code: /*
   * Copyright (c) 2019 the Eclipse Milo Authors
   *
   * This program and the accompanying materials are made
   * available under the terms of the Eclipse Public License 2.0
   * which is available at https://www.eclipse.org/legal/epl-2.0/
   *
   * SPDX-License-Identifier: EPL-2.0
   */
  
  package org.eclipse.milo.opcua.stack.core.channel.headers;
  
  import io.netty.buffer.ByteBuf;
  import org.eclipse.milo.opcua.stack.core.StatusCodes;
  import org.eclipse.milo.opcua.stack.core.UaException;
  import org.eclipse.milo.opcua.stack.core.channel.messages.TcpMessageEncoder;
  
  public interface HeaderDecoder {
  
      long PROTOCOL_VERSION = 0L;
  
      int HEADER_LENGTH = 8;
      int HEADER_LENGTH_INDEX = 4;
  
      /**
       * Get the message length from a {@link ByteBuf} containing a {@link TcpMessageEncoder}. The reader index will not
       * be advanced.
       *
       * @param buffer {@link ByteBuf} to extract from.
       * @return The message length, which includes the size of the header.
       */
      default int getMessageLength(ByteBuf buffer, int maxMessageLength) throws UaException {
          long messageLength = buffer.getUnsignedIntLE(buffer.readerIndex() + HEADER_LENGTH_INDEX);
  
          if (messageLength <= maxMessageLength) {
              return (int) messageLength;
          } else {
              throw new UaException(StatusCodes.Bad_TcpMessageTooLarge,
                  String.format("max message length exceeded (%s > %s)", messageLength, maxMessageLength));
          }
      }
  
  }
  