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# Network Utilities
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Utility functions for buffer management, channel handling, and Netty 3 integration. Provides essential conversion and management utilities for working with Netty 3 networking components in Elasticsearch.
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## Capabilities
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### Netty3Utils Class
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Core utility class providing essential functions for Netty 3 integration, buffer management, and system setup.
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```java { .api }
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/**
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 * Utility class for Netty 3 integration and buffer management
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 */
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public class Netty3Utils {
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    /**
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     * Default gathering flag for composite buffers to enable zero-copy operations
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     */
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    public static final boolean DEFAULT_GATHERING = true;
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    /**
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     * Sets up Netty 3 environment including logging configuration and thread naming.
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     * Must be called before using any Netty 3 functionality.
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     */
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    public static void setup();
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    /**
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     * Converts Elasticsearch BytesReference to Netty ChannelBuffer for network transmission
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     * @param bytes BytesReference containing data to convert
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     * @return ChannelBuffer suitable for Netty operations
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     */
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    public static ChannelBuffer toChannelBuffer(BytesReference bytes);
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    /**
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     * Converts Netty ChannelBuffer to Elasticsearch BytesReference for internal processing
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     * @param buffer ChannelBuffer containing network data
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     * @return BytesReference for Elasticsearch internal use
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     */
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    public static BytesReference toBytesReference(ChannelBuffer buffer);
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    /**
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     * Converts Netty ChannelBuffer to Elasticsearch BytesReference with specified size
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     * @param buffer ChannelBuffer containing network data
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     * @param size Number of bytes to include in the conversion
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     * @return BytesReference with the specified size
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     */
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    public static BytesReference toBytesReference(ChannelBuffer buffer, int size);
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    /**
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     * Closes a collection of Netty channels gracefully
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     * @param channels Collection of Channel objects to close
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     */
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    public static void closeChannels(Collection<Channel> channels);
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    /**
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     * Handles fatal errors by rethrowing them on a separate thread to prevent blocking
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     * @param t Throwable representing the fatal error
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     */
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    public static void maybeDie(Throwable t);
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}
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```
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**Usage Examples:**
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```java
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import org.elasticsearch.transport.netty3.Netty3Utils;
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import org.elasticsearch.common.bytes.BytesReference;
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import org.jboss.netty.buffer.ChannelBuffer;
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// Setup Netty 3 environment (called automatically by plugin)
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Netty3Utils.setup();
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// Convert Elasticsearch bytes to Netty buffer for transmission
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BytesReference elasticsearchData = // ... some data
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ChannelBuffer nettyBuffer = Netty3Utils.toChannelBuffer(elasticsearchData);
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// Convert received Netty buffer back to Elasticsearch bytes
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ChannelBuffer receivedBuffer = // ... received from network
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BytesReference elasticsearchBytes = Netty3Utils.toBytesReference(receivedBuffer);
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// Convert with specific size limit
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BytesReference limitedBytes = Netty3Utils.toBytesReference(receivedBuffer, 1024);
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// Close multiple channels at once
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List<Channel> channels = // ... collection of channels
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Netty3Utils.closeChannels(channels);
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```
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### Channel Management Utilities
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Additional utilities for managing Netty channel lifecycle and connection tracking.
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```java { .api }
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/**
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 * Handler for tracking and managing open Netty channels
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 */
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public class Netty3OpenChannelsHandler extends SimpleChannelUpstreamHandler implements Releasable {
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    /**
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     * Constructor for channel tracking handler
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     * @param logger Logger instance for debugging and monitoring
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     */
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    public Netty3OpenChannelsHandler(Logger logger);
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    /**
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     * Handles upstream channel events for connection tracking
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     * @param ctx Channel handler context
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     * @param e Channel event to process
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     */
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    public void handleUpstream(ChannelHandlerContext ctx, ChannelEvent e);
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    /**
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     * Returns the current number of open channels
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     * @return int count of currently open channels
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     */
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    public int numberOfOpenChannels();
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    /**
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     * Returns the total number of channels that have been created
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     * @return long total channel count since startup
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     */
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    public long totalChannels();
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    /**
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     * Closes all currently tracked open channels
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     */
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    public void close();
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}
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```
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### Buffer Reference Implementation
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Specialized BytesReference implementation that wraps Netty ChannelBuffer for efficient memory management.
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```java { .api }
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/**
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 * BytesReference implementation that wraps a Netty ChannelBuffer
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 * Provides efficient access to network buffer data without copying
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 */
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public class ChannelBufferBytesReference implements BytesReference {
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    /**
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     * Constructor wrapping a ChannelBuffer with specified size
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     * @param buffer ChannelBuffer to wrap
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     * @param size Number of bytes to include from the buffer
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     */
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    public ChannelBufferBytesReference(ChannelBuffer buffer, int size);
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    /**
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     * Gets a single byte at the specified index
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     * @param index Position to read from
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     * @return byte value at the index
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     */
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    public byte get(int index);
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    /**
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     * Returns the total length of available data
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     * @return int length in bytes
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     */
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    public int length();
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    /**
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     * Creates a slice of the buffer for the specified range
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     * @param from Starting position (inclusive)
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     * @param length Number of bytes to include
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     * @return BytesReference containing the slice
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     */
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    public BytesReference slice(int from, int length);
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    /**
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     * Creates a stream input for reading the buffer data
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     * @return StreamInput for sequential reading
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     */
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    public StreamInput streamInput();
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    /**
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     * Writes the buffer contents to an output stream
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     * @param out OutputStream to write to
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     */
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    public void writeTo(OutputStream out);
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}
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```
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### Stream Input Implementation
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StreamInput implementation for reading from Netty ChannelBuffer data.
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```java { .api }
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/**
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 * StreamInput implementation for reading from ChannelBuffer data
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 */
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public class ChannelBufferStreamInput extends StreamInput {
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    /**
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     * Constructor for creating stream input from ChannelBuffer
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     * @param buffer ChannelBuffer containing data to read
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     * @param size Number of bytes available for reading
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     */
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    public ChannelBufferStreamInput(ChannelBuffer buffer, int size);
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    /**
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     * Reads a single byte from the stream
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     * @return int byte value (0-255) or -1 if end of stream
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     */
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    public int read();
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    /**
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     * Reads multiple bytes into a byte array
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     * @param b Destination byte array
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     * @param off Offset in the destination array
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     * @param len Maximum number of bytes to read
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     * @return int number of bytes actually read
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     */
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    public int read(byte[] b, int off, int len);
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    /**
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     * Resets the stream position to the beginning
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     */
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    public void reset();
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    /**
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     * Closes the stream and releases resources
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     */
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    public void close();
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}
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```
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### Error Handling and Logging
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The utilities include comprehensive error handling and logging integration.
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```java { .api }
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/**
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 * Internal logger adapter for Netty 3 integration with Elasticsearch logging
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 */
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public class Netty3InternalESLogger implements InternalLogger {
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    // Provides bridge between Netty 3 logging and Elasticsearch logging system
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    // Handles log level mapping and message formatting
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}
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```
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**Setup and Integration:**
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```java
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// The setup() method configures:
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// - Netty 3 logging to use Elasticsearch's logging framework
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// - Thread naming patterns for better debugging
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// - System property configuration for optimal performance
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// - Error handling integration
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public static void setup() {
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    // Configure Netty logging to use ES logging
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    InternalLoggerFactory.setDefaultFactory(new Netty3InternalESLoggerFactory());
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    // Set thread naming pattern for Netty threads
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    System.setProperty("io.netty.threadLocalDirectBufferSize", /* optimized size */);
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    // Additional Netty 3 system optimizations
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    // ...
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}
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```
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### Memory Management
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The utilities provide efficient memory management for network operations:
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- **Zero-Copy Operations**: ChannelBuffer conversions avoid unnecessary data copying
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- **Composite Buffers**: Support for gathering multiple buffer segments efficiently
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- **Buffer Pooling**: Integration with Netty's buffer pooling for memory efficiency
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- **Resource Cleanup**: Automatic cleanup of network resources and buffer references