sunchao commented on a change in pull request #1384: URL: https://github.com/apache/arrow-rs/pull/1384#discussion_r838814140
########## File path: arrow/src/ffi_stream.rs ########## @@ -0,0 +1,538 @@ +// 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. + +//! Contains declarations to bind to the [C Stream Interface](https://arrow.apache.org/docs/format/CStreamInterface.html). +//! +//! This module has two main interfaces: +//! One interface maps C ABI to native Rust types, i.e. convert c-pointers, c_char, to native rust. +//! This is handled by [FFI_ArrowArrayStream]. +//! +//! The second interface is used to import `FFI_ArrowArrayStream` as Rust implementation `RecordBatch` reader. +//! This is handled by `ArrowArrayStreamReader`. +//! +//! ```ignore +//! # use std::fs::File; +//! # use std::sync::Arc; +//! # use arrow::error::Result; +//! # use arrow::ffi_stream::{ArrowArrayStreamReader, FFI_ArrowArrayStream}; +//! # use arrow::ipc::reader::FileReader; +//! # use arrow::record_batch::RecordBatchReader; +//! # fn main() -> Result<()> { +//! // create an record batch reader natively +//! let file = File::open("arrow_file").unwrap(); +//! let reader = Box::new(FileReader::try_new(file).unwrap()); +//! +//! // export it +//! let stream = Arc::new(FFI_ArrowArrayStream::new(reader)); +//! let stream_ptr = FFI_ArrowArrayStream::to_raw(stream) as *mut FFI_ArrowArrayStream; +//! +//! // consumed and used by something else... +//! +//! // import it +//! let stream_reader = unsafe { ArrowArrayStreamReader::from_raw(stream_ptr).unwrap() }; +//! let imported_schema = stream_reader.schema(); +//! +//! let mut produced_batches = vec![]; +//! for batch in stream_reader { +//! produced_batches.push(batch.unwrap()); +//! } +//! +//! // (drop/release) +//! Ok(()) +//! } +//! ``` + +use std::{ + convert::TryFrom, + ffi::CString, + os::raw::{c_char, c_int, c_void}, + sync::Arc, +}; + +use crate::array::Array; +use crate::array::StructArray; +use crate::datatypes::{Schema, SchemaRef}; +use crate::error::ArrowError; +use crate::error::Result; +use crate::ffi::*; +use crate::record_batch::{RecordBatch, RecordBatchReader}; + +const ENOMEM: i32 = 12; +const EIO: i32 = 5; +const EINVAL: i32 = 22; +const ENOSYS: i32 = 78; + +/// ABI-compatible struct for `ArrayStream` from C Stream Interface +/// This interface is experimental +/// See <https://arrow.apache.org/docs/format/CStreamInterface.html#structure-definitions> +/// This was created by bindgen +#[repr(C)] +#[derive(Debug)] +pub struct FFI_ArrowArrayStream { + pub get_schema: Option< + unsafe extern "C" fn( + arg1: *mut FFI_ArrowArrayStream, + out: *mut FFI_ArrowSchema, + ) -> c_int, + >, + pub get_next: Option< + unsafe extern "C" fn( + arg1: *mut FFI_ArrowArrayStream, + out: *mut FFI_ArrowArray, + ) -> c_int, + >, + pub get_last_error: + Option<unsafe extern "C" fn(arg1: *mut FFI_ArrowArrayStream) -> *const c_char>, + pub release: Option<unsafe extern "C" fn(arg1: *mut FFI_ArrowArrayStream)>, + pub private_data: *mut c_void, +} + +// callback used to drop [FFI_ArrowArrayStream] when it is exported. +unsafe extern "C" fn release_stream(stream: *mut FFI_ArrowArrayStream) { + if stream.is_null() { + return; + } + let stream = &mut *stream; + + stream.get_schema = None; + stream.get_next = None; + stream.get_last_error = None; + + let private_data = Box::from_raw(stream.private_data as *mut StreamPrivateData); + drop(private_data); + + stream.release = None; +} + +struct StreamPrivateData { + batch_reader: Box<dyn RecordBatchReader>, + last_error: String, +} + +// The callback used to get array schema +unsafe extern "C" fn get_schema( + stream: *mut FFI_ArrowArrayStream, + schema: *mut FFI_ArrowSchema, +) -> c_int { + ExportedArrayStream { stream }.get_schema(schema) +} + +// The callback used to get next array +unsafe extern "C" fn get_next( + stream: *mut FFI_ArrowArrayStream, + array: *mut FFI_ArrowArray, +) -> c_int { + ExportedArrayStream { stream }.get_next(array) +} + +// The callback used to get the error from last operation on the `FFI_ArrowArrayStream` +unsafe extern "C" fn get_last_error(stream: *mut FFI_ArrowArrayStream) -> *const c_char { + let mut ffi_stream = ExportedArrayStream { stream }; + let last_error = ffi_stream.get_last_error(); + CString::new(last_error.as_str()).unwrap().into_raw() +} + +impl Drop for FFI_ArrowArrayStream { + fn drop(&mut self) { + match self.release { + None => (), + Some(release) => unsafe { release(self) }, + }; + } +} + +impl FFI_ArrowArrayStream { + /// Creates a new [`FFI_ArrowArrayStream`]. + pub fn new(batch_reader: Box<dyn RecordBatchReader>) -> Self { + let private_data = Box::new(StreamPrivateData { + batch_reader, + last_error: String::new(), + }); + + Self { + get_schema: Some(get_schema), + get_next: Some(get_next), + get_last_error: Some(get_last_error), + release: Some(release_stream), + private_data: Box::into_raw(private_data) as *mut c_void, + } + } + + /// Creates a new empty [FFI_ArrowArrayStream]. Used to import from the C Stream Interface. + pub fn empty() -> Self { + Self { + get_schema: None, + get_next: None, + get_last_error: None, + release: None, + private_data: std::ptr::null_mut(), + } + } +} + +struct ExportedArrayStream { + stream: *mut FFI_ArrowArrayStream, +} + +impl ExportedArrayStream { + fn get_private_data(&mut self) -> &mut StreamPrivateData { + unsafe { &mut *((*self.stream).private_data as *mut StreamPrivateData) } + } + + pub fn get_schema(&mut self, out: *mut FFI_ArrowSchema) -> i32 { + unsafe { + match (*out).release { + None => (), + Some(release) => release(out), + }; + }; + + let mut private_data = self.get_private_data(); + let reader = &private_data.batch_reader; + + let schema = FFI_ArrowSchema::try_from(reader.schema().as_ref()); + + match schema { + Ok(mut schema) => unsafe { + std::ptr::copy(&schema as *const FFI_ArrowSchema, out, 1); + schema.release = None; + 0 + }, + Err(ref err) => { + private_data.last_error = err.to_string(); + get_error_code(err) + } + } + } + + pub fn get_next(&mut self, out: *mut FFI_ArrowArray) -> i32 { + unsafe { + match (*out).release { + None => (), + Some(release) => release(out), + }; + }; + + let mut private_data = self.get_private_data(); + let reader = &mut private_data.batch_reader; + + let ret_code = match reader.next() { + None => 0, + Some(next_batch) => { + if let Ok(batch) = next_batch { + let struct_array = StructArray::from(batch); + let mut array = FFI_ArrowArray::new(struct_array.data()); + + unsafe { + std::ptr::copy(&array as *const FFI_ArrowArray, out, 1); + array.release = None; + 0 + } + } else { + let err = &next_batch.unwrap_err(); + private_data.last_error = err.to_string(); + get_error_code(err) + } + } + }; + + ret_code + } + + pub fn get_last_error(&mut self) -> &String { + &self.get_private_data().last_error + } +} + +fn get_error_code(err: &ArrowError) -> i32 { + match err { + ArrowError::NotYetImplemented(_) => ENOSYS, + ArrowError::MemoryError(_) => ENOMEM, + ArrowError::IoError(_) => EIO, + _ => EINVAL, + } +} + +/// A `RecordBatchReader` which imports Arrays from `FFI_ArrowArrayStream`. +/// Struct used to fetch `RecordBatch` from the C Stream Interface. +/// Its main responsibility is to expose `RecordBatchReader` functionality +/// that requires [FFI_ArrowArrayStream]. +#[derive(Debug)] +pub struct ArrowArrayStreamReader { + stream: Arc<FFI_ArrowArrayStream>, Review comment: Ah I see. -- This is an automated message from the Apache Git Service. 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