Add a VertxConnectionTest reproducing the flush before close on exception

Covers the fix at the connection layer: a write queued (unflushed) when a caught exception triggers the close must reach the channel before it closes, otherwise Netty's ChannelOutboundBuffer discards the unflushed entry. The test fails without the VertxHandler.exceptionCaught change and passes with it.

Signed-off-by: Alexandru Salajan <alexandru17@gmail.com>

Author: asalajan

vertx-core/src/test/java/io/vertx/tests/net/VertxConnectionTest.java

@@ -778,4 +778,27 @@ public void testResumeWhenReadInProgress() {
     outbound = ch.readOutbound();
     assertSame(expected, outbound);
   }
+
+  @Test
+  public void testFlushPendingWriteOnExceptionClose() {
+    EmbeddedChannel ch = new EmbeddedChannel();
+    ChannelPipeline pipeline = ch.pipeline();
+    pipeline.addLast(VertxHandler.create(chctx -> new TestConnection(chctx)));
+    TestConnection connection = (TestConnection) pipeline.get(VertxHandler.class).getConnection();
+    connection.exceptionHandler(err -> {});
+    // Queue a write without flushing it: this is the state produced when a response is written
+    // while a read is in progress (e.g. an inbound codec failing mid-decode, which is how a
+    // request-body decompression failure surfaces). The message sits in the channel outbound
+    // buffer as an unflushed entry.
+    Object response = new Object();
+    connection.unsafeWrite(response, false);
+    assertNull(ch.readOutbound());
+    // The failure surfaces as a caught exception that asks the connection to close. The close
+    // must flush the pending write before closing the channel, otherwise Netty's
+    // ChannelOutboundBuffer discards the unflushed entry and the peer never sees the response.
+    pipeline.fireExceptionCaught(new RuntimeException());
+    ch.runPendingTasks();
+    assertSame(response, ch.readOutbound());
+    assertFalse(ch.isOpen());
+  }
 }