// Header type.// Copyright (C) 2008-2010 Malcolm Crowe, Lex Li, and other contributors.// // Permission is hereby granted, free of charge, to any person obtaining a copy of this// software and associated documentation files (the "Software"), to deal in the Software// without restriction, including without limitation the rights to use, copy, modify, merge,// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons// to whom the Software is furnished to do so, subject to the following conditions:// // The above copyright notice and this permission notice shall be included in all copies or// substantial portions of the Software.// // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER// DEALINGS IN THE SOFTWARE. using System;using System.Globalization; namespace GSF.Net.Snmp{    /// <summary>    /// Header segment.    /// </summary>    public sealed class Header : ISegment    {        private readonly Integer32 _messageId;        private readonly Integer32 _maxSize;        private readonly OctetString _flags;        private readonly Integer32 _securityModel;        private static readonly Integer32 DefaultSecurityModel = new Integer32(3);        private static readonly Integer32 DefaultMaxMessageSize = new Integer32(MaxMessageSize);        private static readonly Header EmptyHeader = new Header();        private readonly Sequence _container;         /// <summary>        /// Max message size used in #SNMP.         /// </summary>        /// <remarks>        /// You can use any value for your own application.         /// Also this value may be changed in #SNMP in future releases.        /// </remarks>        public const int MaxMessageSize = 0xFFE3;         private Header() : this(null, DefaultMaxMessageSize, 0)        {                    }         /// <summary>        /// Initializes a new instance of the <see cref="Header"/> class.        /// </summary>        /// <param name="messageId">The message identifier.</param>        public Header(int messageId) : this(new Integer32(messageId), DefaultMaxMessageSize, 0)        {        }         /// <summary>        /// Initializes a new instance of the <see cref="Header"/> class.        /// </summary>        /// <param name="data">The data.</param>        public Header(ISnmpData data)        {            if (data == null)            {                throw new ArgumentNullException(nameof(data));            }             _container = (Sequence)data;            _messageId = (Integer32)_container[0];            _maxSize = (Integer32)_container[1];            _flags = (OctetString)_container[2];            SecurityLevel = _flags.ToLevels();            _securityModel = (Integer32)_container[3];        }         /// <summary>        /// Initializes a new instance of the <see cref="Header"/> class.        /// </summary>        /// <param name="messageId">The message id.</param>        /// <param name="maxMessageSize">Size of the max message.</param>        /// <param name="securityLevel">The security level.</param>        /// <remarks>If you want an empty header, please use <see cref="Empty"/>.</remarks>        public Header(Integer32 messageId, Integer32 maxMessageSize, Levels securityLevel)        {            if (maxMessageSize == null)            {                throw new ArgumentNullException(nameof(maxMessageSize));            }             _messageId = messageId;            _maxSize = maxMessageSize;            SecurityLevel = securityLevel;            _flags = new OctetString(SecurityLevel);            _securityModel = DefaultSecurityModel;        }                /// <summary>        /// Empty header.        /// </summary>        public static Header Empty        {            get { return EmptyHeader; }        }                        /// <summary>        /// Security flags.        /// </summary>        public Levels SecurityLevel { get; private set; }         /// <summary>        /// Gets the message ID.        /// </summary>        /// <value>The message ID.</value>        public int MessageId        {            get { return _messageId.ToInt32(); }        }         #region ISegment Members         /// <summary>        /// Converts to <see cref="Sequence"/> object.        /// </summary>        /// <returns></returns>        public Sequence ToSequence()        {            return _container ?? new Sequence(null, _messageId, _maxSize, _messageId == null ? null : _flags, _securityModel);        }         /// <summary>        /// Gets the data.        /// </summary>        /// <param name="version">The version.</param>        /// <returns></returns>        public ISnmpData GetData(VersionCode version)        {            return version == VersionCode.V3 ? ToSequence() : null;        }         #endregion         /// <summary>        /// Returns a <see cref="System.String"/> that represents this instance.        /// </summary>        /// <returns>        /// A <see cref="System.String"/> that represents this instance.        /// </returns>        public override string ToString()        {            return string.Format(CultureInfo.InvariantCulture, "Header: messageId: {0};maxMessageSize: {1};securityBits: 0x{2};securityModel: {3}", MessageId, _maxSize, _flags.ToHexString(), _securityModel);        }         /// <summary>        /// Gets or sets the size of the max.        /// </summary>        /// <value>The size of the max.</value>        public int MaxSize        {            get { return _maxSize.ToInt32(); }        }    }}