ByzzFuzz network faults: drop messages instead of setting node partitions

Author: joaomlneto

simulator/src/main/java/byzzbench/simulator/faults/behaviors/ByzzFuzzDropMessageBehavior.java

@@ -0,0 +1,107 @@
+package byzzbench.simulator.faults.behaviors;
+
+import byzzbench.simulator.faults.FaultBehavior;
+import byzzbench.simulator.faults.FaultContext;
+import byzzbench.simulator.transport.Event;
+import byzzbench.simulator.transport.MessageEvent;
+import byzzbench.simulator.transport.Router;
+import lombok.extern.java.Log;
+
+import java.util.Collection;
+import java.util.Optional;
+
+@Log
+public class ByzzFuzzDropMessageBehavior implements FaultBehavior {
+    /**
+     * Router helper to determine if two nodes are connected
+     */
+    Router router = new Router();
+
+    /**
+     * Memoized name of the fault
+     */
+    String name;
+
+    /**
+     * Create a new CreateNetworkPartitionsBehavior
+     *
+     * @param partitions A list of partitions to create
+     */
+    public ByzzFuzzDropMessageBehavior(String[][] partitions) {
+        for (String[] partition : partitions) {
+            router.isolateNodes(partition);
+        }
+    }
+
+    /**
+     * Create a new CreateNetworkPartitionsBehavior
+     *
+     * @param partition A single partition to create
+     */
+    public ByzzFuzzDropMessageBehavior(String[] partition) {
+        this(new String[][]{partition});
+    }
+
+    /**
+     * Create a new CreateNetworkPartitionsBehavior
+     *
+     * @param partition A single partition to create
+     */
+    public ByzzFuzzDropMessageBehavior(Collection<String> partition) {
+        this(partition.toArray(new String[0]));
+    }
+
+    /**
+     * Create a new CreateNetworkPartitionsBehavior
+     *
+     * @param partition The ID of the node to isolate
+     */
+    public ByzzFuzzDropMessageBehavior(String partition) {
+        this(new String[]{partition});
+    }
+
+    @Override
+    public String getId() {
+        return "createnetworkpartitions-%s".formatted(this.router.getReversePartitionsMapping());
+    }
+
+    @Override
+    public String getName() {
+        if (this.name == null) {
+            // convert the array of arrays into a string
+            String partitions = this.router.getReversePartitionsMapping().stream()
+                    .map(p -> "[" + String.join(",", p) + "]")
+                    .reduce("", (a, b) -> a + b);
+            this.name = "Drop message based on partitions %s".formatted(partitions);
+        }
+        return this.name;
+    }
+
+    @Override
+    public void accept(FaultContext context) {
+        Optional<Event> event = context.getEvent();
+
+        if (event.isEmpty()) {
+            log.warning("No event to mutate");
+            return;
+        }
+
+        Event e = event.get();
+
+        if (!(e instanceof MessageEvent messageEvent)) {
+            log.warning("Event is not a message event");
+            return;
+        }
+
+        String sender = messageEvent.getSenderId();
+        String recipient = messageEvent.getRecipientId();
+
+        // if the sender and recipient are in the same partition, do nothing
+        if (router.haveConnectivity(sender, recipient)) {
+            return;
+        }
+
+        // otherwise, drop the message: the sender and recipient are in different partitions
+        context.getScenario().getTransport().dropEvent(e.getEventId());
+    }
+}

simulator/src/main/java/byzzbench/simulator/faults/faults/ByzzFuzzNetworkFault.java

@@ -1,7 +1,7 @@
 package byzzbench.simulator.faults.faults;
 
 import byzzbench.simulator.faults.BaseFault;
-import byzzbench.simulator.faults.behaviors.CreateNetworkPartitionsBehavior;
+import byzzbench.simulator.faults.behaviors.ByzzFuzzDropMessageBehavior;
 import byzzbench.simulator.faults.predicates.MessageRoundPredicate;
 
 import java.util.Set;
@@ -23,7 +23,7 @@ public ByzzFuzzNetworkFault(Set<String> partition, int round) {
         super(
                 "byzzfuzznetworkfault-%d-%s".formatted(round, String.join("-", partition)),
                 new MessageRoundPredicate(round),
-                new CreateNetworkPartitionsBehavior(partition)
+                new ByzzFuzzDropMessageBehavior(partition)
         );
     }
 }

simulator/src/main/java/byzzbench/simulator/transport/Transport.java

@@ -190,12 +190,12 @@ private synchronized void appendEvent(Event event) {
         // add the event to the map
         this.events.put(event.getEventId(), event);
 
+        // notify observers
+        this.observers.forEach(o -> o.onEventAdded(event));
+
         // apply automatic faults
         this.automaticFaults.values()
                 .forEach(f -> f.testAndAccept(new FaultContext(this.scenario, event)));
-
-        // notify observers
-        this.observers.forEach(o -> o.onEventAdded(event));
     }
 
     /**