From 176f496c6564762d586ef4f3ec367f982f86a8c0 Mon Sep 17 00:00:00 2001
From: Francois Massot <francois.massot@datadoghq.com>
Date: Sun, 19 Jul 2026 03:14:47 +0200
Subject: [PATCH] fix(cluster): avoid panicking when a change stream is dropped

---
 quickwit/quickwit-cluster/src/cluster.rs      | 56 +++++++++++++++----
 .../src/datafusion_api/setup.rs               |  5 +-
 quickwit/quickwit-serve/src/lib.rs            |  2 +-
 3 files changed, 48 insertions(+), 15 deletions(-)

diff --git a/quickwit/quickwit-cluster/src/cluster.rs b/quickwit/quickwit-cluster/src/cluster.rs
index 9ae1600d420..e53d0de8a4a 100644
--- a/quickwit/quickwit-cluster/src/cluster.rs
+++ b/quickwit/quickwit-cluster/src/cluster.rs
@@ -300,18 +300,7 @@ impl Cluster {
         let (change_stream, change_stream_tx) = ClusterChangeStream::new_unbounded();
         let inner = self.inner.clone();
         // We spawn a task so the signature of this function is sync.
-        let future = async move {
-            let mut inner = inner.write().await;
-            for node in inner.live_nodes.values() {
-                if node.is_ready {
-                    change_stream_tx
-                        .send(ClusterChange::Add(node.clone()))
-                        .expect("receiver end of the channel should be open");
-                }
-            }
-            inner.change_stream_subscribers.push(change_stream_tx);
-        };
-        tokio::spawn(future);
+        tokio::spawn(register_change_stream_subscriber(inner, change_stream_tx));
         change_stream
     }
 
@@ -516,6 +505,23 @@ impl Cluster {
     }
 }
 
+async fn register_change_stream_subscriber(
+    inner: Arc<RwLock<InnerCluster>>,
+    change_stream_tx: mpsc::UnboundedSender<ClusterChange>,
+) {
+    let mut inner = inner.write().await;
+    for node in inner.live_nodes.values() {
+        if node.is_ready
+            && change_stream_tx
+                .send(ClusterChange::Add(node.clone()))
+                .is_err()
+        {
+            return;
+        }
+    }
+    inner.change_stream_subscribers.push(change_stream_tx);
+}
+
 /// Parses indexing tasks from the chitchat node state.
 pub fn parse_indexing_tasks(node_state: &NodeState) -> Vec<IndexingTask> {
     node_state
@@ -879,6 +885,32 @@ mod tests {
         node.leave().await;
     }
 
+    #[tokio::test]
+    async fn test_register_change_stream_subscriber_with_dropped_receiver() {
+        let transport = ChitchatTransport::default();
+        let node = create_cluster_for_test(Vec::new(), &[], &transport, true)
+            .await
+            .unwrap();
+        let node_clone = node.clone();
+        wait_until_predicate(
+            move || {
+                let node_clone = node_clone.clone();
+                async move { node_clone.ready_nodes().await.len() == 1 }
+            },
+            Duration::from_secs(5),
+            Duration::from_millis(10),
+        )
+        .await
+        .unwrap();
+
+        let (change_stream, change_stream_tx) = ClusterChangeStream::new_unbounded();
+        drop(change_stream);
+        register_change_stream_subscriber(node.inner.clone(), change_stream_tx).await;
+
+        assert!(node.inner.read().await.change_stream_subscribers.is_empty());
+        node.leave().await;
+    }
+
     #[tokio::test]
     async fn test_cluster_multiple_nodes() -> anyhow::Result<()> {
         let transport = ChitchatTransport::default();
diff --git a/quickwit/quickwit-serve/src/datafusion_api/setup.rs b/quickwit/quickwit-serve/src/datafusion_api/setup.rs
index aad5e45a57b..655792c3b46 100644
--- a/quickwit/quickwit-serve/src/datafusion_api/setup.rs
+++ b/quickwit/quickwit-serve/src/datafusion_api/setup.rs
@@ -26,7 +26,7 @@ use std::time::Duration;
 use anyhow::Context;
 use bytesize::ByteSize;
 use futures::{StreamExt, stream};
-use quickwit_cluster::{ClusterChange, ClusterChangeStream, ClusterNode};
+use quickwit_cluster::{Cluster, ClusterChange, ClusterChangeStream, ClusterNode};
 use quickwit_common::tower::Change;
 use quickwit_config::NodeConfig;
 use quickwit_config::service::QuickwitService;
@@ -65,7 +65,7 @@ use crate::QuickwitServices;
 /// per-query registry refresh.
 pub(crate) fn build_datafusion_session_builder(
     node_config: &NodeConfig,
-    cluster_change_stream: ClusterChangeStream,
+    cluster: &Cluster,
     metastore: MetastoreServiceClient,
     storage_resolver: StorageResolver,
 ) -> anyhow::Result<Option<Arc<DataFusionSessionBuilder>>> {
@@ -76,6 +76,7 @@ pub(crate) fn build_datafusion_session_builder(
         return Ok(None);
     }
 
+    let cluster_change_stream = cluster.change_stream();
     let metrics_source = Arc::new(MetricsDataSource::new(metastore));
     let schema_source = Arc::clone(&metrics_source);
     let datafusion_worker_pool = setup_datafusion_worker_pool(
diff --git a/quickwit/quickwit-serve/src/lib.rs b/quickwit/quickwit-serve/src/lib.rs
index fdcfe78f194..82a250a6f9b 100644
--- a/quickwit/quickwit-serve/src/lib.rs
+++ b/quickwit/quickwit-serve/src/lib.rs
@@ -848,7 +848,7 @@ pub async fn serve_quickwit(
     #[cfg(feature = "datafusion")]
     let datafusion_session_builder = datafusion_api::setup::build_datafusion_session_builder(
         &node_config,
-        cluster.change_stream(),
+        &cluster,
         metastore_through_control_plane.clone(),
         storage_resolver.clone(),
     )?;