Channel Management

/**
 * Netty4 server channel implementation for TCP transport
 * Binds to configured address and accepts connections from cluster peers
 */
public class Netty4TcpServerChannel implements TcpServerChannel {
    /**
     * Adds listener to be notified when server channel closes
     * Useful for cleanup and monitoring of server lifecycle
     * @param listener Callback invoked when channel closes
     */
    void addCloseListener(ActionListener<Void> listener);
    
    /**
     * Checks if server channel is currently open and accepting connections
     * @return true if server is bound and accepting, false otherwise
     */
    boolean isOpen();
    
    /**
     * Gets local socket address this server channel is bound to
     * Includes IP address and port number for client connections
     * @return Local InetSocketAddress for bound server socket
     */
    InetSocketAddress getLocalAddress();
    
    /**
     * Closes server channel and stops accepting new connections
     * Existing connections continue until naturally closed
     */
    void close();
}

// Server channel created by transport layer during startup
Netty4TcpServerChannel serverChannel = // from transport initialization

// Monitor server lifecycle
serverChannel.addCloseListener(ActionListener.wrap(
    () -> {
        logger.info("Transport server channel closed");
        // Perform cleanup operations
    },
    exception -> {
        logger.error("Transport server channel close failed", exception);
        // Handle close failure
    }
));

// Check server status
if (serverChannel.isOpen()) {
    InetSocketAddress address = serverChannel.getLocalAddress();
    logger.info("Transport server listening on {}:{}", 
                address.getHostString(), address.getPort());
} else {
    logger.warn("Transport server channel is not accepting connections");
}

/**
 * Netty4 client channel implementation for TCP transport
 * Handles individual connections to remote cluster nodes
 */
public class Netty4TcpChannel implements TcpChannel {
    /**
     * Adds listener to be notified when channel closes
     * Called for both normal and exceptional channel closure
     * @param listener Callback invoked on channel close
     */
    void addCloseListener(ActionListener<Void> listener);
    
    /**
     * Checks if channel is currently open and connected
     * @return true if channel is active, false if closed or closing
     */
    boolean isOpen();
    
    /**
     * Gets local socket address for this connection
     * @return Local InetSocketAddress of client socket
     */
    InetSocketAddress getLocalAddress();
    
    /**
     * Gets remote socket address for this connection
     * @return Remote InetSocketAddress of connected peer node
     */
    InetSocketAddress getRemoteAddress();
    
    /**
     * Sends message bytes to remote peer asynchronously
     * Messages are queued and sent in order
     * @param reference Serialized message bytes to transmit
     * @param listener Callback for send completion or failure
     */
    void sendMessage(BytesReference reference, ActionListener<Void> listener);
    
    /**
     * Closes channel connection to remote peer
     * Pending operations complete before channel closure
     */
    void close();
}

// Client channel obtained from transport connection
Netty4TcpChannel clientChannel = // from transport.openConnection()

// Send cluster message to remote node
TransportMessage message = // serialized cluster message
BytesReference messageBytes = // serialized message content

clientChannel.sendMessage(messageBytes, ActionListener.wrap(
    response -> {
        logger.debug("Message sent successfully to {}", 
                    clientChannel.getRemoteAddress());
    },
    exception -> {
        logger.error("Failed to send message to {}: {}", 
                    clientChannel.getRemoteAddress(), exception.getMessage());
        // Handle send failure - may trigger connection retry
    }
));

// Monitor connection health
clientChannel.addCloseListener(ActionListener.wrap(
    () -> {
        logger.info("Connection to {} closed", clientChannel.getRemoteAddress());
        // Update node connection status
    },
    exception -> {
        logger.warn("Connection to {} closed with error: {}", 
                   clientChannel.getRemoteAddress(), exception.getMessage());
        // Trigger connection retry if appropriate
    }
));

/**
 * Netty4 HTTP server channel implementation
 * Binds to HTTP port and accepts client connections for REST API access
 */
public class Netty4HttpServerChannel implements HttpServerChannel {
    /**
     * Gets local socket address HTTP server is bound to
     * Includes bind address and port for HTTP client connections
     * @return Local InetSocketAddress for HTTP server
     */
    InetSocketAddress getLocalAddress();
    
    /**
     * Adds listener to be notified when HTTP server channel closes
     * Useful for monitoring HTTP service availability
     * @param listener Callback invoked on server close
     */
    void addCloseListener(ActionListener<Void> listener);
    
    /**
     * Checks if HTTP server is currently open and accepting connections
     * @return true if server is bound and accepting HTTP requests
     */
    boolean isOpen();
    
    /**
     * Closes HTTP server channel and stops accepting connections
     * Existing HTTP connections complete current requests before closing
     */
    void close();
}

// HTTP server channel created during HTTP transport startup
Netty4HttpServerChannel httpServer = // from HTTP transport initialization

// Check HTTP server status
if (httpServer.isOpen()) {
    InetSocketAddress httpAddress = httpServer.getLocalAddress();
    logger.info("HTTP server accepting connections on {}:{}", 
                httpAddress.getHostString(), httpAddress.getPort());
    
    // HTTP server is ready for client requests
    // Clients can now send REST API requests to this address
} else {
    logger.error("HTTP server failed to bind - REST API unavailable");
}

// Monitor HTTP server lifecycle
httpServer.addCloseListener(ActionListener.wrap(
    () -> {
        logger.info("HTTP server stopped - REST API no longer available");
        // Update service registry or load balancer
    },
    exception -> {
        logger.error("HTTP server close failed", exception);
        // Handle server shutdown issues
    }
));

/**
 * Netty4 HTTP client channel implementation
 * Handles individual HTTP connections from clients to process REST requests
 */
public class Netty4HttpChannel implements HttpChannel {
    /**
     * Sends HTTP response to client asynchronously
     * Response is queued and transmitted to client
     * @param response HTTP response object with status, headers, and body
     * @param listener Callback for response transmission completion
     */
    void sendResponse(HttpResponse response, ActionListener<Void> listener);
    
    /**
     * Gets local address for this HTTP connection
     * @return Local InetSocketAddress of server side
     */
    InetSocketAddress getLocalAddress();
    
    /**
     * Gets remote client address for this HTTP connection
     * @return Remote InetSocketAddress of HTTP client
     */
    InetSocketAddress getRemoteAddress();
    
    /**
     * Closes HTTP connection to client
     * Connection may be kept alive for reuse depending on HTTP headers
     */
    void close();
}

// HTTP channel created for each client connection
Netty4HttpChannel httpChannel = // from HTTP request pipeline

// Process HTTP request and send response
RestResponse restResponse = // from REST handler processing
HttpResponse httpResponse = // converted to HTTP format

httpChannel.sendResponse(httpResponse, ActionListener.wrap(
    response -> {
        logger.debug("HTTP response sent to client {}", 
                    httpChannel.getRemoteAddress());
        // Response successfully transmitted
    },
    exception -> {
        logger.warn("Failed to send HTTP response to {}: {}", 
                   httpChannel.getRemoteAddress(), exception.getMessage());
        // Client may have disconnected or network error occurred
    }
));

// Log client connection info
InetSocketAddress clientAddr = httpChannel.getRemoteAddress();
InetSocketAddress serverAddr = httpChannel.getLocalAddress();
logger.debug("Processing HTTP request from {} to {}", clientAddr, serverAddr);

/**
 * Custom NIO socket channel with Elasticsearch-specific optimizations
 * Extends Netty's NioSocketChannel with additional features
 */
public class Netty4NioSocketChannel extends NioSocketChannel {
    // Enhanced socket channel with ES-specific networking optimizations
    // Provides better integration with Elasticsearch's networking stack
}

/**
 * Socket channel implementation that copies bytes for certain operations
 * Provides additional safety for buffer management in specific scenarios
 */
public class CopyBytesSocketChannel extends Netty4NioSocketChannel {
    // Specialized channel that copies bytes when needed
    // Used for scenarios requiring buffer isolation or special handling
}

/**
 * Server socket channel that copies bytes for connection handling
 * Provides enhanced buffer management for server-side operations
 */
public class CopyBytesServerSocketChannel extends NioServerSocketChannel {
    // Server-side equivalent of CopyBytesSocketChannel
    // Handles incoming connections with specialized byte copying behavior
}

// TCP transport channel settings
Settings tcpSettings = Settings.builder()
    .put("transport.tcp.port", "9300-9400") // Port range
    .put("transport.bind_host", "0.0.0.0") // Bind address
    .put("transport.publish_host", "192.168.1.100") // Advertised address
    .put("transport.tcp.connect_timeout", "30s") // Connection timeout
    .put("transport.tcp.compress", true) // Message compression
    .build();

// HTTP server channel settings
Settings httpSettings = Settings.builder()
    .put("http.port", "9200-9300") // HTTP port range
    .put("http.bind_host", "0.0.0.0") // HTTP bind address
    .put("http.publish_host", "192.168.1.100") // HTTP advertised address
    .put("http.max_content_length", "100mb") // Request size limit
    .put("http.compression", true) // Response compression
    .put("http.cors.enabled", true) // CORS support
    .build();