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SuprDewd on 07/23/10

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Last Edited at 07/23/10 09:46am

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Bencoding encoder and decoder

/ Published in: C#

For those having trouble with encoding and decoding bencode, here is something to help you.

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/*****
     * Encoding usage:
     * 
     * new BDictionary()
     * {
     *  {"Some Key", "Some Value"},
     *  {"Another Key", 42}
     * }.ToBencodedString();
     * 
     * Decoding usage:
     * 
     * BencodeDecoder.Decode("d8:Some Key10:Some Value13:Another Valuei42ee");
     * 
     * Feel free to use it.
     * More info about Bencoding at http://wiki.theory.org/BitTorrentSpecification#bencoding
     * 
     * Originally posted at http://snipplr.com/view/37790/ by SuprDewd.
     * */

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Bencoding
{
   	/// <summary>
	/// A class used for decoding Bencoding.
	/// </summary>
	public static class BencodeDecoder
	{
		/// <summary>
		/// Decodes the string.
		/// </summary>
		/// <param name="bencodedString">The bencoded string.</param>
		/// <returns>An array of root elements.</returns>
		public static BElement[] Decode(string bencodedString)
		{
			int index = 0;

try
			{
				if (bencodedString == null) return null;

List<BElement> rootElements = new List<BElement>();
				while (bencodedString.Length > index)
				{
					rootElements.Add(ReadElement(ref bencodedString, ref index));
				}

return rootElements.ToArray();
			}
			catch (BencodingException) { throw; }
			catch (Exception e) { throw Error(e); }
		}

private static BElement ReadElement(ref string bencodedString, ref int index)
		{
			switch (bencodedString[index])
			{
				case '0':
				case '1':
				case '2':
				case '3':
				case '4':
				case '5':
				case '6':
				case '7':
				case '8':
				case '9': return ReadString(ref bencodedString, ref index);
				case 'i': return ReadInteger(ref bencodedString, ref index);
				case 'l': return ReadList(ref bencodedString, ref index);
				case 'd': return ReadDictionary(ref bencodedString, ref index);
				default: throw Error();
			}
		}

private static BDictionary ReadDictionary(ref string bencodedString, ref int index)
		{
			index++;
			BDictionary dict = new BDictionary();

try
			{
				while (bencodedString[index] != 'e')
				{
					BString K = ReadString(ref bencodedString, ref index);
					BElement V = ReadElement(ref bencodedString, ref index);
					dict.Add(K, V);
				}
			}
			catch (BencodingException) { throw; }
			catch (Exception e) { throw Error(e); }

index++;
			return dict;
		}

private static BList ReadList(ref string bencodedString, ref int index)
		{
			index++;
			BList lst = new BList();

try
			{
				while (bencodedString[index] != 'e')
				{
					lst.Add(ReadElement(ref bencodedString, ref index));
				}
			}
			catch (BencodingException) { throw; }
			catch (Exception e) { throw Error(e); }

index++;
			return lst;
		}

private static BInteger ReadInteger(ref string bencodedString, ref int index)
		{
			index++;

int end = bencodedString.IndexOf('e', index);
			if (end == -1) throw Error();

long integer;

try
			{
				integer = Convert.ToInt64(bencodedString.Substring(index, end - index));
				index = end + 1;
			}
			catch (Exception e) { throw Error(e); }

return new BInteger(integer);
		}

private static BString ReadString(ref string bencodedString, ref int index)
		{
			int length, colon;

try
			{
				colon = bencodedString.IndexOf(':', index);
				if (colon == -1) throw Error();
				length = Convert.ToInt32(bencodedString.Substring(index, colon - index));
			}
			catch (Exception e) { throw Error(e); }

index = colon + 1;
			int tmpIndex = index;
			index += length;

try
			{
				return new BString(bencodedString.Substring(tmpIndex, length));
			}
			catch (Exception e) { throw Error(e); }
		}

private static Exception Error(Exception e)
		{
			return new BencodingException("Bencoded string invalid.", e);
		}

private static Exception Error()
		{
			return new BencodingException("Bencoded string invalid.");
		}
	}

/// <summary>
	/// An interface for bencoded elements.
	/// </summary>
	public interface BElement
	{
		/// <summary>
		/// Generates the bencoded equivalent of the element.
		/// </summary>
		/// <returns>The bencoded equivalent of the element.</returns>
		string ToBencodedString();

/// <summary>
		/// Generates the bencoded equivalent of the element.
		/// </summary>
		/// <param name="u">The StringBuilder to append to.</param>
		/// <returns>The bencoded equivalent of the element.</returns>
		StringBuilder ToBencodedString(StringBuilder u);
	}

/// <summary>
	/// A bencode integer.
	/// </summary>
	public class BInteger : BElement, IComparable<BInteger>
	{
		/// <summary>
		/// Allows you to set an integer to a BInteger.
		/// </summary>
		/// <param name="i">The integer.</param>
		/// <returns>The BInteger.</returns>
		public static implicit operator BInteger(int i)
		{
			return new BInteger(i);
		}

/// <summary>
		/// The value of the bencoded integer.
		/// </summary>
		public long Value { get; set; }

/// <summary>
		/// The main constructor.
		/// </summary>
		/// <param name="value">The value of the bencoded integer.</param>
		public BInteger(long value)
		{
			this.Value = value;
		}

/// <summary>
		/// Generates the bencoded equivalent of the integer.
		/// </summary>
		/// <returns>The bencoded equivalent of the integer.</returns>
		public string ToBencodedString()
		{
			return this.ToBencodedString(new StringBuilder()).ToString();
		}

/// <summary>
		/// Generates the bencoded equivalent of the integer.
		/// </summary>
		/// <returns>The bencoded equivalent of the integer.</returns>
		public StringBuilder ToBencodedString(StringBuilder u)
		{
			if (u == null) u = new StringBuilder('i');
			else u.Append('i');
			return u.Append(Value.ToString()).Append('e');
		}

/// <see cref="Object.GetHashCode()"/>
		public override int GetHashCode()
		{
			return this.Value.GetHashCode();
		}

/// <summary>
		/// Int32.Equals(object)
		/// </summary>
		public override bool Equals(object obj)
		{
			try
			{
				return this.Value.Equals(((BInteger)obj).Value);
			}
			catch { return false; }
		}

/// <see cref="Object.ToString()"/>
		public override string ToString()
		{
			return this.Value.ToString();
		}

/// <see cref="IComparable.CompareTo(object)"/>
		public int CompareTo(BInteger other)
		{
			return this.Value.CompareTo(other.Value);
		}
	}

/// <summary>
	/// A bencode string.
	/// </summary>
	public class BString : BElement, IComparable<BString>
	{
		/// <summary>
		/// Allows you to set a string to a BString.
		/// </summary>
		/// <param name="s">The string.</param>
		/// <returns>The BString.</returns>
		public static implicit operator BString(string s)
		{
			return new BString(s);
		}

/// <summary>
		/// The value of the bencoded integer.
		/// </summary>
		public string Value { get; set; }

/// <summary>
		/// The main constructor.
		/// </summary>
		/// <param name="value"></param>
		public BString(string value)
		{
			this.Value = value;
		}

/// <summary>
		/// Generates the bencoded equivalent of the string.
		/// </summary>
		/// <returns>The bencoded equivalent of the string.</returns>
		public string ToBencodedString()
		{
			return this.ToBencodedString(new StringBuilder()).ToString();
		}

/// <summary>
		/// Generates the bencoded equivalent of the string.
		/// </summary>
		/// <param name="u">The StringBuilder to append to.</param>
		/// <returns>The bencoded equivalent of the string.</returns>
		public StringBuilder ToBencodedString(StringBuilder u)
		{
			if (u == null) u = new StringBuilder(this.Value.Length);
			else u.Append(this.Value.Length);
			return u.Append(':').Append(this.Value);
		}

/// <see cref="Object.GetHashCode()"/>
		public override int GetHashCode()
		{
			return this.Value.GetHashCode();
		}

/// <summary>
		/// String.Equals(object)
		/// </summary>
		public override bool Equals(object obj)
		{
			try
			{
				return this.Value.Equals(((BString)obj).Value);
			}
			catch { return false; }
		}

/// <see cref="Object.ToString()"/>
		public override string ToString()
		{
			return this.Value.ToString();
		}

/// <see cref="IComparable.CompareTo(Object)"/>
		public int CompareTo(BString other)
		{
			return this.Value.CompareTo(other.Value);
		}
	}

/// <summary>
	/// A bencode list.
	/// </summary>
	public class BList : List<BElement>, BElement
	{
		/// <summary>
		/// Generates the bencoded equivalent of the list.
		/// </summary>
		/// <returns>The bencoded equivalent of the list.</returns>
		public string ToBencodedString()
		{
			return this.ToBencodedString(new StringBuilder()).ToString();
		}

/// <summary>
		/// Generates the bencoded equivalent of the list.
		/// </summary>
		/// <param name="u">The StringBuilder to append to.</param>
		/// <returns>The bencoded equivalent of the list.</returns>
		public StringBuilder ToBencodedString(StringBuilder u)
		{
			if (u == null) u = new StringBuilder('l');
			else u.Append('l');

foreach (BElement element in base.ToArray())
			{
				element.ToBencodedString(u);
			}

return u.Append('e');
		}

/// <summary>
		/// Adds the specified value to the list.
		/// </summary>
		/// <param name="value">The specified value.</param>
		public void Add(string value)
		{
			base.Add(new BString(value));
		}

/// <summary>
		/// Adds the specified value to the list.
		/// </summary>
		/// <param name="value">The specified value.</param>
		public void Add(int value)
		{
			base.Add(new BInteger(value));
		}
	}

/// <summary>
	/// A bencode dictionary.
	/// </summary>
	public class BDictionary : SortedDictionary<BString, BElement>, BElement
	{
		/// <summary>
		/// Generates the bencoded equivalent of the dictionary.
		/// </summary>
		/// <returns>The bencoded equivalent of the dictionary.</returns>
		public string ToBencodedString()
		{
			return this.ToBencodedString(new StringBuilder()).ToString();
		}

/// <summary>
		/// Generates the bencoded equivalent of the dictionary.
		/// </summary>
		/// <param name="u">The StringBuilder to append to.</param>
		/// <returns>The bencoded equivalent of the dictionary.</returns>
		public StringBuilder ToBencodedString(StringBuilder u)
		{
			if (u == null) u = new StringBuilder('d');
			else u.Append('d');

for (int i = 0; i < base.Count; i++)
			{
				base.Keys.ElementAt(i).ToBencodedString(u);
				base.Values.ElementAt(i).ToBencodedString(u);
			}

return u.Append('e');
		}

/// <summary>
		/// Adds the specified key-value pair to the dictionary.
		/// </summary>
		/// <param name="key">The specified key.</param>
		/// <param name="value">The specified value.</param>
		public void Add(string key, BElement value)
		{
			base.Add(new BString(key), value);
		}

/// <summary>
		/// Adds the specified key-value pair to the dictionary.
		/// </summary>
		/// <param name="key">The specified key.</param>
		/// <param name="value">The specified value.</param>
		public void Add(string key, string value)
		{
			base.Add(new BString(key), new BString(value));
		}

/// <summary>
		/// Adds the specified key-value pair to the dictionary.
		/// </summary>
		/// <param name="key">The specified key.</param>
		/// <param name="value">The specified value.</param>
		public void Add(string key, int value)
		{
			base.Add(new BString(key), new BInteger(value));
		}

/// <summary>
		/// Gets or sets the value assosiated with the specified key.
		/// </summary>
		/// <param name="key">The key of the value to get or set.</param>
		/// <returns>The value assosiated with the specified key.</returns>
		public BElement this[string key]
		{
			get
			{
				return this[new BString(key)];
			}
			set
			{
				this[new BString(key)] = value;
			}
		}
	}

/// <summary>
	/// A bencoding exception.
	/// </summary>
	public class BencodingException : FormatException
	{
		/// <summary>
		/// Creates a new BencodingException.
		/// </summary>
		public BencodingException() { }

/// <summary>
		/// Creates a new BencodingException.
		/// </summary>
		/// <param name="message">The message.</param>
		public BencodingException(string message) : base(message) { }

/// <summary>
		/// Creates a new BencodingException.
		/// </summary>
		/// <param name="message">The message.</param>
		/// <param name="inner">The inner exception.</param>
		public BencodingException(string message, Exception inner) : base(message, inner) { }
	}

/// <summary>
	/// A class with extension methods for use with Bencoding.
	/// </summary>
	public static class BencodingExtensions
	{
		/// <summary>
		/// Decode the current instance.
		/// </summary>
		/// <param name="s">The current instance.</param>
		/// <returns>The root elements of the decoded string.</returns>
		public static BElement[] BDecode(this string s)
		{
			return BencodeDecoder.Decode(s);
		}
	}
}

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