Fixed writing to unaligned pointers

arrow-pyarrow-integration-testing/src/c_stream.rs

@@ -3,7 +3,8 @@
 use pyo3::ffi::Py_uintptr_t;
 use pyo3::prelude::*;
 
-use arrow2::array::Int32Array;
+use arrow2::array::{Int32Array, StructArray};
+use arrow2::datatypes::DataType;
 use arrow2::ffi;
 
 use super::*;
@@ -31,15 +32,19 @@ pub fn to_rust_iterator(ob: PyObject, py: Python) -> PyResult<Vec<PyObject>> {
 pub fn from_rust_iterator(py: Python) -> PyResult<PyObject> {
     // initialize an array
     let array = Int32Array::from(&[Some(2), None, Some(1), None]);
+    let array = StructArray::from_data(
+        DataType::Struct(vec![Field::new("a", array.data_type().clone(), true)]),
+        vec![Arc::new(array)],
+        None,
+    );
     // and a field with its datatype
     let field = Field::new("a", array.data_type().clone(), true);
 
     // Arc it, since it will be shared with an external program
     let array: Arc<dyn Array> = Arc::new(array.clone());
 
     // create an iterator of arrays
-    //let arrays = vec![array.clone(), array.clone(), array];
-    let arrays: Vec<Arc<dyn Array>> = vec![];
+    let arrays = vec![array.clone(), array.clone(), array];
     let iter = Box::new(arrays.clone().into_iter().map(Ok)) as _;
 
     // create an [`ArrowArrayStream`] based on this iterator and field

arrow-pyarrow-integration-testing/tests/test_c_stream.py

@@ -18,10 +18,12 @@ def test_rust_reads(self):
         array = arrays[0].field(0)
         assert array == a
 
-    # see https://issues.apache.org/jira/browse/ARROW-15747
-    def _test_pyarrow_reads(self):
+    def test_pyarrow_reads(self):
         stream = arrow_pyarrow_integration_testing.from_rust_iterator()
 
         arrays = [a for a in stream]
 
-        assert False
+        expected = pyarrow.RecordBatch.from_arrays([pyarrow.array([2, None, 1, None], pyarrow.int32())], names=["a"])
+        expected = [expected, expected, expected]
+
+        self.assertEqual(arrays, expected)

src/ffi/mod.rs

@@ -26,14 +26,14 @@ pub use stream::{export_iterator, ArrowArrayStreamReader};
 pub unsafe fn export_array_to_c(array: Arc<dyn Array>, ptr: *mut ArrowArray) {
     let array = bridge::align_to_c_data_interface(array);
 
-    *ptr = ArrowArray::new(array);
+    std::ptr::write_unaligned(ptr, ArrowArray::new(array));
 }
 
 /// Exports a [`Field`] to the C data interface.
 /// # Safety
 /// The pointer `ptr` must be allocated and valid
 pub unsafe fn export_field_to_c(field: &Field, ptr: *mut ArrowSchema) {
-    *ptr = ArrowSchema::new(field)
+    std::ptr::write_unaligned(ptr, ArrowSchema::new(field));
 }
 
 /// Imports a [`Field`] from the C data interface.

src/ffi/stream.rs

@@ -159,7 +159,8 @@ unsafe extern "C" fn get_next(iter: *mut ArrowArrayStream, array: *mut ArrowArra
             2001 // custom application specific error (since this is never a result of this interface)
         }
         None => {
-            *array = ArrowArray::empty();
+            let a = ArrowArray::empty();
+            std::ptr::write_unaligned(array, a);
             private.error = None;
             0
         }