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//! Given a stream of streams CSV data, rechunk the stream sizes.
use csv;
use std::{cell::Cell, cmp::min, io, rc::Rc};
use tokio::sync::mpsc;
use crate::common::*;
use crate::concat::concatenate_csv_streams;
use crate::tokio_glue::{SyncStreamReader, SyncStreamWriter};
/// Max buffer size for `csv::Writer`.
const MAX_CSV_BUFFER_SIZE: usize = 8 * (1 << 10);
/// Given a stream of streams CSV data, return another stream of CSV streams
/// where the CSV data is approximately `chunk_size` long whenever possible.
pub fn rechunk_csvs(
ctx: Context,
chunk_size: usize,
streams: BoxStream<CsvStream>,
) -> Result<BoxStream<CsvStream>> {
// Convert out input `BoxStream<CsvStream>` into a single, concatenated
// synchronous `Read` object.
let ctx = ctx.child(o!("streams_transform" => "rechunk_csvs"));
let input_csv_stream = concatenate_csv_streams(ctx.clone(), streams)?;
let csv_rdr = SyncStreamReader::new(ctx.clone(), input_csv_stream.data);
// Create a channel to which we can write `CsvStream` values once we've
// created them.
let (mut csv_stream_sender, csv_stream_receiver) =
mpsc::channel::<Result<CsvStream>>(1);
// Run a synchronous background worker thread that parsers our sync CSV
// `Read`er into a stream of `CsvStream`s.
let name = "rechunk".to_owned();
let worker_ctx = ctx.clone();
let worker_fut = run_sync_fn_in_background(name, move || -> Result<()> {
let mut rdr = csv::Reader::from_reader(csv_rdr);
let hdr = rdr
.byte_headers()
.context("cannot read chunk header")?
.to_owned();
/// A single output chunk. The state we need to generate a single
/// `CsvStream`.
struct Chunk<W: Write> {
/// Write to this to add data to the chunk.
wtr: csv::Writer<W>,
/// Approximately how much data have we written, not counting the
/// buffer in `wtr`?
total_written: Rc<Cell<usize>>,
/// The `CsvStream` which will output the data produced by `wtr`.
/// Once we publish this vaue to `csv_stream_sender`, we'll set the
/// field `csv_stream` to `None`.
csv_stream: Option<CsvStream>,
}
// What chunk number are we on? Used to give unique names to
// `CsvStream`s.
let mut chunk_id: usize = 0;
// Construct a new `CsvStream`, and return a `Chunk` with a
// `csv::Writer` which can be used to write data to it.
let mut new_chunk = || -> Result<Chunk<_>> {
chunk_id = chunk_id.checked_add(1).expect("too many chunks");
trace!(worker_ctx.log(), "starting new CSV chunk {}", chunk_id);
// Build a `CsvStream` that we can write to synchronously using
// `wtr`. Here, `wtr` is a synchronous `Write` implementation,
// and `data` is an `impl Stream<Item = BytesMut, ..>`.
let (wtr, data) = SyncStreamWriter::pipe(worker_ctx.clone());
let csv_stream = CsvStream {
name: format!("chunk_{:04}", chunk_id),
data: Box::new(data),
};
// Keep rough track of how many bytes we've written.
let wtr = CountingWriter::new(wtr);
let total_written = wtr.total_written();
// Now, make a `csv::Writer` we can write to. We limit our buffer
// size so that `chunk_size` is vaguely accurate.
let wtr = csv::WriterBuilder::default()
.buffer_capacity(min(MAX_CSV_BUFFER_SIZE, chunk_size))
.from_writer(wtr);
Ok(Chunk {
wtr,
total_written,
csv_stream: Some(csv_stream),
})
};
let mut chunk = new_chunk()?;
for row in rdr.byte_records() {
let row = row.context("cannot read row")?;
// If this is the first row we've seen, we can safely send our
// `CsvStream` to our `csv_stream_sender: BoxStream<CsvStream>`. We
// do this before writing any data, including the headers, so that
// somebody hooks up a consumer and prevents `chunk.wtr` from
// blocking forever.
if let Some(csv_stream) = chunk.csv_stream.take() {
csv_stream_sender = csv_stream_sender.send(Ok(csv_stream)).wait()?;
// Now that we potentially have a consumer, we can safely write our
// headers.
chunk
.wtr
.write_byte_record(&hdr)
.context("cannot write chunk header")?;
}
// Write our row.
chunk
.wtr
.write_byte_record(&row)
.context("cannot write row")?;
// If total written exceeds chunk size, then start a new chunk.
if chunk.total_written.get() >= chunk_size {
trace!(worker_ctx.log(), "finishing chunk");
chunk = new_chunk()?;
}
}
trace!(worker_ctx.log(), "finished rechunking CSV data");
Ok(())
});
ctx.spawn_worker(worker_fut.boxed().compat());
// Fix up our `csv_stream_receiver`'s type so it's what what we want.
let csv_stream_receiver = csv_stream_receiver
// Change `Error` from `mpsc::Error` to our standard `Error`.
.map_err(|_| format_err!("stream read error"))
// Change `Item` from `Result<CsvStream>` to `CsvStream`, pushing
// the error into the stream's `Error` channel instead.
.and_then(|result| result);
let csv_streams = Box::new(csv_stream_receiver) as BoxStream<CsvStream>;
Ok(csv_streams)
}
#[test]
fn rechunk_csvs_honors_chunk_size() {
use std::str;
let inputs: &[&[u8]] = &[b"a,b\n1,1\n2,1\n", b"a,b\n1,2\n2,2\n"];
let expected: &[&[u8]] =
&[b"a,b\n1,1\n", b"a,b\n2,1\n", b"a,b\n1,2\n", b"a,b\n2,2\n"];
let (ctx, worker_fut) = Context::create_for_test("rechunk_csvs");
let cmd_fut = async move {
debug!(ctx.log(), "testing rechunk_csvs");
// Build our `BoxStream<CsvStream>`.
let (mut sender, receiver) = mpsc::channel(2);
for &input in inputs {
sender = sender
.send(CsvStream::from_bytes(input).await)
.compat()
.await
.unwrap();
}
drop(sender);
let csv_streams =
Box::new(receiver.map_err(|e| e.into())) as BoxStream<CsvStream>;
let rechunked_csv_streams = rechunk_csvs(ctx.clone(), 7, csv_streams).unwrap();
let outputs = rechunked_csv_streams
.map(move |csv_stream| {
let ctx = ctx.clone();
let fut = async move {
let bytes = csv_stream.into_bytes(ctx.clone()).await.unwrap();
trace!(
ctx.log(),
"collected CSV stream: {:?}",
str::from_utf8(&bytes).unwrap()
);
Ok(bytes)
};
fut.boxed().compat()
})
.buffered(4)
.collect()
.compat()
.await
.unwrap();
assert_eq!(outputs.len(), expected.len());
for (output, &expected) in outputs.into_iter().zip(expected) {
assert_eq!(output, expected);
}
Ok(())
};
run_futures_with_runtime(cmd_fut.boxed(), worker_fut).unwrap();
}
/// A `Write` implementation that keeps track of how much data has been written
/// so far. Note that if you wrap this in a buffered type like `csv::Writer`, it
/// won't keep track of the data in `csv::Writer`'s buffer, only the data that
/// has been flushed.
struct CountingWriter<W: Write> {
/// Our writer.
inner: W,
/// The total data that we've written. This is wrapped in `Rc<Cell<_>>` so
/// that is can be easily accessed from anywhere in the same thread even if
/// the `CountingWriter` is completely owned by another type such as
/// `csv::Writer`.
total_written: Rc<Cell<usize>>,
}
impl<W: Write> CountingWriter<W> {
/// Create a new `CountingWriter` that wraps `inner`.
fn new(inner: W) -> Self {
Self {
inner,
total_written: Rc::new(Cell::new(0)),
}
}
/// How much data has been written? This returns an `Rc<Cell<_>>` that will
/// be updated by this `CountingWriter`. Setting the value in this `Cell`
/// directly may result in future reads returning an unspecified value.
fn total_written(&self) -> Rc<Cell<usize>> {
self.total_written.clone()
}
}
impl<W: Write> Write for CountingWriter<W> {
fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
let written = self.inner.write(buf)?;
let total_written = self.total_written.get() + written;
self.total_written.set(total_written);
Ok(written)
}
fn flush(&mut self) -> io::Result<()> {
self.inner.flush()
}
}