[#275 & #686] Ability to pass a custom parameter to Bootstrap.connect() / Replace Bootstrap.newBootstrap() with duplicate()

- Add Bootstrap.attr() and ServerBootstrap.attr()/childAttr() so that a
  user can initialize the attribute map from the beginning.
- Replace newBootstrap() with duplicate()

transport/src/main/java/io/netty/bootstrap/AbstractBootstrap.java

@@ -16,19 +16,20 @@
 
 package io.netty.bootstrap;
 
+import io.netty.channel.Channel;
+import io.netty.channel.ChannelException;
+import io.netty.channel.ChannelFuture;
+import io.netty.channel.ChannelHandler;
+import io.netty.channel.ChannelOption;
+import io.netty.channel.EventLoopGroup;
+import io.netty.util.AttributeKey;
+
 import java.net.InetAddress;
 import java.net.InetSocketAddress;
 import java.net.SocketAddress;
 import java.util.LinkedHashMap;
 import java.util.Map;
 
-import io.netty.channel.Channel;
-import io.netty.channel.EventLoopGroup;
-import io.netty.channel.ChannelFuture;
-import io.netty.channel.ChannelOption;
-import io.netty.channel.ChannelHandler;
-import io.netty.channel.ChannelException;
-
 /**
  * {@link AbstractBootstrap} is a helper class that makes it easy to bootstrap a {@link Channel}. It support
  * method-chaining to provide an easy way to configure the {@link AbstractBootstrap}.
@@ -39,6 +40,7 @@ public abstract class AbstractBootstrap<B extends AbstractBootstrap<?>> {
     private ChannelFactory factory;
     private SocketAddress localAddress;
     private final Map<ChannelOption<?>, Object> options = new LinkedHashMap<ChannelOption<?>, Object>();
+    private final Map<AttributeKey<?>, Object> attrs = new LinkedHashMap<AttributeKey<?>, Object>();
     private ChannelHandler handler;
 
     /**
@@ -137,6 +139,23 @@ public abstract class AbstractBootstrap<B extends AbstractBootstrap<?>> {
         return (B) this;
     }
 
+    /**
+     * Allow to specify an initial attribute of the newly created {@link Channel}.  If the {@code value} is
+     * {@code null}, the attribute of the specified {@code key} is removed.
+     */
+    public <T> B attr(AttributeKey<T> key, T value) {
+        if (key == null) {
+            throw new NullPointerException("key");
+        }
+        if (value == null) {
+            attrs.remove(key);
+        } else {
+            attrs.put(key, value);
+        }
+
+        return (B) this;
+    }
+
     /**
      * Shutdown the {@link AbstractBootstrap} and the {@link EventLoopGroup} which is
      * used by it. Only call this if you don't share the {@link EventLoopGroup}
@@ -224,6 +243,10 @@ public abstract class AbstractBootstrap<B extends AbstractBootstrap<?>> {
         return options;
     }
 
+    protected final Map<AttributeKey<?>, Object> attrs() {
+        return attrs;
+    }
+
     private final class BootstrapChannelFactory implements ChannelFactory {
         private final Class<? extends Channel> clazz;
 

transport/src/main/java/io/netty/bootstrap/Bootstrap.java

@@ -16,13 +16,13 @@
 package io.netty.bootstrap;
 
 import io.netty.channel.Channel;
-import io.netty.channel.ChannelHandler;
-import io.netty.channel.ChannelPipeline;
-import io.netty.channel.ChannelFutureListener;
 import io.netty.channel.ChannelFuture;
+import io.netty.channel.ChannelFutureListener;
 import io.netty.channel.ChannelOption;
+import io.netty.channel.ChannelPipeline;
 import io.netty.logging.InternalLogger;
 import io.netty.logging.InternalLoggerFactory;
+import io.netty.util.AttributeKey;
 
 import java.net.InetAddress;
 import java.net.InetSocketAddress;
@@ -149,6 +149,10 @@ public class Bootstrap extends AbstractBootstrap<Bootstrap> {
             }
         }
 
+        for (Entry<AttributeKey<?>, Object> e: attrs().entrySet()) {
+            channel.attr((AttributeKey<Object>) e.getKey()).set(e.getValue());
+        }
+
         group().register(channel).syncUninterruptibly();
     }
 
@@ -161,22 +165,16 @@ public class Bootstrap extends AbstractBootstrap<Bootstrap> {
     }
 
     /**
-     * Create a new {@link Bootstrap} using this "full-setup" {@link Bootstrap} as template.
-     * Only the given parameters are replaced, the rest is configured exactly the same way as the template.
+     * Create a new {@link Bootstrap} which has the identical configuration with this {@link Bootstrap}.
+     * This method is useful when you make multiple connections with similar settings.
      */
-    public Bootstrap newBootstrap(SocketAddress localAddress, SocketAddress remoteAddress, ChannelHandler handler) {
+    public Bootstrap duplicate() {
         validate();
-        Bootstrap cb = new Bootstrap().handler(handler).channelFactory(factory()).group(group())
-                .localAddress(localAddress).remoteAddress(remoteAddress);
-        cb.options().putAll(options());
-        return cb;
-    }
-
-    /**
-     * Create a new {@link Bootstrap} using this "full-setup" {@link Bootstrap} as template.
-     * Only the given parameters are replaced, the rest is configured exactly the same way as the template.
-     */
-    public Bootstrap newBootstrap(SocketAddress localAddress, SocketAddress remoteAddress) {
-        return newBootstrap(localAddress, remoteAddress, handler());
+        Bootstrap b = new Bootstrap()
+                .group(group()).channelFactory(factory()).handler(handler())
+                .localAddress(localAddress()).remoteAddress(remoteAddress);
+        b.options().putAll(options());
+        b.attrs().putAll(attrs());
+        return b;
     }
 }

transport/src/main/java/io/netty/bootstrap/ServerBootstrap.java

@@ -32,6 +32,7 @@ import io.netty.channel.ServerChannel;
 import io.netty.channel.socket.SocketChannel;
 import io.netty.logging.InternalLogger;
 import io.netty.logging.InternalLoggerFactory;
+import io.netty.util.AttributeKey;
 import io.netty.util.NetworkConstants;
 
 import java.net.InetSocketAddress;
@@ -57,6 +58,7 @@ public class ServerBootstrap extends AbstractBootstrap<ServerBootstrap> {
     };
 
     private final Map<ChannelOption<?>, Object> childOptions = new LinkedHashMap<ChannelOption<?>, Object>();
+    private final Map<AttributeKey<?>, Object> childAttrs = new LinkedHashMap<AttributeKey<?>, Object>();
     private EventLoopGroup childGroup;
     private ChannelHandler childHandler;
 
@@ -116,6 +118,18 @@ public class ServerBootstrap extends AbstractBootstrap<ServerBootstrap> {
         return this;
     }
 
+    public <T> ServerBootstrap childAttr(AttributeKey<T> childKey, T value) {
+        if (childKey == null) {
+            throw new NullPointerException("childKey");
+        }
+        if (value == null) {
+            childAttrs.remove(childKey);
+        } else {
+            childAttrs.put(childKey, value);
+        }
+        return this;
+    }
+
     /**
      * Set the {@link ChannelHandler} which is used to server the request for the {@link Channel}'s.
      */
@@ -151,6 +165,10 @@ public class ServerBootstrap extends AbstractBootstrap<ServerBootstrap> {
             return future;
         }
 
+        for (Entry<AttributeKey<?>, Object> e: attrs().entrySet()) {
+            channel.attr((AttributeKey<Object>) e.getKey()).set(e.getValue());
+        }
+
         ChannelPipeline p = future.channel().pipeline();
         if (handler() != null) {
             p.addLast(handler());
@@ -227,6 +245,10 @@ public class ServerBootstrap extends AbstractBootstrap<ServerBootstrap> {
                     }
                 }
 
+                for (Entry<AttributeKey<?>, Object> e: childAttrs.entrySet()) {
+                    child.attr((AttributeKey<Object>) e.getKey()).set(e.getValue());
+                }
+
                 try {
                     childGroup.register(child);
                 } catch (Throwable t) {