Bencoding implementation

gistfile1.rb

require 'stringio'

module EM::Bittorrent
  module Benc
    def self.decode(input)
      Stream.new(input).decode
    end

    class Stream
      def initialize(input)
        if input.is_a?(String)
          @io = ::StringIO.new(input)
        elsif input.is_a?(StringIO)
          @io = input
        elsif input.is_a?(File)
          @io = input
        else
          raise ArgumentError.new "You must supply either a String or an IO object as input"
        end
      end

      def decode
        begin
          @c = @io.getc
          if @c == ?i
            decode_int
          elsif @c == ?l
            decode_array
          elsif @c == ?d
            decode_hash
          elsif @c =~ /[0-9]/
            decode_string
          else # 'e' - end of element
            nil
          end
        rescue TypeError
          puts "Died at character #{@c}, position #{@io.pos}"
          raise
        end
      end

      private

      def decode_string
        ::String.new.tap do |str|
          len = ::String.new
          len << @c
          until ((@c = @io.getc) == ?:)
            len << @c
          end
          str << @io.read(len.to_i)
        end
      end

      def decode_int
        ::String.new.tap do |str|
          until ((@c = @io.getc) == ?e)
            str << @c
          end
        end.to_i
      end

      def decode_array
        ::Array.new.tap do |array|
          while (value = decode)
            array << value
          end
        end
      end

      def decode_hash
        ::Hash.new.tap do |hash|
          while (key = decode)
            value = decode
            hash[key] = value
          end
        end
      end
    end

    module Symbol
      def to_benc
        self.to_s.to_benc
      end
    end

    module String
      def to_benc
        self.class.new.tap do |s|
          s << self.length.to_s
          s << ?:
          s << self
        end
      end
    end

    module Integer
      def to_benc
        ::String.new.tap do |s|
          s << ?i
          s << self.to_s
          s << ?e
        end
      end
    end

    module Array
      def to_benc
        ::String.new.tap do |s|
          s << ?l
          self.each do |item|
            s << item.to_benc
          end
          s << ?e
        end
      end
    end

    module Hash
      def to_benc
        ::String.new.tap do |s|
          s << ?d
          self.each do |k, v|
            s << k.to_benc
            s << v.to_benc
          end
          s << ?e
        end
      end
    end
  end
end

Symbol.send(:include, EM::Bittorrent::Benc::Symbol)
String.send(:include, EM::Bittorrent::Benc::String)
Integer.send(:include, EM::Bittorrent::Benc::Integer)
Array.send(:include, EM::Bittorrent::Benc::Array)
Hash.send(:include, EM::Bittorrent::Benc::Hash)