Fixes accidental state store updates from output-side fixups.

agent/agent_endpoint.go

@@ -146,9 +146,11 @@ func (s *HTTPServer) AgentServices(resp http.ResponseWriter, req *http.Request)
 	}
 
 	// Use empty list instead of nil
-	for _, s := range services {
+	for id, s := range services {
 		if s.Tags == nil {
-			s.Tags = make([]string, 0)
+			clone := *s
+			clone.Tags = make([]string, 0)
+			services[id] = &clone
 		}
 	}
 
@@ -170,10 +172,11 @@ func (s *HTTPServer) AgentChecks(resp http.ResponseWriter, req *http.Request) (i
 	}
 
 	// Use empty list instead of nil
-	// checks needs to be a deep copy for this not be racy
-	for _, c := range checks {
+	for id, c := range checks {
 		if c.ServiceTags == nil {
-			c.ServiceTags = make([]string, 0)
+			clone := *c
+			clone.ServiceTags = make([]string, 0)
+			checks[id] = &clone
 		}
 	}
 

agent/agent_test.go

@@ -547,26 +547,42 @@ func TestAgent_RemoveServiceRemovesAllChecks(t *testing.T) {
 	}
 }
 
-// TestAgent_ServiceWithTagChurn is designed to detect a class of issues where
-// we would have unnecessary catalog churn for services with tags. See issues
-// #3259, #3642, and #3845.
-func TestAgent_ServiceWithTagChurn(t *testing.T) {
+// TestAgent_IndexChurn is designed to detect a class of issues where
+// we would have unnecessary catalog churn from anti-entropy. See issues
+// #3259, #3642, #3845, and #3866.
+func TestAgent_IndexChurn(t *testing.T) {
 	t.Parallel()
+
+	t.Run("no tags", func(t *testing.T) {
+		verifyIndexChurn(t, nil)
+	})
+
+	t.Run("with tags", func(t *testing.T) {
+		verifyIndexChurn(t, []string{"foo", "bar"})
+	})
+}
+
+// verifyIndexChurn registers some things and runs anti-entropy a bunch of times
+// in a row to make sure there are no index bumps.
+func verifyIndexChurn(t *testing.T, tags []string) {
+	t.Helper()
+
 	a := NewTestAgent(t.Name(), "")
 	defer a.Shutdown()
 
 	svc := &structs.NodeService{
 		ID:      "redis",
 		Service: "redis",
 		Port:    8000,
-		Tags:    []string{"has", "tags"},
+		Tags:    tags,
 	}
 	if err := a.AddService(svc, nil, true, ""); err != nil {
 		t.Fatalf("err: %v", err)
 	}
 
 	chk := &structs.HealthCheck{
 		CheckID:   "redis-check",
+		Name:      "Service-level check",
 		ServiceID: "redis",
 		Status:    api.HealthCritical,
 	}
@@ -577,18 +593,34 @@ func TestAgent_ServiceWithTagChurn(t *testing.T) {
 		t.Fatalf("err: %v", err)
 	}
 
+	chk = &structs.HealthCheck{
+		CheckID: "node-check",
+		Name:    "Node-level check",
+		Status:  api.HealthCritical,
+	}
+	chkt = &structs.CheckType{
+		TTL: time.Hour,
+	}
+	if err := a.AddCheck(chk, chkt, true, ""); err != nil {
+		t.Fatalf("err: %v", err)
+	}
+
 	if err := a.sync.State.SyncFull(); err != nil {
 		t.Fatalf("err: %v", err)
 	}
+
 	args := &structs.ServiceSpecificRequest{
 		Datacenter:  "dc1",
 		ServiceName: "redis",
 	}
-	var before structs.IndexedHealthChecks
-	if err := a.RPC("Health.ServiceChecks", args, &before); err != nil {
+	var before structs.IndexedCheckServiceNodes
+	if err := a.RPC("Health.ServiceNodes", args, &before); err != nil {
 		t.Fatalf("err: %v", err)
 	}
-	if got, want := len(before.HealthChecks), 1; got != want {
+	if got, want := len(before.Nodes), 1; got != want {
+		t.Fatalf("got %d want %d", got, want)
+	}
+	if got, want := len(before.Nodes[0].Checks), 3; /* incl. serfHealth */ got != want {
 		t.Fatalf("got %d want %d", got, want)
 	}
 
@@ -598,8 +630,8 @@ func TestAgent_ServiceWithTagChurn(t *testing.T) {
 		}
 	}
 
-	var after structs.IndexedHealthChecks
-	if err := a.RPC("Health.ServiceChecks", args, &after); err != nil {
+	var after structs.IndexedCheckServiceNodes
+	if err := a.RPC("Health.ServiceNodes", args, &after); err != nil {
 		t.Fatalf("err: %v", err)
 	}
 	verify.Values(t, "", after, before)

agent/catalog_endpoint.go

@@ -201,9 +201,11 @@ func (s *HTTPServer) CatalogServiceNodes(resp http.ResponseWriter, req *http.Req
 	if out.ServiceNodes == nil {
 		out.ServiceNodes = make(structs.ServiceNodes, 0)
 	}
-	for _, s := range out.ServiceNodes {
+	for i, s := range out.ServiceNodes {
 		if s.ServiceTags == nil {
-			s.ServiceTags = make([]string, 0)
+			clone := *s
+			clone.ServiceTags = make([]string, 0)
+			out.ServiceNodes[i] = &clone
 		}
 	}
 	metrics.IncrCounterWithLabels([]string{"client", "api", "success", "catalog_service_nodes"}, 1,
@@ -244,6 +246,15 @@ func (s *HTTPServer) CatalogNodeServices(resp http.ResponseWriter, req *http.Req
 		s.agent.TranslateAddresses(args.Datacenter, out.NodeServices.Node)
 	}
 
+	// TODO: The NodeServices object in IndexedNodeServices is a pointer to
+	// something that's created for each request by the state store way down
+	// in https://github.com/hashicorp/consul/blob/v1.0.4/agent/consul/state/catalog.go#L953-L963.
+	// Since this isn't a pointer to a real state store object, it's safe to
+	// modify out.NodeServices.Services in the loop below without making a
+	// copy here. Same for the Tags in each service entry, since that was
+	// created by .ToNodeService() which made a copy. This is safe as-is but
+	// this whole business is tricky and subtle. See #3867 for more context.
+
 	// Use empty list instead of nil
 	if out.NodeServices != nil {
 		for _, s := range out.NodeServices.Services {

agent/health_endpoint.go

@@ -42,9 +42,11 @@ func (s *HTTPServer) HealthChecksInState(resp http.ResponseWriter, req *http.Req
 	if out.HealthChecks == nil {
 		out.HealthChecks = make(structs.HealthChecks, 0)
 	}
-	for _, c := range out.HealthChecks {
+	for i, c := range out.HealthChecks {
 		if c.ServiceTags == nil {
-			c.ServiceTags = make([]string, 0)
+			clone := *c
+			clone.ServiceTags = make([]string, 0)
+			out.HealthChecks[i] = &clone
 		}
 	}
 	return out.HealthChecks, nil
@@ -80,9 +82,11 @@ func (s *HTTPServer) HealthNodeChecks(resp http.ResponseWriter, req *http.Reques
 	if out.HealthChecks == nil {
 		out.HealthChecks = make(structs.HealthChecks, 0)
 	}
-	for _, c := range out.HealthChecks {
+	for i, c := range out.HealthChecks {
 		if c.ServiceTags == nil {
-			c.ServiceTags = make([]string, 0)
+			clone := *c
+			clone.ServiceTags = make([]string, 0)
+			out.HealthChecks[i] = &clone
 		}
 	}
 	return out.HealthChecks, nil
@@ -120,9 +124,11 @@ func (s *HTTPServer) HealthServiceChecks(resp http.ResponseWriter, req *http.Req
 	if out.HealthChecks == nil {
 		out.HealthChecks = make(structs.HealthChecks, 0)
 	}
-	for _, c := range out.HealthChecks {
+	for i, c := range out.HealthChecks {
 		if c.ServiceTags == nil {
-			c.ServiceTags = make([]string, 0)
+			clone := *c
+			clone.ServiceTags = make([]string, 0)
+			out.HealthChecks[i] = &clone
 		}
 	}
 	return out.HealthChecks, nil
@@ -194,19 +200,20 @@ func (s *HTTPServer) HealthServiceNodes(resp http.ResponseWriter, req *http.Requ
 		out.Nodes = make(structs.CheckServiceNodes, 0)
 	}
 	for i := range out.Nodes {
-		// TODO (slackpad) It's lame that this isn't a slice of pointers
-		// but it's not a well-scoped change to fix this. We should
-		// change this at the next opportunity.
 		if out.Nodes[i].Checks == nil {
 			out.Nodes[i].Checks = make(structs.HealthChecks, 0)
 		}
-		for _, c := range out.Nodes[i].Checks {
+		for j, c := range out.Nodes[i].Checks {
 			if c.ServiceTags == nil {
-				c.ServiceTags = make([]string, 0)
+				clone := *c
+				clone.ServiceTags = make([]string, 0)
+				out.Nodes[i].Checks[j] = &clone
 			}
 		}
 		if out.Nodes[i].Service != nil && out.Nodes[i].Service.Tags == nil {
-			out.Nodes[i].Service.Tags = make([]string, 0)
+			clone := *out.Nodes[i].Service
+			clone.Tags = make([]string, 0)
+			out.Nodes[i].Service = &clone
 		}
 	}
 	return out.Nodes, nil

agent/structs/structs.go

@@ -600,6 +600,8 @@ type IndexedServiceNodes struct {
 }
 
 type IndexedNodeServices struct {
+	// TODO: This should not be a pointer, see comments in
+	// agent/catalog_endpoint.go.
 	NodeServices *NodeServices
 	QueryMeta
 }