feat: Add NDJson sink for the new streaming engine

.typos.toml

@@ -30,5 +30,6 @@ Fo = "Fo"
 ND = "ND"
 nd = "nd"
 NDJson = "NDJson"
+NDJsonSinkNode = "NDJsonSinkNode"
 NDJsonReadOptions = "NDJsonReadOptions"
 opt_nd = "opt_nd"

crates/polars-stream/src/nodes/io_sinks/json.rs

@@ -0,0 +1,123 @@
+use std::cmp::Reverse;
+use std::io::Write;
+use std::path::{Path, PathBuf};
+
+use polars_error::PolarsResult;
+use polars_expr::state::ExecutionState;
+use polars_io::json::BatchedWriter;
+use polars_utils::priority::Priority;
+
+use crate::async_primitives::linearizer::Linearizer;
+use crate::nodes::{ComputeNode, JoinHandle, MorselSeq, PortState, TaskPriority, TaskScope};
+use crate::pipe::{RecvPort, SendPort};
+use crate::DEFAULT_LINEARIZER_BUFFER_SIZE;
+
+pub struct NDJsonSinkNode {
+    path: PathBuf,
+}
+
+impl NDJsonSinkNode {
+    pub fn new(path: &Path) -> PolarsResult<Self> {
+        Ok(Self {
+            path: path.to_path_buf(),
+        })
+    }
+}
+
+impl ComputeNode for NDJsonSinkNode {
+    fn name(&self) -> &str {
+        "ndjson_sink"
+    }
+
+    fn update_state(&mut self, recv: &mut [PortState], send: &mut [PortState]) -> PolarsResult<()> {
+        assert!(send.is_empty());
+        assert!(recv.len() == 1);
+
+        // We are always ready to receive, unless the sender is done, then we're
+        // also done.
+        if recv[0] != PortState::Done {
+            recv[0] = PortState::Ready;
+        }
+
+        Ok(())
+    }
+
+    fn spawn<'env, 's>(
+        &'env mut self,
+        scope: &'s TaskScope<'s, 'env>,
+        recv_ports: &mut [Option<RecvPort<'_>>],
+        send_ports: &mut [Option<SendPort<'_>>],
+        _state: &'s ExecutionState,
+        join_handles: &mut Vec<JoinHandle<PolarsResult<()>>>,
+    ) {
+        assert!(recv_ports.len() == 1);
+        assert!(send_ports.is_empty());
+
+        // .. -> Encode task
+        let receivers = recv_ports[0].take().unwrap().parallel();
+        // Encode tasks -> IO task
+        let (mut linearizer, senders) = Linearizer::<Priority<Reverse<MorselSeq>, Vec<u8>>>::new(
+            receivers.len(),
+            DEFAULT_LINEARIZER_BUFFER_SIZE,
+        );
+
+        let slf = &*self;
+
+        // 16MB
+        const DEFAULT_ALLOCATION_SIZE: usize = 1 << 24;
+
+        // Encode task.
+        //
+        // Task encodes the columns into their corresponding CSV encoding.
+        for (mut receiver, mut sender) in receivers.into_iter().zip(senders) {
+            join_handles.push(scope.spawn_task(TaskPriority::High, async move {
+                // Amortize the allocations over time. If we see that we need to do way larger
+                // allocations, we adjust to that over time.
+                let mut allocation_size = DEFAULT_ALLOCATION_SIZE;
+
+                while let Ok(morsel) = receiver.recv().await {
+                    let (df, seq, _, _) = morsel.into_inner();
+
+                    let mut buffer = Vec::with_capacity(allocation_size);
+                    let mut writer = BatchedWriter::new(&mut buffer);
+
+                    writer.write_batch(&df)?;
+
+                    allocation_size = allocation_size.max(buffer.len());
+                    sender.insert(Priority(Reverse(seq), buffer)).await.unwrap();
+                }
+
+                PolarsResult::Ok(())
+            }));
+        }
+
+        // IO task.
+        //
+        // Task that will actually do write to the target file.
+        let io_runtime = polars_io::pl_async::get_runtime();
+
+        let path = slf.path.clone();
+        let io_task = io_runtime.spawn(async move {
+            use tokio::fs::OpenOptions;
+
+            let file = OpenOptions::new()
+                .write(true)
+                .create(true)
+                .truncate(true)
+                .open(path.as_path())
+                .await
+                .map_err(|err| polars_utils::_limit_path_len_io_err(path.as_path(), err))?;
+
+            let mut file = file.into_std().await;
+
+            // Write the header
+            while let Some(Priority(_, buffer)) = linearizer.get().await {
+                file.write_all(&buffer)?;
+            }
+
+            PolarsResult::Ok(())
+        });
+        join_handles
+            .push(scope.spawn_task(TaskPriority::Low, async move { io_task.await.unwrap() }));
+    }
+}

crates/polars-stream/src/nodes/io_sinks/mod.rs

@@ -2,5 +2,7 @@
 pub mod csv;
 #[cfg(feature = "ipc")]
 pub mod ipc;
+#[cfg(feature = "json")]
+pub mod json;
 #[cfg(feature = "parquet")]
 pub mod parquet;

crates/polars-stream/src/physical_plan/lower_ir.rs

@@ -245,7 +245,15 @@ pub fn lower_ir(
                             input: phys_input,
                         }
                     },
-                    _ => todo!(),
+                    #[cfg(feature = "json")]
+                    FileType::Json(_) => {
+                        let phys_input = lower_ir!(*input)?;
+                        PhysNodeKind::FileSink {
+                            path,
+                            file_type,
+                            input: phys_input,
+                        }
+                    },
                 }
             },
         },

crates/polars-stream/src/physical_plan/to_graph.rs

@@ -221,6 +221,11 @@ fn to_graph_rec<'a>(
                     nodes::io_sinks::ipc::IpcSinkNode::new(input_schema, path, ipc_writer_options)?,
                     [(input_key, input.port)],
                 ),
+                #[cfg(feature = "json")]
+                FileType::Json(_) => ctx.graph.add_node(
+                    nodes::io_sinks::json::NDJsonSinkNode::new(path)?,
+                    [(input_key, input.port)],
+                ),
                 #[cfg(feature = "parquet")]
                 FileType::Parquet(parquet_writer_options) => ctx.graph.add_node(
                     nodes::io_sinks::parquet::ParquetSinkNode::new(
@@ -235,7 +240,6 @@ fn to_graph_rec<'a>(
                     nodes::io_sinks::csv::CsvSinkNode::new(input_schema, path, csv_writer_options)?,
                     [(input_key, input.port)],
                 ),
-                _ => todo!(),
             }
         },