Added example

Cargo.toml

@@ -83,7 +83,8 @@ flate2 = "1"
 doc-comment = "0.3"
 crossbeam-channel = "0.5.1"
 # used to test async readers
-tokio = { version = "1", features = ["macros", "rt"] }
+tokio = { version = "1", features = ["macros", "rt", "fs"] }
+tokio-util = { version = "0.6", features = ["compat"] }
 # used to run formal property testing
 proptest = { version = "1", default_features = false, features = ["std"] }
 

examples/csv_read_async.rs

@@ -0,0 +1,36 @@
+use std::sync::Arc;
+
+use futures::io::Cursor;
+use tokio::fs::File;
+use tokio_util::compat::*;
+
+use arrow2::array::*;
+use arrow2::error::Result;
+use arrow2::io::csv::read_async::*;
+
+#[tokio::main(flavor = "current_thread")]
+async fn main() -> Result<()> {
+    use std::env;
+    let args: Vec<String> = env::args().collect();
+
+    let file_path = &args[1];
+
+    let file = File::open(file_path).await?.compat();
+
+    let mut reader = AsyncReaderBuilder::new().create_reader(file);
+
+    let schema = Arc::new(infer_schema(&mut reader, None, true, &infer).await?);
+
+    let mut rows = vec![ByteRecord::default(); 100];
+    let rows_read = read_rows(&mut reader, 0, &mut rows).await?;
+
+    let batch = deserialize_batch(
+        &rows[..rows_read],
+        schema.fields(),
+        None,
+        0,
+        deserialize_column,
+    )?;
+    println!("{}", batch.column(0));
+    Ok(())
+}

guide/src/io/csv_reader.md

@@ -30,6 +30,19 @@ thereby maximizing IO throughput. The example below shows how to do just that:
 {{#include ../../../examples/csv_read_parallel.rs}}
 ```
 
+## Async
+
+This crate also supports reading from a CSV asyncronously through the `csv-async` crate.
+The example below demonstrates this:
+
+```rust
+{{#include ../../../examples/csv_read_async.rs}}
+```
+
+Note that the deserialization _should_ be performed on a separate thread to not
+block (see also [here](https://ryhl.io/blog/async-what-is-blocking/)), which this
+example does not show.
+
 ## Customization
 
 In the code above, `parser` and `infer` allow for customization: they declare

src/io/csv/mod.rs

@@ -1,17 +1,16 @@
 #![deny(missing_docs)]
-//! Transfer data between the Arrow memory format and CSV (comma-separated values).
+//! Convert data between the Arrow and CSV (comma-separated values).
 
 use crate::error::ArrowError;
 
-pub use csv::Error as CSVError;
-
 #[cfg(any(feature = "io_csv_read_async", feature = "io_csv_read"))]
 mod read_utils;
 #[cfg(any(feature = "io_csv_read_async", feature = "io_csv_read"))]
 mod utils;
 
-impl From<CSVError> for ArrowError {
-    fn from(error: CSVError) -> Self {
+#[cfg(any(feature = "io_csv_read", feature = "io_csv_write"))]
+impl From<csv::Error> for ArrowError {
+    fn from(error: csv::Error) -> Self {
         ArrowError::External("".to_string(), Box::new(error))
     }
 }

src/io/mod.rs

@@ -1,7 +1,18 @@
 //! Contains modules to interface with other formats such as [`csv`],
 //! [`parquet`], [`json`], [`ipc`], [`mod@print`] and [`avro`].
-#[cfg(any(feature = "io_csv_read", feature = "io_csv_write"))]
-#[cfg_attr(docsrs, doc(cfg(feature = "io_csv")))]
+#[cfg(any(
+    feature = "io_csv_read",
+    feature = "io_csv_read_async",
+    feature = "io_csv_write",
+))]
+#[cfg_attr(
+    docsrs,
+    doc(cfg(any(
+        feature = "io_csv_read",
+        feature = "io_csv_read_async",
+        feature = "io_csv_write",
+    )))
+)]
 pub mod csv;
 
 #[cfg(feature = "io_json")]