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# -*- coding: binary -*-
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module Msf
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###
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#
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# This module acts as a base for all handler pseudo-modules.  They aren't
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# really modules, so don't get the wrong idea champs!  They're merely
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# mixed into dynamically generated payloads to handle monitoring for
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# a connection.  Handlers are layered in between the base payload
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# class and any other payload class.  A super cool ASCII diagram would
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# look something like this
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#
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#      Module
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#        ^
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#        |
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#     Payload
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#        ^
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#        |
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#     Handler
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#        ^
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#        |
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#      Stager
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#        ^
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#        |
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#       Stage
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#
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###
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module Handler
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  ##
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  #
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  # Constants used with the ``handler'' method to indicate whether or not the
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  # connection was used.
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  #
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  ##
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  #
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  # Returned by handlers to indicate that a socket has been claimed for use
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  # by the payload.
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  #
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  Claimed = "claimed"
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  #
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  # Returned by handlers to indicate that a socket has not been claimed for
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  # use.
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  #
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  Unused  = "unused"
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  #
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  # Returns the handler type.
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  #
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  def self.handler_type
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    return "none"
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  end
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  #
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  # Returns the transport-independent handler type.
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  #
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  def self.general_handler_type
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    "none"
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  end
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  #
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  # Returns the handler's name, if any.
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  #
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  def handler_name
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    module_info['HandlerName']
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  end
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  #
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  # Initializes the session waiter event and other fun stuff.
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  #
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  def initialize(info = {})
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    super
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    # Initialize the pending_connections counter to 0
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    self.pending_connections = 0
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    # Initialize the sessions counter to 0
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    self.sessions = 0
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    # Create the waiter event with auto_reset set to false so that
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    # if a session is ever created, waiting on it returns immediately.
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    self.session_waiter_event = Rex::Sync::Event.new(false, false)
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  end
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  #
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  # Sets up the connection handler.
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  #
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  def setup_handler
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  end
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  #
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  # Terminates the connection handler.
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  #
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  def cleanup_handler
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  end
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  #
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  # Start monitoring for a connection.
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  #
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  def start_handler
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  end
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  #
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  # Start another connection monitor
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  #
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  def add_handler(opts={})
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  end
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  #
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  # Stop monitoring for a connection.
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  #
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  def stop_handler
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  end
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  #
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  # Checks to see if a payload connection has been established on
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  # the supplied connection.  This is necessary for find-sock style
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  # payloads.
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  #
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  def handler(sock)
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  end
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  #
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  # Handles an established connection supplied in the in and out
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  # handles.  The handles are passed as parameters in case this
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  # handler is capable of handling multiple simultaneous
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  # connections.  The default behavior is to attempt to create a session for
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  # the payload.  This path will not be taken for multi-staged payloads.
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  #
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  def handle_connection(conn, opts={})
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    create_session(conn, opts)
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  end
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  #
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  # The amount of time to wait for a session to come in.
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  #
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  def wfs_delay
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    2
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  end
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  #
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  # Waits for a session to be created as the result of a handler connection
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  # coming in.  The return value is a session object instance on success or
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  # nil if the timeout expires.
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  #
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  def wait_for_session(t = wfs_delay)
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    session = nil
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    begin
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      session = session_waiter_event.wait(t)
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    rescue ::Timeout::Error
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    end
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    # If a connection has arrived, wait longer...
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    if (pending_connections > 0)
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      session = session_waiter_event.wait
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    end
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    return session
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  end
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  #
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  # Interrupts a wait_for_session call by notifying with a nil event
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  #
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  def interrupt_wait_for_session
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    return unless session_waiter_event
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    session_waiter_event.notify(nil)
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  end
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  #
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  # Set by the exploit module to configure handler
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  #
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  attr_accessor :exploit_config
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  #
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  # This will be non-nil if the handler has a parent payload that it
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  # was spawned from.  Right now, this is only the case with generic
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  # payloads.  The parent payload is used to create a session
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  # rather than using the instance itself.
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  #
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  attr_accessor :parent_payload
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protected
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  #
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  # Creates a session, if necessary, for the connection that's been handled.
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  # Sessions are only created if the payload that's been mixed in has an
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  # associated session.
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  #
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  def create_session(conn, opts={})
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    # If there is a parent payload, then use that in preference.
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    return parent_payload.create_session(conn, opts) if (parent_payload)
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    # If the payload we merged in with has an associated session factory,
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    # allocate a new session.
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    if (self.session)
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      begin
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        # if there's a create_session method then use it, as this
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        # can form a factory for arb session types based on the
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        # payload.
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        if self.session.respond_to?('create_session')
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          s = self.session.create_session(conn, opts)
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        else
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          s = self.session.new(conn, opts)
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        end
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      rescue ::Exception => e
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        # We just wanna show and log the error, not trying to swallow it.
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        print_error("#{e.class} #{e.message}")
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        elog('Could not allocate a new Session.', error: e)
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        raise e
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      end
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      # Pass along the framework context
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      s.framework = framework
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      # Associate this system with the original exploit
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      # and any relevant information
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      s.set_from_exploit(assoc_exploit)
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      # set injected workspace value if db is active
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      if framework.db.active && wspace = framework.db.find_workspace(s.workspace)
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        framework.db.workspace = wspace
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      end
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      # Pass along any associated payload uuid if specified
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      if opts[:payload_uuid]
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        s.payload_uuid = opts[:payload_uuid]
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        s.payload_uuid.registered = false
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        if framework.db.active
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          payload_info = { uuid: s.payload_uuid.puid_hex, workspace: framework.db.workspace }
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          uuid_info = framework.db.payloads(payload_info).first
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        else
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          print_warning('Without a database connected that payload UUID tracking will not work!')
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        end
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        if s.payload_uuid.respond_to?(:puid_hex) && uuid_info
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          s.payload_uuid.registered = true
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          s.payload_uuid.name = uuid_info['name']
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          s.payload_uuid.timestamp = uuid_info['timestamp']
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        else
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          s.payload_uuid.registered = false
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        end
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      end
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      # If the session is valid, register it with the framework and
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      # notify any waiters we may have.
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      if (s)
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        # Defer the session registration to the Session Manager scheduler
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        registration = Proc.new do
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          register_session(s)
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        end
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        framework.sessions.schedule registration
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      end
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      return s
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    end
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    nil
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  end
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  #
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  # Registers a session with the framework and notifies any waiters of the
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  # new session.
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  #
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  def register_session(session)
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    # Register the session with the framework
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    framework.sessions.register(session)
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    # Call the handler's on_session() method
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    if session.respond_to?(:bootstrap)
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      session.bootstrap(datastore, self)
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      return unless session.alive
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    end
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    # Process the auto-run scripts for this session
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    if session.respond_to?(:process_autoruns)
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      session.process_autoruns(datastore)
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    end
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    # Tell the handler that we have a session
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    on_session(session)
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    # Notify the framework that we have a new session opening up...
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    # Don't let errant event handlers kill our session
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    begin
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      framework.events.on_session_open(session)
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    rescue ::Exception => e
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      wlog("Exception in on_session_open event handler: #{e.class}: #{e}")
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      wlog("Call Stack\n#{e.backtrace.join("\n")}")
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    end
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    # If there is an exploit associated with this payload, then let's notify
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    # anyone who is interested that this exploit succeeded
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    if assoc_exploit
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      framework.events.on_exploit_success(assoc_exploit, session)
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    end
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    # Notify waiters that they should be ready to rock
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    session_waiter_event.notify(session)
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    # Decrement the pending connections counter now that we've processed
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    # one session.
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    self.pending_connections -= 1
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    # Count the number of sessions we have registered
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    self.sessions += 1
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  end
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  attr_accessor :session_waiter_event # :nodoc:
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  attr_accessor :pending_connections  # :nodoc:
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  attr_accessor :sessions # :nodoc:
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end
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end
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