From 8c2d7a4b5e2b15f4ad791a98ebba61555ed4be01 Mon Sep 17 00:00:00 2001
From: Kavya Bhat <kavyabhat@gmail.com>
Date: Wed, 25 Mar 2026 14:32:13 -0600
Subject: [PATCH] Broadcast watermark while reading from filesource

---
 .../src/single_file_custom/source.rs          | 82 ++++++++++++++++++-
 1 file changed, 80 insertions(+), 2 deletions(-)

diff --git a/crates/arroyo-connectors/src/single_file_custom/source.rs b/crates/arroyo-connectors/src/single_file_custom/source.rs
index 8b5c697b6..03fcd7768 100644
--- a/crates/arroyo-connectors/src/single_file_custom/source.rs
+++ b/crates/arroyo-connectors/src/single_file_custom/source.rs
@@ -9,7 +9,7 @@ use arroyo_operator::SourceFinishType;
 use arroyo_rpc::formats::{BadData, Format, Framing};
 use arroyo_rpc::grpc::rpc::{StopMode, TableConfig};
 use arroyo_rpc::ControlMessage;
-use arroyo_types::UserError;
+use arroyo_types::{SignalMessage, UserError, Watermark};
 use async_compression::tokio::bufread::{GzipDecoder, ZstdDecoder};
 use async_trait::async_trait;
 use chrono::{DateTime, Utc};
@@ -175,8 +175,11 @@ impl SingleFileCustomSourceFunc {
                             }
                         }
                         None => {
-                            collector.flush_buffer().await?;
                             info!("Finished reading {} records from {}", self.records_read, self.path);
+                            // Emit a far-future watermark to flush all pending windows
+                            let flush_ts = SystemTime::now() + Duration::from_secs(60 * 60 * 24 * 365);
+                            collector.broadcast(SignalMessage::Watermark(Watermark::EventTime(flush_ts))).await;
+                            collector.flush_buffer().await?;
                             return Ok(SourceFinishType::Final);
                         }
                     }
@@ -190,6 +193,69 @@ impl SingleFileCustomSourceFunc {
         }
     }
 
+    fn get_min_max_timestamp(
+        &self,
+        batch: &RecordBatch,
+        ts_idx: usize,
+    ) -> (Option<SystemTime>, Option<SystemTime>) {
+        use arrow::array::AsArray;
+        use arrow::datatypes::{DataType, TimeUnit};
+
+        let ts_array = batch.column(ts_idx);
+        let data_type = ts_array.data_type().clone();
+
+        let (min_nanos, max_nanos): (Option<i64>, Option<i64>) = match &data_type {
+            DataType::Timestamp(TimeUnit::Millisecond, _) => {
+                let arr = ts_array.as_primitive::<arrow::datatypes::TimestampMillisecondType>();
+                let vals: Vec<i64> = (0..batch.num_rows())
+                    .map(|i| arr.value(i) * 1_000_000)
+                    .collect();
+                (
+                    vals.iter().copied().reduce(i64::min),
+                    vals.iter().copied().reduce(i64::max),
+                )
+            }
+            DataType::Timestamp(TimeUnit::Nanosecond, _) => {
+                let arr = ts_array.as_primitive::<arrow::datatypes::TimestampNanosecondType>();
+                let vals: Vec<i64> = (0..batch.num_rows()).map(|i| arr.value(i)).collect();
+                (
+                    vals.iter().copied().reduce(i64::min),
+                    vals.iter().copied().reduce(i64::max),
+                )
+            }
+            DataType::Timestamp(TimeUnit::Microsecond, _) => {
+                let arr = ts_array.as_primitive::<arrow::datatypes::TimestampMicrosecondType>();
+                let vals: Vec<i64> = (0..batch.num_rows())
+                    .map(|i| arr.value(i) * 1_000)
+                    .collect();
+                (
+                    vals.iter().copied().reduce(i64::min),
+                    vals.iter().copied().reduce(i64::max),
+                )
+            }
+            DataType::Int64 => {
+                let arr = ts_array.as_primitive::<arrow::datatypes::Int64Type>();
+                let vals: Vec<i64> = match self.ts_format {
+                    TsFormat::UnixMillis => (0..batch.num_rows())
+                        .map(|i| arr.value(i) * 1_000_000)
+                        .collect(),
+                    TsFormat::UnixSeconds => (0..batch.num_rows())
+                        .map(|i| arr.value(i) * 1_000_000_000)
+                        .collect(),
+                    _ => vec![],
+                };
+                (
+                    vals.iter().copied().reduce(i64::min),
+                    vals.iter().copied().reduce(i64::max),
+                )
+            }
+            _ => (None, None),
+        };
+
+        let to_systime = |nanos: i64| UNIX_EPOCH + Duration::from_nanos(nanos as u64);
+        (min_nanos.map(to_systime), max_nanos.map(to_systime))
+    }
+
     async fn run_parquet(
         &mut self,
         ctx: &mut SourceContext,
@@ -256,9 +322,21 @@ impl SingleFileCustomSourceFunc {
                 batch = stream.next() => {
                     match batch {
                         Some(Ok(batch)) => {
+                            // Broadcast min timestamp BEFORE collecting so windows aren't dropped as late
+                            let (min_ts, max_ts) = self.get_min_max_timestamp(&batch, ts_idx);
+                            if let Some(ts) = min_ts {
+                                collector.broadcast(SignalMessage::Watermark(Watermark::EventTime(ts))).await;
+                            }
+
                             // Extract timestamps from the batch and add _timestamp column
                             let out_batch = self.add_timestamp_to_batch(&batch, ts_idx)?;
                             collector.collect(out_batch).await;
+
+                            // Advance watermark to max timestamp AFTER collecting
+                            if let Some(ts) = max_ts {
+                                collector.broadcast(SignalMessage::Watermark(Watermark::EventTime(ts))).await;
+                            }
+
                             self.records_read += batch.num_rows() as u64;
 
                             if self.records_read % LOG_INTERVAL == 0 {