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# -*- coding: binary -*-
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require 'rex/post/meterpreter/inbound_packet_handler'
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module Rex
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module Post
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module Meterpreter
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#
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# The various types of channels
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#
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CHANNEL_CLASS_STREAM     = 1
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CHANNEL_CLASS_DATAGRAM   = 2
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CHANNEL_CLASS_POOL       = 3
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#
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# The various flags that can affect how the channel operates
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#
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#   CHANNEL_FLAG_SYNCHRONOUS
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#      Specifies that I/O requests on the channel are blocking.
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#
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#   CHANNEL_FLAG_COMPRESS
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#      Specifies that I/O requests on the channel have their data zlib compressed.
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#
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CHANNEL_FLAG_SYNCHRONOUS = (1 << 0)
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CHANNEL_FLAG_COMPRESS    = (1 << 1)
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#
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# The core types of direct I/O requests
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#
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CHANNEL_DIO_READ         = 'read'
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CHANNEL_DIO_WRITE        = 'write'
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CHANNEL_DIO_CLOSE        = 'close'
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###
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#
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# The channel class represents a logical data pipe that exists between the
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# client and the server.  The purpose and behavior of the channel depends on
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# which type it is.  The three basic types of channels are streams, datagrams,
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# and pools.  Streams are basically equivalent to a TCP connection.
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# Bidirectional, connection-oriented streams.  Datagrams are basically
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# equivalent to a UDP session.  Bidirectional, connectionless.  Pools are
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# basically equivalent to a uni-directional connection, like a file handle.
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# Pools denote channels that only have requests flowing in one direction.
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#
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###
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class Channel
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  # Class modifications to support global channel message
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  # dispatching without having to register a per-instance handler
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  class << self
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    include Rex::Post::Meterpreter::InboundPacketHandler
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    # Class request handler for all channels that dispatches requests
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    # to the appropriate class instance's DIO handler
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    def request_handler(client, packet)
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      cid = packet.get_tlv_value(TLV_TYPE_CHANNEL_ID)
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      # No channel identifier, then drop it
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      if cid.nil?
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        return false
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      end
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      channel = client.find_channel(cid)
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      # No valid channel context? The channel may not be registered yet
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      if channel.nil?
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        return false
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      end
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      dio = channel.dio_map(packet.method)
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      # Supported DIO request? Dump it.
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      if dio.nil?
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        return true
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      end
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      # Call the channel's dio handler and return success or fail
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      # based on what happens
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      channel.dio_handler(dio, packet)
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    end
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  end
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  ##
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  #
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  # Factory
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  #
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  ##
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  #
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  # Creates a logical channel between the client and the server
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  # based on a given type.
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  #
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  def Channel.create(client, type = nil, klass = nil,
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      flags = CHANNEL_FLAG_SYNCHRONOUS, addends = nil, **klass_kwargs)
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    request = Packet.create_request(COMMAND_ID_CORE_CHANNEL_OPEN)
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    # Set the type of channel that we're allocating
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    if !type.nil?
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      request.add_tlv(TLV_TYPE_CHANNEL_TYPE, type)
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    end
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    # If no factory class was provided, use the default native class
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    if klass.nil?
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      klass = self
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    end
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    request.add_tlv(TLV_TYPE_CHANNEL_CLASS, klass.cls)
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    request.add_tlv(TLV_TYPE_FLAGS, flags)
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    request.add_tlvs(addends)
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    # Transmit the request and wait for the response
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    cid = nil
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    begin
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      response = client.send_request(request)
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      cid = response.get_tlv_value(TLV_TYPE_CHANNEL_ID)
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      if cid.nil?
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        raise Rex::Post::Meterpreter::RequestError
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      end
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    end
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    # Create the channel instance
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    klass.new(client, cid, type, flags, response, **klass_kwargs)
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  end
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  ##
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  #
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  # Constructor
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  #
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  ##
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  #
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  # Initializes the instance's attributes, such as client context,
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  # class identifier, type, and flags.
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  #
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  def initialize(client, cid, type, flags, packet, **_)
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    self.client = client
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    self.cid    = cid
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    self.type   = type
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    self.flags  = flags
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    @mutex  = Mutex.new
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    # Add this instance to the list
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    if (cid and client)
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      client.add_channel(self)
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    end
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    # Ensure the remote object is closed when all references are removed
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    ObjectSpace.define_finalizer(self, self.class.finalize(client, cid))
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  end
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  def self.finalize(client, cid)
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    proc {
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      unless cid.nil?
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        deferred_close_proc = proc do
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          begin
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            self._close(client, cid)
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          rescue => e
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            elog("finalize method for Channel failed", error: e)
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          end
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        end
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        # Schedule the finalizing logic out-of-band; as this logic might be called in the context of a Signal.trap, which can't synchronize mutexes
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        client.framework.sessions.schedule(deferred_close_proc)
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      end
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    }
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  end
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  ##
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  #
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  # Channel interaction
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  #
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  ##
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  #
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  # Wrapper around the low-level channel read operation.
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  #
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  def read(length = nil, addends = nil)
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    return _read(length, addends)
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  end
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  #
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  # Reads data from the remote half of the channel.
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  #
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  def _read(length = nil, addends = nil)
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    if self.cid.nil?
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      raise IOError, "Channel has been closed.", caller
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    end
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    request = Packet.create_request(COMMAND_ID_CORE_CHANNEL_READ)
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    if length.nil?
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      # Default block size to a higher amount for passive dispatcher
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      length = self.client.passive_service ? (1024*1024) : 65536
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    end
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    request.add_tlv(TLV_TYPE_CHANNEL_ID, self.cid)
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    request.add_tlv(TLV_TYPE_LENGTH, length)
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    request.add_tlvs(addends)
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    begin
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      response = self.client.send_request(request)
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    rescue
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      return nil
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    end
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    # If the channel is in synchronous mode, the response should contain
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    # data that was read from the remote side of the channel
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    if (flag?(CHANNEL_FLAG_SYNCHRONOUS))
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      data = response.get_tlv(TLV_TYPE_CHANNEL_DATA);
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      if (data != nil)
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        return data.value
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      end
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    else
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      raise NotImplementedError, "Asynchronous channel mode is not implemented", caller
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    end
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    return nil
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  end
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  #
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  # Wrapper around the low-level write.
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  #
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  def write(buf, length = nil, addends = nil)
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    return _write(buf, length, addends)
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  end
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  #
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  # Writes data to the remote half of the channel.
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  #
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  def _write(buf, length = nil, addends = nil)
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    if self.cid.nil?
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      raise IOError, "Channel has been closed.", caller
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    end
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    request = Packet.create_request(COMMAND_ID_CORE_CHANNEL_WRITE)
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    # Truncation and celebration
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    if ((length != nil) &&
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        (buf.length >= length))
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      buf = buf[0..length]
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    else
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      length = buf.length
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    end
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    # Populate the request
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    request.add_tlv(TLV_TYPE_CHANNEL_ID, self.cid)
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    cdata = request.add_tlv(TLV_TYPE_CHANNEL_DATA, buf)
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    if( ( self.flags & CHANNEL_FLAG_COMPRESS ) == CHANNEL_FLAG_COMPRESS )
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      cdata.compress = true
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    end
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    request.add_tlv(TLV_TYPE_LENGTH, length)
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    request.add_tlvs(addends)
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    response = self.client.send_request(request)
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    written  = response.get_tlv(TLV_TYPE_LENGTH)
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    written.nil? ? 0 : written.value
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  end
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  #
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  # Wrapper around check for self.cid
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  #
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  def closed?
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    self.cid.nil?
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  end
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  #
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  # Wrapper around the low-level close.
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  #
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  def close(addends = nil)
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    return _close(addends)
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  end
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  #
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  # Close the channel for future writes.
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  #
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  def close_write
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    return _close
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  end
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  #
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  # Close the channel for future reads.
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  #
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  def close_read
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    return _close
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  end
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  #
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  # Closes the channel.
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  #
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  def self._close(client, cid, addends=nil)
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    if cid.nil?
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      raise IOError, "Channel has been closed.", caller
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    end
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    request = Packet.create_request(COMMAND_ID_CORE_CHANNEL_CLOSE)
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    # Populate the request
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    request.add_tlv(TLV_TYPE_CHANNEL_ID, cid)
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    request.add_tlvs(addends)
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    client.send_request(request, nil)
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    # Disassociate this channel instance
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    client.remove_channel(cid)
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    return true
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  end
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  def _close(addends = nil)
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    # let the finalizer do the work behind the scenes
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    @mutex.synchronize {
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      unless self.cid.nil?
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        ObjectSpace.undefine_finalizer(self)
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        self.class._close(self.client, self.cid, addends)
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        self.cid = nil
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      end
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    }
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  end
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  #
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  # Enables or disables interactive mode.
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  #
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  def interactive(tf = true, addends = nil)
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    if self.cid.nil?
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      raise IOError, "Channel has been closed.", caller
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    end
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    request = Packet.create_request(COMMAND_ID_CORE_CHANNEL_INTERACT)
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    # Populate the request
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    request.add_tlv(TLV_TYPE_CHANNEL_ID, self.cid)
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    request.add_tlv(TLV_TYPE_BOOL, tf)
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    request.add_tlvs(addends)
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    self.client.send_request(request)
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    return true
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  end
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  ##
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  #
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  # Direct I/O
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  #
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  ##
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  #
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  # Handles dispatching I/O requests based on the request packet.
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  # The default implementation does nothing with direct I/O requests.
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  #
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  def dio_handler(dio, packet)
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    if (dio == CHANNEL_DIO_READ)
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      length = packet.get_tlv_value(TLV_TYPE_LENGTH)
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      return dio_read_handler(packet, length)
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    elsif (dio == CHANNEL_DIO_WRITE)
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      data = packet.get_tlv_value(TLV_TYPE_CHANNEL_DATA)
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      return dio_write_handler(packet, data)
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    elsif (dio == CHANNEL_DIO_CLOSE)
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      return dio_close_handler(packet)
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    end
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    return false;
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  end
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  #
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  # Stub read handler.
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  #
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  def dio_read_handler(packet, length)
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    return true
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  end
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  #
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  # Stub write handler.
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  #
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  def dio_write_handler(packet, data)
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    return true
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  end
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  #
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  # Stub close handler.
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  #
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  def dio_close_handler(packet)
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    temp_cid = nil
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    @mutex.synchronize {
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      temp_cid = self.cid
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      self.cid = nil
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    }
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    client.remove_channel(temp_cid)
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    # Trap IOErrors as parts of the channel may have already been closed
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    begin
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      self.cleanup
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    rescue IOError
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    end
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    return true
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  end
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  #
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  # Maps packet request methods to DIO request identifiers on a
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  # per-instance basis as other instances may add custom dio
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  # handlers.
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  #
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  def dio_map(command_id)
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    if command_id == COMMAND_ID_CORE_CHANNEL_READ
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      return CHANNEL_DIO_READ
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    elsif command_id == COMMAND_ID_CORE_CHANNEL_WRITE
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      return CHANNEL_DIO_WRITE
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    elsif command_id == COMMAND_ID_CORE_CHANNEL_CLOSE
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      return CHANNEL_DIO_CLOSE
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    end
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    return nil
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  end
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  ##
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  #
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  # Conditionals
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  #
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  ##
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  #
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  # Checks to see if a flag is set on the instance's flags attribute.
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  #
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  def flag?(flag)
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    return ((self.flags & flag) == flag)
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  end
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  #
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  # Returns whether or not the channel is operating synchronously.
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  #
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  def synchronous?
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    return (self.flags & CHANNEL_FLAG_SYNCHRONOUS)
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  end
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  #
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  # The unique channel identifier.
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  #
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  attr_reader   :cid
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  #
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  # The type of channel.
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  #
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  attr_reader   :type
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  #
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  # The class of channel (stream, datagram, pool).
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  #
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  attr_reader   :cls
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  #
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  # Any channel-specific flag, like synchronous IO.
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  #
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  attr_reader   :flags
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  #
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  # Any channel-specific parameters.
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  #
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  attr_accessor :params
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  #
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  # The associated meterpreter client instance
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  #
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  attr_accessor :client
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protected
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  attr_writer   :cid, :type, :cls, :flags # :nodoc:
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  #
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  # Cleans up any lingering resources
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  #
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  def cleanup
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  end
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end
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end; end; end
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