private String getFatalConnectionString(final int version, final byte authByte) {
    return "serverVersion=" + RpcServer.CURRENT_VERSION + ", clientVersion=" + version
      + ", authMethod=" + authByte +
      // The provider may be null if we failed to parse the header of the request
      ", authName=" + (provider == null ? "unknown" : provider.getSaslAuthMethod().getName())
      + " from " + toString();
  }
Compression codec the client asked us use.
hbase-server/src/main/java/org/apache/hadoop/hbase/ipc/ServerRpcConnection.java