DefaultChannelConfig maxMessagesPerRead default not always set

Motivation:
ChannelMetadata has a field minMaxMessagesPerRead which can be confusing. There are also some cases where static instances are used and the default value for channel type is not being applied.

Modifications:
- use a default value which is set unconditionally to simplify
- make sure static instances of MaxMessagesRecvByteBufAllocator are not used if the intention is that the default maxMessagesPerRead should be derived from the channel type.

Result:
Less confusing interfaces in ChannelMetadata and ChannelConfig. Default maxMessagesPerRead is correctly applied.

microbench/src/main/java/io/netty/microbench/http2/NoPriorityByteDistributionBenchmark.java

@@ -495,6 +495,7 @@ public class NoPriorityByteDistributionBenchmark extends AbstractMicrobenchmark
     }
 
     private static class TestChannel extends AbstractChannel {
+        private static final ChannelMetadata TEST_METADATA = new ChannelMetadata(false);
         private DefaultChannelConfig config = new DefaultChannelConfig(this);
 
         private class TestUnsafe extends AbstractUnsafe {
@@ -536,7 +537,7 @@ public class NoPriorityByteDistributionBenchmark extends AbstractMicrobenchmark
 
         @Override
         public ChannelMetadata metadata() {
-            return null;
+            return TEST_METADATA;
         }
 
         @Override

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

@@ -55,6 +55,10 @@ public class AdaptiveRecvByteBufAllocator extends DefaultMaxMessagesRecvByteBufA
         }
     }
 
+    /**
+     * @deprecated There is state for {@link #maxMessagesPerRead()} which is typically based upon channel type.
+     */
+    @Deprecated
     public static final AdaptiveRecvByteBufAllocator DEFAULT = new AdaptiveRecvByteBufAllocator();
 
     private static int getSizeTableIndex(final int size) {
@@ -132,7 +136,7 @@ public class AdaptiveRecvByteBufAllocator extends DefaultMaxMessagesRecvByteBufA
      * parameters, the expected buffer size starts from {@code 1024}, does not
      * go down below {@code 64}, and does not go up above {@code 65536}.
      */
-    private AdaptiveRecvByteBufAllocator() {
+    public AdaptiveRecvByteBufAllocator() {
         this(DEFAULT_MINIMUM, DEFAULT_INITIAL, DEFAULT_MAXIMUM);
     }
 

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

@@ -23,7 +23,7 @@ import java.net.SocketAddress;
 public final class ChannelMetadata {
 
     private final boolean hasDisconnect;
-    private final int minMaxMessagesPerRead;
+    private final int defaultMaxMessagesPerRead;
 
     /**
      * Create a new instance
@@ -42,15 +42,16 @@ public final class ChannelMetadata {
      * @param hasDisconnect     {@code true} if and only if the channel has the {@code disconnect()} operation
      *                          that allows a user to disconnect and then call {@link Channel#connect(SocketAddress)}
      *                                      again, such as UDP/IP.
-     * @param minMaxMessagesPerRead If a {@link MaxMessagesRecvByteBufAllocator} is in use, then this is the minimum
+     * @param defaultMaxMessagesPerRead If a {@link MaxMessagesRecvByteBufAllocator} is in use, then this value will be
-     * value enforced for {@link MaxMessagesRecvByteBufAllocator#maxMessagesPerRead()}. Must be {@code > 0}.
+     * set for {@link MaxMessagesRecvByteBufAllocator#maxMessagesPerRead()}. Must be {@code > 0}.
      */
-    public ChannelMetadata(boolean hasDisconnect, int minMaxMessagesPerRead) {
+    public ChannelMetadata(boolean hasDisconnect, int defaultMaxMessagesPerRead) {
-        if (minMaxMessagesPerRead <= 0) {
+        if (defaultMaxMessagesPerRead <= 0) {
-            throw new IllegalArgumentException("minMaxMessagesPerRead: " + minMaxMessagesPerRead + " (expected > 0)");
+            throw new IllegalArgumentException("defaultMaxMessagesPerRead: " + defaultMaxMessagesPerRead +
+                                               " (expected > 0)");
         }
         this.hasDisconnect = hasDisconnect;
-        this.minMaxMessagesPerRead = minMaxMessagesPerRead;
+        this.defaultMaxMessagesPerRead = defaultMaxMessagesPerRead;
     }
 
     /**
@@ -63,10 +64,10 @@ public final class ChannelMetadata {
     }
 
     /**
-     * If a {@link MaxMessagesRecvByteBufAllocator} is in use, then this is the minimum value enforced for
+     * If a {@link MaxMessagesRecvByteBufAllocator} is in use, then this is the default value for
      * {@link MaxMessagesRecvByteBufAllocator#maxMessagesPerRead()}.
      */
-    public int minMaxMessagesPerRead() {
+    public int defaultMaxMessagesPerRead() {
-        return minMaxMessagesPerRead;
+        return defaultMaxMessagesPerRead;
     }
 }

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

@@ -34,13 +34,12 @@ import static io.netty.channel.ChannelOption.RCVBUF_ALLOCATOR;
 import static io.netty.channel.ChannelOption.WRITE_BUFFER_HIGH_WATER_MARK;
 import static io.netty.channel.ChannelOption.WRITE_BUFFER_LOW_WATER_MARK;
 import static io.netty.channel.ChannelOption.WRITE_SPIN_COUNT;
+import static io.netty.util.internal.ObjectUtil.checkNotNull;
 
 /**
  * The default {@link SocketChannelConfig} implementation.
  */
 public class DefaultChannelConfig implements ChannelConfig {
-
-    private static final RecvByteBufAllocator DEFAULT_RCVBUF_ALLOCATOR = AdaptiveRecvByteBufAllocator.DEFAULT;
     private static final MessageSizeEstimator DEFAULT_MSG_SIZE_ESTIMATOR = DefaultMessageSizeEstimator.DEFAULT;
 
     private static final int DEFAULT_CONNECT_TIMEOUT = 30000;
@@ -59,7 +58,7 @@ public class DefaultChannelConfig implements ChannelConfig {
     protected final Channel channel;
 
     private volatile ByteBufAllocator allocator = ByteBufAllocator.DEFAULT;
-    private volatile RecvByteBufAllocator rcvBufAllocator = DEFAULT_RCVBUF_ALLOCATOR;
+    private volatile RecvByteBufAllocator rcvBufAllocator;
     private volatile MessageSizeEstimator msgSizeEstimator = DEFAULT_MSG_SIZE_ESTIMATOR;
 
     private volatile int connectTimeoutMillis = DEFAULT_CONNECT_TIMEOUT;
@@ -71,9 +70,11 @@ public class DefaultChannelConfig implements ChannelConfig {
     private volatile int writeBufferLowWaterMark = 32 * 1024;
 
     public DefaultChannelConfig(Channel channel) {
-        if (channel == null) {
+        this(channel, new AdaptiveRecvByteBufAllocator());
-            throw new NullPointerException("channel");
+    }
-        }
+
+    protected DefaultChannelConfig(Channel channel, RecvByteBufAllocator allocator) {
+        setRecvByteBufAllocator(allocator, channel.metadata());
         this.channel = channel;
     }
 
@@ -281,40 +282,26 @@ public class DefaultChannelConfig implements ChannelConfig {
         return (T) rcvBufAllocator;
     }
 
-    /**
-     * {@inheritDoc}
-     * <p>
-     * This method enforces the {@link ChannelMetadata#minMaxMessagesPerRead()}. If these predetermined limits
-     * are not appropriate for your use case consider extending the channel and overriding {@link Channel#metadata()},
-     * or use {@link #setRecvByteBufAllocator(RecvByteBufAllocator, ChannelMetadata)}.
-     */
     @Override
     public ChannelConfig setRecvByteBufAllocator(RecvByteBufAllocator allocator) {
-        return setRecvByteBufAllocator(allocator, channel.metadata());
+        rcvBufAllocator = checkNotNull(allocator, "allocator");
+        return this;
     }
 
     /**
      * Set the {@link RecvByteBufAllocator} which is used for the channel to allocate receive buffers.
      * @param allocator the allocator to set.
-     * @param metadata Used to determine the {@link ChannelMetadata#minMaxMessagesPerRead()} if {@code allocator}
+     * @param metadata Used to set the {@link ChannelMetadata#defaultMaxMessagesPerRead()} if {@code allocator}
      * is of type {@link MaxMessagesRecvByteBufAllocator}.
      * @return this
      */
-    public ChannelConfig setRecvByteBufAllocator(RecvByteBufAllocator allocator, ChannelMetadata metadata) {
+    private void setRecvByteBufAllocator(RecvByteBufAllocator allocator, ChannelMetadata metadata) {
-        if (allocator == null) {
+        if (allocator instanceof MaxMessagesRecvByteBufAllocator) {
+            ((MaxMessagesRecvByteBufAllocator) allocator).maxMessagesPerRead(metadata.defaultMaxMessagesPerRead());
+        } else if (allocator == null) {
             throw new NullPointerException("allocator");
         }
-        if (allocator instanceof MaxMessagesRecvByteBufAllocator) {
-            if (metadata == null) {
-                throw new NullPointerException("metadata");
-            }
-            MaxMessagesRecvByteBufAllocator maxMsgAllocator = (MaxMessagesRecvByteBufAllocator) allocator;
-            if (maxMsgAllocator.maxMessagesPerRead() < metadata.minMaxMessagesPerRead()) {
-                maxMsgAllocator.maxMessagesPerRead(metadata.minMaxMessagesPerRead());
-            }
-        }
         rcvBufAllocator = allocator;
-        return this;
     }
 
     @Override

transport/src/main/java/io/netty/channel/socket/DefaultDatagramChannelConfig.java

@@ -43,8 +43,6 @@ public class DefaultDatagramChannelConfig extends DefaultChannelConfig implement
 
     private static final InternalLogger logger = InternalLoggerFactory.getInstance(DefaultDatagramChannelConfig.class);
 
-    private static final RecvByteBufAllocator DEFAULT_RCVBUF_ALLOCATOR = new FixedRecvByteBufAllocator(2048);
-
     private final DatagramSocket javaSocket;
     private volatile boolean activeOnOpen;
 
@@ -52,12 +50,11 @@ public class DefaultDatagramChannelConfig extends DefaultChannelConfig implement
      * Creates a new instance.
      */
     public DefaultDatagramChannelConfig(DatagramChannel channel, DatagramSocket javaSocket) {
-        super(channel);
+        super(channel, new FixedRecvByteBufAllocator(2048));
         if (javaSocket == null) {
             throw new NullPointerException("javaSocket");
         }
         this.javaSocket = javaSocket;
-        setRecvByteBufAllocator(DEFAULT_RCVBUF_ALLOCATOR);
     }
 
     @Override

transport/src/test/java/io/netty/channel/AbstractChannelTest.java

@@ -99,7 +99,7 @@ public class AbstractChannelTest {
     }
 
     private static class TestChannel extends AbstractChannel {
-
+        private static final ChannelMetadata TEST_METADATA = new ChannelMetadata(false);
         private class TestUnsafe extends AbstractUnsafe {
 
             @Override
@@ -127,7 +127,7 @@ public class AbstractChannelTest {
 
         @Override
         public ChannelMetadata metadata() {
-            return null;
+            return TEST_METADATA;
         }
 
         @Override

transport/src/test/java/io/netty/channel/ChannelOutboundBufferTest.java

@@ -127,6 +127,7 @@ public class ChannelOutboundBufferTest {
     }
 
     private static final class TestChannel extends AbstractChannel {
+        private static final ChannelMetadata TEST_METADATA = new ChannelMetadata(false);
         private final ChannelConfig config = new DefaultChannelConfig(this);
 
         TestChannel() {
@@ -195,7 +196,7 @@ public class ChannelOutboundBufferTest {
 
         @Override
         public ChannelMetadata metadata() {
-            throw new UnsupportedOperationException();
+            return TEST_METADATA;
         }
 
         final class TestUnsafe extends AbstractUnsafe {