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Service for batching and relaying metric traffic to Wavefront
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package com.wavefront.agent.channel;

import javax.annotation.Nullable;

import com.google.common.base.Charsets;

import java.util.List;
import java.util.logging.Logger;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelPipeline;
import io.netty.handler.codec.ByteToMessageDecoder;
import io.netty.handler.codec.compression.ZlibCodecFactory;
import io.netty.handler.codec.compression.ZlibWrapper;
import io.netty.handler.codec.http.HttpContentDecompressor;
import io.netty.handler.codec.http.HttpRequestDecoder;
import io.netty.handler.codec.http.HttpResponseEncoder;
import io.netty.handler.codec.http.cors.CorsConfig;
import io.netty.handler.codec.http.cors.CorsHandler;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;

/**
 * This class handles 2 different protocols on a single port.  Supported protocols include HTTP and
 * a plain text protocol.  It dynamically adds the appropriate encoder/decoder based on the detected
 * protocol. This class was largely adapted from the example provided with netty v4.0
 *
 * @see Netty
 * Port Unification Example
 * @author Mike McLaughlin ([email protected])
 */
public final class PlainTextOrHttpFrameDecoder extends ByteToMessageDecoder {

  protected static final Logger logger = Logger.getLogger(
      PlainTextOrHttpFrameDecoder.class.getName());

  /**
   * The object for handling requests of either protocol
   */
  private final ChannelHandler handler;
  private final boolean detectGzip;
  @Nullable
  private final CorsConfig corsConfig;
  private final int maxLengthPlaintext;
  private final int maxLengthHttp;

  private static final StringDecoder STRING_DECODER = new StringDecoder(Charsets.UTF_8);
  private static final StringEncoder STRING_ENCODER = new StringEncoder(Charsets.UTF_8);

  /**
   * @param handler            the object responsible for handling the incoming messages on
   *                           either protocol.
   * @param corsConfig         enables CORS when {@link CorsConfig} is specified
   * @param maxLengthPlaintext max allowed line length for line-delimiter protocol
   * @param maxLengthHttp      max allowed size for incoming HTTP requests
   */
  public PlainTextOrHttpFrameDecoder(final ChannelHandler handler,
                                     @Nullable final CorsConfig corsConfig,
                                     int maxLengthPlaintext,
                                     int maxLengthHttp) {
    this(handler, corsConfig, maxLengthPlaintext, maxLengthHttp, true);
  }

  private PlainTextOrHttpFrameDecoder(final ChannelHandler handler,
                                      @Nullable final CorsConfig corsConfig,
                                      int maxLengthPlaintext, int maxLengthHttp,
                                      boolean detectGzip) {
    this.handler = handler;
    this.corsConfig = corsConfig;
    this.maxLengthPlaintext = maxLengthPlaintext;
    this.maxLengthHttp = maxLengthHttp;
    this.detectGzip = detectGzip;
  }

  /**
   * Dynamically adds the appropriate encoder/decoder(s) to the pipeline based on the detected
   * protocol.
   */
  @Override
  protected void decode(final ChannelHandlerContext ctx, final ByteBuf buffer, List