Netty Graphite Client

gistfile1.java

package com.outbrain.gruffalo.publish;

import java.util.concurrent.TimeUnit;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.Channel;
import io.netty.channel.ChannelHandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.EventLoop;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;

/**
 * @author Eran Harel
 */
class GraphiteMetricsPublisher implements MetricsPublisher {

  private static final Logger log = LoggerFactory.getLogger(GraphiteHandler.class);
  private static final int RECONNECT_DELAY_SEC = 5;
  private final String graphiteHost;
  private final int graphitePort;
  private final EventLoopGroup eventLoopGroup;
  private final ChannelHandler graphiteHandler = new GraphiteHandler();
  private final GraphiteMetricsPublisher.GraphiteClientChannelInitializer channelInitializer = new GraphiteClientChannelInitializer();
  private Channel channel;

  public GraphiteMetricsPublisher(final String graphiteHost, final int graphitePort, final EventLoopGroup eventLoopGroup) {
    this.graphiteHost = graphiteHost;
    this.graphitePort = graphitePort;
    this.eventLoopGroup = eventLoopGroup;
  }

  private Bootstrap configureBootstrap(EventLoopGroup eventLoopGroup) {
    Bootstrap bootstrap = new Bootstrap();
    bootstrap.remoteAddress(graphiteHost, graphitePort);
    bootstrap.group(eventLoopGroup);
    bootstrap.channel(NioSocketChannel.class);
    bootstrap.handler(channelInitializer);

    return bootstrap;
  }

  public void connect() {
    channel = configureBootstrap(eventLoopGroup).connect().channel();
  }

  @Override
  public void publishMetrics(String metrics) {
    channel.writeAndFlush(metrics);
  }

  private class GraphiteClientChannelInitializer extends ChannelInitializer<Channel> {

    private final StringDecoder DECODER = new StringDecoder();
    private final StringEncoder ENCODER = new StringEncoder();

    @Override
    protected void initChannel(Channel channel) throws Exception {
      ChannelPipeline pipeline = channel.pipeline();

      pipeline.addLast("decoder", DECODER);
      pipeline.addLast("encoder", ENCODER); // we don't really read responses...

      pipeline.addLast("handler", graphiteHandler);
    }
  }

  @ChannelHandler.Sharable
  private class GraphiteHandler extends SimpleChannelInboundHandler<String> {

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
      log.warn("Got an unexpected downstream message: " + msg);
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
      log.info("Connected to: {}", ctx.channel().remoteAddress());
    }

    @Override
    public void channelUnregistered(ChannelHandlerContext ctx) throws Exception {
      log.warn("Got disconnected... will try to reconnect in {} sec...", RECONNECT_DELAY_SEC);

      final EventLoop loop = ctx.channel().eventLoop();
      loop.schedule(new Runnable() {
        @Override
        public void run() {
          log.info("Reconnecting to {}:{}", graphiteHost, graphitePort);
          connect();
        }
      }, RECONNECT_DELAY_SEC, TimeUnit.SECONDS);
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
      log.error("Unexpected exception from downstream.", cause);
      ctx.close();
    }
  }
}

GraphiteHandler instance can be static and so shared