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# -*- coding: binary -*-
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module Rex
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module Proto
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##
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#
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# Minimal support for the newer Kademlia protocol, referred to here and often
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# elsewhere as Kademlia2.  It is unclear how this differs from the old protocol.
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#
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# Protocol details are hard to come by because most documentation is academic
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# in nature and glosses over the low-level network details.  The best
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# documents I found on the protocol are:
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#
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# http://gbmaster.wordpress.com/2013/05/05/botnets-surrounding-us-an-initial-focus-on-kad/
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# http://gbmaster.wordpress.com/2013/06/16/botnets-surrounding-us-sending-kademlia2_bootstrap_req-kademlia2_hello_req-and-their-strict-cousins/
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# http://gbmaster.wordpress.com/2013/11/23/botnets-surrounding-us-performing-requests-sending-out-kademlia2_req-and-asking-contact-where-art-thou/
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#
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##
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module Kademlia
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  # A simple Kademlia message
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  class Message
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    # The header that non-compressed Kad messages use
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    STANDARD_PACKET = 0xE4
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    # The header that compressed Kad messages use, which is currently unsupported
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    COMPRESSED_PACKET = 0xE5
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    # @return [Integer] the message type
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    attr_reader :type
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    # @return [String] the message body
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    attr_reader :body
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    # Construct a new Message from the provided type and body
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    #
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    # @param type [String] the message type
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    # @param body [String] the message body
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    def initialize(type, body = '')
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      @type = type
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      @body = body
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    end
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    # Construct a new Message from the provided data
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    #
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    # @param data [String] the data to interpret as a Kademlia message
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    # @return [Message] the message if valid, nil otherwise
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    def self.from_data(data)
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      return if data.length < 2
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      header, type = data.unpack('CC')
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      if header == COMPRESSED_PACKET
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        fail NotImplementedError, "Unable to handle #{data.length}-byte compressed Kademlia message"
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      end
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      return if header != STANDARD_PACKET
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      Message.new(type, data[2, data.length])
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    end
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    # Get this Message as a String
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    #
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    # @return [String] the string representation of this Message
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    def to_str
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      [STANDARD_PACKET, @type].pack('CC') + @body
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    end
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    # Compares this Message and another Message for equality
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    #
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    # @param other [Message] the Message to compare
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    # @return [Boolean] true iff the two messages have equal types and bodies, false otherwise
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    def ==(other)
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      type == other.type && body == other.body
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    end
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  end
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end
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end
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end
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