[#1058] Add Channel/ChannelHandlerContext/ChannelPipeline.isWritable()

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

@@ -133,6 +133,11 @@ public abstract class AbstractChannel extends DefaultAttributeMap implements Cha
         });
     }
 
+    @Override
+    public boolean isWritable() {
+        return pipeline.isWritable();
+    }
+
     @Override
     public final Integer id() {
         return id;

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

@@ -108,6 +108,11 @@ public interface Channel extends AttributeMap, ChannelOutboundInvoker, ChannelPr
      */
     boolean isActive();
 
+    /**
+     * Return {@code true} if the outbound buffer of the {@link Channel} is writable.
+     */
+    boolean isWritable();
+
     /**
      * Return the {@link ChannelMetadata} of the {@link Channel} which describe the nature of the {@link Channel}.
      */

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

@@ -128,6 +128,12 @@ public interface ChannelHandlerContext
          extends AttributeMap, ChannelPropertyAccess,
                  ChannelInboundInvoker, ChannelOutboundInvoker {
 
+    /**
+     * Return {@link true} if the {@link ChannelHandlerContext} is writable, which means if the outbound buffer of
+     * the next in the {@link ChannelPipeline} is writable.
+     */
+    boolean isWritable();
+
     /**
      * Return the {@link Channel} which is bound to the {@link ChannelHandlerContext}.
      */

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

@@ -732,6 +732,11 @@ public interface ChannelPipeline extends ChannelInboundInvoker, ChannelOutboundI
      */
     Map<String, ChannelHandler> toMap();
 
+    /**
+     * Return {@code true} if the outbound buffer is writable.
+     */
+    boolean isWritable();
+
     @Override
     ChannelPipeline fireChannelRegistered();
 

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

@@ -1554,6 +1554,21 @@ final class DefaultChannelHandlerContext extends DefaultAttributeMap implements
         return channel().newFailedFuture(cause);
     }
 
+    @Override
+    public boolean isWritable() {
+        DefaultChannelHandlerContext ctx = prev;
+        for (;;) {
+            if (ctx.hasOutboundByteBuffer()) {
+                return ctx.isWritable();
+            }
+
+            if (ctx.hasOutboundMessageBuffer()) {
+                return ctx.isWritable();
+            }
+            ctx = ctx.prev;
+        }
+    }
+
     private boolean isInboundBufferFreed() {
         return pipeline.inboundBufferFreed;
     }

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

@@ -1336,4 +1336,9 @@ final class DefaultChannelPipeline implements ChannelPipeline {
     public Iterator<Map.Entry<String, ChannelHandler>> iterator() {
         return toMap().entrySet().iterator();
     }
+
+    @Override
+    public boolean isWritable() {
+        return tail.isWritable();
+    }
 }