Added support to read Arrow streams asynchronously

Cargo.toml

@@ -111,6 +111,7 @@ full = [
     "io_ipc",
     "io_flight",
     "io_ipc_write_async",
+    "io_ipc_read_async",
     "io_ipc_compression",
     "io_json_integration",
     "io_print",
@@ -132,6 +133,7 @@ io_csv_write = ["csv", "streaming-iterator", "lexical-core"]
 io_json = ["serde", "serde_json", "streaming-iterator", "fallible-streaming-iterator", "indexmap", "lexical-core"]
 io_ipc = ["arrow-format"]
 io_ipc_write_async = ["io_ipc", "futures"]
+io_ipc_read_async = ["io_ipc", "futures"]
 io_ipc_compression = ["lz4", "zstd"]
 io_flight = ["io_ipc", "arrow-format/flight-data"]
 # base64 + io_ipc because arrow schemas are stored as base64-encoded ipc format.

src/io/ipc/read/mod.rs

@@ -16,6 +16,9 @@ mod read_basic;
 mod reader;
 mod schema;
 mod stream;
+#[cfg(feature = "io_ipc_read_async")]
+#[cfg_attr(docsrs, doc(cfg(feature = "io_ipc_read_async")))]
+pub mod stream_async;
 
 pub use common::{read_dictionary, read_record_batch};
 pub use reader::{read_file_metadata, FileMetadata, FileReader};

src/io/ipc/read/schema.rs

@@ -8,7 +8,10 @@ use crate::{
     error::{ArrowError, Result},
 };
 
-use super::super::{IpcField, IpcSchema};
+use super::{
+    super::{IpcField, IpcSchema},
+    StreamMetadata,
+};
 
 fn try_unzip_vec<A, B, I: Iterator<Item = Result<(A, B)>>>(iter: I) -> Result<(Vec<A>, Vec<B>)> {
     let mut a = vec![];
@@ -370,3 +373,28 @@ pub(super) fn fb_to_schema(schema: arrow_format::ipc::SchemaRef) -> Result<(Sche
         },
     ))
 }
+
+pub(super) fn deserialize_stream_metadata(meta: &[u8]) -> Result<StreamMetadata> {
+    let message = arrow_format::ipc::MessageRef::read_as_root(meta).map_err(|err| {
+        ArrowError::OutOfSpec(format!("Unable to get root as message: {:?}", err))
+    })?;
+    let version = message.version()?;
+    // message header is a Schema, so read it
+    let header = message
+        .header()?
+        .ok_or_else(|| ArrowError::oos("Unable to read the first IPC message"))?;
+    let schema = if let arrow_format::ipc::MessageHeaderRef::Schema(schema) = header {
+        schema
+    } else {
+        return Err(ArrowError::oos(
+            "The first IPC message of the stream must be a schema",
+        ));
+    };
+    let (schema, ipc_schema) = fb_to_schema(schema)?;
+
+    Ok(StreamMetadata {
+        schema,
+        version,
+        ipc_schema,
+    })
+}

src/io/ipc/read/stream.rs

@@ -12,7 +12,7 @@ use crate::io::ipc::IpcSchema;
 
 use super::super::CONTINUATION_MARKER;
 use super::common::*;
-use super::schema::fb_to_schema;
+use super::schema::deserialize_stream_metadata;
 use super::Dictionaries;
 
 /// Metadata of an Arrow IPC stream, written at the start of the stream
@@ -45,29 +45,7 @@ pub fn read_stream_metadata<R: Read>(reader: &mut R) -> Result<StreamMetadata> {
     let mut meta_buffer = vec![0; meta_len as usize];
     reader.read_exact(&mut meta_buffer)?;
 
-    let message =
-        arrow_format::ipc::MessageRef::read_as_root(meta_buffer.as_slice()).map_err(|err| {
-            ArrowError::OutOfSpec(format!("Unable to get root as message: {:?}", err))
-        })?;
-    let version = message.version()?;
-    // message header is a Schema, so read it
-    let header = message
-        .header()?
-        .ok_or_else(|| ArrowError::oos("Unable to read the first IPC message"))?;
-    let schema = if let arrow_format::ipc::MessageHeaderRef::Schema(schema) = header {
-        schema
-    } else {
-        return Err(ArrowError::oos(
-            "The first IPC message of the stream must be a schema",
-        ));
-    };
-    let (schema, ipc_schema) = fb_to_schema(schema)?;
-
-    Ok(StreamMetadata {
-        schema,
-        version,
-        ipc_schema,
-    })
+    deserialize_stream_metadata(&meta_buffer)
 }
 
 /// Encodes the stream's status after each read.

src/io/ipc/read/stream_async.rs

@@ -0,0 +1,212 @@
+//! APIs to read Arrow streams asynchronously
+use std::sync::Arc;
+
+use arrow_format::ipc::planus::ReadAsRoot;
+use futures::future::BoxFuture;
+use futures::AsyncRead;
+use futures::AsyncReadExt;
+use futures::Stream;
+
+use crate::array::*;
+use crate::chunk::Chunk;
+use crate::error::{ArrowError, Result};
+
+use super::super::CONTINUATION_MARKER;
+use super::common::{read_dictionary, read_record_batch};
+use super::schema::deserialize_stream_metadata;
+use super::Dictionaries;
+use super::StreamMetadata;
+
+/// A (private) state of stream messages
+struct ReadState<R> {
+    pub reader: R,
+    pub metadata: StreamMetadata,
+    pub dictionaries: Dictionaries,
+    /// The internal buffer to read data inside the messages (records and dictionaries) to
+    pub data_buffer: Vec<u8>,
+    /// The internal buffer to read messages to
+    pub message_buffer: Vec<u8>,
+}
+
+/// The state of an Arrow stream
+enum StreamState<R> {
+    /// The stream does not contain new chunks (and it has not been closed)
+    Waiting(ReadState<R>),
+    /// The stream contain a new chunk
+    Some((ReadState<R>, Chunk<Arc<dyn Array>>)),
+}
+
+/// Reads the [`StreamMetadata`] of the Arrow stream asynchronously
+pub async fn read_stream_metadata_async<R: AsyncRead + Unpin + Send>(
+    reader: &mut R,
+) -> Result<StreamMetadata> {
+    // determine metadata length
+    let mut meta_size: [u8; 4] = [0; 4];
+    reader.read_exact(&mut meta_size).await?;
+    let meta_len = {
+        // If a continuation marker is encountered, skip over it and read
+        // the size from the next four bytes.
+        if meta_size == CONTINUATION_MARKER {
+            reader.read_exact(&mut meta_size).await?;
+        }
+        i32::from_le_bytes(meta_size)
+    };
+
+    let mut meta_buffer = vec![0; meta_len as usize];
+    reader.read_exact(&mut meta_buffer).await?;
+
+    deserialize_stream_metadata(&meta_buffer)
+}
+
+/// Reads the next item, yielding `None` if the stream has been closed,
+/// or a [`StreamState`] otherwise.
+async fn maybe_next<R: AsyncRead + Unpin + Send>(
+    mut state: ReadState<R>,
+) -> Result<Option<StreamState<R>>> {
+    // determine metadata length
+    let mut meta_length: [u8; 4] = [0; 4];
+
+    match state.reader.read_exact(&mut meta_length).await {
+        Ok(()) => (),
+        Err(e) => {
+            return if e.kind() == std::io::ErrorKind::UnexpectedEof {
+                // Handle EOF without the "0xFFFFFFFF 0x00000000"
+                // valid according to:
+                // https://arrow.apache.org/docs/format/Columnar.html#ipc-streaming-format
+                Ok(Some(StreamState::Waiting(state)))
+            } else {
+                Err(ArrowError::from(e))
+            };
+        }
+    }
+
+    let meta_length = {
+        // If a continuation marker is encountered, skip over it and read
+        // the size from the next four bytes.
+        if meta_length == CONTINUATION_MARKER {
+            state.reader.read_exact(&mut meta_length).await?;
+        }
+        i32::from_le_bytes(meta_length) as usize
+    };
+
+    if meta_length == 0 {
+        // the stream has ended, mark the reader as finished
+        return Ok(None);
+    }
+
+    state.message_buffer.clear();
+    state.message_buffer.resize(meta_length, 0);
+    state.reader.read_exact(&mut state.message_buffer).await?;
+
+    let message =
+        arrow_format::ipc::MessageRef::read_as_root(&state.message_buffer).map_err(|err| {
+            ArrowError::OutOfSpec(format!("Unable to get root as message: {:?}", err))
+        })?;
+    let header = message.header()?.ok_or_else(|| {
+        ArrowError::oos("IPC: unable to fetch the message header. The file or stream is corrupted.")
+    })?;
+
+    match header {
+        arrow_format::ipc::MessageHeaderRef::Schema(_) => Err(ArrowError::oos("A stream ")),
+        arrow_format::ipc::MessageHeaderRef::RecordBatch(batch) => {
+            // read the block that makes up the record batch into a buffer
+            state.data_buffer.clear();
+            state.data_buffer.resize(message.body_length()? as usize, 0);
+            state.reader.read_exact(&mut state.data_buffer).await?;
+
+            read_record_batch(
+                batch,
+                &state.metadata.schema.fields,
+                &state.metadata.ipc_schema,
+                None,
+                &state.dictionaries,
+                state.metadata.version,
+                &mut std::io::Cursor::new(&state.data_buffer),
+                0,
+            )
+            .map(|chunk| Some(StreamState::Some((state, chunk))))
+        }
+        arrow_format::ipc::MessageHeaderRef::DictionaryBatch(batch) => {
+            // read the block that makes up the dictionary batch into a buffer
+            let mut buf = vec![0; message.body_length()? as usize];
+            state.reader.read_exact(&mut buf).await?;
+
+            let mut dict_reader = std::io::Cursor::new(buf);
+
+            read_dictionary(
+                batch,
+                &state.metadata.schema.fields,
+                &state.metadata.ipc_schema,
+                &mut state.dictionaries,
+                &mut dict_reader,
+                0,
+            )?;
+
+            // read the next message until we encounter a Chunk<Arc<dyn Array>> message
+            Ok(Some(StreamState::Waiting(state)))
+        }
+        t => Err(ArrowError::OutOfSpec(format!(
+            "Reading types other than record batches not yet supported, unable to read {:?} ",
+            t
+        ))),
+    }
+}
+
+/// A [`Stream`] over an Arrow IPC stream that asynchronously yields [`Chunk`]s.
+pub struct AsyncStreamReader<R: AsyncRead + Unpin + Send + 'static> {
+    metadata: StreamMetadata,
+    future: Option<BoxFuture<'static, Result<Option<StreamState<R>>>>>,
+}
+
+impl<R: AsyncRead + Unpin + Send + 'static> AsyncStreamReader<R> {
+    /// Creates a new [`AsyncStreamReader`]
+    pub fn new(reader: R, metadata: StreamMetadata) -> Self {
+        let state = ReadState {
+            reader,
+            metadata: metadata.clone(),
+            dictionaries: Default::default(),
+            data_buffer: Default::default(),
+            message_buffer: Default::default(),
+        };
+        let future = Some(Box::pin(maybe_next(state)) as _);
+        Self { metadata, future }
+    }
+
+    /// Return the schema of the stream
+    pub fn metadata(&self) -> &StreamMetadata {
+        &self.metadata
+    }
+}
+
+impl<R: AsyncRead + Unpin + Send> Stream for AsyncStreamReader<R> {
+    type Item = Result<Chunk<Arc<dyn Array>>>;
+
+    fn poll_next(
+        self: std::pin::Pin<&mut Self>,
+        cx: &mut std::task::Context<'_>,
+    ) -> std::task::Poll<Option<Self::Item>> {
+        use std::pin::Pin;
+        use std::task::Poll;
+        let me = Pin::into_inner(self);
+
+        match &mut me.future {
+            Some(fut) => match fut.as_mut().poll(cx) {
+                Poll::Ready(Ok(None)) => {
+                    me.future = None;
+                    Poll::Ready(None)
+                }
+                Poll::Ready(Ok(Some(StreamState::Some((state, batch))))) => {
+                    me.future = Some(Box::pin(maybe_next(state)));
+                    Poll::Ready(Some(Ok(batch)))
+                }
+                Poll::Ready(Ok(Some(StreamState::Waiting(_)))) => Poll::Pending,
+                Poll::Ready(Err(err)) => {
+                    me.future = None;
+                    Poll::Ready(Some(Err(err)))
+                }
+                Poll::Pending => Poll::Pending,
+            },
+            None => Poll::Ready(None),
+        }
+    }
+}

tests/it/io/ipc/mod.rs

@@ -6,3 +6,6 @@ pub use common::read_gzip_json;
 
 #[cfg(feature = "io_ipc_write_async")]
 mod write_async;
+
+#[cfg(feature = "io_ipc_read_async")]
+mod read_stream_async;

tests/it/io/ipc/read_stream_async.rs

@@ -0,0 +1,45 @@
+use futures::StreamExt;
+use tokio::fs::File;
+use tokio_util::compat::*;
+
+use arrow2::error::Result;
+use arrow2::io::ipc::read::stream_async::*;
+
+use crate::io::ipc::common::read_gzip_json;
+
+async fn test_file(version: &str, file_name: &str) -> Result<()> {
+    let testdata = crate::test_util::arrow_test_data();
+    let mut file = File::open(format!(
+        "{}/arrow-ipc-stream/integration/{}/{}.stream",
+        testdata, version, file_name
+    ))
+    .await?
+    .compat();
+
+    let metadata = read_stream_metadata_async(&mut file).await?;
+    let mut reader = AsyncStreamReader::new(file, metadata);
+
+    // read expected JSON output
+    let (schema, ipc_fields, batches) = read_gzip_json(version, file_name)?;
+
+    assert_eq!(&schema, &reader.metadata().schema);
+    assert_eq!(&ipc_fields, &reader.metadata().ipc_schema.fields);
+
+    let mut items = vec![];
+    while let Some(item) = reader.next().await {
+        items.push(item?)
+    }
+
+    batches
+        .iter()
+        .zip(items.into_iter())
+        .for_each(|(lhs, rhs)| {
+            assert_eq!(lhs, &rhs);
+        });
+    Ok(())
+}
+
+#[tokio::test]
+async fn write_async() -> Result<()> {
+    test_file("1.0.0-littleendian", "generated_primitive").await
+}