From 50fabe261d6e8ddb1a313444ec226aedb02ebf08 Mon Sep 17 00:00:00 2001
From: Derek Collison <derek@nats.io>
Date: Wed, 21 Apr 2021 15:31:46 -0700
Subject: [PATCH] Check for overlapping subjects on stream update.

Signed-off-by: Derek Collison <derek@nats.io>
---
 server/jetstream_cluster.go      | 16 ++++++++++++++
 server/jetstream_cluster_test.go | 37 ++++++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+)

diff --git a/server/jetstream_cluster.go b/server/jetstream_cluster.go
index 7fa3a5c1..92b79347 100644
--- a/server/jetstream_cluster.go
+++ b/server/jetstream_cluster.go
@@ -3466,6 +3466,22 @@ func (s *Server) jsClusteredStreamUpdateRequest(ci *ClientInfo, acc *Account, su
 		return
 	}
 
+	// Check for subject collisions here.
+	for _, sa := range cc.streams[acc.Name] {
+		if sa == osa {
+			continue
+		}
+		for _, subj := range sa.Config.Subjects {
+			for _, tsubj := range newCfg.Subjects {
+				if SubjectsCollide(tsubj, subj) {
+					resp.Error = jsError(fmt.Errorf("subjects overlap with an existing stream"))
+					s.sendAPIErrResponse(ci, acc, subject, reply, string(rmsg), s.jsonResponse(&resp))
+					return
+				}
+			}
+		}
+	}
+
 	sa := &streamAssignment{Group: osa.Group, Config: newCfg, Subject: subject, Reply: reply, Client: ci}
 	cc.meta.Propose(encodeUpdateStreamAssignment(sa))
 }
diff --git a/server/jetstream_cluster_test.go b/server/jetstream_cluster_test.go
index 364fa9ac..1524ee23 100644
--- a/server/jetstream_cluster_test.go
+++ b/server/jetstream_cluster_test.go
@@ -5880,6 +5880,43 @@ func TestJetStreamClusterCreateConcurrentDurableConsumers(t *testing.T) {
 	}
 }
 
+// https://github.com/nats-io/nats-server/issues/2144
+func TestJetStreamClusterUpdateStreamToExisting(t *testing.T) {
+	c := createJetStreamClusterExplicit(t, "MSL", 3)
+	defer c.shutdown()
+
+	// Client for API requests.
+	nc, js := jsClientConnect(t, c.randomServer())
+	defer nc.Close()
+
+	_, err := js.AddStream(&nats.StreamConfig{
+		Name:     "ORDERS1",
+		Replicas: 3,
+		Subjects: []string{"foo"},
+	})
+	if err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+
+	_, err = js.AddStream(&nats.StreamConfig{
+		Name:     "ORDERS2",
+		Replicas: 3,
+		Subjects: []string{"bar"},
+	})
+	if err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+
+	_, err = js.UpdateStream(&nats.StreamConfig{
+		Name:     "ORDERS2",
+		Replicas: 3,
+		Subjects: []string{"foo"},
+	})
+	if err == nil {
+		t.Fatalf("Expected an error but got none")
+	}
+}
+
 // Support functions
 
 // Used to setup superclusters for tests.