fix: harden multi-pod delivery and load verification

server/cluster_overload_test.go

@@ -0,0 +1,35 @@
+package main
+
+import (
+	"errors"
+	"net/http"
+	"testing"
+	"time"
+
+	"github.com/tinode/chat/server/store/types"
+)
+
+func TestClusterReqShardIsStablePerTenantTopic(t *testing.T) {
+	req := &ClusterReq{TenantID: types.TenantID(6), RcptTo: "p2p-topic"}
+	want := clusterReqShard(req, 16)
+	for i := 0; i < 100; i++ {
+		if got := clusterReqShard(req, 16); got != want {
+			t.Fatalf("unstable shard: got=%d want=%d", got, want)
+		}
+	}
+	if got := clusterReqShard(req, 1); got != 0 {
+		t.Fatalf("single worker shard=%d", got)
+	}
+}
+
+func TestClusterRouteErrorReplySeparatesOverloadFromDisconnect(t *testing.T) {
+	msg := &ClientComMessage{Id: "test", Timestamp: time.Now()}
+	overload := clusterRouteErrorReply(msg, errClusterLoadExceeded)
+	if overload.Ctrl == nil || overload.Ctrl.Code != http.StatusServiceUnavailable || overload.Ctrl.Text != "cluster overloaded" {
+		t.Fatalf("unexpected overload reply: %+v", overload.Ctrl)
+	}
+	disconnected := clusterRouteErrorReply(msg, errors.New("disconnected"))
+	if disconnected.Ctrl == nil || disconnected.Ctrl.Code != http.StatusBadGateway {
+		t.Fatalf("unexpected disconnected reply: %+v", disconnected.Ctrl)
+	}
+}