(results)
}

unsafe extern "C" fn supports_filters_pushdown_fn_wrapper(
    provider: &FFI_TableProvider,
    filters_serialized: RVec<u8>,
) -> FFIResult<RVec<FFI_TableProviderFilterPushDown>> {
    let logical_codec: Arc<dyn LogicalExtensionCodec> = (&provider.logical_codec).into();
    let task_ctx = rresult_return!(<Arc<TaskContext>>::try_from(
        &provider.logical_codec.task_ctx_provider
    ));
    supports_filters_pushdown_internal(
        provider.inner(),
        &filters_serialized,
        &task_ctx,
        logical_codec.as_ref(),
    )
    .map_err(|e| e.to_string().into())
    .into()
}

unsafe extern "C" fn scan_fn_wrapper(
    provider: &FFI_TableProvider,
    session: FFI_SessionRef,
    projections: ROption<RVec<usize>>,
    filters_serialized: RVec<u8>,
    limit: ROption<usize>,
) -> FfiFuture<FFIResult<FFI_ExecutionPlan>> {
    let task_ctx: Result<Arc<TaskContext>, DataFusionError> =
        (&provider.logical_codec.task_ctx_provider).try_into();
    let runtime = provider.runtime().clone();
    let logical_codec: Arc<dyn LogicalExtensionCodec> = (&provider.logical_codec).into();
    let internal_provider = Arc::clone(provider.inner());

    async move {
        let mut foreign_session = None;
        let session = rresult_return!(
            session
                .as_local()
                .map(Ok::<&(dyn Session + Send + Sync), DataFusionError>)
                .unwrap_or_else(|| {
                    foreign_session = Some(ForeignSession::try_from(&session)?);
                    Ok(foreign_session.as_ref().unwrap())
                })
        );

        let task_ctx = rresult_return!(task_ctx);
        let filters = match filters_serialized.is_empty() {
            true => vec![],
            false => {
                let proto_filters =
                    rresult_return!(LogicalExprList::decode(filters_serialized.as_ref()));

                rresult_return!(parse_exprs(
                    proto_filters.expr.iter(),
                    task_ctx.as_ref(),
                    logical_codec.as_ref(),
                ))
            }
        };

        let projections: Option<Vec<usize>> =
            projections.into_option().map(|p| p.into_iter().collect());

        let plan = rresult_return!(
            internal_provider
                .scan(session, projections.as_ref(), &filters, limit.into())
                .await
        );

        RResult::ROk(FFI_ExecutionPlan::new(plan, runtime.clone()))
    }
    .into_ffi()
}

unsafe extern "C" fn insert_into_fn_wrapper(
    provider: &FFI_TableProvider,
    session: FFI_SessionRef,
    input: &FFI_ExecutionPlan,
    insert_op: FFI_InsertOp,
) -> FfiFuture<FFIResult<FFI_ExecutionPlan>> {
    let runtime = provider.runtime().clone();
    let internal_provider = Arc::clone(provider.inner());
    let input = input.clone();

    async move {
        let mut foreign_session = None;
        let session = rresult_return!(
            session
                .as_local()
                .map(Ok::<&(dyn Session + Send + Sync), DataFusionError>)
                .unwrap_or_else(|| {
                    foreign_session = Some(ForeignSession::try_from(&session)?);
                    Ok(foreign_session.as_ref().unwrap())
                })
        );

        let input = rresult_return!(<Arc<dyn ExecutionPlan>>::try_from(&input));

        let insert_op = InsertOp::from(insert_op);

        let plan = rresult_return!(
            internal_provider
                .insert_into(session, input, insert_op)
                .await
        );

        RResult::ROk(FFI_ExecutionPlan::new(plan, runtime.clone()))
    }
    .into_ffi()
}

unsafe extern "C" fn release_fn_wrapper(provider: &mut FFI_TableProvider) {
    unsafe {
        debug_assert!(!provider.private_data.is_null());
        let private_data =
            Box::from_raw(provider.private_data as *mut ProviderPrivateData);
        drop(private_data);
        provider.private_data = std::ptr::null_mut();
    }
}

unsafe extern "C" fn clone_fn_wrapper(provider: &FFI_TableProvider) -> FFI_TableProvider {
    let runtime = provider.runtime().clone();
    let old_provider = Arc::clone(provider.inner());

    let private_data = Box::into_raw(Box::new(ProviderPrivateData {
        provider: old_provider,
        runtime,
    })) as *mut c_void;

    FFI_TableProvider {
        schema: schema_fn_wrapper,
        scan: scan_fn_wrapper,
        table_type: table_type_fn_wrapper,
        supports_filters_pushdown: provider.supports_filters_pushdown,
        insert_into: provider.insert_into,
        logical_codec: provider.logical_codec.clone(),
        clone: clone_fn_wrapper,
        release: release_fn_wrapper,
        version: super::version,
        private_data,
        library_marker_id: crate::get_library_marker_id,
    }
}

impl Drop for FFI_TableProvider {
    fn drop(&mut self) {
        unsafe { (self.release)(self) }
    }
}

impl FFI_TableProvider {
    /// Creates a new [`FFI_TableProvider`].
    pub fn new(
        provider: Arc<dyn TableProvider + Send>,
        can_support_pushdown_filters: bool,
        runtime: Option<Handle>,
        task_ctx_provider: impl Into<FFI_TaskContextProvider>,
        logical_codec: Option<Arc<dyn LogicalExtensionCodec>>,
    ) -> Self {
        let task_ctx_provider = task_ctx_provider.into();
        let logical_codec =
            logical_codec.unwrap_or_else(|| Arc::new(DefaultLogicalExtensionCodec {}));
        let logical_codec = FFI_LogicalExtensionCodec::new(
            logical_codec,
            runtime.clone(),
            task_ctx_provider.clone(),
        );
        Self::new_with_ffi_codec(
            provider,
            can_support_pushdown_filters,
            runtime,
            logical_codec,
        )
    }

    pub fn new_with_ffi_codec(
        provider: Arc<dyn TableProvider + Send>,
        can_support_pushdown_filters: bool,
        runtime: Option<Handle>,
        logical_codec: FFI_LogicalExtensionCodec,
    ) -> Self {
        let private_data = Box::new(ProviderPrivateData { provider, runtime });

        Self {
            schema: schema_fn_wrapper,
            scan: scan_fn_wrapper,
            table_type: table_type_fn_wrapper,
            supports_filters_pushdown: match can_support_pushdown_filters {
                true => Some(supports_filters_pushdown_fn_wrapper),
                false => None,
            },
            insert_into: insert_into_fn_wrapper,
            logical_codec,
            clone: clone_fn_wrapper,
            release: release_fn_wrapper,
            version: super::version,
            private_data: Box::into_raw(private_data) as *mut c_void,
            library_marker_id: crate::get_library_marker_id,
        }
    }
}

/// This wrapper struct exists on the receiver side of the FFI interface, so it has
/// no guarantees about being able to access the data in `private_data`. Any functions
/// defined on this struct must only use the stable functions provided in
/// FFI_TableProvider to interact with the foreign table provider.
#[derive(Debug)]
pub struct ForeignTableProvider(pub FFI_TableProvider);

unsafe impl Send for ForeignTableProvider {}
unsafe impl Sync for ForeignTableProvider {}

impl From<&FFI_TableProvider> for Arc<dyn TableProvider> {
    fn from(provider: &FFI_TableProvider) -> Self {
        if (provider.library_marker_id)() == crate::get_library_marker_id() {
            Arc::clone(provider.inner()) as Arc<dyn TableProvider>
        } else {
            Arc::new(ForeignTableProvider(provider.clone()))
        }
    }
}

impl Clone for FFI_TableProvider {
    fn clone(&self) -> Self {
        unsafe { (self.clone)(self) }
    }
}

#[async_trait]
impl TableProvider for ForeignTableProvider {
    fn as_any(&self) -> &dyn Any {
        self
    }

    fn schema(&self) -> SchemaRef {
        let wrapped_schema = unsafe { (self.0.schema)(&self.0) };
        wrapped_schema.into()
    }

    fn table_type(&self) -> TableType {
        unsafe { (self.0.table_type)(&self.0).into() }
    }

    async fn scan(
        &self,
        session: &dyn Session,
        projection: Option<&Vec<usize>>,
        filters: &[Expr],
        limit: Option<usize>,
    ) -> Result<Arc<dyn ExecutionPlan>> {
        let session = FFI_SessionRef::new(session, None, self.0.logical_codec.clone());

        let projections: ROption<RVec<usize>> = projection
            .map(|p| p.iter().map(|v| v.to_owned()).collect())
            .into();

        let codec: Arc<dyn LogicalExtensionCodec> = (&self.0.logical_codec).into();
        let filter_list = LogicalExprList {
            expr: serialize_exprs(filters, codec.as_ref())?,
        };
        let filters_serialized = filter_list.encode_to_vec().into();

        let plan = unsafe {
            let maybe_plan = (self.0.scan)(
                &self.0,
                session,
                projections,
                filters_serialized,
                limit.into(),
            )
            .await;

            <Arc<dyn ExecutionPlan>>::try_from(&df_result!(maybe_plan)?)?
        };

        Ok(plan)
    }

    /// Tests whether the table provider can make use of a filter expression
    /// to optimize data retrieval.
    fn supports_filters_pushdown(
        &self,
        filters: &[&Expr],
    ) -> Result<Vec<TableProviderFilterPushDown>> {
        unsafe {
            let pushdown_fn = match self.0.supports_filters_pushdown {
                Some(func) => func,
                None => {
                    return Ok(vec![
                        TableProviderFilterPushDown::Unsupported;
                        filters.len()
                    ]);
                }
            };

            let codec: Arc<dyn LogicalExtensionCodec> = (&self.0.logical_codec).into();

            let expr_list = LogicalExprList {
                expr: serialize_exprs(
                    filters.iter().map(|f| f.to_owned()),
                    codec.as_ref(),
                )?,
            };
            let serialized_filters = expr_list.encode_to_vec();

            let pushdowns = df_result!(pushdown_fn(&self.0, serialized_filters.into()))?;

            Ok(pushdowns.iter().map(|v| v.into()).collect())
        }
    }

    async fn insert_into(
        &self,
        session: &dyn Session,
        input: Arc<dyn ExecutionPlan>,
        insert_op: InsertOp,
    ) -> Result<Arc<dyn ExecutionPlan>> {
        let session = FFI_SessionRef::new(session, None, self.0.logical_codec.clone());

        let rc = Handle::try_current().ok();
        let input = FFI_ExecutionPlan::new(input, rc);
        let insert_op: FFI_InsertOp = insert_op.into();

        let plan = unsafe {
            let maybe_plan =
                (self.0.insert_into)(&self.0, session, &input, insert_op).await;

            <Arc<dyn ExecutionPlan>>::try_from(&df_result!(maybe_plan)?)?
        };

        Ok(plan)
    }
}

#[cfg(test)]
mod tests {
    use arrow::datatypes::Schema;
    use datafusion::prelude::{SessionContext, col, lit};
    use datafusion_execution::TaskContextProvider;

    use super::*;

    fn create_test_table_provider() -> Result<Arc<dyn TableProvider>> {
        use arrow::datatypes::Field;
        use datafusion::arrow::array::Float32Array;
        use datafusion::arrow::datatypes::DataType;
        use datafusion::arrow::record_batch::RecordBatch;
        use datafusion::datasource::MemTable;

        let schema =
            Arc::new(Schema::new(vec![Field::new("a", DataType::Float32, false)]));

        // define data in two partitions
        let batch1 = RecordBatch::try_new(
            Arc::clone(&schema),
            vec![Arc::new(Float32Array::from(vec![2.0, 4.0, 8.0]))],
        )?;
        let batch2 = RecordBatch::try_new(
            Arc::clone(&schema),
            vec![Arc::new(Float32Array::from(vec![64.0]))],
        )?;

        Ok(Arc::new(MemTable::try_new(
            schema,
            vec![vec![batch1], vec![batch2]],
        )?))
    }

    #[tokio::test]
    async fn test_round_trip_ffi_table_provider_scan() -> Result<()> {
        let provider = create_test_table_provider()?;
        let ctx = Arc::new(SessionContext::new());
        let task_ctx_provider = Arc::clone(&ctx) as Arc<dyn TaskContextProvider>;
        let task_ctx_provider = FFI_TaskContextProvider::from(&task_ctx_provider);

        let mut ffi_provider =
            FFI_TableProvider::new(provider, true, None, task_ctx_provider, None);
        ffi_provider.library_marker_id = crate::mock_foreign_marker_id;

        let foreign_table_provider: Arc<dyn TableProvider> = (&ffi_provider).into();

        ctx.register_table("t", foreign_table_provider)?;

        let df = ctx.table("t").await?;

        df.select(vec![col("a")])?
            .filter(col("a").gt(lit(3.0)))?
            .show()
            .await?;

        Ok(())
    }

    #[tokio::test]
    async fn test_round_trip_ffi_table_provider_insert_into() -> Result<()> {
        let provider = create_test_table_provider()?;
        let ctx = Arc::new(SessionContext::new());
        let task_ctx_provider = Arc::clone(&ctx) as Arc<dyn TaskContextProvider>;
        let task_ctx_provider = FFI_TaskContextProvider::from(&task_ctx_provider);

        let mut ffi_provider =
            FFI_TableProvider::new(provider, true, None, task_ctx_provider, None);
        ffi_provider.library_marker_id = crate::mock_foreign_marker_id;

        let foreign_table_provider: Arc<dyn TableProvider> = (&ffi_provider).into();

        ctx.register_table("t", foreign_table_provider)?;

        let result = ctx
            .sql("INSERT INTO t VALUES (128.0);")
            .await?
            .collect()
            .await?;

        assert!(result.len() == 1 && result[0].num_rows() == 1);

        ctx.table("t")
            .await?
            .select(vec![col("a")])?
            .filter(col("a").gt(lit(3.0)))?
            .show()
            .await?;

        Ok(())
    }

    #[tokio::test]
    async fn test_aggregation() -> Result<()> {
        use arrow::datatypes::Field;
        use datafusion::arrow::array::Float32Array;
        use datafusion::arrow::datatypes::DataType;
        use datafusion::arrow::record_batch::RecordBatch;
        use datafusion::common::assert_batches_eq;
        use datafusion::datasource::MemTable;

        let schema =
            Arc::new(Schema::new(vec![Field::new("a", DataType::Float32, false)]));

        // define data in two partitions
        let batch1 = RecordBatch::try_new(
            Arc::clone(&schema),
            vec![Arc::new(Float32Array::from(vec![2.0, 4.0, 8.0]))],
        )?;

        let ctx = Arc::new(SessionContext::new());
        let task_ctx_provider = Arc::clone(&ctx) as Arc<dyn TaskContextProvider>;
        let task_ctx_provider = FFI_TaskContextProvider::from(&task_ctx_provider);

        let provider = Arc::new(MemTable::try_new(schema, vec![vec![batch1]])?);

        let mut ffi_provider =
            FFI_TableProvider::new(provider, true, None, task_ctx_provider, None);
        ffi_provider.library_marker_id = crate::mock_foreign_marker_id;

        let foreign_table_provider: Arc<dyn TableProvider> = (&ffi_provider).into();

        ctx.register_table("t", foreign_table_provider)?;

        let result = ctx
            .sql("SELECT COUNT(*) as cnt FROM t")
            .await?
            .collect()
            .await?;
        #[rustfmt::skip]
        let expected = [
            "+-----+",
            "| cnt |",
            "+-----+",
            "| 3   |",
            "+-----+"
        ];
        assert_batches_eq!(expected, &result);
        Ok(())
    }

    #[test]
    fn test_ffi_table_provider_local_bypass() -> Result<()> {
        let table_provider = create_test_table_provider()?;

        let ctx = Arc::new(SessionContext::new()) as Arc<dyn TaskContextProvider>;
        let task_ctx_provider = FFI_TaskContextProvider::from(&ctx);
        let mut ffi_table =
            FFI_TableProvider::new(table_provider, false, None, task_ctx_provider, None);

        // Verify local libraries can be downcast to their original
        let foreign_table: Arc<dyn TableProvider> = (&ffi_table).into();
        assert!(
            foreign_table
                .as_any()
                .downcast_ref::<datafusion::datasource::MemTable>()
                .is_some()
        );

        // Verify different library markers generate foreign providers
        ffi_table.library_marker_id = crate::mock_foreign_marker_id;
        let foreign_table: Arc<dyn TableProvider> = (&ffi_table).into();
        assert!(
            foreign_table
                .as_any()
                .downcast_ref::<ForeignTableProvider>()
                .is_some()
        );

        Ok(())
    }

    #[tokio::test]
    async fn test_scan_with_none_projection_returns_all_columns() -> Result<()> {
        use arrow::datatypes::Field;
        use datafusion::arrow::array::Float32Array;
        use datafusion::arrow::datatypes::DataType;
        use datafusion::arrow::record_batch::RecordBatch;
        use datafusion::datasource::MemTable;
        use datafusion::physical_plan::collect;

        let schema = Arc::new(Schema::new(vec![
            Field::new("a", DataType::Float32, false),
            Field::new("b", DataType::Float32, false),
            Field::new("c", DataType::Float32, false),
        ]));

        let batch = RecordBatch::try_new(
            Arc::clone(&schema),
            vec![
                Arc::new(Float32Array::from(vec![1.0, 2.0])),
                Arc::new(Float32Array::from(vec![3.0, 4.0])),
                Arc::new(Float32Array::from(vec![5.0, 6.0])),
            ],
        )?;

        let provider =
            Arc::new(MemTable::try_new(Arc::clone(&schema), vec![vec![batch]])?);

        let ctx = Arc::new(SessionContext::new());
        let task_ctx_provider = Arc::clone(&ctx) as Arc<dyn TaskContextProvider>;
        let task_ctx_provider = FFI_TaskContextProvider::from(&task_ctx_provider);

        // Wrap in FFI and force the foreign path (not local bypass)
        let mut ffi_provider =
            FFI_TableProvider::new(provider, true, None, task_ctx_provider, None);
        ffi_provider.library_marker_id = crate::mock_foreign_marker_id;

        let foreign_table_provider: Arc<dyn TableProvider> = (&ffi_provider).into();

        // Call scan with projection=None, meaning "return all columns"
        let plan = foreign_table_provider
            .scan(&ctx.state(), None, &[], None)
            .await?;
        assert_eq!(
            plan.schema().fields().len(),
            3,
            "scan(projection=None) should return all columns; got {}",
            plan.schema().fields().len()
        );

        // Also verify we can execute and get correct data
        let batches = collect(plan, ctx.task_ctx()).await?;
        assert_eq!(batches.len(), 1);
        assert_eq!(batches[0].num_columns(), 3);
        assert_eq!(batches[0].num_rows(), 2);

        Ok(())
    }
}