ln.snmp/BasicEncodingRules.cs

// /**
//  * File: EncodingRules.cs
//  * Author: haraldwolff
//  *
//  * This file and it's content is copyrighted by the Author and / or copyright holder.
//  * Any use wihtout proper permission is illegal and may lead to legal actions.
//  *
//  *
//  **/
using System;
using System.IO;
using System.Net;
using System.Collections.Generic;
namespace ln.snmp
{
    public enum IdentifierClass : int
    {
        UNIVERSAL = 0,
        APPLICATION = 1,
        CONTEXT = 2,
        PRIVATE = 3
    }
    public struct Identifier
    {
        public IdentifierClass IdentifierClass;
        public bool Constructed;
        public ulong Number;

        public Identifier(IdentifierClass identifierClass, bool constructed, ulong number)
        {
            IdentifierClass = identifierClass;
            Constructed = constructed;
            Number = number;
        }

        public bool Is(IdentifierClass identifierClass, bool constructed, ulong number)
        {
            return ((IdentifierClass == identifierClass) && (Constructed == constructed) && (Number == number));
        }

        public byte Firstbyte
        {
            get
            {
                return (byte)(
                                        ((int)IdentifierClass << 6) |
                                        (Constructed ? 0x20 : 0x00) |
                                        (int)((Number < 31) ? Number : 0x1F)
                                    );
            }
        }

        public override string ToString()
        {
            return String.Format("[ASN.1 Type Class={0} Constructed={1} Number={2} FirstByte=0x{3,2:X}]",IdentifierClass,Constructed,Number,Firstbyte);
        }



    }

    public static class BasicEncodingRules
    {

        public static Identifier ReadIdentifier(Stream stream)
        {
            Identifier identifier = new Identifier();

            int b = stream.ReadByte();
            identifier.IdentifierClass = (IdentifierClass)((b >> 6) & 0x03);
            identifier.Constructed = (b & 0x20) != 0;
            identifier.Number = (ulong)(b & 0x1F);

            if (identifier.Number == 0x1F)
            {
                identifier.Number = 0;
                do
                {
                    b = stream.ReadByte();
                    if (b == -1)
                        throw new EndOfStreamException();

                    identifier.Number <<= 7;
                    identifier.Number |= ((uint)(b & 0x7F));
                } while ((b & 0x80) == 0x80);
            }

            return identifier;
        }

        public static void WriteIdentifier(Stream stream,Identifier identifier)
        {
            if (identifier.Number < 31)
            {
                byte bid = (byte)(
                        ((int)identifier.IdentifierClass << 6) |
                        ( identifier.Constructed ? 0x20 : 0x00) |
                        (int)identifier.Number
                    );
                stream.WriteByte(bid);
            }
            else
            {
                byte bid = (byte)(
                        ((int)identifier.IdentifierClass << 6) |
                        (identifier.Constructed ? 0x20 : 0x00) |
                        (int)0x1F
                    );
                stream.WriteByte(bid);
                byte[] n = EncodeInteger((long)identifier.Number);
                stream.Write(n, 0, n.Length);
            }
        }


        public static int ReadLength(Stream stream)
        {
            int b = stream.ReadByte();
            if ((b & 0x80) == 0)
            {
                return b;
            }

            b &= 0x7F;
            int length = 0;

            for (int n=0;n<b;n++)
            {
                length <<= 8;
                length |= stream.ReadByte();
            }
            return length;
        }
        public static void WriteLength(Stream stream,int length)
        {
            if (length < 128)
            {
                stream.WriteByte((byte)length);
            }
            else
            {
                byte[] bytes = BitConverter.GetBytes(length);
                int n;
                for (n = 3; n > 0 && bytes[n] == 0; n--) { }
                n++;
                byte[] finalbytes = new byte[n];
                Array.Copy(bytes, finalbytes, n);

                byte bl = (byte)(0x80 | finalbytes.Length);
                stream.WriteByte(bl);
                stream.Write(finalbytes, 0, finalbytes.Length);
            }

        }

        public static byte[] EncodeInteger(long i)
        {
            byte[] bits = BitConverter.GetBytes(i);
            int n = bits.Length;
            while (
                (n > 1) && (
                    ((bits[n-1] == 0xFF) && ((bits[n - 2] & 0x80) == 0x80)) ||
                    ((bits[n-1] == 0x00) && ((bits[n - 2] & 0x80) == 0x00))
                )
            )
            {
                n--;
            }

            if (n == 8)
            {
                Array.Reverse(bits);
                return bits;
            }
            else
            {
                byte[] encodedbits = new byte[n];
                Array.Copy(bits, encodedbits, n);
                Array.Reverse(encodedbits);
                return encodedbits;
            }
        }
        public static long DecodeInteger(byte[] bits)
        {
            byte[] decodedbits = bits;
            if (bits.Length < 8)
            {
                decodedbits = new byte[8];
                Array.Copy(bits, decodedbits, bits.Length);
                byte fill = (byte)(((bits[bits.Length - 1] & 0x80) == 0x80) ? 0xFF : 0x00);
                for (int n=bits.Length;n<8;n++)
                {
                    decodedbits[n] = fill;
                }
            }
            return BitConverter.ToInt64(decodedbits,0);
        }


        public static int[] DecodeOID(byte[] bytes)
        {
            List<int> oid = new List<int>();

            MemoryStream memoryStream = new MemoryStream(bytes);
            int b = memoryStream.ReadByte();
            int e = 0;

            oid.Add(b / 40);
            oid.Add(b % 40);

            while (memoryStream.Position < memoryStream.Length)
            {
                e = 0;
                do
                {
                    b = memoryStream.ReadByte();
                    e <<= 7;
                    e |= (ushort)(b & 0x7F);

                    if ((b & 0x80) == 0x00)
                    {
                        oid.Add(e);
                        e = 0;
                    }
                }
                while ((b & 0x80) == 0x80);
            }

            return oid.ToArray();
        }
        public static byte[] EncodeOID(int[] oid)
        {
            MemoryStream memoryStream = new MemoryStream();
            byte pseudo = (byte)( (oid[0] * 40) + oid[1] );
            memoryStream.WriteByte(pseudo);

            for (int n = 2; n < oid.Length; n++)
            {
                int e = oid[n];

                if (e < 128)
                {
                    memoryStream.WriteByte((byte)e);
                }
                else
                {
                    List<byte> bytes = new List<byte>();
                    bytes.Add((byte)(e & 0x7f));

                    while (e > 127)
                    {
                        e >>= 7;
                        bytes.Add((byte)(0x80 | (e & 0x7f)));
                    }
                    bytes.Reverse();

                    memoryStream.Write(bytes.ToArray(), 0, bytes.Count);
                }
            }

            return memoryStream.ToArray();
        }


    }
}