Issue #3746 - fix WriteFlusher ClassCastException if Callback throws (#3778)

Signed-off-by: Lachlan Roberts <lachlan@webtide.com>

jetty-io/src/main/java/org/eclipse/jetty/io/WriteFlusher.java

@@ -307,9 +307,36 @@ abstract public class WriteFlusher
 
     private void fail(Callback callback, Throwable... suppressed)
     {
-        FailedState failed = (FailedState)_state.get();
+        Throwable cause;
+        loop:
+        while (true)
+        {
+            State state = _state.get();
+
+            switch (state.getType())
+            {
+                case FAILED:
+                {
+                    FailedState failed = (FailedState)state;
+                    cause = failed.getCause();
+                    break loop;
+                }
+
+                case IDLE:
+                    for (Throwable t : suppressed)
+                        LOG.warn(t);
+                    return;
+
+                default:
+                    Throwable t = new IllegalStateException();
+                    if (!_state.compareAndSet(state, new FailedState(t)))
+                        continue;
+
+                    cause = t;
+                    break loop;
+            }
+        }
 
-        Throwable cause = failed.getCause();
         for (Throwable t : suppressed)
         {
             if (t != cause)

jetty-io/src/test/java/org/eclipse/jetty/io/WriteFlusherTest.java

@@ -18,14 +18,6 @@
 
 package org.eclipse.jetty.io;
 
-import static org.hamcrest.MatcherAssert.assertThat;
-import static org.hamcrest.Matchers.containsString;
-import static org.hamcrest.Matchers.instanceOf;
-import static org.junit.jupiter.api.Assertions.assertEquals;
-import static org.junit.jupiter.api.Assertions.assertFalse;
-import static org.junit.jupiter.api.Assertions.assertThrows;
-import static org.junit.jupiter.api.Assertions.assertTrue;
-
 import java.io.IOException;
 import java.io.InterruptedIOException;
 import java.nio.ByteBuffer;
@@ -43,10 +35,18 @@ import java.util.concurrent.atomic.AtomicBoolean;
 import org.eclipse.jetty.util.BufferUtil;
 import org.eclipse.jetty.util.Callback;
 import org.eclipse.jetty.util.FutureCallback;
+import org.eclipse.jetty.util.log.StacklessLogging;
 import org.hamcrest.Matchers;
-
 import org.junit.jupiter.api.Test;
 
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.containsString;
+import static org.hamcrest.Matchers.instanceOf;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
 public class WriteFlusherTest
 {
     @Test
@@ -159,6 +159,43 @@ public class WriteFlusherTest
         assertTrue(flusher.isIdle());
     }
 
+    @Test
+    public void testCallbackThrows() throws Exception
+    {
+        ByteArrayEndPoint endPoint = new ByteArrayEndPoint(new byte[0], 100);
+
+        AtomicBoolean incompleteFlush = new AtomicBoolean(false);
+        WriteFlusher flusher = new WriteFlusher(endPoint)
+        {
+            @Override
+            protected void onIncompleteFlush()
+            {
+                incompleteFlush.set(true);
+            }
+        };
+
+        FutureCallback callback = new FutureCallback()
+        {
+            @Override
+            public void succeeded()
+            {
+                super.succeeded();
+                throw new IllegalStateException();
+            }
+        };
+
+        try (StacklessLogging stacklessLogging = new StacklessLogging(WriteFlusher.class))
+        {
+            flusher.write(callback, BufferUtil.toBuffer("How now brown cow!"));
+            callback.get(100, TimeUnit.MILLISECONDS);
+        }
+
+        assertEquals("How now brown cow!", endPoint.takeOutputString());
+        assertTrue(callback.isDone());
+        assertFalse(incompleteFlush.get());
+        assertTrue(flusher.isIdle());
+    }
+
     @Test
     public void testCloseWhileBlocking() throws Exception
     {