Repository: jorgecarleitao/arrow2 (rust)

Issue:
Align FFI API with arrow's C++ API
Generally, the FFI should support the possibility of an external consumer to allocate the bridge structs (`ArrowArray` and `ArrowSchema`).

This requires that the bridge struct is not allocated by us; we should instead expect an allocated and aligned pointer that we can write the struct to it. Such change is backward-incompatible.

Pull request description:
Added API to FFI `Field`
So that the fields can be imported and exported from the C data interface.

The public API is different since ownership rules changed (#328); see `examples/ffi.rs` with a complete example.

Closes #328.



Patch:
diff --git a/.github/workflows/integration-ffi.yml b/.github/workflows/integration-ffi.yml
index 8f0797eea1..3fce8f24fd 100644
--- a/.github/workflows/integration-ffi.yml
+++ b/.github/workflows/integration-ffi.yml
@@ -38,6 +38,6 @@ jobs:
           python -m venv venv
           source venv/bin/activate
 
-          pip install maturin==0.10.2 toml==0.10.1 pyarrow==4.0.0
+          pip install maturin==0.10.2 toml==0.10.1 pyarrow==5.0.0
           maturin develop
           python -m unittest discover tests
diff --git a/examples/ffi.rs b/examples/ffi.rs
new file mode 100644
index 0000000000..172c3159b4
--- /dev/null
+++ b/examples/ffi.rs
@@ -0,0 +1,55 @@
+use arrow2::array::{Array, PrimitiveArray};
+use arrow2::datatypes::Field;
+use arrow2::error::Result;
+use arrow2::ffi;
+use std::sync::Arc;
+
+unsafe fn export(
+    array: Arc<dyn Array>,
+    array_ptr: *mut ffi::Ffi_ArrowArray,
+    schema_ptr: *mut ffi::Ffi_ArrowSchema,
+) {
+    let field = Field::new("a", array.data_type().clone(), true);
+    ffi::export_array_to_c(array, array_ptr);
+    ffi::export_field_to_c(&field, schema_ptr);
+}
+
+fn import(
+    array: Box<ffi::Ffi_ArrowArray>,
+    schema: &ffi::Ffi_ArrowSchema,
+) -> Result<Box<dyn Array>> {
+    let field = ffi::import_field_from_c(schema)?;
+    ffi::import_array_from_c(array, &field)
+}
+
+fn main() -> Result<()> {
+    // let's assume that we have an array:
+    let array = Arc::new(PrimitiveArray::<i32>::from([Some(1), None, Some(123)])) as Arc<dyn Array>;
+
+    // the goal is to export this array and import it back via FFI.
+    // to import, we initialize the structs that will receive the data
+    let array_ptr = Box::new(ffi::Ffi_ArrowArray::empty());
+    let schema_ptr = Box::new(ffi::Ffi_ArrowSchema::empty());
+
+    // since FFIs work in raw pointers, let's temporarily relinquish ownership so that producers
+    // can write into it in a thread-safe manner
+    let array_ptr = Box::into_raw(array_ptr);
+    let schema_ptr = Box::into_raw(schema_ptr);
+
+    // this is where a producer (in this case also us ^_^) writes to the pointers' location.
+    // `array` here could be anything or not even be available, if this was e.g. from Python.
+    // Safety: we just allocated the pointers correctly.
+    unsafe { export(array.clone(), array_ptr, schema_ptr) };
+
+    // we can now take ownership back, since we are responsible for deallocating this memory.
+    // Safety: we just into_raw them.
+    let array_ptr = unsafe { Box::from_raw(array_ptr) };
+    let schema_ptr = unsafe { Box::from_raw(schema_ptr) };
+
+    // and finally interpret the written memory into a new array.
+    let new_array = import(array_ptr, schema_ptr.as_ref())?;
+
+    // which is equal to the exported array
+    assert_eq!(array.as_ref(), new_array.as_ref());
+    Ok(())
+}
diff --git a/guide/src/ffi.md b/guide/src/ffi.md
index 2cf87b0b9c..40d01984c3 100644
--- a/guide/src/ffi.md
+++ b/guide/src/ffi.md
@@ -5,58 +5,9 @@ has a specification, which allows languages to share data
 structures via foreign interfaces at zero cost (i.e. via pointers).
 This is known as the [C Data interface](https://arrow.apache.org/docs/format/CDataInterface.html).
 
-This crate supports importing from and exporting to most of `DataType`s.
-Types currently not supported:
-
-* `FixedSizeBinary`
-* `Union`
-* `Dictionary`
-* `FixedSizeList`
-* `Null`
-
-## Export
-
-The API to export an `Array` is as follows:
-
-```rust
-use std::sync::Arc;
-use arrow2::array::{Array, PrimitiveArray};
-use arrow2::datatypes::DataType;
-use arrow2::ffi::ArrowArray;
-
-# fn main() {
-// Example of an array:
-let array = [Some(1), None, Some(123)]
-    .iter()
-    .collect::<PrimitiveArray<i32>>();
-
-// export the array.
-let ffi_array = ffi::export_to_c(Arc::new(array))?;
-
-// these are mutable pointers to `ArrowArray` and `ArrowSchema` of the C data interface
-let (array_ptr, schema_ptr) = ffi_array.references();
-# }
-```
-
-## Import
-
-The API to import works similarly:
+This crate supports importing from and exporting to all `DataType`s. Follow the
+example below to learn how to import and export:
 
 ```rust
-use arrow2::array::Array;
-use arrow2::ffi;
-
-let array = Arc::new(ffi::create_empty());
-
-// non-owned mutable pointers.
-let (array_ptr, schema_ptr) = array.references();
-
-// write to the pointers using any C data interface exporter
-
-// consume it to a `Box<dyn Array>`
-let array = ffi::try_from(array)?;
+{{#include ../../examples/ffi.rs}}
 ```
-
-This assumes that the exporter writes to `array_ptr` and `schema_ptr` 
-according to the c data interface. This is an intrinsically `unsafe` operation.
-Failing to do so results in UB.
diff --git a/src/array/binary/ffi.rs b/src/array/binary/ffi.rs
index a216be7b42..63d0ea66f3 100644
--- a/src/array/binary/ffi.rs
+++ b/src/array/binary/ffi.rs
@@ -25,7 +25,7 @@ unsafe impl<O: Offset> ToFfi for BinaryArray<O> {
 
 unsafe impl<O: Offset, A: ffi::ArrowArrayRef> FromFfi<A> for BinaryArray<O> {
     fn try_from_ffi(array: A) -> Result<Self> {
-        let data_type = array.field()?.data_type().clone();
+        let data_type = array.field().data_type().clone();
         let expected = if O::is_large() {
             DataType::LargeBinary
         } else {
diff --git a/src/array/boolean/ffi.rs b/src/array/boolean/ffi.rs
index b141c3a3a6..9dedfbc41d 100644
--- a/src/array/boolean/ffi.rs
+++ b/src/array/boolean/ffi.rs
@@ -23,7 +23,7 @@ unsafe impl ToFfi for BooleanArray {
 
 unsafe impl<A: ffi::ArrowArrayRef> FromFfi<A> for BooleanArray {
     fn try_from_ffi(array: A) -> Result<Self> {
-        let data_type = array.field()?.data_type().clone();
+        let data_type = array.field().data_type().clone();
         assert_eq!(data_type, DataType::Boolean);
         let length = array.array().len();
         let offset = array.array().offset();
diff --git a/src/array/list/ffi.rs b/src/array/list/ffi.rs
index 63d6e8f586..97bea8cbc3 100644
--- a/src/array/list/ffi.rs
+++ b/src/array/list/ffi.rs
@@ -24,7 +24,7 @@ unsafe impl<O: Offset> ToFfi for ListArray<O> {
 
 unsafe impl<O: Offset, A: ffi::ArrowArrayRef> FromFfi<A> for ListArray<O> {
     fn try_from_ffi(array: A) -> Result<Self> {
-        let data_type = array.field()?.data_type().clone();
+        let data_type = array.field().data_type().clone();
         let length = array.array().len();
         let offset = array.array().offset();
         let mut validity = unsafe { array.validity() }?;
diff --git a/src/array/primitive/ffi.rs b/src/array/primitive/ffi.rs
index 5168f322b7..1c3f534970 100644
--- a/src/array/primitive/ffi.rs
+++ b/src/array/primitive/ffi.rs
@@ -24,7 +24,7 @@ unsafe impl<T: NativeType> ToFfi for PrimitiveArray<T> {
 
 unsafe impl<T: NativeType, A: ffi::ArrowArrayRef> FromFfi<A> for PrimitiveArray<T> {
     fn try_from_ffi(array: A) -> Result<Self> {
-        let data_type = array.field()?.data_type().clone();
+        let data_type = array.field().data_type().clone();
         let length = array.array().len();
         let offset = array.array().offset();
         let mut validity = unsafe { array.validity() }?;
diff --git a/src/array/struct_.rs b/src/array/struct_.rs
index 9a6191a5d4..41763c464e 100644
--- a/src/array/struct_.rs
+++ b/src/array/struct_.rs
@@ -153,7 +153,7 @@ unsafe impl ToFfi for StructArray {
 
 unsafe impl<A: ffi::ArrowArrayRef> FromFfi<A> for StructArray {
     fn try_from_ffi(array: A) -> Result<Self> {
-        let field = array.field()?;
+        let field = array.field();
         let fields = Self::get_fields(field.data_type()).to_vec();
 
         let length = array.array().len();
diff --git a/src/array/union/ffi.rs b/src/array/union/ffi.rs
index 7028480e04..f07b7092ea 100644
--- a/src/array/union/ffi.rs
+++ b/src/array/union/ffi.rs
@@ -29,7 +29,7 @@ unsafe impl ToFfi for UnionArray {
 
 unsafe impl<A: ffi::ArrowArrayRef> FromFfi<A> for UnionArray {
     fn try_from_ffi(array: A) -> Result<Self> {
-        let field = array.field()?;
+        let field = array.field();
         let data_type = field.data_type().clone();
         let fields = Self::get_fields(field.data_type());
 
diff --git a/src/ffi/array.rs b/src/ffi/array.rs
index 8f947d1b1c..833657bc27 100644
--- a/src/ffi/array.rs
+++ b/src/ffi/array.rs
@@ -32,8 +32,7 @@ use crate::{
 /// * the data type is not supported
 /// * the interface is not valid (e.g. a null pointer)
 pub fn try_from<A: ArrowArrayRef>(array: A) -> Result<Box<dyn Array>> {
-    let field = array.field()?;
-    let array: Box<dyn Array> = match field.data_type() {
+    let array: Box<dyn Array> = match array.field().data_type() {
         DataType::Boolean => Box::new(BooleanArray::try_from_ffi(array)?),
         DataType::Int8 => Box::new(PrimitiveArray::<i8>::try_from_ffi(array)?),
         DataType::Int16 => Box::new(PrimitiveArray::<i16>::try_from_ffi(array)?),
diff --git a/src/ffi/ffi.rs b/src/ffi/ffi.rs
index 756b0b04da..cbb08f2fa6 100644
--- a/src/ffi/ffi.rs
+++ b/src/ffi/ffi.rs
@@ -17,7 +17,6 @@
 
 use std::{ptr::NonNull, sync::Arc};
 
-use super::schema::{to_field, Ffi_ArrowSchema};
 use crate::{
     array::{buffers_children_dictionary, Array},
     bitmap::{utils::bytes_for, Bitmap},
@@ -27,6 +26,7 @@ use crate::{
     },
     datatypes::{DataType, Field},
     error::{ArrowError, Result},
+    ffi::schema::get_field_child,
     types::NativeType,
 };
 
@@ -95,7 +95,7 @@ impl Ffi_ArrowArray {
     /// # Safety
     /// This method releases `buffers`. Consumers of this struct *must* call `release` before
     /// releasing this struct, or contents in `buffers` leak.
-    fn new(array: Arc<dyn Array>) -> Self {
+    pub(crate) fn new(array: Arc<dyn Array>) -> Self {
         let (buffers, children, dictionary) = buffers_children_dictionary(array.as_ref());
 
         let buffers_ptr = buffers
@@ -142,7 +142,7 @@ impl Ffi_ArrowArray {
     }
 
     // create an empty `Ffi_ArrowArray`, which can be used to import data into
-    fn empty() -> Self {
+    pub fn empty() -> Self {
         Self {
             length: 0,
             null_count: 0,
@@ -158,22 +158,17 @@ impl Ffi_ArrowArray {
     }
 
     /// the length of the array
-    pub fn len(&self) -> usize {
+    pub(crate) fn len(&self) -> usize {
         self.length as usize
     }
 
-    /// whether the array is empty
-    pub fn is_empty(&self) -> bool {
-        self.length == 0
-    }
-
     /// the offset of the array
-    pub fn offset(&self) -> usize {
+    pub(crate) fn offset(&self) -> usize {
         self.offset as usize
     }
 
     /// the null count of the array
-    pub fn null_count(&self) -> usize {
+    pub(crate) fn null_count(&self) -> usize {
         self.null_count as usize
     }
 }
@@ -283,31 +278,32 @@ fn buffer_len(array: &Ffi_ArrowArray, data_type: &DataType, i: usize) -> Result<
 
 fn create_child(
     array: &Ffi_ArrowArray,
-    schema: &Ffi_ArrowSchema,
+    field: &Field,
     parent: Arc<ArrowArray>,
     index: usize,
 ) -> Result<ArrowArrayChild<'static>> {
+    let field = get_field_child(field, index)?;
     assert!(index < array.n_children as usize);
     assert!(!array.children.is_null());
     unsafe {
         let arr_ptr = *array.children.add(index);
-        let schema_ptr = schema.child(index);
         assert!(!arr_ptr.is_null());
         let arr_ptr = &*arr_ptr;
-        Ok(ArrowArrayChild::from_raw(arr_ptr, schema_ptr, parent))
+
+        Ok(ArrowArrayChild::from_raw(arr_ptr, field, parent))
     }
 }
 
 fn create_dictionary(
     array: &Ffi_ArrowArray,
-    schema: &Ffi_ArrowSchema,
+    field: &Field,
     parent: Arc<ArrowArray>,
 ) -> Result<Option<ArrowArrayChild<'static>>> {
-    let schema = schema.dictionary();
-    if let Some(schema) = schema {
+    if let DataType::Dictionary(_, values) = field.data_type() {
+        let field = Field::new("", values.as_ref().clone(), true);
         assert!(!array.dictionary.is_null());
         let array = unsafe { &*array.dictionary };
-        Ok(Some(ArrowArrayChild::from_raw(array, schema, parent)))
+        Ok(Some(ArrowArrayChild::from_raw(array, field, parent)))
     } else {
         Ok(None)
     }
@@ -339,7 +335,7 @@ pub trait ArrowArrayRef {
         // +1 to ignore null bitmap
         create_buffer::<T>(
             self.array(),
-            self.field()?.data_type(),
+            self.field().data_type(),
             self.deallocation(),
             index + 1,
         )
@@ -354,17 +350,16 @@ pub trait ArrowArrayRef {
     }
 
     fn child(&self, index: usize) -> Result<ArrowArrayChild> {
-        create_child(self.array(), self.schema(), self.parent().clone(), index)
+        create_child(self.array(), self.field(), self.parent().clone(), index)
     }
 
     fn dictionary(&self) -> Result<Option<ArrowArrayChild>> {
-        create_dictionary(self.array(), self.schema(), self.parent().clone())
+        create_dictionary(self.array(), self.field(), self.parent().clone())
     }
 
     fn parent(&self) -> &Arc<ArrowArray>;
     fn array(&self) -> &Ffi_ArrowArray;
-    fn schema(&self) -> &Ffi_ArrowSchema;
-    fn field(&self) -> Result<Field>;
+    fn field(&self) -> &Field;
 }
 
 /// Struct used to move an Array from and to the C Data Interface.
@@ -388,14 +383,20 @@ pub trait ArrowArrayRef {
 /// Furthermore, this struct assumes that the incoming data agrees with the C data interface.
 #[derive(Debug)]
 pub struct ArrowArray {
-    array: Arc<Ffi_ArrowArray>,
-    schema: Arc<Ffi_ArrowSchema>,
+    array: Box<Ffi_ArrowArray>,
+    field: Field,
+}
+
+impl ArrowArray {
+    pub fn new(array: Box<Ffi_ArrowArray>, field: Field) -> Self {
+        Self { array, field }
+    }
 }
 
 impl ArrowArrayRef for Arc<ArrowArray> {
     /// the data_type as declared in the schema
-    fn field(&self) -> Result<Field> {
-        to_field(&self.schema)
+    fn field(&self) -> &Field {
+        &self.field
     }
 
     fn parent(&self) -> &Arc<ArrowArray> {
@@ -405,23 +406,19 @@ impl ArrowArrayRef for Arc<ArrowArray> {
     fn array(&self) -> &Ffi_ArrowArray {
         self.array.as_ref()
     }
-
-    fn schema(&self) -> &Ffi_ArrowSchema {
-        self.schema.as_ref()
-    }
 }
 
 #[derive(Debug)]
 pub struct ArrowArrayChild<'a> {
     array: &'a Ffi_ArrowArray,
-    schema: &'a Ffi_ArrowSchema,
+    field: Field,
     parent: Arc<ArrowArray>,
 }
 
 impl<'a> ArrowArrayRef for ArrowArrayChild<'a> {
     /// the data_type as declared in the schema
-    fn field(&self) -> Result<Field> {
-        to_field(self.schema)
+    fn field(&self) -> &Field {
+        &self.field
     }
 
     fn parent(&self) -> &Arc<ArrowArray> {
@@ -431,48 +428,14 @@ impl<'a> ArrowArrayRef for ArrowArrayChild<'a> {
     fn array(&self) -> &Ffi_ArrowArray {
         self.array
     }
-
-    fn schema(&self) -> &Ffi_ArrowSchema {
-        self.schema
-    }
 }
 
 impl<'a> ArrowArrayChild<'a> {
-    fn from_raw(
-        array: &'a Ffi_ArrowArray,
-        schema: &'a Ffi_ArrowSchema,
-        parent: Arc<ArrowArray>,
-    ) -> Self {
+    fn from_raw(array: &'a Ffi_ArrowArray, field: Field, parent: Arc<ArrowArray>) -> Self {
         Self {
             array,
-            schema,
+            field,
             parent,
         }
     }
 }
-
-/// Exports an `Array` to the C data interface.
-pub fn export_to_c(array: Arc<dyn Array>) -> Result<ArrowArray> {
-    let field = Field::new("", array.data_type().clone(), array.null_count() != 0);
-
-    Ok(ArrowArray {
-        array: Arc::new(Ffi_ArrowArray::new(array)),
-        schema: Arc::new(Ffi_ArrowSchema::try_new(field)?),
-    })
-}
-
-pub fn create_empty() -> ArrowArray {
-    ArrowArray {
-        array: Arc::new(Ffi_ArrowArray::empty()),
-        schema: Arc::new(Ffi_ArrowSchema::empty()),
-    }
-}
-
-impl ArrowArray {
-    pub fn references(&self) -> (*mut Ffi_ArrowArray, *mut Ffi_ArrowSchema) {
-        (
-            self.array.as_ref() as *const Ffi_ArrowArray as *mut Ffi_ArrowArray,
-            self.schema.as_ref() as *const Ffi_ArrowSchema as *mut Ffi_ArrowSchema,
-        )
-    }
-}
diff --git a/src/ffi/mod.rs b/src/ffi/mod.rs
index 19fa83a8fb..15504487c9 100644
--- a/src/ffi/mod.rs
+++ b/src/ffi/mod.rs
@@ -5,5 +5,40 @@ mod array;
 mod ffi;
 mod schema;
 
-pub use array::try_from;
-pub use ffi::{create_empty, export_to_c, ArrowArray, ArrowArrayRef};
+pub(crate) use array::try_from;
+pub(crate) use ffi::{ArrowArray, ArrowArrayRef};
+
+use std::sync::Arc;
+
+use crate::array::Array;
+use crate::datatypes::Field;
+use crate::error::Result;
+
+pub use ffi::Ffi_ArrowArray;
+pub use schema::Ffi_ArrowSchema;
+
+use self::schema::to_field;
+
+/// Exports an `Array` to the C data interface.
+/// # Safety
+/// The pointer must be allocated and valid
+pub unsafe fn export_array_to_c(array: Arc<dyn Array>, ptr: *mut Ffi_ArrowArray) {
+    *ptr = Ffi_ArrowArray::new(array);
+}
+
+/// Exports a [`Field`] to the C data interface.
+/// # Safety
+/// The pointer must be allocated and valid
+pub unsafe fn export_field_to_c(field: &Field, ptr: *mut Ffi_ArrowSchema) {
+    *ptr = Ffi_ArrowSchema::new(field)
+}
+
+/// Imports a [`Field`] from the C data interface.
+pub fn import_field_from_c(field: &Ffi_ArrowSchema) -> Result<Field> {
+    to_field(field)
+}
+
+/// Imports a [`Field`] from the C data interface.
+pub fn import_array_from_c(array: Box<Ffi_ArrowArray>, field: &Field) -> Result<Box<dyn Array>> {
+    try_from(Arc::new(ArrowArray::new(array, field.clone())))
+}
diff --git a/src/ffi/schema.rs b/src/ffi/schema.rs
index 926871af11..75a0665000 100644
--- a/src/ffi/schema.rs
+++ b/src/ffi/schema.rs
@@ -7,14 +7,13 @@ use crate::{
 
 #[allow(dead_code)]
 struct SchemaPrivateData {
-    field: Field,
     children_ptr: Box<[*mut Ffi_ArrowSchema]>,
     dictionary: Option<*mut Ffi_ArrowSchema>,
 }
 
 /// ABI-compatible struct for `ArrowSchema` from C Data Interface
 /// See <https://arrow.apache.org/docs/format/CDataInterface.html#structure-definitions>
-/// This was created by bindgen
+// This was created by bindgen
 #[repr(C)]
 #[derive(Debug)]
 pub struct Ffi_ArrowSchema {
@@ -52,27 +51,27 @@ unsafe extern "C" fn c_release_schema(schema: *mut Ffi_ArrowSchema) {
 }
 
 impl Ffi_ArrowSchema {
-    /// create a new [`Ffi_ArrowSchema`]. This fails if the fields' [`DataType`] is not supported.
-    pub fn try_new(field: Field) -> Result<Ffi_ArrowSchema> {
-        let format = to_format(field.data_type())?;
+    /// creates a new [Ffi_ArrowSchema]
+    pub(crate) fn new(field: &Field) -> Self {
+        let format = to_format(field.data_type());
         let name = field.name().clone();
 
         // allocate (and hold) the children
         let children_vec = match field.data_type() {
             DataType::List(field) => {
-                vec![Box::new(Ffi_ArrowSchema::try_new(field.as_ref().clone())?)]
+                vec![Box::new(Ffi_ArrowSchema::new(field.as_ref()))]
             }
             DataType::LargeList(field) => {
-                vec![Box::new(Ffi_ArrowSchema::try_new(field.as_ref().clone())?)]
+                vec![Box::new(Ffi_ArrowSchema::new(field.as_ref()))]
             }
             DataType::Struct(fields) => fields
                 .iter()
-                .map(|field| Ok(Box::new(Ffi_ArrowSchema::try_new(field.clone())?)))
-                .collect::<Result<Vec<_>>>()?,
+                .map(|field| Box::new(Ffi_ArrowSchema::new(field)))
+                .collect::<Vec<_>>(),
             DataType::Union(fields, _, _) => fields
                 .iter()
-                .map(|field| Ok(Box::new(Ffi_ArrowSchema::try_new(field.clone())?)))
-                .collect::<Result<Vec<_>>>()?,
+                .map(|field| Box::new(Ffi_ArrowSchema::new(field)))
+                .collect::<Vec<_>>(),
             _ => vec![],
         };
         // note: this cannot be done along with the above because the above is fallible and this op leaks.
@@ -86,20 +85,19 @@ impl Ffi_ArrowSchema {
 
         let dictionary = if let DataType::Dictionary(_, values) = field.data_type() {
             // we do not store field info in the dict values, so can't recover it all :(
-            let field = Field::new("item", values.as_ref().clone(), true);
-            Some(Box::new(Ffi_ArrowSchema::try_new(field)?))
+            let field = Field::new("", values.as_ref().clone(), true);
+            Some(Box::new(Ffi_ArrowSchema::new(&field)))
         } else {
             None
         };
 
         let mut private = Box::new(SchemaPrivateData {
-            field,
             children_ptr,
             dictionary: dictionary.map(Box::into_raw),
         });
 
         // <https://arrow.apache.org/docs/format/CDataInterface.html#c.ArrowSchema>
-        Ok(Ffi_ArrowSchema {
+        Self {
             format: CString::new(format).unwrap().into_raw(),
             name: CString::new(name).unwrap().into_raw(),
             metadata: std::ptr::null_mut(),
@@ -109,7 +107,7 @@ impl Ffi_ArrowSchema {
             dictionary: private.dictionary.unwrap_or(std::ptr::null_mut()),
             release: Some(c_release_schema),
             private_data: Box::into_raw(private) as *mut ::std::os::raw::c_void,
-        })
+        }
     }
 
     /// create an empty [Ffi_ArrowSchema]
@@ -128,7 +126,7 @@ impl Ffi_ArrowSchema {
     }
 
     /// returns the format of this schema.
-    pub fn format(&self) -> &str {
+    pub(crate) fn format(&self) -> &str {
         assert!(!self.format.is_null());
         // safe because the lifetime of `self.format` equals `self`
         unsafe { CStr::from_ptr(self.format) }
@@ -137,26 +135,26 @@ impl Ffi_ArrowSchema {
     }
 
     /// returns the name of this schema.
-    pub fn name(&self) -> &str {
+    pub(crate) fn name(&self) -> &str {
         assert!(!self.name.is_null());
         // safe because the lifetime of `self.name` equals `self`
         unsafe { CStr::from_ptr(self.name) }.to_str().unwrap()
     }
 
-    pub fn child(&self, index: usize) -> &'static Self {
+    pub(crate) fn child(&self, index: usize) -> &'static Self {
         assert!(index < self.n_children as usize);
         assert!(!self.name.is_null());
         unsafe { self.children.add(index).as_ref().unwrap().as_ref().unwrap() }
     }
 
-    pub fn dictionary(&self) -> Option<&'static Self> {
+    pub(crate) fn dictionary(&self) -> Option<&'static Self> {
         if self.dictionary.is_null() {
             return None;
         };
         Some(unsafe { self.dictionary.as_ref().unwrap() })
     }
 
-    pub fn nullable(&self) -> bool {
+    pub(crate) fn nullable(&self) -> bool {
         (self.flags / 2) & 1 == 1
     }
 }
@@ -174,8 +172,11 @@ pub fn to_field(schema: &Ffi_ArrowSchema) -> Result<Field> {
     let dictionary = schema.dictionary();
     let data_type = if let Some(dictionary) = dictionary {
         let indices_data_type = to_data_type(schema)?;
-        let values_data_type = to_data_type(dictionary)?;
-        DataType::Dictionary(Box::new(indices_data_type), Box::new(values_data_type))
+        let values = to_field(dictionary)?;
+        DataType::Dictionary(
+            Box::new(indices_data_type),
+            Box::new(values.data_type().clone()),
+        )
     } else {
         to_data_type(schema)?
     };
@@ -285,56 +286,62 @@ fn to_data_type(schema: &Ffi_ArrowSchema) -> Result<DataType> {
 }
 
 /// the inverse of [to_field]
-fn to_format(data_type: &DataType) -> Result<String> {
-    Ok(match data_type {
-        DataType::Null => "n",
-        DataType::Boolean => "b",
-        DataType::Int8 => "c",
-        DataType::UInt8 => "C",
-        DataType::Int16 => "s",
-        DataType::UInt16 => "S",
-        DataType::Int32 => "i",
-        DataType::UInt32 => "I",
-        DataType::Int64 => "l",
-        DataType::UInt64 => "L",
-        DataType::Float16 => "e",
-        DataType::Float32 => "f",
-        DataType::Float64 => "g",
-        DataType::Binary => "z",
-        DataType::LargeBinary => "Z",
-        DataType::Utf8 => "u",
-        DataType::LargeUtf8 => "U",
-        DataType::Date32 => "tdD",
-        DataType::Date64 => "tdm",
-        DataType::Time32(TimeUnit::Second) => "tts",
-        DataType::Time32(TimeUnit::Millisecond) => "ttm",
-        DataType::Time64(TimeUnit::Microsecond) => "ttu",
-        DataType::Time64(TimeUnit::Nanosecond) => "ttn",
-        DataType::Duration(TimeUnit::Second) => "tDs",
-        DataType::Duration(TimeUnit::Millisecond) => "tDm",
-        DataType::Duration(TimeUnit::Microsecond) => "tDu",
-        DataType::Duration(TimeUnit::Nanosecond) => "tDn",
-        DataType::Interval(IntervalUnit::YearMonth) => "tiM",
-        DataType::Interval(IntervalUnit::DayTime) => "tiD",
+fn to_format(data_type: &DataType) -> String {
+    match data_type {
+        DataType::Null => "n".to_string(),
+        DataType::Boolean => "b".to_string(),
+        DataType::Int8 => "c".to_string(),
+        DataType::UInt8 => "C".to_string(),
+        DataType::Int16 => "s".to_string(),
+        DataType::UInt16 => "S".to_string(),
+        DataType::Int32 => "i".to_string(),
+        DataType::UInt32 => "I".to_string(),
+        DataType::Int64 => "l".to_string(),
+        DataType::UInt64 => "L".to_string(),
+        DataType::Float16 => "e".to_string(),
+        DataType::Float32 => "f".to_string(),
+        DataType::Float64 => "g".to_string(),
+        DataType::Binary => "z".to_string(),
+        DataType::LargeBinary => "Z".to_string(),
+        DataType::Utf8 => "u".to_string(),
+        DataType::LargeUtf8 => "U".to_string(),
+        DataType::Date32 => "tdD".to_string(),
+        DataType::Date64 => "tdm".to_string(),
+        DataType::Time32(TimeUnit::Second) => "tts".to_string(),
+        DataType::Time32(TimeUnit::Millisecond) => "ttm".to_string(),
+        DataType::Time32(_) => {
+            unreachable!("Time32 is only supported for seconds and milliseconds")
+        }
+        DataType::Time64(TimeUnit::Microsecond) => "ttu".to_string(),
+        DataType::Time64(TimeUnit::Nanosecond) => "ttn".to_string(),
+        DataType::Time64(_) => {
+            unreachable!("Time64 is only supported for micro and nanoseconds")
+        }
+        DataType::Duration(TimeUnit::Second) => "tDs".to_string(),
+        DataType::Duration(TimeUnit::Millisecond) => "tDm".to_string(),
+        DataType::Duration(TimeUnit::Microsecond) => "tDu".to_string(),
+        DataType::Duration(TimeUnit::Nanosecond) => "tDn".to_string(),
+        DataType::Interval(IntervalUnit::YearMonth) => "tiM".to_string(),
+        DataType::Interval(IntervalUnit::DayTime) => "tiD".to_string(),
         DataType::Timestamp(unit, tz) => {
             let unit = match unit {
-                TimeUnit::Second => "s",
-                TimeUnit::Millisecond => "m",
-                TimeUnit::Microsecond => "u",
-                TimeUnit::Nanosecond => "n",
+                TimeUnit::Second => "s".to_string(),
+                TimeUnit::Millisecond => "m".to_string(),
+                TimeUnit::Microsecond => "u".to_string(),
+                TimeUnit::Nanosecond => "n".to_string(),
             };
-            return Ok(format!(
+            format!(
                 "ts{}:{}",
                 unit,
                 tz.as_ref().map(|x| x.as_ref()).unwrap_or("")
-            ));
+            )
         }
-        DataType::Decimal(precision, scale) => return Ok(format!("d:{},{}", precision, scale)),
-        DataType::List(_) => "+l",
-        DataType::LargeList(_) => "+L",
-        DataType::Struct(_) => "+s",
-        DataType::FixedSizeBinary(size) => return Ok(format!("w{}", size)),
-        DataType::FixedSizeList(_, size) => return Ok(format!("+w:{}", size)),
+        DataType::Decimal(precision, scale) => format!("d:{},{}", precision, scale),
+        DataType::List(_) => "+l".to_string(),
+        DataType::LargeList(_) => "+L".to_string(),
+        DataType::Struct(_) => "+s".to_string(),
+        DataType::FixedSizeBinary(size) => format!("w{}", size),
+        DataType::FixedSizeList(_, size) => format!("+w:{}", size),
         DataType::Union(f, ids, is_sparse) => {
             let sparsness = if *is_sparse { 's' } else { 'd' };
             let mut r = format!("+u{}:", sparsness);
@@ -346,10 +353,21 @@ fn to_format(data_type: &DataType) -> Result<String> {
             };
             let ids = &ids[..ids.len() - 1]; // take away last ","
             r.push_str(ids);
-            return Ok(r);
+            r
         }
-        DataType::Dictionary(index, _) => return to_format(index.as_ref()),
-        _ => todo!(),
+        DataType::Dictionary(index, _) => to_format(index.as_ref()),
+    }
+}
+
+pub(super) fn get_field_child(field: &Field, index: usize) -> Result<Field> {
+    match (index, field.data_type()) {
+        (0, DataType::List(field)) => Ok(field.as_ref().clone()),
+        (0, DataType::LargeList(field)) => Ok(field.as_ref().clone()),
+        (index, DataType::Struct(fields)) => Ok(fields[index].clone()),
+        (index, DataType::Union(fields, _, _)) => Ok(fields[index].clone()),
+        (child, data_type) => Err(ArrowError::Ffi(format!(
+            "Requested child {} to type {:?} that has no such child",
+            child, data_type
+        ))),
     }
-    .to_string())
 }


Test patch:
diff --git a/arrow-pyarrow-integration-testing/Cargo.toml b/arrow-pyarrow-integration-testing/Cargo.toml
index 97a64a9c50..551868e30e 100644
--- a/arrow-pyarrow-integration-testing/Cargo.toml
+++ b/arrow-pyarrow-integration-testing/Cargo.toml
@@ -17,13 +17,9 @@
 
 [package]
 name = "arrow-pyarrow-integration-testing"
-description = ""
-version = "4.0.0-SNAPSHOT"
-homepage = "https://github.com/apache/arrow-rs"
-repository = "https://github.com/apache/arrow-rs"
-authors = ["Apache Arrow <dev@arrow.apache.org>"]
+version = "0.0.0"
+authors = ["Jorge C. Leitao <jorgecarleitao@gmail.com>", "Apache Arrow <dev@arrow.apache.org>"]
 license = "Apache-2.0"
-keywords = [ "arrow" ]
 edition = "2018"
 
 [lib]
@@ -31,8 +27,8 @@ name = "arrow_pyarrow_integration_testing"
 crate-type = ["cdylib"]
 
 [dependencies]
-arrow2 = { path = "../", default-features = false, features = ["compute"] }
-pyo3 = { version = "0.12.1", features = ["extension-module"] }
+arrow2 = { path = "../", default-features = false }
+pyo3 = { version = "0.14", features = ["extension-module"] }
 
 [package.metadata.maturin]
 requires-dist = ["pyarrow>=1"]
diff --git a/arrow-pyarrow-integration-testing/src/lib.rs b/arrow-pyarrow-integration-testing/src/lib.rs
index 666f433879..0f6bdf8e2f 100644
--- a/arrow-pyarrow-integration-testing/src/lib.rs
+++ b/arrow-pyarrow-integration-testing/src/lib.rs
@@ -1,20 +1,3 @@
-// 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.
-
 //! This library demonstrates a minimal usage of Rust's C data interface to pass
 //! arrays from and to Python.
 
@@ -23,15 +6,11 @@ use std::fmt;
 use std::sync::Arc;
 
 use pyo3::exceptions::PyOSError;
+use pyo3::ffi::Py_uintptr_t;
+use pyo3::prelude::*;
 use pyo3::wrap_pyfunction;
-use pyo3::{libc::uintptr_t, prelude::*};
-
-use arrow2::array::{Array, Int64Array};
-use arrow2::ffi;
-use arrow2::{array::PrimitiveArray, compute};
-use arrow2::{datatypes::DataType, error::ArrowError};
 
-type ArrayRef = Arc<dyn Array>;
+use arrow2::{array::Array, datatypes::Field, error::ArrowError, ffi};
 
 /// an error that bridges ArrowError with a Python error
 #[derive(Debug)]
@@ -70,130 +49,107 @@ impl From<PyO3ArrowError> for PyErr {
     }
 }
 
-fn to_rust(ob: PyObject, py: Python) -> PyResult<ArrayRef> {
+fn to_rust_array(ob: PyObject, py: Python) -> PyResult<Arc<dyn Array>> {
     // prepare a pointer to receive the Array struct
-    let array = Arc::new(ffi::create_empty());
-    let (array_ptr, schema_ptr) = array.references();
+    let array = Box::new(ffi::Ffi_ArrowArray::empty());
+    let schema = Box::new(ffi::Ffi_ArrowSchema::empty());
+
+    let array_ptr = &*array as *const ffi::Ffi_ArrowArray;
+    let schema_ptr = &*schema as *const ffi::Ffi_ArrowSchema;
 
     // make the conversion through PyArrow's private API
     // this changes the pointer's memory and is thus unsafe. In particular, `_export_to_c` can go out of bounds
     ob.call_method1(
         py,
         "_export_to_c",
-        (array_ptr as uintptr_t, schema_ptr as uintptr_t),
+        (array_ptr as Py_uintptr_t, schema_ptr as Py_uintptr_t),
     )?;
 
-    Ok(ffi::try_from(array).map_err(PyO3ArrowError::from)?.into())
+    let field = ffi::import_field_from_c(schema.as_ref()).map_err(PyO3ArrowError::from)?;
+    let array = ffi::import_array_from_c(array, &field).map_err(PyO3ArrowError::from)?;
+
+    Ok(array.into())
 }
 
-fn to_py(array: ArrayRef, py: Python) -> PyResult<PyObject> {
-    let array_ptr = ffi::export_to_c(array).map_err(PyO3ArrowError::from)?;
+fn to_py_array(array: Arc<dyn Array>, py: Python) -> PyResult<PyObject> {
+    let array_ptr = Box::new(ffi::Ffi_ArrowArray::empty());
+    let schema_ptr = Box::new(ffi::Ffi_ArrowSchema::empty());
+
+    let array_ptr = Box::into_raw(array_ptr);
+    let schema_ptr = Box::into_raw(schema_ptr);
 
-    let (array_ptr, schema_ptr) = array_ptr.references();
+    unsafe {
+        ffi::export_field_to_c(&Field::new("", array.data_type().clone(), true), schema_ptr);
+        ffi::export_array_to_c(array, array_ptr);
+    };
 
     let pa = py.import("pyarrow")?;
 
     let array = pa.getattr("Array")?.call_method1(
         "_import_from_c",
-        (array_ptr as uintptr_t, schema_ptr as uintptr_t),
+        (array_ptr as Py_uintptr_t, schema_ptr as Py_uintptr_t),
     )?;
 
-    Ok(array.to_object(py))
-}
+    unsafe {
+        Box::from_raw(array_ptr);
+        Box::from_raw(schema_ptr);
+    };
 
-/// Returns `array + array` of an int64 array.
-#[pyfunction]
-fn double(array: PyObject, py: Python) -> PyResult<PyObject> {
-    // import
-    let array = to_rust(array, py)?;
-
-    // perform some operation
-    let array = array.as_any().downcast_ref::<Int64Array>().ok_or_else(|| {
-        PyO3ArrowError::ArrowError(ArrowError::Ffi("Expects an int64".to_string()))
-    })?;
-    let array =
-        compute::arithmetics::basic::add::add(&array, &array).map_err(PyO3ArrowError::from)?;
-    let array = Arc::new(array);
-
-    // export
-    to_py(array, py)
+    Ok(array.to_object(py))
 }
 
-/// calls a lambda function that receives and returns an array
-/// whose result must be the array multiplied by two
-#[pyfunction]
-fn double_py(lambda: PyObject, py: Python) -> PyResult<bool> {
-    // create
-    let array = Arc::new(PrimitiveArray::<i64>::from(vec![Some(1), None, Some(3)]));
-    let expected = Arc::new(PrimitiveArray::<i64>::from(vec![Some(2), None, Some(6)])) as ArrayRef;
+fn to_rust_field(ob: PyObject, py: Python) -> PyResult<Field> {
+    // prepare a pointer to receive the Array struct
+    let schema = Box::new(ffi::Ffi_ArrowSchema::empty());
 
-    // to py
-    let array = to_py(array, py)?;
+    let schema_ptr = &*schema as *const ffi::Ffi_ArrowSchema;
 
-    let array = lambda.call1(py, (array,))?;
+    // make the conversion through PyArrow's private API
+    // this changes the pointer's memory and is thus unsafe. In particular, `_export_to_c` can go out of bounds
+    ob.call_method1(py, "_export_to_c", (schema_ptr as Py_uintptr_t,))?;
 
-    let array = to_rust(array, py)?;
+    let field = ffi::import_field_from_c(schema.as_ref()).map_err(PyO3ArrowError::from)?;
 
-    Ok(array == expected)
+    Ok(field)
 }
 
-/// Returns the substring
-#[pyfunction]
-fn substring(array: PyObject, start: i64, py: Python) -> PyResult<PyObject> {
-    // import
-    let array = to_rust(array, py)?;
+fn to_py_field(field: &Field, py: Python) -> PyResult<PyObject> {
+    let schema_ptr = Box::new(ffi::Ffi_ArrowSchema::empty());
+    let schema_ptr = Box::into_raw(schema_ptr);
 
-    // substring
-    let array = compute::substring::substring(array.as_ref(), start, &None)
-        .map_err(PyO3ArrowError::from)?
-        .into();
+    unsafe {
+        ffi::export_field_to_c(field, schema_ptr);
+    };
 
-    // export
-    to_py(array, py)
-}
+    let pa = py.import("pyarrow")?;
 
-/// Returns the concatenate
-#[pyfunction]
-fn concatenate(array: PyObject, py: Python) -> PyResult<PyObject> {
-    // import
-    let array = to_rust(array, py)?;
+    let array = pa
+        .getattr("Field")?
+        .call_method1("_import_from_c", (schema_ptr as Py_uintptr_t,))?;
 
-    // concat
-    let array = compute::concat::concatenate(&[array.as_ref(), array.as_ref()])
-        .map_err(PyO3ArrowError::from)?
-        .into();
+    unsafe { Box::from_raw(schema_ptr) };
 
-    // export
-    to_py(array, py)
+    Ok(array.to_object(py))
 }
 
 /// Converts to rust and back to python
 #[pyfunction]
-fn round_trip(array: PyObject, py: Python) -> PyResult<PyObject> {
+fn round_trip_array(array: PyObject, py: Python) -> PyResult<PyObject> {
     // import
-    let array = to_rust(array, py)?;
+    let array = to_rust_array(array, py)?;
 
     // export
-    to_py(array, py)
+    to_py_array(array, py)
 }
 
 /// Converts to rust and back to python
 #[pyfunction]
-fn import_primitive(array: PyObject, py: Python) -> PyResult<bool> {
-    let array = to_rust(array, py)?;
-    let expected = Arc::new(PrimitiveArray::<i64>::from(vec![Some(2), None, Some(6)])) as ArrayRef;
-
-    Ok(array == expected)
-}
-
-/// Converts to rust and back to python
-#[pyfunction]
-fn export_primitive(py: Python) -> PyResult<PyObject> {
-    let array = Arc::new(PrimitiveArray::<i64>::from(vec![Some(2), None, Some(6)])) as ArrayRef;
-
-    let array = to_py(array, py)?;
+fn round_trip_field(array: PyObject, py: Python) -> PyResult<PyObject> {
+    // import
+    let field = to_rust_field(array, py)?;
 
-    Ok(array)
+    // export
+    to_py_field(&field, py)
 }
 
 #[pyfunction]
@@ -203,13 +159,8 @@ fn total_allocated_bytes() -> PyResult<isize> {
 
 #[pymodule]
 fn arrow_pyarrow_integration_testing(_py: Python, m: &PyModule) -> PyResult<()> {
-    m.add_wrapped(wrap_pyfunction!(total_allocated_bytes))?;
-    m.add_wrapped(wrap_pyfunction!(export_primitive))?;
-    m.add_wrapped(wrap_pyfunction!(import_primitive))?;
-    m.add_wrapped(wrap_pyfunction!(double))?;
-    m.add_wrapped(wrap_pyfunction!(double_py))?;
-    m.add_wrapped(wrap_pyfunction!(substring))?;
-    m.add_wrapped(wrap_pyfunction!(concatenate))?;
-    m.add_wrapped(wrap_pyfunction!(round_trip))?;
+    m.add_function(wrap_pyfunction!(total_allocated_bytes, m)?)?;
+    m.add_function(wrap_pyfunction!(round_trip_array, m)?)?;
+    m.add_function(wrap_pyfunction!(round_trip_field, m)?)?;
     Ok(())
 }
diff --git a/arrow-pyarrow-integration-testing/tests/test_sql.py b/arrow-pyarrow-integration-testing/tests/test_sql.py
index d891eb27b9..e28834b1da 100644
--- a/arrow-pyarrow-integration-testing/tests/test_sql.py
+++ b/arrow-pyarrow-integration-testing/tests/test_sql.py
@@ -40,60 +40,12 @@ class TestCase(unittest.TestCase):
         # No leak of C++ memory
         self.assertEqual(self.old_allocated_cpp, pyarrow.total_allocated_bytes())
 
-    def test_primitive_python(self):
-        """
-        Python -> Rust -> Python
-        """
-        a = pyarrow.array([1, 2, 3])
-        b = arrow_pyarrow_integration_testing.double(a)
-        self.assertEqual(b, pyarrow.array([2, 4, 6]))
-
-    def test_primitive_rust(self):
-        """
-        Rust -> Python -> Rust
-        """
-
-        def double(array):
-            array = array.to_pylist()
-            return pyarrow.array([x * 2 if x is not None else None for x in array])
-
-        is_correct = arrow_pyarrow_integration_testing.double_py(double)
-        self.assertTrue(is_correct)
-
-    def test_import_primitive(self):
-        """
-        Python -> Rust
-        """
-        old_allocated = pyarrow.total_allocated_bytes()
-
-        a = pyarrow.array([2, None, 6])
-
-        is_correct = arrow_pyarrow_integration_testing.import_primitive(a)
-        self.assertTrue(is_correct)
-        # No leak of C++ memory
-        del a
-        self.assertEqual(old_allocated, pyarrow.total_allocated_bytes())
-
-    def test_export_primitive(self):
-        """
-        Python -> Rust
-        """
-        old_allocated = pyarrow.total_allocated_bytes()
-
-        expected = pyarrow.array([2, None, 6])
-
-        result = arrow_pyarrow_integration_testing.export_primitive()
-        self.assertEqual(expected, result)
-        # No leak of C++ memory
-        del expected
-        self.assertEqual(old_allocated, pyarrow.total_allocated_bytes())
-
     def test_string_roundtrip(self):
         """
         Python -> Rust -> Python
         """
         a = pyarrow.array(["a", None, "ccc"])
-        b = arrow_pyarrow_integration_testing.round_trip(a)
+        b = arrow_pyarrow_integration_testing.round_trip_array(a)
         c = pyarrow.array(["a", None, "ccc"])
         self.assertEqual(b, c)
 
@@ -107,26 +59,9 @@ class TestCase(unittest.TestCase):
             None,
         ]
         a = pyarrow.array(data, pyarrow.decimal128(5, 2))
-        b = arrow_pyarrow_integration_testing.round_trip(a)
+        b = arrow_pyarrow_integration_testing.round_trip_array(a)
         self.assertEqual(a, b)
 
-    def test_string_python(self):
-        """
-        Python -> Rust -> Python
-        """
-        a = pyarrow.array(["a", None, "ccc"])
-        b = arrow_pyarrow_integration_testing.substring(a, 1)
-        self.assertEqual(b, pyarrow.array(["", None, "cc"]))
-
-    def test_time32_python(self):
-        """
-        Python -> Rust -> Python
-        """
-        a = pyarrow.array([None, 1, 2], pyarrow.time32("s"))
-        b = arrow_pyarrow_integration_testing.concatenate(a)
-        expected = pyarrow.array([None, 1, 2] + [None, 1, 2], pyarrow.time32("s"))
-        self.assertEqual(b, expected)
-
     def test_list_array(self):
         """
         Python -> Rust -> Python
@@ -135,7 +70,7 @@ class TestCase(unittest.TestCase):
             a = pyarrow.array(
                 [[], None, [1, 2], [4, 5, 6]], pyarrow.list_(pyarrow.int64())
             )
-            b = arrow_pyarrow_integration_testing.round_trip(a)
+            b = arrow_pyarrow_integration_testing.round_trip_array(a)
 
             b.validate(full=True)
             assert a.to_pylist() == b.to_pylist()
@@ -159,7 +94,7 @@ class TestCase(unittest.TestCase):
             ],
             pyarrow.struct(fields),
         )
-        b = arrow_pyarrow_integration_testing.round_trip(a)
+        b = arrow_pyarrow_integration_testing.round_trip_array(a)
 
         b.validate(full=True)
         assert a.to_pylist() == b.to_pylist()
@@ -174,7 +109,7 @@ class TestCase(unittest.TestCase):
                 [[None], None, [[1], [2]], [[4, 5], [6]]],
                 pyarrow.list_(pyarrow.list_(pyarrow.int64())),
             )
-            b = arrow_pyarrow_integration_testing.round_trip(a)
+            b = arrow_pyarrow_integration_testing.round_trip_array(a)
 
             b.validate(full=True)
             assert a.to_pylist() == b.to_pylist()
@@ -188,7 +123,7 @@ class TestCase(unittest.TestCase):
             ["a", "a", "b", None, "c"],
             pyarrow.dictionary(pyarrow.int64(), pyarrow.utf8()),
         )
-        b = arrow_pyarrow_integration_testing.round_trip(a)
+        b = arrow_pyarrow_integration_testing.round_trip_array(a)
 
         b.validate(full=True)
         assert a.to_pylist() == b.to_pylist()
@@ -205,7 +140,7 @@ class TestCase(unittest.TestCase):
                 pyarrow.array([0, 1, 2, None, 0], pyarrow.int64()),
             ],
         )
-        b = arrow_pyarrow_integration_testing.round_trip(a)
+        b = arrow_pyarrow_integration_testing.round_trip_array(a)
 
         b.validate(full=True)
         assert a.to_pylist() == b.to_pylist()
@@ -223,8 +158,24 @@ class TestCase(unittest.TestCase):
                 pyarrow.array([0, 1, 2, None, 0], pyarrow.int64()),
             ],
         )
-        b = arrow_pyarrow_integration_testing.round_trip(a)
+        b = arrow_pyarrow_integration_testing.round_trip_array(a)
 
         b.validate(full=True)
         assert a.to_pylist() == b.to_pylist()
         assert a.type == b.type
+
+    def test_field(self):
+        field = pyarrow.field("aa", pyarrow.bool_())
+        result = arrow_pyarrow_integration_testing.round_trip_field(field)
+        assert field == result
+
+    def test_field_nested(self):
+        field = pyarrow.field("aa", pyarrow.list_(pyarrow.field("ab", pyarrow.bool_())))
+        result = arrow_pyarrow_integration_testing.round_trip_field(field)
+        assert field == result
+
+    def test_field_metadata(self):
+        field = pyarrow.field("aa", pyarrow.bool_(), {"a": "b"})
+        result = arrow_pyarrow_integration_testing.round_trip_field(field)
+        assert field == result
+        assert field.metadata == result.metadata
diff --git a/tests/it/ffi.rs b/tests/it/ffi.rs
index fba1a17986..d76cf5b32b 100644
--- a/tests/it/ffi.rs
+++ b/tests/it/ffi.rs
@@ -1,38 +1,56 @@
 use arrow2::array::*;
-use arrow2::datatypes::{DataType, TimeUnit};
-use arrow2::ffi::try_from;
+use arrow2::datatypes::{DataType, Field, TimeUnit};
 use arrow2::{error::Result, ffi};
 use std::sync::Arc;
 
-fn test_release(expected: impl Array + 'static) -> Result<()> {
-    // create a `ArrowArray` from the data.
-    let b: Arc<dyn Array> = Arc::new(expected);
+fn test_round_trip(expected: impl Array + Clone + 'static) -> Result<()> {
+    let array: Arc<dyn Array> = Arc::new(expected.clone());
+    let field = Field::new("a", array.data_type().clone(), true);
+    let expected = Box::new(expected) as Box<dyn Array>;
+
+    let array_ptr = Box::new(ffi::Ffi_ArrowArray::empty());
+    let schema_ptr = Box::new(ffi::Ffi_ArrowSchema::empty());
 
-    // export the array as 2 pointers.
-    let _ = ffi::export_to_c(b)?;
+    let array_ptr = Box::into_raw(array_ptr);
+    let schema_ptr = Box::into_raw(schema_ptr);
 
+    unsafe {
+        ffi::export_array_to_c(array, array_ptr);
+        ffi::export_field_to_c(&field, schema_ptr);
+    }
+
+    let array_ptr = unsafe { Box::from_raw(array_ptr) };
+    let schema_ptr = unsafe { Box::from_raw(schema_ptr) };
+
+    // import references
+    let result_field = ffi::import_field_from_c(schema_ptr.as_ref())?;
+    let result_array = ffi::import_array_from_c(array_ptr, &result_field)?;
+
+    assert_eq!(&result_array, &expected);
+    assert_eq!(result_field, field);
     Ok(())
 }
 
-fn test_round_trip(expected: impl Array + Clone + 'static) -> Result<()> {
-    let b: Arc<dyn Array> = Arc::new(expected.clone());
-    let expected = Box::new(expected) as Box<dyn Array>;
-
+fn test_round_trip_schema(field: Field) -> Result<()> {
     // create a `ArrowArray` from the data.
-    let array = Arc::new(ffi::export_to_c(b)?);
+    let schema_ptr = Box::new(ffi::Ffi_ArrowSchema::empty());
+
+    let schema_ptr = Box::into_raw(schema_ptr);
+
+    unsafe { ffi::export_field_to_c(&field, schema_ptr) };
 
-    let (_, _) = array.references();
+    let schema_ptr = unsafe { Box::from_raw(schema_ptr) };
 
-    let result = try_from(array)?;
+    let result = ffi::import_field_from_c(schema_ptr.as_ref())?;
 
-    assert_eq!(&result, &expected);
+    assert_eq!(result, field);
     Ok(())
 }
 
 #[test]
 fn u32() -> Result<()> {
     let data = Int32Array::from(&[Some(2), None, Some(1), None]);
-    test_release(data)
+    test_round_trip(data)
 }
 
 #[test]
@@ -130,3 +148,20 @@ fn dict() -> Result<()> {
 
     test_round_trip(array)
 }
+
+#[test]
+fn schema() -> Result<()> {
+    let field = Field::new(
+        "a",
+        DataType::List(Box::new(Field::new("a", DataType::UInt32, true))),
+        true,
+    );
+    test_round_trip_schema(field)?;
+
+    let field = Field::new(
+        "a",
+        DataType::Dictionary(Box::new(DataType::UInt32), Box::new(DataType::Utf8)),
+        true,
+    );
+    test_round_trip_schema(field)
+}