[#2618] Introduce ChannelPromise.unvoid() and ChannelFuture.isVoid()

Motivation:

There is no way for a ChannelHandler to check if the passed in ChannelPromise for a write(...) call is a VoidChannelPromise. This is a problem as some handlers need to add listeners to the ChannelPromise which is not possible in the case of a VoidChannelPromise.

Modification:

- Introduce ChannelFuture.isVoid() which will return true if it is not possible to add listeners or wait on the result.
- Add ChannelPromise.unvoid() which allows to create a ChannelFuture out of a void ChannelFuture which supports all the operations.

Result:

It's now easy to write ChannelHandler implementations which also works when a void ChannelPromise is used.

handler/src/main/java/io/netty/handler/timeout/IdleStateHandler.java

@@ -256,14 +256,15 @@ public class IdleStateHandler extends ChannelDuplexHandler {
 
     @Override
     public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
-        promise.addListener(new ChannelFutureListener() {
+        ChannelPromise unvoid = promise.unvoid();
+        unvoid.addListener(new ChannelFutureListener() {
             @Override
             public void operationComplete(ChannelFuture future) throws Exception {
                 lastWriteTime = System.nanoTime();
                 firstWriterIdleEvent = firstAllIdleEvent = true;
             }
         });
-        ctx.write(msg, promise);
+        ctx.write(msg, unvoid);
     }
 
     private void initialize(ChannelHandlerContext ctx) {

handler/src/main/java/io/netty/handler/timeout/WriteTimeoutHandler.java

@@ -103,37 +103,38 @@ public class WriteTimeoutHandler extends ChannelOutboundHandlerAdapter {
 
     @Override
     public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
-        scheduleTimeout(ctx, promise);
+        if (timeoutNanos > 0) {
+            promise = promise.unvoid();
+            scheduleTimeout(ctx, promise);
+        }
         ctx.write(msg, promise);
     }
 
     private void scheduleTimeout(final ChannelHandlerContext ctx, final ChannelPromise future) {
-        if (timeoutNanos > 0) {
-            // Schedule a timeout.
-            final ScheduledFuture<?> sf = ctx.executor().schedule(new Runnable() {
-                @Override
-                public void run() {
-                    // Was not written yet so issue a write timeout
-                    // The future itself will be failed with a ClosedChannelException once the close() was issued
-                    // See https://github.com/netty/netty/issues/2159
-                    if (!future.isDone()) {
-                        try {
-                            writeTimedOut(ctx);
-                        } catch (Throwable t) {
-                            ctx.fireExceptionCaught(t);
-                        }
+        // Schedule a timeout.
+        final ScheduledFuture<?> sf = ctx.executor().schedule(new Runnable() {
+            @Override
+            public void run() {
+                // Was not written yet so issue a write timeout
+                // The future itself will be failed with a ClosedChannelException once the close() was issued
+                // See https://github.com/netty/netty/issues/2159
+                if (!future.isDone()) {
+                    try {
+                        writeTimedOut(ctx);
+                    } catch (Throwable t) {
+                        ctx.fireExceptionCaught(t);
                     }
                 }
-            }, timeoutNanos, TimeUnit.NANOSECONDS);
+            }
+        }, timeoutNanos, TimeUnit.NANOSECONDS);
 
-            // Cancel the scheduled timeout if the flush future is complete.
-            future.addListener(new ChannelFutureListener() {
-                @Override
-                public void operationComplete(ChannelFuture future) throws Exception {
-                    sf.cancel(false);
-                }
-            });
-        }
+        // Cancel the scheduled timeout if the flush future is complete.
+        future.addListener(new ChannelFutureListener() {
+            @Override
+            public void operationComplete(ChannelFuture future) throws Exception {
+                sf.cancel(false);
+            }
+        });
     }
 
     /**

transport/src/main/java/io/netty/channel/ChannelFuture.java

@@ -193,4 +193,20 @@ public interface ChannelFuture extends Future<Void> {
 
     @Override
     ChannelFuture awaitUninterruptibly();
+
+    /**
+     * Returns {@code true} if this {@link ChannelFuture} is a void future and so not allow to call any of the
+     * following methods:
+     * <ul>
+     *     <li>{@link #addListener(GenericFutureListener)}</li>
+     *     <li>{@link #addListeners(GenericFutureListener[])}</li>
+     *     <li>{@link #await()}</li>
+     *     <li>{@link #await(long, TimeUnit)} ()}</li>
+     *     <li>{@link #await(long)} ()}</li>
+     *     <li>{@link #awaitUninterruptibly()}</li>
+     *     <li>{@link #sync()}</li>
+     *     <li>{@link #syncUninterruptibly()}</li>
+     * </ul>
+     */
+    boolean isVoid();
 }

transport/src/main/java/io/netty/channel/ChannelProgressivePromise.java

@@ -59,4 +59,7 @@ public interface ChannelProgressivePromise extends ProgressivePromise<Void>, Cha
 
     @Override
     ChannelProgressivePromise setProgress(long progress, long total);
+
+    @Override
+    ChannelProgressivePromise unvoid();
 }

transport/src/main/java/io/netty/channel/ChannelPromise.java

@@ -60,4 +60,9 @@ public interface ChannelPromise extends ChannelFuture, Promise<Void> {
 
     @Override
     ChannelPromise awaitUninterruptibly();
+
+    /**
+     * Returns a new {@link ChannelPromise} if {@link #isVoid()} returns {@code true} otherwise itself.
+     */
+    ChannelPromise unvoid();
 }

transport/src/main/java/io/netty/channel/CompleteChannelFuture.java

@@ -104,4 +104,9 @@ abstract class CompleteChannelFuture extends CompleteFuture<Void> implements Cha
     public Void getNow() {
         return null;
     }
+
+    @Override
+    public boolean isVoid() {
+        return false;
+    }
 }

transport/src/main/java/io/netty/channel/DefaultChannelProgressivePromise.java

@@ -166,4 +166,14 @@ public class DefaultChannelProgressivePromise
             super.checkDeadLock();
         }
     }
+
+    @Override
+    public ChannelProgressivePromise unvoid() {
+        return this;
+    }
+
+    @Override
+    public boolean isVoid() {
+        return false;
+    }
 }

transport/src/main/java/io/netty/channel/DefaultChannelPromise.java

@@ -157,4 +157,14 @@ public class DefaultChannelPromise extends DefaultPromise<Void> implements Chann
             super.checkDeadLock();
         }
     }
+
+    @Override
+    public ChannelPromise unvoid() {
+        return this;
+    }
+
+    @Override
+    public boolean isVoid() {
+        return false;
+    }
 }

transport/src/main/java/io/netty/channel/VoidChannelPromise.java

@@ -193,6 +193,27 @@ final class VoidChannelPromise extends AbstractFuture<Void> implements ChannelPr
         return null;
     }
 
+    @Override
+    public ChannelPromise unvoid() {
+        ChannelPromise promise = new DefaultChannelPromise(channel);
+        if (fireException) {
+            promise.addListener(new ChannelFutureListener() {
+                @Override
+                public void operationComplete(ChannelFuture future) throws Exception {
+                    if (!future.isSuccess()) {
+                        fireException(future.cause());
+                    }
+                }
+            });
+        }
+        return promise;
+    }
+
+    @Override
+    public boolean isVoid() {
+        return true;
+    }
+
     private void fireException(Throwable cause) {
         // Only fire the exception if the channel is open and registered
         // if not the pipeline is not setup and so it would hit the tail