Correct processing of unhandled messages

Unhandled messages in the in memory messaging network can disrupt runNetwork(), as they
result in getNextQueue() returning null, irrespective of whether there is further work
which could be done. This modifies the flow to loop through the remaining transfers on
the queue before giving up, rather than stopping after the first.

node/src/main/kotlin/com/r3corda/node/services/network/InMemoryMessagingNetwork.kt

@@ -283,10 +283,18 @@ class InMemoryMessagingNetwork(val sendManuallyPumped: Boolean) : SingletonSeria
             return pumpReceiveInternal(block)
         }
 
-        private fun pumpReceiveInternal(block: Boolean): MessageTransfer? {
+        /**
-            val q = getQueueForHandle(handle)
+         * Get the next transfer, and matching queue, that is ready to handle. Any pending transfers without handlers
+         * are placed into `pendingRedelivery` to try again later.
+         *
+         * @param block if this should block until a message it can process.
+         */
+        private fun getNextQueue(q: LinkedBlockingQueue<MessageTransfer>, block: Boolean): Pair<MessageTransfer, List<Handler>>? {
+            var deliverTo: List<Handler>? = null
+            // Pop transfers off the queue until we run out (and are not blocking), or find something we can process
+            while (deliverTo == null) {
                 val transfer = (if (block) q.take() else q.poll()) ?: return null
-            val deliverTo = state.locked {
+                deliverTo = state.locked {
                     val h = handlers.filter { if (it.topic.isBlank()) true else transfer.message.topic == it.topic }
 
                     if (h.isEmpty()) {
@@ -296,11 +304,25 @@ class InMemoryMessagingNetwork(val sendManuallyPumped: Boolean) : SingletonSeria
                         // up a handler for yet. Most unit tests don't run threaded, but we want to test true parallelism at
                         // least sometimes.
                         pendingRedelivery.add(transfer)
+                        null
+                    } else {
+                        h
+                    }
+                }
+                if (deliverTo != null) {
+                    return Pair(transfer, deliverTo)
+                }
+            }
             return null
         }
 
-                h
+        private fun pumpReceiveInternal(block: Boolean): MessageTransfer? {
+            val q = getQueueForHandle(handle)
+            val next = getNextQueue(q, block)
+            if (next == null) {
+                return null
             }
+            val (transfer, deliverTo) = next
 
             for (handler in deliverTo) {
                 // Now deliver via the requested executor, or on this thread if no executor was provided at registration time.

node/src/test/kotlin/com/r3corda/node/messaging/InMemoryMessagingTests.kt

@@ -82,4 +82,37 @@ class InMemoryMessagingTests {
         network.runNetwork(rounds = 1)
         assertEquals(3, counter)
     }
+
+    /**
+     * Tests that unhandled messages in the received queue are skipped and the next message processed, rather than
+     * causing processing to return null as if there was no message.
+     */
+    @Test
+    fun `skip unhandled messages`() {
+        val node1 = network.createNode()
+        val node2 = network.createNode()
+        var received: Int = 0
+
+        node1.net.addMessageHandler("valid_message") { msg, reg ->
+            received++
+        }
+
+        val invalidMessage = node2.net.createMessage("invalid_message", ByteArray(0))
+        val validMessage = node2.net.createMessage("valid_message", ByteArray(0))
+        node2.net.send(invalidMessage, node1.net.myAddress)
+        network.runNetwork()
+        assertEquals(0, received)
+
+        node2.net.send(validMessage, node1.net.myAddress)
+        network.runNetwork()
+        assertEquals(1, received)
+
+        // Here's the core of the test; previously the unhandled message would cause runNetwork() to abort early, so
+        // this would fail.
+        node2.net.send(invalidMessage, node1.net.myAddress)
+        node2.net.send(validMessage, node1.net.myAddress)
+        network.runNetwork()
+        assertEquals(2, received)
+
+    }
 }