Added first impl of mmap

src/ffi/array.rs

@@ -493,7 +493,7 @@ impl InternalArrowArray {
     }
 }
 
-impl ArrowArrayRef for Box<InternalArrowArray> {
+impl ArrowArrayRef for InternalArrowArray {
     /// the data_type as declared in the schema
     fn data_type(&self) -> &DataType {
         &self.data_type

src/ffi/mmap.rs

@@ -0,0 +1,154 @@
+use std::collections::VecDeque;
+
+use crate::array::{Array, BooleanArray, FromFfi};
+use crate::datatypes::DataType;
+use crate::error::Error;
+
+use crate::io::ipc::read::OutOfSpecKind;
+use crate::io::ipc::read::{IpcBuffer, Node};
+
+use super::{ArrowArray, InternalArrowArray};
+
+#[allow(dead_code)]
+struct PrivateData<T> {
+    // the owner of the pointers' regions
+    data: T,
+    buffers_ptr: Box<[*const std::os::raw::c_void]>,
+    //children_ptr: Box<[*mut ArrowArray]>,
+    dictionary_ptr: Option<*mut ArrowArray>,
+}
+
+fn get_buffer(buffers: &mut VecDeque<IpcBuffer>) -> Result<(usize, usize), Error> {
+    let buffer = buffers
+        .pop_front()
+        .ok_or_else(|| Error::from(OutOfSpecKind::ExpectedBuffer))?;
+
+    let offset: usize = buffer
+        .offset()
+        .try_into()
+        .map_err(|_| Error::from(OutOfSpecKind::NegativeFooterLength))?;
+
+    let length: usize = buffer
+        .length()
+        .try_into()
+        .map_err(|_| Error::from(OutOfSpecKind::NegativeFooterLength))?;
+
+    Ok((offset, length))
+}
+
+// callback used to drop [ArrowArray] when it is exported
+unsafe extern "C" fn release<T>(array: *mut ArrowArray) {
+    if array.is_null() {
+        return;
+    }
+    let array = &mut *array;
+
+    // take ownership of `private_data`, therefore dropping it
+    let private = Box::from_raw(array.private_data as *mut PrivateData<T>);
+    /*for child in private.children_ptr.iter() {
+        let _ = Box::from_raw(*child);
+    }*/
+
+    if let Some(ptr) = private.dictionary_ptr {
+        let _ = Box::from_raw(ptr);
+    }
+
+    array.release = None;
+}
+
+fn mmap_boolean<T: Clone + AsRef<[u8]>>(
+    data: T,
+    node: &Node,
+    block_offset: usize,
+    buffers: &mut VecDeque<IpcBuffer>,
+) -> Result<ArrowArray, Error> {
+    let num_rows: usize = node
+        .length()
+        .try_into()
+        .map_err(|_| Error::from(OutOfSpecKind::NegativeFooterLength))?;
+
+    let null_count: usize = node
+        .null_count()
+        .try_into()
+        .map_err(|_| Error::from(OutOfSpecKind::NegativeFooterLength))?;
+
+    let data_ref = data.as_ref();
+
+    let validity = get_buffer(buffers)?;
+    let (offset, length) = validity;
+
+    let validity = if null_count > 0 {
+        // verify that they are in-bounds and get its pointer
+        Some(data_ref[block_offset + offset..block_offset + offset + length].as_ptr())
+    } else {
+        None
+    };
+
+    let values = get_buffer(buffers)?;
+    let (offset, length) = values;
+
+    // verify that they are in-bounds and get its pointer
+    let values = data_ref[block_offset + offset..block_offset + offset + length].as_ptr();
+
+    // NOTE: this is valid for Boolean, but for others (e.g. Utf8), we need to validate other invariants
+    // or mark this as unsafe
+
+    let buffers_ptr = [validity, Some(values)]
+        .iter()
+        .map(|maybe_buffer| match maybe_buffer {
+            Some(b) => *b as *const std::os::raw::c_void,
+            None => std::ptr::null(),
+        })
+        .collect::<Box<[_]>>();
+    let n_buffers = buffers.len() as i64;
+
+    let mut private_data = Box::new(PrivateData::<T> {
+        data: data.clone(),
+        buffers_ptr,
+        dictionary_ptr: None,
+    });
+
+    Ok(ArrowArray {
+        length: num_rows as i64,
+        null_count: null_count as i64,
+        offset: 0,
+        n_buffers,
+        n_children: 0,
+        buffers: private_data.buffers_ptr.as_mut_ptr(),
+        children: std::ptr::null_mut(),
+        dictionary: private_data.dictionary_ptr.unwrap_or(std::ptr::null_mut()),
+        release: Some(release::<T>),
+        private_data: Box::into_raw(private_data) as *mut ::std::os::raw::c_void,
+    })
+}
+
+fn boolean<T: Clone + AsRef<[u8]>>(
+    data: T,
+    node: &Node,
+    block_offset: usize,
+    buffers: &mut VecDeque<IpcBuffer>,
+    data_type: DataType,
+) -> Result<BooleanArray, Error> {
+    let array = mmap_boolean(data, node, block_offset, buffers)?;
+    let array = InternalArrowArray::new(array, data_type);
+    // this is safe because we just (correctly) constructed `ArrowArray`
+    unsafe { BooleanArray::try_from_ffi(array) }
+}
+
+/// Maps a memory region to an [`Array`].
+pub fn mmap<T: Clone + AsRef<[u8]>>(
+    data: T,
+    block_offset: usize,
+    data_type: DataType,
+    field_nodes: &mut VecDeque<Node>,
+    buffers: &mut VecDeque<IpcBuffer>,
+) -> Result<Box<dyn Array>, Error> {
+    use crate::datatypes::PhysicalType::*;
+    let node = field_nodes
+        .pop_front()
+        .ok_or_else(|| Error::from(OutOfSpecKind::ExpectedBuffer))?;
+    match data_type.to_physical_type() {
+        Boolean => boolean(data, &node, block_offset, buffers, data_type).map(|x| x.boxed()),
+        _ => todo!(),
+    }
+}

src/ffi/mod.rs

@@ -3,9 +3,16 @@
 mod array;
 mod bridge;
 mod generated;
+#[cfg(feature = "io_ipc")]
+#[cfg_attr(docsrs, doc(cfg(feature = "io_ipc")))]
+mod mmap;
 mod schema;
 mod stream;
 
+#[cfg(feature = "io_ipc")]
+#[cfg_attr(docsrs, doc(cfg(feature = "io_ipc")))]
+pub use mmap::mmap;
+
 pub(crate) use array::try_from;
 pub(crate) use array::{ArrowArrayRef, InternalArrowArray};
 
@@ -44,5 +51,5 @@ pub unsafe fn import_array_from_c(
     array: ArrowArray,
     data_type: DataType,
 ) -> Result<Box<dyn Array>> {
-    try_from(Box::new(InternalArrowArray::new(array, data_type)))
+    try_from(InternalArrowArray::new(array, data_type))
 }

src/io/ipc/mmap.rs

@@ -0,0 +1,72 @@
+//! Memory maps regions defined on the IPC format into [`Array`].
+use std::collections::VecDeque;
+
+use crate::array::Array;
+use crate::error::Error;
+use crate::ffi::mmap;
+
+use super::read::read_file_metadata;
+use super::read::reader::get_serialized_batch;
+use super::read::OutOfSpecKind;
+use super::CONTINUATION_MARKER;
+
+use arrow_format::ipc::planus::ReadAsRoot;
+
+/// something
+pub fn map_chunk<T: Clone + AsRef<[u8]>>(data: T, index: usize) -> Result<Box<dyn Array>, Error> {
+    let mut bytes = data.as_ref();
+    let metadata = read_file_metadata(&mut std::io::Cursor::new(bytes))?;
+
+    let block = metadata.blocks[index];
+
+    let offset: usize = block
+        .offset
+        .try_into()
+        .map_err(|_| Error::from(OutOfSpecKind::NegativeFooterLength))?;
+
+    let meta_data_length: usize = block
+        .meta_data_length
+        .try_into()
+        .map_err(|_| Error::from(OutOfSpecKind::NegativeFooterLength))?;
+
+    bytes = &bytes[offset..];
+    let mut message_length = bytes[..4].try_into().unwrap();
+    bytes = &bytes[4..];
+
+    if message_length == CONTINUATION_MARKER {
+        // continuation marker encountered, read message next
+        message_length = bytes[..4].try_into().unwrap();
+        bytes = &bytes[4..];
+    };
+
+    let message_length: usize = i32::from_le_bytes(message_length)
+        .try_into()
+        .map_err(|_| Error::from(OutOfSpecKind::NegativeFooterLength))?;
+
+    let message = arrow_format::ipc::MessageRef::read_as_root(&bytes[..message_length])
+        .map_err(|err| Error::from(OutOfSpecKind::InvalidFlatbufferMessage(err)))?;
+
+    let batch = get_serialized_batch(&message)?;
+
+    let buffers = batch
+        .buffers()
+        .map_err(|err| Error::from(OutOfSpecKind::InvalidFlatbufferBuffers(err)))?
+        .ok_or_else(|| Error::from(OutOfSpecKind::MissingMessageBuffers))?;
+    let mut buffers = buffers.iter().collect::<VecDeque<_>>();
+
+    let field_nodes = batch
+        .nodes()
+        .map_err(|err| Error::from(OutOfSpecKind::InvalidFlatbufferNodes(err)))?
+        .ok_or_else(|| Error::from(OutOfSpecKind::MissingMessageNodes))?;
+    let mut field_nodes = field_nodes.iter().collect::<VecDeque<_>>();
+
+    let data_type = metadata.schema.fields[0].data_type.clone();
+
+    mmap(
+        data.clone(),
+        offset + meta_data_length,
+        data_type,
+        &mut field_nodes,
+        &mut buffers,
+    )
+}

src/io/ipc/mod.rs

@@ -77,6 +77,7 @@ mod compression;
 mod endianess;
 
 pub mod append;
+pub mod mmap;
 pub mod read;
 pub mod write;
 

src/io/ipc/read/reader.rs

@@ -230,7 +230,7 @@ pub fn read_file_metadata<R: Read + Seek>(reader: &mut R) -> Result<FileMetadata
     deserialize_footer(&serialized_footer, end - start)
 }
 
-pub(super) fn get_serialized_batch<'a>(
+pub(crate) fn get_serialized_batch<'a>(
     message: &'a arrow_format::ipc::MessageRef,
 ) -> Result<arrow_format::ipc::RecordBatchRef<'a>> {
     let header = message
@@ -268,6 +268,11 @@ pub fn read_batch<R: Read + Seek>(
         .try_into()
         .map_err(|_| Error::from(OutOfSpecKind::NegativeFooterLength))?;
 
+    let length: u64 = block
+        .meta_data_length
+        .try_into()
+        .map_err(|_| Error::from(OutOfSpecKind::NegativeFooterLength))?;
+
     // read length
     reader.seek(SeekFrom::Start(offset))?;
     let mut meta_buf = [0; 4];
@@ -292,16 +297,6 @@ pub fn read_batch<R: Read + Seek>(
 
     let batch = get_serialized_batch(&message)?;
 
-    let offset: u64 = block
-        .offset
-        .try_into()
-        .map_err(|_| Error::from(OutOfSpecKind::NegativeFooterLength))?;
-
-    let length: u64 = block
-        .meta_data_length
-        .try_into()
-        .map_err(|_| Error::from(OutOfSpecKind::NegativeFooterLength))?;
-
     read_record_batch(
         batch,
         &metadata.schema.fields,

tests/it/io/ipc/read/mmap.rs

@@ -0,0 +1,40 @@
+use arrow2::error::Result;
+use arrow2::io::ipc::mmap::map_chunk;
+
+use super::super::common::read_gzip_json;
+
+#[derive(Clone)]
+struct Mmap(pub std::sync::Arc<Vec<u8>>);
+
+impl AsRef<[u8]> for Mmap {
+    #[inline]
+    fn as_ref(&self) -> &[u8] {
+        self.0.as_ref()
+    }
+}
+
+fn test_file(version: &str, file_name: &str) -> Result<()> {
+    let testdata = crate::test_util::arrow_test_data();
+
+    let arrow_file = format!(
+        "{}/arrow-ipc-stream/integration/{}/{}.arrow_file",
+        testdata, version, file_name
+    );
+
+    let data = std::fs::read(arrow_file).unwrap();
+
+    let data = Mmap(std::sync::Arc::new(data));
+
+    // read expected JSON output
+    let (_schema, _, batches) = read_gzip_json(version, file_name)?;
+
+    let array = map_chunk(data, 0)?;
+
+    assert_eq!(batches[0].arrays()[0], array);
+    Ok(())
+}
+
+#[test]
+fn read_generated_100_primitive() -> Result<()> {
+    test_file("1.0.0-littleendian", "generated_primitive")
+}

tests/it/io/ipc/read/mod.rs

@@ -1,2 +1,3 @@
 mod file;
+mod mmap;
 mod stream;