Fix FFI array offset handling (#5964)

Author: tustvold

arrow-array/src/ffi.rs

@@ -425,32 +425,32 @@ impl<'a> ImportedArrowArray<'a> {
                 (length + 1) * (bits / 8)
             }
             (DataType::Utf8, 2) | (DataType::Binary, 2) => {
-                // the len of the data buffer (buffer 2) equals the difference between the last value
-                // and the first value of the offset buffer (buffer 1).
+                if self.array.is_empty() {
+                    return Ok(0);
+                }
+
+                // the len of the data buffer (buffer 2) equals the last value of the offset buffer (buffer 1)
                 let len = self.buffer_len(1, dt)?;
                 // first buffer is the null buffer => add(1)
                 // we assume that pointer is aligned for `i32`, as Utf8 uses `i32` offsets.
                 #[allow(clippy::cast_ptr_alignment)]
                 let offset_buffer = self.array.buffer(1) as *const i32;
-                // get first offset
-                let start = (unsafe { *offset_buffer.add(0) }) as usize;
                 // get last offset
-                let end = (unsafe { *offset_buffer.add(len / size_of::<i32>() - 1) }) as usize;
-                end - start
+                (unsafe { *offset_buffer.add(len / size_of::<i32>() - 1) }) as usize
             }
             (DataType::LargeUtf8, 2) | (DataType::LargeBinary, 2) => {
-                // the len of the data buffer (buffer 2) equals the difference between the last value
-                // and the first value of the offset buffer (buffer 1).
+                if self.array.is_empty() {
+                    return Ok(0);
+                }
+
+                // the len of the data buffer (buffer 2) equals the last value of the offset buffer (buffer 1)
                 let len = self.buffer_len(1, dt)?;
                 // first buffer is the null buffer => add(1)
                 // we assume that pointer is aligned for `i64`, as Large uses `i64` offsets.
                 #[allow(clippy::cast_ptr_alignment)]
                 let offset_buffer = self.array.buffer(1) as *const i64;
-                // get first offset
-                let start = (unsafe { *offset_buffer.add(0) }) as usize;
                 // get last offset
-                let end = (unsafe { *offset_buffer.add(len / size_of::<i64>() - 1) }) as usize;
-                end - start
+                (unsafe { *offset_buffer.add(len / size_of::<i64>() - 1) }) as usize
             }
             // buffer len of primitive types
             _ => {

arrow-data/src/ffi.rs

@@ -131,37 +131,6 @@ impl FFI_ArrowArray {
             data.buffers().iter().map(|b| Some(b.clone())).collect()
         };
 
-        // Handle buffer offset for offset buffer.
-        let offset_offset = match data.data_type() {
-            DataType::Utf8 | DataType::Binary => {
-                // Offset buffer is possible a slice of the buffer.
-                // If we use slice pointer as exported buffer pointer, it will cause
-                // the consumer to calculate incorrect length of data buffer (buffer 1).
-                // We need to get the offset of the offset buffer and fill it in
-                // the `FFI_ArrowArray` offset field.
-                Some(data.buffers()[0].ptr_offset() / std::mem::size_of::<i32>())
-            }
-            DataType::LargeUtf8 | DataType::LargeBinary => {
-                // Offset buffer is possible a slice of the buffer.
-                // If we use slice pointer as exported buffer pointer, it will cause
-                // the consumer to calculate incorrect length of data buffer (buffer 1).
-                // We need to get the offset of the offset buffer and fill it in
-                // the `FFI_ArrowArray` offset field.
-                Some(data.buffers()[0].ptr_offset() / std::mem::size_of::<i64>())
-            }
-            _ => None,
-        };
-
-        let offset = if let Some(offset) = offset_offset {
-            if data.offset() != 0 {
-                // TODO: Adjust for data offset
-                panic!("The ArrayData of a slice offset buffer should not have offset");
-            }
-            offset
-        } else {
-            data.offset()
-        };
-
         // `n_buffers` is the number of buffers by the spec.
         let n_buffers = {
             data_layout.buffers.len() + {
@@ -174,25 +143,9 @@ impl FFI_ArrowArray {
 
         let buffers_ptr = buffers
             .iter()
-            .enumerate()
-            .flat_map(|(buffer_idx, maybe_buffer)| match maybe_buffer {
-                Some(b) => {
-                    match (data.data_type(), buffer_idx) {
-                        (
-                            DataType::Utf8
-                            | DataType::LargeUtf8
-                            | DataType::Binary
-                            | DataType::LargeBinary,
-                            1,
-                        ) => {
-                            // For offset buffer, take original pointer without offset.
-                            // Buffer offset should be handled by `FFI_ArrowArray` offset field.
-                            Some(b.data_ptr().as_ptr() as *const c_void)
-                        }
-                        // For other buffers, note that `raw_data` takes into account the buffer's offset
-                        _ => Some(b.as_ptr() as *const c_void),
-                    }
-                }
+            .flat_map(|maybe_buffer| match maybe_buffer {
+                // note that `raw_data` takes into account the buffer's offset
+                Some(b) => Some(b.as_ptr() as *const c_void),
                 // This is for null buffer. We only put a null pointer for
                 // null buffer if by spec it can contain null mask.
                 None if data_layout.can_contain_null_mask => Some(std::ptr::null()),
@@ -233,7 +186,7 @@ impl FFI_ArrowArray {
         Self {
             length: data.len() as i64,
             null_count: null_count as i64,
-            offset: offset as i64,
+            offset: data.offset() as i64,
             n_buffers,
             n_children,
             buffers: private_data.buffers_ptr.as_mut_ptr(),