# Rekall Memory Forensics
# Copyright (C) 2007,2008 Volatile Systems
# Copyright (C) 2004,2005,2006 4tphi Research
# Copyright 2013 Google Inc. All Rights Reserved.
#
# Authors:
# {npetroni,awalters}@4tphi.net (Nick Petroni and AAron Walters)
# Michael Cohen <scudette@users.sourceforge.net>
# Mike Auty <mike.auty@gmail.com>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or (at
# your option) any later version.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
#

""" These are standard address spaces supported by Rekall Memory Forensics """
from future import standard_library
standard_library.install_aliases()
from builtins import object
import io
import struct
import os
import weakref

from rekall import addrspace
from rekall import config


config.DeclareOption(
    "-o", "--file_offset",
    type="IntParser", help="A Relative offset for image file.")


class FDAddressSpace(addrspace.BaseAddressSpace):
    """An address space which operated on a file like object."""

    __name = "filelike"

    # We should be first.
    order = 0

    def __init__(self, base=None, fhandle=None, **kwargs):
        self.as_assert(base == None, "Base passed to FDAddressSpace.")
        self.as_assert(fhandle is not None, 'file handle must be provided')

        self.fhandle = fhandle
        try:
            self.fhandle.seek(0, 2)
            self.fsize = self.fhandle.tell()
        except IOError:
            # We failed to seek to the end - this is usual with devices so we
            # assume they are volatile to be safe.
            self.fsize = 0
            self.volatile = True
            self.session.logging.warn(
                "Unable to determine file size, assuming file is volatile.")

        self.offset = 0

        super(FDAddressSpace, self).__init__(**kwargs)

    def read(self, addr, length):
        length = int(length)
        addr = int(addr)
        try:
            self.fhandle.seek(addr)
            data = self.fhandle.read(length)

            return data + addrspace.ZEROER.GetZeros(length - len(data))
        except (IOError, OverflowError):
            return addrspace.ZEROER.GetZeros(length)


    def read_long(self, addr):
        string = self.read(addr, 4)
        (longval,) = struct.unpack('=I', string)
        return longval

    def get_mappings(self, start=0, end=2**64):
        _ = end
        yield addrspace.Run(start=0, end=self.fsize,
                            file_offset=0, address_space=self)

    def is_valid_address(self, addr):
        if addr == None:
            return False
        return True

    def close(self):
        self.fhandle.close()

    def __eq__(self, other):
        return (self.__class__ == other.__class__ and
                self.fname == other.fname)


class FileAddressSpace(FDAddressSpace):
    """ This is a direct file AS.

    For this AS to be instantiated, we need

    1) A valid config.filename

    2) no one else has picked the AS before us

    3) base == None (we dont operate on anyone else so we need to be
    right at the bottom of the AS stack.)
    """

    __name = "file"

    # We should be the AS of last resort
    order = 100

    # This address space handles images.
    __image = True

    def __init__(self, base=None, filename=None, session=None, **kwargs):
        self.as_assert(base == None, 'Must be first Address Space')

        self.session = session
        path = filename or (session and session.GetParameter("filename"))
        self.as_assert(path, "Filename must be specified in session (e.g. "
                       "session.SetParameter('filename', 'MyFile.raw').")

        self.name = os.path.basename(path)
        self.fname = os.path.abspath(path)
        self.mode = 'rb'

        if path.startswith(r"\\\\.\\"):
            raise RuntimeError(
                "Unable to open a device without the win32file package "
                "installed.")

        try:
            fhandle = open(self.fname, self.mode)
        except (IOError, OSError) as e:
            raise addrspace.ASAssertionError("%s" % e)

        self._closer = weakref.ref(self, lambda x: fhandle.close())

        super(FileAddressSpace, self).__init__(
            fhandle=fhandle, session=session, **kwargs)


class GlobalOffsetAddressSpace(addrspace.RunBasedAddressSpace):
    """An address space to add a constant offset."""

    __image = True

    # Must come after all other address space.
    order = 120

    def __init__(self, **kwargs):
        super(GlobalOffsetAddressSpace, self).__init__(**kwargs)
        self.file_offset = self.session.GetParameter("file_offset")

        self.as_assert(self.file_offset, "File offset not specified.")
        self.as_assert(self.base.__class__ is not GlobalOffsetAddressSpace,
                       "Can not stack on GlobalOffsetAddressSpace")

        self.add_run(0, self.file_offset, self.base.end())


class WritableAddressSpaceMixIn(object):
    """This address space can be used to create new files.

    NOTE: This does not participate in voting or gets automatically
    selected. It can only be instantiated directly.
    """

    def write(self, addr, data):
        self.fhandle.seek(addr)
        self.fhandle.write(data)
        self.fhandle.flush()

        return len(data)

    def is_valid_address(self, unused_addr):
        # All addresses are valid, we just grow the file there.
        return True

    def end(self):
        self.fhandle.seek(0, 2)
        return self.fhandle.tell()

    def read(self, addr, length):
        try:
            # Just null pad the file - even if we read past the end.
            self.fhandle.seek(addr)
            data = self.fhandle.read(length)
        except OverflowError:
            data = b""

        if len(data) < length:
            data += addrspace.ZEROER.GetZeros(length - len(data))

        return data


class WritableAddressSpace(WritableAddressSpaceMixIn, FDAddressSpace):

    def __init__(self, filename=None, mode="w+b", **kwargs):
        self.as_assert(filename, "Filename must be specified.")
        self.name = os.path.abspath(filename)
        self.fname = self.name
        self.mode = mode

        fhandle = open(self.fname, self.mode)
        self._closer = weakref.ref(self, lambda x: fhandle.close())

        super(WritableAddressSpace, self).__init__(fhandle=fhandle, **kwargs)


class WritableFDAddressSpace(WritableAddressSpaceMixIn, FDAddressSpace):
    """An address space which can be initialized from a file handle.

    Note that file handle must be writable.
    """


class DummyAddressSpace(WritableAddressSpaceMixIn, FDAddressSpace):
    """An AS which always returns nulls."""
    __name = 'dummy'

    def __init__(self, size=10 * 1024, session=None, **_):
        super(DummyAddressSpace, self).__init__(
            session=session,
            fhandle=io.BytesIO(size * b"\x00"))

    def getvalue(self):
        """Dump the entire address space as a byte string."""
        return self.fhandle.getvalue()
