Merge remote-tracking branch 'origin/topic/awelzel/4136-cluster-backend-pre-work'

* origin/topic/awelzel/4136-cluster-backend-pre-work:
  cluster/zeromq: Fix Unsubscribe() bug caused by \x00 prefix
  cluster: Add SubscribeCallback support
  cluster/zeromq: Fix XSUB threading issues
  cluster/zeromq: Use NodeId(), drop my_node_id
  cluster/Backend: Pass node_id via Init()
  cluster/Backend: Make backend event processing customizable
  cluster/broker/Serializer: Fix adaptor to adapter
  cluster/Backend: Do not use const std::string_view&
  cluster/serializer/broker: Fix handler lookup
  broker/Manager: Move name in PublishEvent()
  btest/zeromq/test-bootstrap: Fix port parsing
  EventHandler: Support operator!=

CHANGES

@@ -1,3 +1,61 @@
+7.2.0-dev.169 | 2025-02-05 11:10:21 +0100
+
+  * cluster/zeromq: Fix Unsubscribe() bug caused by \x00 prefix (Arne Welzel, Corelight)
+
+  * cluster: Add SubscribeCallback support (Arne Welzel, Corelight)
+
+    This allows callers of Subscribe() to pass in a callback that will be invoked
+    once the subscription is established or failed to establish. It is the
+    backend's responsibility to execute the callback on the main thread either
+    synchronously, or preferably asynchronously at a later point, by
+    scheduling a task on the IO main loop.
+
+    This turns on ZMQ_XPUB_VERBOSE for ZeroMQ so that notifications about
+    subscriptions are raised even if the subscriptions has previously been
+    observed.
+
+  * cluster/zeromq: Fix XSUB threading issues (Arne Welzel, Corelight)
+
+    It is not safe to use the same socket from different threads, but the
+    current code used the xsub socket directly from the main thread (to setup
+    subscriptions) and from the internal thread for polling and reading.
+
+    Leverage the PAIR socket already in use for forwarding publish operations
+    to the internal thread also for subscribe and unsubscribe.
+
+    The failure mode is/was a bit annoying. Essentially, closing of the
+    context would hang indefinitely in zmq_ctx_term().
+
+  * cluster/zeromq: Use NodeId(), drop my_node_id (Arne Welzel, Corelight)
+
+  * cluster/Backend: Pass node_id via Init() (Arne Welzel, Corelight)
+
+  * cluster/Backend: Make backend event processing customizable (Arne Welzel, Corelight)
+
+    This allows configurability at the code level to decide what to do with
+    a received remote events and events produced by a backend. For now, only
+    enqueue events into the process's script layer, but for the WebSocket
+    interface, the action would be to send out the event on a WebSocket
+    connection instead.
+
+  * cluster/broker/Serializer: Fix adaptor to adapter (Arne Welzel, Corelight)
+
+  * cluster/Backend: Do not use const std::string_view& (Arne Welzel, Corelight)
+
+  * cluster/serializer/broker: Fix handler lookup (Arne Welzel, Corelight)
+
+    Handler overwrites operator bool, so need to explicitly test for nullptr
+    rather than not having any handlers defined.
+
+  * broker/Manager: Move name in PublishEvent() (Arne Welzel, Corelight)
+
+  * btest/zeromq/test-bootstrap: Fix port parsing (Arne Welzel, Corelight)
+
+    to_port() will produce an error on empty strings which extract_count()
+    does not.
+
+  * EventHandler: Support operator!= (Arne Welzel, Corelight)
+
 7.2.0-dev.156 | 2025-02-05 09:05:00 +0000
 
   * IPv6 support for detect-external-names and testcase (Johanna Amann, Corelight)

VERSION

@@ -1 +1 @@
-7.2.0-dev.156
+7.2.0-dev.169

scripts/base/frameworks/cluster/main.zeek

@@ -585,7 +585,7 @@ function log(msg: string)
 
 function init(): bool
 	{
-	return Cluster::Backend::__init();
+	return Cluster::Backend::__init(Cluster::node_id());
 	}
 
 function subscribe(topic: string): bool

scripts/policy/frameworks/cluster/backend/zeromq/main.zeek

@@ -162,7 +162,8 @@ export {
 
 	## Bitmask to enable low-level stderr based debug printing.
 	##
-	##     poll debugging: 1 (produce verbose zmq::poll() output)
+	##     poll:   1 (produce verbose zmq::poll() output)
+	##     thread: 2 (produce thread related output)
 	##
 	## Or values from the above list together and set debug_flags
 	## to the result. E.g. use 7 to select 4, 2 and 1. Only use this

src/EventHandler.h

@@ -101,6 +101,8 @@ public:
 
     bool operator==(const EventHandlerPtr& h) const { return handler == h.handler; }
 
+    bool operator!=(const EventHandlerPtr& h) const { return ! (*this == h); }
+
     EventHandler* Ptr() { return handler; }
 
     explicit operator bool() const { return handler && *handler; }

src/broker/Manager.cc

@@ -213,7 +213,7 @@ std::string RenderEvent(const std::string& topic, const std::string& name, const
 } // namespace
 #endif
 
-Manager::Manager(bool arg_use_real_time) : Backend(nullptr, nullptr) {
+Manager::Manager(bool arg_use_real_time) : Backend(nullptr, nullptr, nullptr) {
     bound_port = 0;
     use_real_time = arg_use_real_time;
     peer_count = 0;
@@ -558,7 +558,7 @@ bool Manager::DoPublishEvent(const std::string& topic, const cluster::detail::Ev
     }
 
     std::string name(event.HandlerName());
-    return PublishEvent(topic, name, std::move(xs), event.timestamp);
+    return PublishEvent(topic, std::move(name), std::move(xs), event.timestamp);
 }
 
 bool Manager::PublishEvent(string topic, std::string name, broker::vector args, double ts) {
@@ -946,10 +946,13 @@ zeek::RecordValPtr Manager::MakeEvent(ArgsSpan args, zeek::detail::Frame* frame)
     return rval;
 }
 
-bool Manager::DoSubscribe(const string& topic_prefix) {
+bool Manager::DoSubscribe(const string& topic_prefix, SubscribeCallback cb) {
     DBG_LOG(DBG_BROKER, "Subscribing to topic prefix %s", topic_prefix.c_str());
     bstate->subscriber.add_topic(topic_prefix, ! run_state::detail::zeek_init_done);
 
+    if ( cb )
+        cb(topic_prefix, {CallbackStatus::NotImplemented});
+
     return true;
 }
 

src/broker/Manager.h

@@ -380,7 +380,7 @@ public:
 
 private:
     // Register interest in peer event messages that use a certain topic prefix.
-    bool DoSubscribe(const std::string& topic_prefix) override;
+    bool DoSubscribe(const std::string& topic_prefix, SubscribeCallback cb) override;
 
     // Unregister interest in peer event messages.
     bool DoUnsubscribe(const std::string& topic_prefix) override;

src/broker/Plugin.cc

@@ -15,8 +15,9 @@ zeek::plugin::Configuration Plugin::Configure() {
     // instantiated in zeek-setup.cc. Don't even allow to instantiate
     // a second one via the plugin mechanism. In the future, this could
     // be changed so that broker is instantiated on demand only.
-    auto fail_instantiate = [](std::unique_ptr<cluster::EventSerializer>,
+    auto fail_instantiate =
-                               std::unique_ptr<cluster::LogSerializer>) -> std::unique_ptr<cluster::Backend> {
+        [](std::unique_ptr<cluster::EventSerializer>, std::unique_ptr<cluster::LogSerializer>,
+           std::unique_ptr<cluster::detail::EventHandlingStrategy>) -> std::unique_ptr<cluster::Backend> {
         zeek::reporter->FatalError("do not instantiate broker explicitly");
         return nullptr;
     };

src/cluster/Backend.cc

@@ -13,9 +13,20 @@
 #include "zeek/cluster/Serializer.h"
 #include "zeek/iosource/Manager.h"
 #include "zeek/logging/Manager.h"
+#include "zeek/util.h"
 
 using namespace zeek::cluster;
 
+
+bool detail::LocalEventHandlingStrategy::DoHandleRemoteEvent(std::string_view topic, detail::Event e) {
+    zeek::event_mgr.Enqueue(e.Handler(), std::move(e.args), util::detail::SOURCE_BROKER, 0, nullptr, e.timestamp);
+    return true;
+}
+
+void detail::LocalEventHandlingStrategy::DoEnqueueLocalEvent(EventHandlerPtr h, zeek::Args args) {
+    zeek::event_mgr.Enqueue(h, std::move(args));
+}
+
 std::optional<zeek::Args> detail::check_args(const zeek::FuncValPtr& handler, zeek::ArgsSpan args) {
     const auto& func_type = handler->GetType<zeek::FuncType>();
 
@@ -58,6 +69,10 @@ std::optional<zeek::Args> detail::check_args(const zeek::FuncValPtr& handler, ze
     return result;
 }
 
+Backend::Backend(std::unique_ptr<EventSerializer> es, std::unique_ptr<LogSerializer> ls,
+                 std::unique_ptr<detail::EventHandlingStrategy> ehs)
+    : event_serializer(std::move(es)), log_serializer(std::move(ls)), event_handling_strategy(std::move(ehs)) {}
+
 std::optional<detail::Event> Backend::MakeClusterEvent(FuncValPtr handler, ArgsSpan args, double timestamp) const {
     auto checked_args = detail::check_args(handler, args);
     if ( ! checked_args )
@@ -96,7 +111,11 @@ bool Backend::DoPublishLogWrites(const zeek::logging::detail::LogWriteHeader& he
     return DoPublishLogWrites(header, log_serializer->Name(), buf);
 }
 
-bool Backend::ProcessEventMessage(const std::string_view& topic, const std::string_view& format,
+void Backend::EnqueueEvent(EventHandlerPtr h, zeek::Args args) {
+    event_handling_strategy->EnqueueLocalEvent(h, std::move(args));
+}
+
+bool Backend::ProcessEventMessage(std::string_view topic, std::string_view format,
                                   const detail::byte_buffer_span payload) {
     if ( format != event_serializer->Name() ) {
         zeek::reporter->Error("ProcessEventMessage: Wrong format: %s vs %s", std::string{format}.c_str(),
@@ -113,14 +132,10 @@ bool Backend::ProcessEventMessage(const std::string_view& topic, const std::stri
         return false;
     }
 
-    auto& event = *r;
+    return event_handling_strategy->HandleRemoteEvent(topic, std::move(*r));
-    zeek::event_mgr.Enqueue(event.Handler(), std::move(event.args), util::detail::SOURCE_BROKER, 0, nullptr,
-                            event.timestamp);
-
-    return true;
 }
 
-bool Backend::ProcessLogMessage(const std::string_view& format, detail::byte_buffer_span payload) {
+bool Backend::ProcessLogMessage(std::string_view format, detail::byte_buffer_span payload) {
     // We could also dynamically lookup the right de-serializer, but
     // for now assume we just receive what is configured.
     if ( format != log_serializer->Name() ) {

src/cluster/Backend.h

@@ -53,6 +53,75 @@ public:
     const EventHandlerPtr& Handler() const { return handler; }
 };
 
+/**
+ * Interface for processing cluster::Event instances received
+ * on a given topic.
+ *
+ * An instances is injected into Backend instances to allow
+ * modifying the behavior for received events. For instance,
+ * for backends instantiated for WebSocket clients, events
+ * should not be raised as Zeek events locally and instead
+ * transmitted to the WebSocket client.
+ */
+class EventHandlingStrategy {
+public:
+    virtual ~EventHandlingStrategy() = default;
+
+    /**
+     * Method for processing a remote event received on the given topic.
+     *
+     * When handling the remote event fails, this method should return false.
+     *
+     * @param topic The topic on which the event was received.
+     * @param ev The parsed event that was received.
+     *
+     * @return true if the remote event was handled successfully, else false.
+     */
+    bool HandleRemoteEvent(std::string_view topic, Event e) { return DoHandleRemoteEvent(topic, std::move(e)); }
+
+    /**
+     * Method for enquing backend specific events.
+     *
+     * Some backend's may raise events destined for the local
+     * scripting layer. That's usually wanted, but not always.
+     * When the backend is instantiated for a WebSocket client,
+     * local scripting layer should not raise events for the
+     * WebSocket client.
+
+     * @param h The event handler to use.
+     * @param args The event arguments.
+     */
+    void EnqueueLocalEvent(EventHandlerPtr h, zeek::Args args) { DoEnqueueLocalEvent(h, std::move(args)); }
+
+private:
+    /**
+     * Hook method for implementing HandleRemoteEvent().
+     *
+     * @param topic The topic on which the event was received.
+     * @param ev The parsed event that was received.
+     *
+     * @return true if the remote event was handled successfully, else false.
+     */
+    virtual bool DoHandleRemoteEvent(std::string_view topic, Event e) = 0;
+
+    /**
+     * Hook method for implementing EnqueueLocalEvent().
+     *
+     * @param h The event handler to use.
+     * @param args The event arguments.
+     */
+    virtual void DoEnqueueLocalEvent(EventHandlerPtr h, zeek::Args args) = 0;
+};
+
+/**
+ * Strategy enqueueing events into this process's Zeek event loop.
+ */
+class LocalEventHandlingStrategy : public EventHandlingStrategy {
+private:
+    bool DoHandleRemoteEvent(std::string_view topic, Event e) override;
+    void DoEnqueueLocalEvent(EventHandlerPtr h, zeek::Args args) override;
+};
+
 /**
  * Validate that the provided args are suitable for handler.
  *
@@ -80,8 +149,14 @@ public:
 
     /**
      * Method invoked from the Cluster::Backend::__init() bif.
+     *
+     * @param nid The node identifier to use.
      */
-    bool Init() { return DoInit(); }
+    bool Init(std::string nid) {
+        node_id = std::move(nid);
+
+        return DoInit();
+    }
 
     /**
      * Hook invoked when Zeek is about to terminate.
@@ -110,13 +185,40 @@ public:
         return DoPublishEvent(topic, event);
     }
 
+    /**
+     * Status codes for callbacks.
+     */
+    enum class CallbackStatus {
+        Success,
+        Error,
+        NotImplemented,
+    };
+
+    /**
+     * Information for subscription callbacks.
+     */
+    struct SubscriptionCallbackInfo {
+        CallbackStatus status;              // The status of the operation.
+        std::optional<std::string> message; // Optional message.
+    };
+
+    using SubscribeCallback =
+        std::function<void(const std::string& topic_prefix, const SubscriptionCallbackInfo& info)>;
+
     /**
      * Register interest in messages that use a certain topic prefix.
      *
+     * Invoking cb may happen while Subscribe() executes, for example if the
+     * call to Subscribe() is synchronous, or an error is discovered before
+     * submitting any work.
+     *
      * @param topic_prefix a prefix to match against remote message topics.
+     * @param cb callback invoked when the subscription was processed.
      * @return true if it's a new event subscription and it is now registered.
      */
-    bool Subscribe(const std::string& topic_prefix) { return DoSubscribe(topic_prefix); }
+    bool Subscribe(const std::string& topic_prefix, SubscribeCallback cb = SubscribeCallback()) {
+        return DoSubscribe(topic_prefix, std::move(cb));
+    }
 
     /**
      * Unregister interest in messages on a certain topic.
@@ -140,23 +242,42 @@ public:
         return DoPublishLogWrites(header, records);
     }
 
+    /**
+     * @return This backend's node identifier.
+     */
+    const std::string& NodeId() const { return node_id; }
+
 protected:
     /**
      * Constructor.
+     *
+     * @param es The event serializer to use.
+     * @param ls The log batch serializer to use.
+     * @param ehs The event handling strategy to use for this backend.
      */
-    Backend(std::unique_ptr<EventSerializer> es, std::unique_ptr<LogSerializer> ls)
+    Backend(std::unique_ptr<EventSerializer> es, std::unique_ptr<LogSerializer> ls,
-        : event_serializer(std::move(es)), log_serializer(std::move(ls)) {}
+            std::unique_ptr<detail::EventHandlingStrategy> ehs);
+
+    /**
+     * Enqueue an event to be raised to this process Zeek scripting layer.
+     *
+     * When a backend is used for a WebSocket client connection, events
+     * raised through this method are blackholed.
+     *
+     * @param h The event handler.
+     * @param args The event arguments.
+     */
+    void EnqueueEvent(EventHandlerPtr h, zeek::Args args);
 
     /**
      * Process an incoming event message.
      */
-    bool ProcessEventMessage(const std::string_view& topic, const std::string_view& format,
+    bool ProcessEventMessage(std::string_view topic, std::string_view format, detail::byte_buffer_span payload);
-                             detail::byte_buffer_span payload);
 
     /**
      * Process an incoming log message.
      */
-    bool ProcessLogMessage(const std::string_view& format, detail::byte_buffer_span payload);
+    bool ProcessLogMessage(std::string_view format, detail::byte_buffer_span payload);
 
 private:
     /**
@@ -220,13 +341,19 @@ private:
      * Register interest in messages that use a certain topic prefix.
      *
      * If the backend hasn't yet established a connection, any subscriptions
-     * should be queued until they can be processed.
+     * should be queued until they can be processed. If a callback is given,
+     * it should be called once the subscription can be determined to be
+     * active. The callback has to be invoked from Zeek's main thread. If
+     * the backend does not implement callbacks, it should invoke the callback
+     * with CallbackStatus::NotImplemented, which will act as success, but
+     * provides a way to distinguish behavior.
      *
      * @param topic_prefix a prefix to match against remote message topics.
+     * @param cb callback to invoke when the subscription is active
      *
      * @return true if it's a new event subscription and now registered.
      */
-    virtual bool DoSubscribe(const std::string& topic_prefix) = 0;
+    virtual bool DoSubscribe(const std::string& topic_prefix, SubscribeCallback cb) = 0;
 
     /**
      * Unregister interest in messages on a certain topic.
@@ -278,6 +405,12 @@ private:
 
     std::unique_ptr<EventSerializer> event_serializer;
     std::unique_ptr<LogSerializer> log_serializer;
+    std::unique_ptr<detail::EventHandlingStrategy> event_handling_strategy;
+
+    /**
+     * The backend's instance cluster node identifier.
+     */
+    std::string node_id;
 };
 
 /**

src/cluster/Component.h

@@ -13,7 +13,8 @@ namespace zeek::cluster {
 class BackendComponent : public plugin::Component {
 public:
     using factory_callback = std::unique_ptr<Backend> (*)(std::unique_ptr<EventSerializer>,
-                                                          std::unique_ptr<LogSerializer>);
+                                                          std::unique_ptr<LogSerializer>,
+                                                          std::unique_ptr<detail::EventHandlingStrategy>);
 
     /**
      * Constructor.

src/cluster/Manager.cc

@@ -11,11 +11,14 @@ Manager::Manager()
       event_serializers(plugin::ComponentManager<EventSerializerComponent>("Cluster", "EventSerializerTag")),
       log_serializers(plugin::ComponentManager<LogSerializerComponent>("Cluster", "LogSerializerTag")) {}
 
-std::unique_ptr<Backend> Manager::InstantiateBackend(const zeek::EnumValPtr& tag,
+std::unique_ptr<Backend> Manager::InstantiateBackend(
-                                                     std::unique_ptr<EventSerializer> event_serializer,
+    const zeek::EnumValPtr& tag, std::unique_ptr<EventSerializer> event_serializer,
-                                                     std::unique_ptr<LogSerializer> log_serializer) {
+    std::unique_ptr<LogSerializer> log_serializer,
-    const BackendComponent* c = Backends().Lookup(tag);
+    std::unique_ptr<detail::EventHandlingStrategy> event_handling_strategy) {
-    return c ? c->Factory()(std::move(event_serializer), std::move(log_serializer)) : nullptr;
+    if ( const auto* c = Backends().Lookup(tag) )
+        return c->Factory()(std::move(event_serializer), std::move(log_serializer), std::move(event_handling_strategy));
+
+    return nullptr;
 }
 
 std::unique_ptr<EventSerializer> Manager::InstantiateEventSerializer(const zeek::EnumValPtr& tag) {

src/cluster/Manager.h

@@ -27,12 +27,14 @@ public:
      * @param tag The enum value identifying the backend.
      * @param event_serializer The event serializer to inject.
      * @param log_serializer The log serializer to inject.
+     * @param event_handling_strategy The event handling strategy to inject.
      *
      * @return New ClusterBackend instance, or null if there's no such component.
      */
     std::unique_ptr<Backend> InstantiateBackend(const EnumValPtr& tag,
                                                 std::unique_ptr<EventSerializer> event_serializer,
-                                                std::unique_ptr<LogSerializer> log_serializer);
+                                                std::unique_ptr<LogSerializer> log_serializer,
+                                                std::unique_ptr<detail::EventHandlingStrategy> event_handling_strategy);
 
     /**
      * Instantiate a event serializer with the given enum value.

src/cluster/backend/zeromq/ZeroMQ-Proxy.cc

@@ -39,6 +39,12 @@ bool ProxyThread::Start() {
     zmq::socket_t xpub(ctx, zmq::socket_type::xpub);
     zmq::socket_t xsub(ctx, zmq::socket_type::xsub);
 
+    // Enable XPUB_VERBOSE unconditional to enforce nodes receiving
+    // notifications about any new subscriptions, even if they have
+    // seen them before. This is needed to for the subscribe callback
+    // functionality to work reliably.
+    xpub.set(zmq::sockopt::xpub_verbose, 1);
+
     xpub.set(zmq::sockopt::xpub_nodrop, xpub_nodrop);
 
     try {

src/cluster/backend/zeromq/ZeroMQ.cc

@@ -14,7 +14,7 @@
 #include <zmq.hpp>
 
 #include "zeek/DebugLogger.h"
-#include "zeek/Event.h"
+#include "zeek/EventHandler.h"
 #include "zeek/EventRegistry.h"
 #include "zeek/IntrusivePtr.h"
 #include "zeek/Reporter.h"
@@ -23,6 +23,7 @@
 #include "zeek/cluster/Serializer.h"
 #include "zeek/cluster/backend/zeromq/Plugin.h"
 #include "zeek/cluster/backend/zeromq/ZeroMQ-Proxy.h"
+#include "zeek/util.h"
 
 namespace zeek {
 
@@ -37,6 +38,7 @@ namespace cluster::zeromq {
 enum class DebugFlag : zeek_uint_t {
     NONE = 0,
     POLL = 1,
+    THREAD = 2,
 };
 
 constexpr DebugFlag operator&(zeek_uint_t x, DebugFlag y) {
@@ -66,22 +68,16 @@ void self_thread_fun(void* arg) {
 } // namespace
 
 
-// Constructor.
+ZeroMQBackend::ZeroMQBackend(std::unique_ptr<EventSerializer> es, std::unique_ptr<LogSerializer> ls,
-ZeroMQBackend::ZeroMQBackend(std::unique_ptr<EventSerializer> es, std::unique_ptr<LogSerializer> ls)
+                             std::unique_ptr<detail::EventHandlingStrategy> ehs)
-    : ThreadedBackend(std::move(es), std::move(ls)) {
+    : ThreadedBackend(std::move(es), std::move(ls), std::move(ehs)) {
-    xsub = zmq::socket_t(ctx, zmq::socket_type::xsub);
-    xpub = zmq::socket_t(ctx, zmq::socket_type::xpub);
     log_push = zmq::socket_t(ctx, zmq::socket_type::push);
-    log_pull = zmq::socket_t(ctx, zmq::socket_type::pull);
-
     main_inproc = zmq::socket_t(ctx, zmq::socket_type::pair);
-    child_inproc = zmq::socket_t(ctx, zmq::socket_type::pair);
 }
 
 void ZeroMQBackend::DoInitPostScript() {
     ThreadedBackend::DoInitPostScript();
 
-    my_node_id = zeek::id::find_val<zeek::StringVal>("Cluster::Backend::ZeroMQ::my_node_id")->ToStdString();
     listen_xpub_endpoint =
         zeek::id::find_val<zeek::StringVal>("Cluster::Backend::ZeroMQ::listen_xpub_endpoint")->ToStdString();
     listen_xsub_endpoint =
@@ -99,9 +95,6 @@ void ZeroMQBackend::DoInitPostScript() {
 
     event_unsubscription = zeek::event_registry->Register("Cluster::Backend::ZeroMQ::unsubscription");
     event_subscription = zeek::event_registry->Register("Cluster::Backend::ZeroMQ::subscription");
-
-    main_inproc.bind("inproc://publish-bridge");
-    child_inproc.connect("inproc://publish-bridge");
 }
 
 
@@ -111,13 +104,12 @@ void ZeroMQBackend::DoTerminate() {
     ZEROMQ_DEBUG("Joining self_thread");
     if ( self_thread.joinable() )
         self_thread.join();
+    ZEROMQ_DEBUG("Joined self_thread");
 
+    // Close the sockets that are used from the main thread,
+    // the remaining sockets are closed by self_thread.
     log_push.close();
-    log_pull.close();
-    xsub.close();
-    xpub.close();
     main_inproc.close();
-    child_inproc.close();
 
     ZEROMQ_DEBUG("Closing ctx");
     ctx.close();
@@ -132,12 +124,23 @@ void ZeroMQBackend::DoTerminate() {
 }
 
 bool ZeroMQBackend::DoInit() {
+    xsub = zmq::socket_t(ctx, zmq::socket_type::xsub);
+    xpub = zmq::socket_t(ctx, zmq::socket_type::xpub);
+    log_pull = zmq::socket_t(ctx, zmq::socket_type::pull);
+    child_inproc = zmq::socket_t(ctx, zmq::socket_type::pair);
+
     auto linger_ms = static_cast<int>(zeek::id::find_val<zeek::IntVal>("Cluster::Backend::ZeroMQ::linger_ms")->AsInt());
     int xpub_nodrop = zeek::id::find_val<zeek::BoolVal>("Cluster::Backend::ZeroMQ::xpub_nodrop")->AsBool() ? 1 : 0;
 
     xpub.set(zmq::sockopt::linger, linger_ms);
     xpub.set(zmq::sockopt::xpub_nodrop, xpub_nodrop);
 
+    // Enable XPUB_VERBOSE unconditional to enforce nodes receiving
+    // notifications about any new subscriptions, even if they have
+    // seen them before. This is needed to for the subscribe callback
+    // functionality to work reliably.
+    xpub.set(zmq::sockopt::xpub_verbose, 1);
+
     try {
         xsub.connect(connect_xsub_endpoint);
     } catch ( zmq::error_t& err ) {
@@ -220,6 +223,10 @@ bool ZeroMQBackend::DoInit() {
     // following post might be useful:
     //
     // https://funcptr.net/2012/09/10/zeromq---edge-triggered-notification/
+
+    // Setup connectivity between main and child thread.
+    main_inproc.bind("inproc://inproc-bridge");
+    child_inproc.connect("inproc://inproc-bridge");
     self_thread = std::thread(self_thread_fun, this);
 
     // After connecting, call ThreadedBackend::DoInit() to register
@@ -242,7 +249,7 @@ bool ZeroMQBackend::DoPublishEvent(const std::string& topic, const std::string&
     // * The serialized event itself.
     std::array<zmq::const_buffer, 4> parts = {
         zmq::const_buffer(topic.data(), topic.size()),
-        zmq::const_buffer(my_node_id.data(), my_node_id.size()),
+        zmq::const_buffer(NodeId().data(), NodeId().size()),
         zmq::const_buffer(format.data(), format.size()),
         zmq::const_buffer(buf.data(), buf.size()),
     };
@@ -263,18 +270,25 @@ bool ZeroMQBackend::DoPublishEvent(const std::string& topic, const std::string&
     return true;
 }
 
-bool ZeroMQBackend::DoSubscribe(const std::string& topic_prefix) {
+bool ZeroMQBackend::DoSubscribe(const std::string& topic_prefix, SubscribeCallback cb) {
     ZEROMQ_DEBUG("Subscribing to %s", topic_prefix.c_str());
     try {
         // Prepend 0x01 byte to indicate subscription to XSUB socket
         // This is the XSUB API instead of setsockopt(ZMQ_SUBSCRIBE).
         std::string msg = "\x01" + topic_prefix;
-        xsub.send(zmq::const_buffer(msg.data(), msg.size()));
+        main_inproc.send(zmq::const_buffer(msg.data(), msg.size()));
     } catch ( zmq::error_t& err ) {
         zeek::reporter->Error("Failed to subscribe to topic %s: %s", topic_prefix.c_str(), err.what());
+        if ( cb )
+            cb(topic_prefix, {CallbackStatus::Error, err.what()});
+
         return false;
     }
 
+    // Store the callback for later.
+    if ( cb )
+        subscription_callbacks.insert({topic_prefix, cb});
+
     return true;
 }
 
@@ -283,8 +297,8 @@ bool ZeroMQBackend::DoUnsubscribe(const std::string& topic_prefix) {
     try {
         // Prepend 0x00 byte to indicate subscription to XSUB socket.
         // This is the XSUB API instead of setsockopt(ZMQ_SUBSCRIBE).
-        std::string msg = "\x00" + topic_prefix;
+        std::string msg = '\0' + topic_prefix;
-        xsub.send(zmq::const_buffer(msg.data(), msg.size()));
+        main_inproc.send(zmq::const_buffer(msg.data(), msg.size()));
     } catch ( zmq::error_t& err ) {
         zeek::reporter->Error("Failed to unsubscribe from topic %s: %s", topic_prefix.c_str(), err.what());
         return false;
@@ -306,7 +320,7 @@ bool ZeroMQBackend::DoPublishLogWrites(const logging::detail::LogWriteHeader& he
     // * The serialized log write itself.
     std::array<zmq::const_buffer, 4> parts = {
         zmq::const_buffer{message_type.data(), message_type.size()},
-        zmq::const_buffer(my_node_id.data(), my_node_id.size()),
+        zmq::const_buffer(NodeId().data(), NodeId().size()),
         zmq::const_buffer{format.data(), format.size()},
         zmq::const_buffer{buf.data(), buf.size()},
     };
@@ -342,6 +356,9 @@ bool ZeroMQBackend::DoPublishLogWrites(const logging::detail::LogWriteHeader& he
 }
 
 void ZeroMQBackend::Run() {
+    util::detail::set_thread_name(zeek::util::fmt("zmq-%p", this));
+    ZEROMQ_DEBUG_THREAD_PRINTF(DebugFlag::THREAD, "Thread starting (%p)\n", this);
+
     using MultipartMessage = std::vector<zmq::message_t>;
 
     auto HandleLogMessages = [this](const std::vector<MultipartMessage>& msgs) {
@@ -364,31 +381,52 @@ void ZeroMQBackend::Run() {
     };
 
     auto HandleInprocMessages = [this](std::vector<MultipartMessage>& msgs) {
-        // Forward messages from the inprocess bridge to xpub.
+        // Forward messages from the inprocess bridge to XSUB for subscription
+        // subscription handling (1 part) or XPUB for publishing (4 parts).
         for ( auto& msg : msgs ) {
-            assert(msg.size() == 4);
+            assert(msg.size() == 1 || msg.size() == 4);
-
+            if ( msg.size() == 1 ) {
+                xsub.send(msg[0], zmq::send_flags::none);
+            }
+            else {
                 for ( auto& part : msg ) {
                     zmq::send_flags flags = zmq::send_flags::dontwait;
                     if ( part.more() )
                         flags = flags | zmq::send_flags::sndmore;
 
                     zmq::send_result_t result;
+                    int tries = 0;
                     do {
                         try {
                             result = xpub.send(part, flags);
                         } catch ( zmq::error_t& err ) {
-                        // XXX: Not sure if the return false is so great here.
+                            if ( err.num() == ETERM )
-                        //
+                                return;
-                        // Also, if we fail to publish, should we block rather
+
-                        // than discard?
+                            // XXX: What other error can happen here? How should we react?
-                        ZEROMQ_THREAD_PRINTF("xpub: Failed to publish: %s (%d)", err.what(), err.num());
+                            ZEROMQ_THREAD_PRINTF("xpub: Failed to publish with error %s (%d)\n", err.what(), err.num());
                             break;
                         }
-                    // EAGAIN returns empty result, means try again!
+
+                        // Empty result means xpub.send() returned EAGAIN. The
+                        // socket reached its high water mark and we should
+                        // relax / backoff a bit. Otherwise we'll be spinning
+                        // unproductively very fast here. Note that this is going
+                        // to build up backpressure and eventually inproc.send()
+                        // will block from the main thread.
+                        if ( ! result ) {
+                            ++tries;
+                            auto sleep_for = std::min(tries * 10, 500);
+                            ZEROMQ_THREAD_PRINTF(
+                                "xpub: Failed forward inproc to xpub! Overloaded? (tries=%d sleeping %d ms)\n", tries,
+                                sleep_for);
+
+                            std::this_thread::sleep_for(std::chrono::milliseconds(sleep_for));
+                        }
                     } while ( ! result );
                 }
             }
+        }
     };
 
     auto HandleXPubMessages = [this](const std::vector<MultipartMessage>& msgs) {
@@ -439,7 +477,7 @@ void ZeroMQBackend::Run() {
 
             // Filter out messages that are coming from this node.
             std::string sender(msg[1].data<const char>(), msg[1].size());
-            if ( sender == my_node_id )
+            if ( sender == NodeId() )
                 continue;
 
             detail::byte_buffer payload{msg[3].data<std::byte>(), msg[3].data<std::byte>() + msg[3].size()};
@@ -451,6 +489,16 @@ void ZeroMQBackend::Run() {
         QueueForProcessing(std::move(qmsgs));
     };
 
+    // Helper class running at destruction.
+    class Deferred {
+    public:
+        Deferred(std::function<void()> deferred) : closer(std::move(deferred)) {}
+        ~Deferred() { closer(); }
+
+    private:
+        std::function<void()> closer;
+    };
+
     struct SocketInfo {
         zmq::socket_ref socket;
         std::string name;
@@ -464,6 +512,15 @@ void ZeroMQBackend::Run() {
         {.socket = log_pull, .name = "log_pull", .handler = HandleLogMessages},
     };
 
+    // Called when Run() terminates.
+    auto deferred_close = Deferred([this]() {
+        child_inproc.close();
+        xpub.close();
+        xsub.close();
+        log_pull.close();
+        ZEROMQ_DEBUG_THREAD_PRINTF(DebugFlag::THREAD, "Thread sockets closed (%p)\n", this);
+    });
+
     std::vector<zmq::pollitem_t> poll_items(sockets.size());
 
     while ( true ) {
@@ -532,10 +589,12 @@ void ZeroMQBackend::Run() {
                 rcv_messages[i].pop_back();
             }
         } catch ( zmq::error_t& err ) {
-            if ( err.num() == ETERM )
+            if ( err.num() != ETERM )
-                return;
-
                 throw;
+
+            // Shutdown.
+            ZEROMQ_DEBUG_THREAD_PRINTF(DebugFlag::THREAD, "Thread terminating (%p)\n", this);
+            break;
         }
 
         // At this point, we've received anything that was readable from the sockets.
@@ -552,10 +611,33 @@ void ZeroMQBackend::Run() {
 bool ZeroMQBackend::DoProcessBackendMessage(int tag, detail::byte_buffer_span payload) {
     if ( tag == 0 || tag == 1 ) {
         std::string topic{reinterpret_cast<const char*>(payload.data()), payload.size()};
-        zeek::EventHandlerPtr eh = tag == 1 ? event_subscription : event_unsubscription;
+        zeek::EventHandlerPtr eh;
+
+        if ( tag == 1 ) {
+            // If this is the first time the subscription was observed, raise
+            // the ZeroMQ internal event.
+            if ( xpub_subscriptions.count(topic) == 0 ) {
+                eh = event_subscription;
+                xpub_subscriptions.insert(topic);
+            }
+
+            if ( const auto& cbit = subscription_callbacks.find(topic); cbit != subscription_callbacks.end() ) {
+                const auto& cb = cbit->second;
+                if ( cb )
+                    cb(topic, {CallbackStatus::Success, "success"});
+
+                subscription_callbacks.erase(cbit);
+            }
+        }
+        else if ( tag == 0 ) {
+            eh = event_unsubscription;
+            xpub_subscriptions.erase(topic);
+        }
+
+        ZEROMQ_DEBUG("BackendMessage: %s for %s", eh != nullptr ? eh->Name() : "<raising no event>", topic.c_str());
+        if ( eh )
+            EnqueueEvent(eh, zeek::Args{zeek::make_intrusive<zeek::StringVal>(topic)});
 
-        ZEROMQ_DEBUG("BackendMessage: %s for %s", eh->Name(), topic.c_str());
-        zeek::event_mgr.Enqueue(eh, zeek::make_intrusive<zeek::StringVal>(topic));
         return true;
     }
     else {

src/cluster/backend/zeromq/ZeroMQ.h

@@ -17,7 +17,8 @@ public:
     /**
      * Constructor.
      */
-    ZeroMQBackend(std::unique_ptr<EventSerializer> es, std::unique_ptr<LogSerializer> ls);
+    ZeroMQBackend(std::unique_ptr<EventSerializer> es, std::unique_ptr<LogSerializer> ls,
+                  std::unique_ptr<detail::EventHandlingStrategy> ehs);
 
     /**
      * Spawns a thread running zmq_proxy() for the configured XPUB/XSUB listen
@@ -34,8 +35,9 @@ public:
      * Component factory.
      */
     static std::unique_ptr<Backend> Instantiate(std::unique_ptr<EventSerializer> event_serializer,
-                                                std::unique_ptr<LogSerializer> log_serializer) {
+                                                std::unique_ptr<LogSerializer> log_serializer,
-        return std::make_unique<ZeroMQBackend>(std::move(event_serializer), std::move(log_serializer));
+                                                std::unique_ptr<detail::EventHandlingStrategy> ehs) {
+        return std::make_unique<ZeroMQBackend>(std::move(event_serializer), std::move(log_serializer), std::move(ehs));
     }
 
 private:
@@ -48,7 +50,7 @@ private:
     bool DoPublishEvent(const std::string& topic, const std::string& format,
                         const cluster::detail::byte_buffer& buf) override;
 
-    bool DoSubscribe(const std::string& topic_prefix) override;
+    bool DoSubscribe(const std::string& topic_prefix, SubscribeCallback cb) override;
 
     bool DoUnsubscribe(const std::string& topic_prefix) override;
 
@@ -60,7 +62,6 @@ private:
     bool DoProcessBackendMessage(int tag, detail::byte_buffer_span payload) override;
 
     // Script level variables.
-    std::string my_node_id;
     std::string connect_xsub_endpoint;
     std::string connect_xpub_endpoint;
     std::string listen_xsub_endpoint;
@@ -94,6 +95,10 @@ private:
     std::thread self_thread;
 
     std::unique_ptr<ProxyThread> proxy_thread;
+
+    // Tracking the subscriptions on the local XPUB socket.
+    std::map<std::string, SubscribeCallback> subscription_callbacks;
+    std::set<std::string> xpub_subscriptions;
 };
 
 } // namespace zeek::cluster::zeromq

src/cluster/cluster.bif

@@ -64,9 +64,9 @@ function Cluster::__unsubscribe%(topic_prefix: string%): bool
 ## Initialize the global cluster backend.
 ##
 ## Returns: true on success.
-function Cluster::Backend::__init%(%): bool
+function Cluster::Backend::__init%(nid: string%): bool
 	%{
-	auto rval = zeek::cluster::backend->Init();
+	auto rval = zeek::cluster::backend->Init(nid->ToStdString());
 	return zeek::val_mgr->Bool(rval);
 	%}
 

src/cluster/serializer/broker/Serializer.cc

@@ -76,7 +76,7 @@ std::optional<detail::Event> to_zeek_event(const broker::zeek::Event& ev) {
 
     zeek::Args vl;
     zeek::EventHandlerPtr handler = zeek::event_registry->Lookup(name);
-    if ( ! handler ) {
+    if ( handler == nullptr ) {
         zeek::reporter->Error("Failed to lookup handler for '%s'", std::string(name).c_str());
         return std::nullopt;
     }
@@ -165,8 +165,8 @@ bool detail::BrokerJsonV1_Serializer::SerializeEvent(byte_buffer& buf, const det
     if ( ! ev )
         return false;
 
-    auto push_back_adaptor = PushBackAdapter(buf);
+    auto push_back_adapter = PushBackAdapter(buf);
-    broker::format::json::v1::encode(ev->move_data(), std::back_inserter(push_back_adaptor));
+    broker::format::json::v1::encode(ev->move_data(), std::back_inserter(push_back_adapter));
     return true;
 }
 

src/zeek-setup.cc

@@ -849,8 +849,12 @@ SetupResult setup(int argc, char** argv, Options* zopts) {
                 exit(1);
             }
 
-            auto backend = cluster::manager->InstantiateBackend(cluster_backend_val, std::move(event_serializer),
+            auto event_handling_strategy = std::make_unique<cluster::detail::LocalEventHandlingStrategy>();
-                                                                std::move(log_serializer));
+
+            auto backend =
+                cluster::manager->InstantiateBackend(cluster_backend_val, std::move(event_serializer),
+                                                     std::move(log_serializer), std::move(event_handling_strategy));
+
             if ( ! backend ) {
                 reporter->Error("Failed to instantiate cluster backend: %s",
                                 zeek::obj_desc_short(cluster_backend_val.get()).c_str());

testing/btest/Baseline/cluster.generic.publish-no-handler/..manager..stderr

@@ -0,0 +1,2 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+received termination signal

testing/btest/Baseline/cluster.generic.publish-no-handler/..manager.out

@@ -0,0 +1,3 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+node_up, worker-1
+node_down, worker-1

testing/btest/Baseline/cluster.generic.publish-no-handler/..worker..stderr

@@ -0,0 +1,2 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+received termination signal

testing/btest/Baseline/cluster.generic.publish-no-handler/..worker.out

@@ -0,0 +1,2 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+got finish

testing/btest/Baseline/cluster.zeromq.unsubscribe/..manager.out

@@ -0,0 +1,5 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+node_up, worker-1
+subscription, /test/worker/topic
+unsubscription, /test/worker/topic
+node_down, worker-1

testing/btest/Baseline/cluster.zeromq.unsubscribe/..worker.out

@@ -0,0 +1,5 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+start_test
+subscription, /test/manager/topic
+unsubscription, /test/manager/topic
+done

testing/btest/Files/zeromq/test-bootstrap.zeek

@@ -5,7 +5,7 @@
 @load frameworks/cluster/backend/zeromq
 @load frameworks/cluster/backend/zeromq/connect
 
-redef Cluster::Backend::ZeroMQ::listen_xpub_endpoint = fmt("tcp://127.0.0.1:%s", extract_count(getenv("XPUB_PORT")));
+redef Cluster::Backend::ZeroMQ::listen_xpub_endpoint = fmt("tcp://127.0.0.1:%s", port_to_count(to_port(getenv("XPUB_PORT"))));
-redef Cluster::Backend::ZeroMQ::listen_xsub_endpoint = fmt("tcp://127.0.0.1:%s", extract_count(getenv("XSUB_PORT")));
+redef Cluster::Backend::ZeroMQ::listen_xsub_endpoint = fmt("tcp://127.0.0.1:%s", port_to_count(to_port(getenv("XSUB_PORT"))));
-redef Cluster::Backend::ZeroMQ::connect_xpub_endpoint = fmt("tcp://127.0.0.1:%s", extract_count(getenv("XSUB_PORT")));
+redef Cluster::Backend::ZeroMQ::connect_xpub_endpoint = fmt("tcp://127.0.0.1:%s", port_to_count(to_port(getenv("XSUB_PORT"))));
-redef Cluster::Backend::ZeroMQ::connect_xsub_endpoint = fmt("tcp://127.0.0.1:%s", extract_count(getenv("XPUB_PORT")));
+redef Cluster::Backend::ZeroMQ::connect_xsub_endpoint = fmt("tcp://127.0.0.1:%s", port_to_count(to_port(getenv("XPUB_PORT"))));

testing/btest/cluster/generic/publish-no-handler.zeek

@@ -0,0 +1,66 @@
+# @TEST-DOC: A worker receiving an event without a handler implemented would produce a reporter error
+#
+# @TEST-REQUIRES: have-zeromq
+#
+# @TEST-GROUP: cluster-zeromq
+#
+# @TEST-PORT: XPUB_PORT
+# @TEST-PORT: XSUB_PORT
+# @TEST-PORT: LOG_PULL_PORT
+#
+# @TEST-EXEC: cp $FILES/zeromq/cluster-layout-simple.zeek cluster-layout.zeek
+# @TEST-EXEC: cp $FILES/zeromq/test-bootstrap.zeek zeromq-test-bootstrap.zeek
+#
+# @TEST-EXEC: zeek --parse-only manager.zeek worker.zeek
+#
+# @TEST-EXEC: btest-bg-run manager "ZEEKPATH=$ZEEKPATH:.. && CLUSTER_NODE=manager zeek -b ../manager.zeek >out"
+# @TEST-EXEC: btest-bg-run worker "ZEEKPATH=$ZEEKPATH:.. && CLUSTER_NODE=worker-1 zeek -b ../worker.zeek >out"
+#
+# @TEST-EXEC: btest-bg-wait 30
+# @TEST-EXEC: btest-diff ./manager/out
+# @TEST-EXEC: btest-diff ./manager/.stderr
+# @TEST-EXEC: btest-diff ./worker/out
+# @TEST-EXEC: btest-diff ./worker/.stderr
+
+
+# @TEST-START-FILE common.zeek
+@load ./zeromq-test-bootstrap
+
+
+global hello: event() &is_used;
+global finish: event() &is_used;
+# @TEST-END-FILE
+
+# @TEST-START-FILE manager.zeek
+@load ./common.zeek
+event send_finish(id: string)
+	{
+	Cluster::publish(Cluster::nodeid_topic(id), finish);
+	}
+# If a node comes up that isn't us, send it a hello and
+# schedule sending a my_finish
+event Cluster::node_up(name: string, id: string)
+	{
+	print "node_up", name;
+	Cluster::publish(Cluster::nodeid_topic(id), hello);
+	schedule 20msec { send_finish(id) };
+	}
+
+# If the worker vanishes, finish the test.
+event Cluster::node_down(name: string, id: string)
+	{
+	print "node_down", name;
+	terminate();
+	}
+# @TEST-END-FILE
+
+# @TEST-START-FILE worker.zeek
+@load ./common.zeek
+# The worker does not implement hello!
+
+event finish()
+	{
+	print "got finish";
+	terminate();
+	}
+# @TEST-END-FILE

testing/btest/cluster/zeromq/unsubscribe.zeek

@@ -0,0 +1,84 @@
+# @TEST-DOC: Regression test for unsubscriptions not actually unsubscribing because of "\x00" usage.
+#
+# @TEST-REQUIRES: have-zeromq
+#
+# @TEST-GROUP: cluster-zeromq
+#
+# @TEST-PORT: XPUB_PORT
+# @TEST-PORT: XSUB_PORT
+# @TEST-PORT: LOG_PULL_PORT
+#
+# @TEST-EXEC: cp $FILES/zeromq/cluster-layout-simple.zeek cluster-layout.zeek
+# @TEST-EXEC: cp $FILES/zeromq/test-bootstrap.zeek zeromq-test-bootstrap.zeek
+#
+# @TEST-EXEC: zeek --parse-only ./manager.zeek ./worker.zeek
+#
+# @TEST-EXEC: btest-bg-run manager "ZEEKPATH=$ZEEKPATH:.. && CLUSTER_NODE=manager zeek -b ../manager.zeek >out"
+# @TEST-EXEC: btest-bg-run worker "ZEEKPATH=$ZEEKPATH:.. && CLUSTER_NODE=worker-1 zeek -b ../worker.zeek >out"
+#
+# @TEST-EXEC: btest-bg-wait 30
+# @TEST-EXEC: btest-diff ./manager/out
+# @TEST-EXEC: btest-diff ./worker/out
+
+
+# @TEST-START-FILE common.zeek
+@load ./zeromq-test-bootstrap
+
+global start_test: event() &is_used;
+
+# @TEST-END-FILE
+
+# @TEST-START-FILE manager.zeek
+@load ./common.zeek
+
+event Cluster::Backend::ZeroMQ::subscription(topic: string) {
+	if ( topic == "/test/worker/topic" ) {
+		print "subscription", topic;
+		Cluster::subscribe("/test/manager/topic");
+	}
+}
+
+event Cluster::Backend::ZeroMQ::unsubscription(topic: string) {
+	if ( topic == "/test/worker/topic" ) {
+		print "unsubscription", topic;
+		Cluster::unsubscribe("/test/manager/topic");
+	}
+}
+
+event Cluster::node_up(name: string, id: string) {
+	print "node_up", name;
+	Cluster::publish(Cluster::nodeid_topic(id), start_test);
+}
+
+event Cluster::node_down(name: string, id: string) {
+	print "node_down", name;
+	terminate();
+}
+# @TEST-END-FILE
+
+# @TEST-START-FILE worker.zeek
+@load ./common.zeek
+
+event start_test() {
+	print "start_test";
+	Cluster::subscribe("/test/worker/topic");
+}
+
+event Cluster::Backend::ZeroMQ::subscription(topic: string) {
+	if ( topic == "/test/manager/topic" ) {
+		print "subscription", topic;
+		Cluster::unsubscribe("/test/worker/topic");
+	}
+}
+
+event Cluster::Backend::ZeroMQ::unsubscription(topic: string) {
+	if ( topic == "/test/manager/topic" ) {
+		print "unsubscription", topic;
+		terminate();
+	}
+}
+
+event zeek_done() {
+	print "done";
+}
+# @TEST-END-FILE