Add a copy of blendfile.py API from BAM repository (WARNING! Please keep in sync!)

This is a (still not complete) python module able to read and write a .blend file.

utils/blendfile.py

+# ***** BEGIN GPL LICENSE BLOCK *****
+#
+# 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.
+#
+# ***** END GPL LICENCE BLOCK *****
+#
+# (c) 2009, At Mind B.V. - Jeroen Bakker
+# (c) 2014, Blender Foundation - Campbell Barton
+
+import os
+import struct
+import logging
+import gzip
+import tempfile
+
+log = logging.getLogger("blendfile")
+log.setLevel(logging.ERROR)
+
+FILE_BUFFER_SIZE = 1024 * 1024
+
+
+# -----------------------------------------------------------------------------
+# module global routines
+#
+# read routines
+# open a filename
+# determine if the file is compressed
+# and returns a handle
+def open_blend(filename, access="rb"):
+    """Opens a blend file for reading or writing pending on the access
+    supports 2 kind of blend files. Uncompressed and compressed.
+    Known issue: does not support packaged blend files
+    """
+    handle = open(filename, access)
+    magic_test = b"BLENDER"
+    magic = handle.read(len(magic_test))
+    if magic == magic_test:
+        log.debug("normal blendfile detected")
+        handle.seek(0, os.SEEK_SET)
+        bfile = BlendFile(handle)
+        bfile.is_compressed = False
+        bfile.filepath_orig = filename
+        return bfile
+    elif magic[:2] == b'\x1f\x8b':
+        log.debug("gzip blendfile detected")
+        handle.close()
+        log.debug("decompressing started")
+        fs = gzip.open(filename, "rb")
+        data = fs.read(FILE_BUFFER_SIZE)
+        magic = data[:len(magic_test)]
+        if magic == magic_test:
+            handle = tempfile.TemporaryFile()
+            while data:
+                handle.write(data)
+                data = fs.read(FILE_BUFFER_SIZE)
+            log.debug("decompressing finished")
+            fs.close()
+            log.debug("resetting decompressed file")
+            handle.seek(os.SEEK_SET, 0)
+            bfile = BlendFile(handle)
+            bfile.is_compressed = True
+            bfile.filepath_orig = filename
+            return bfile
+        else:
+            raise Exception("filetype inside gzip not a blend")
+    else:
+        raise Exception("filetype not a blend or a gzip blend")
+
+
+def align(offset, by):
+    n = by - 1
+    return (offset + n) & ~n
+
+
+# -----------------------------------------------------------------------------
+# module classes
+
+
+class BlendFile:
+    """
+    Blend file.
+    """
+    __slots__ = (
+        # file (result of open())
+        "handle",
+        # str (original name of the file path)
+        "filepath_orig",
+        # BlendFileHeader
+        "header",
+        # struct.Struct
+        "block_header_struct",
+        # BlendFileBlock
+        "blocks",
+        # [DNAStruct, ...]
+        "structs",
+        # dict {b'StructName': sdna_index}
+        # (where the index is an index into 'structs')
+        "sdna_index_from_id",
+        # dict {addr_old: block}
+        "block_from_offset",
+        # int
+        "code_index",
+        # bool (did we make a change)
+        "is_modified",
+        # bool (is file gzipped)
+        "is_compressed",
+        )
+
+    def __init__(self, handle):
+        log.debug("initializing reading blend-file")
+        self.handle = handle
+        self.header = BlendFileHeader(handle)
+        self.block_header_struct = self.header.create_block_header_struct()
+        self.blocks = []
+        self.code_index = {}
+
+        block = BlendFileBlock(handle, self)
+        while block.code != b'ENDB':
+            if block.code == b'DNA1':
+                (self.structs,
+                 self.sdna_index_from_id,
+                 ) = BlendFile.decode_structs(self.header, block, handle)
+            else:
+                handle.seek(block.size, os.SEEK_CUR)
+
+            self.blocks.append(block)
+            self.code_index.setdefault(block.code, []).append(block)
+
+            block = BlendFileBlock(handle, self)
+        self.is_modified = False
+        self.blocks.append(block)
+
+        # cache (could lazy init, incase we never use?)
+        self.block_from_offset = {block.addr_old: block for block in self.blocks if block.code != b'ENDB'}
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, type, value, traceback):
+        self.close()
+
+    def find_blocks_from_code(self, code):
+        assert(type(code) == bytes)
+        if code not in self.code_index:
+            return []
+        return self.code_index[code]
+
+    def find_block_from_offset(self, offset):
+        # same as looking looping over all blocks,
+        # then checking ``block.addr_old == offset``
+        assert(type(offset) is int)
+        return self.block_from_offset.get(offset)
+
+    def close(self):
+        """
+        Close the blend file
+        writes the blend file to disk if changes has happened
+        """
+        if not self.is_modified:
+            self.handle.close()
+        else:
+            handle = self.handle
+            if self.is_compressed:
+                log.debug("close compressed blend file")
+                handle.seek(os.SEEK_SET, 0)
+                log.debug("compressing started")
+                fs = gzip.open(self.filepath_orig, "wb")
+                data = handle.read(FILE_BUFFER_SIZE)
+                while data:
+                    fs.write(data)
+                    data = handle.read(FILE_BUFFER_SIZE)
+                fs.close()
+                log.debug("compressing finished")
+
+            handle.close()
+
+    def ensure_subtype_smaller(self, sdna_index_curr, sdna_index_next):
+        # never refine to a smaller type
+        if (self.structs[sdna_index_curr].size >
+            self.structs[sdna_index_next].size):
+
+            raise RuntimeError("cant refine to smaller type (%s -> %s)" %
+                               (self.structs[sdna_index_curr].dna_type_id.decode('ascii'),
+                                self.structs[sdna_index_next].dna_type_id.decode('ascii')))
+
+    @staticmethod
+    def decode_structs(header, block, handle):
+        """
+        DNACatalog is a catalog of all information in the DNA1 file-block
+        """
+        log.debug("building DNA catalog")
+        shortstruct = DNA_IO.USHORT[header.endian_index]
+        shortstruct2 = struct.Struct(header.endian_str + b'HH')
+        intstruct = DNA_IO.UINT[header.endian_index]
+
+        data = handle.read(block.size)
+        types = []
+        names = []
+
+        structs = []
+        sdna_index_from_id = {}
+
+        offset = 8
+        names_len = intstruct.unpack_from(data, offset)[0]
+        offset += 4
+
+        log.debug("building #%d names" % names_len)
+        for i in range(names_len):
+            tName = DNA_IO.read_data0_offset(data, offset)
+            offset = offset + len(tName) + 1
+            names.append(DNAName(tName))
+        del names_len
+
+        offset = align(offset, 4)
+        offset += 4
+        types_len = intstruct.unpack_from(data, offset)[0]
+        offset += 4
+        log.debug("building #%d types" % types_len)
+        for i in range(types_len):
+            dna_type_id = DNA_IO.read_data0_offset(data, offset)
+            # None will be replaced by the DNAStruct, below
+            types.append(DNAStruct(dna_type_id))
+            offset += len(dna_type_id) + 1
+
+        offset = align(offset, 4)
+        offset += 4
+        log.debug("building #%d type-lengths" % types_len)
+        for i in range(types_len):
+            tLen = shortstruct.unpack_from(data, offset)[0]
+            offset = offset + 2
+            types[i].size = tLen
+        del types_len
+
+        offset = align(offset, 4)
+        offset += 4
+
+        structs_len = intstruct.unpack_from(data, offset)[0]
+        offset += 4
+        log.debug("building #%d structures" % structs_len)
+        for sdna_index in range(structs_len):
+            d = shortstruct2.unpack_from(data, offset)
+            struct_type_index = d[0]
+            offset += 4
+            dna_struct = types[struct_type_index]
+            sdna_index_from_id[dna_struct.dna_type_id] = sdna_index
+            structs.append(dna_struct)
+
+            fields_len = d[1]
+            dna_offset = 0
+
+            for field_index in range(fields_len):
+                d2 = shortstruct2.unpack_from(data, offset)
+                field_type_index = d2[0]
+                field_name_index = d2[1]
+                offset += 4
+                dna_type = types[field_type_index]
+                dna_name = names[field_name_index]
+                if dna_name.is_pointer or dna_name.is_method_pointer:
+                    dna_size = header.pointer_size * dna_name.array_size
+                else:
+                    dna_size = dna_type.size * dna_name.array_size
+
+                field = DNAField(dna_type, dna_name, dna_size, dna_offset)
+                dna_struct.fields.append(field)
+                dna_struct.field_from_name[dna_name.name_only] = field
+                dna_offset += dna_size
+
+        return structs, sdna_index_from_id
+
+
+class BlendFileBlock:
+    """
+    Instance of a struct.
+    """
+    __slots__ = (
+        # BlendFile
+        "file",
+        "code",
+        "size",
+        "addr_old",
+        "sdna_index",
+        "count",
+        "file_offset",
+        "user_data",
+        )
+
+    def __str__(self):
+        return ("<%s.%s (%s), size=%d at %s>" %
+                # fields=[%s]
+                (self.__class__.__name__,
+                 self.dna_type.dna_type_id.decode('ascii'),
+                 self.code.decode(),
+                 self.size,
+                 # b", ".join(f.dna_name.name_only for f in self.dna_type.fields).decode('ascii'),
+                 hex(self.addr_old),
+                 ))
+
+    def __init__(self, handle, bfile):
+        OLDBLOCK = struct.Struct(b'4sI')
+
+        self.file = bfile
+        self.user_data = None
+
+        data = handle.read(bfile.block_header_struct.size)
+        # header size can be 8, 20, or 24 bytes long
+        # 8: old blend files ENDB block (exception)
+        # 20: normal headers 32 bit platform
+        # 24: normal headers 64 bit platform
+        if len(data) > 15:
+
+            blockheader = bfile.block_header_struct.unpack(data)
+            self.code = blockheader[0].partition(b'\0')[0]
+            if self.code != b'ENDB':
+                self.size = blockheader[1]
+                self.addr_old = blockheader[2]
+                self.sdna_index = blockheader[3]
+                self.count = blockheader[4]
+                self.file_offset = handle.tell()
+            else:
+                self.size = 0
+                self.addr_old = 0
+                self.sdna_index = 0
+                self.count = 0
+                self.file_offset = 0
+        else:
+            blockheader = OLDBLOCK.unpack(data)
+            self.code = blockheader[0].partition(b'\0')[0]
+            self.code = DNA_IO.read_data0(blockheader[0])
+            self.size = 0
+            self.addr_old = 0
+            self.sdna_index = 0
+            self.count = 0
+            self.file_offset = 0
+
+    @property
+    def dna_type(self):
+        return self.file.structs[self.sdna_index]
+
+    def refine_type_from_index(self, sdna_index_next):
+        assert(type(sdna_index_next) is int)
+        sdna_index_curr = self.sdna_index
+        self.file.ensure_subtype_smaller(sdna_index_curr, sdna_index_next)
+        self.sdna_index = sdna_index_next
+
+    def refine_type(self, dna_type_id):
+        assert(type(dna_type_id) is bytes)
+        self.refine_type_from_index(self.file.sdna_index_from_id[dna_type_id])
+
+    def get_file_offset(self, path,
+            default=...,
+            sdna_index_refine=None,
+            base_index=0,
+            ):
+        """
+        Return (offset, length)
+        """
+        assert(type(path) is bytes)
+
+        ofs = self.file_offset
+        if base_index != 0:
+            assert(base_index < self.count)
+            ofs += (self.size // self.count) * base_index
+        self.file.handle.seek(ofs, os.SEEK_SET)
+
+        if sdna_index_refine is None:
+            sdna_index_refine = self.sdna_index
+        else:
+            self.file.ensure_subtype_smaller(self.sdna_index, sdna_index_refine)
+
+        dna_struct = self.file.structs[sdna_index_refine]
+        field = dna_struct.field_from_path(
+                self.file.header, self.file.handle, path)
+
+        return (self.file.handle.tell(), field.dna_name.array_size)
+
+    def get(self, path,
+            default=...,
+            sdna_index_refine=None,
+            use_nil=True, use_str=True,
+            base_index=0,
+            ):
+
+        ofs = self.file_offset
+        if base_index != 0:
+            assert(base_index < self.count)
+            ofs += (self.size // self.count) * base_index
+        self.file.handle.seek(ofs, os.SEEK_SET)
+
+        if sdna_index_refine is None:
+            sdna_index_refine = self.sdna_index
+        else:
+            self.file.ensure_subtype_smaller(self.sdna_index, sdna_index_refine)
+
+        dna_struct = self.file.structs[sdna_index_refine]
+        return dna_struct.field_get(
+                self.file.header, self.file.handle, path,
+                default=default,
+                use_nil=use_nil, use_str=use_str,
+                )
+
+    def set(self, path, value,
+            sdna_index_refine=None,
+            ):
+
+        if sdna_index_refine is None:
+            sdna_index_refine = self.sdna_index
+        else:
+            self.file.ensure_subtype_smaller(self.sdna_index, sdna_index_refine)
+
+        dna_struct = self.file.structs[sdna_index_refine]
+        self.file.handle.seek(self.file_offset, os.SEEK_SET)
+        self.file.is_modified = True
+        return dna_struct.field_set(
+                self.file.header, self.file.handle, path, value)
+
+    # ---------------
+    # Utility get/set
+    #
+    #   avoid inline pointer casting
+    def get_pointer(
+            self, path,
+            default=...,
+            sdna_index_refine=None,
+            base_index=0,
+            ):
+        if sdna_index_refine is None:
+            sdna_index_refine = self.sdna_index
+        result = self.get(path, default, sdna_index_refine=sdna_index_refine, base_index=base_index)
+
+        # default
+        if type(result) is not int:
+            return result
+
+        assert(self.file.structs[sdna_index_refine].field_from_path(self.file.header, self.file.handle, path).dna_name.is_pointer)
+        if result != 0:
+            # possible (but unlikely)
+            # that this fails and returns None
+            # maybe we want to raise some exception in this case
+            return self.file.find_block_from_offset(result)
+        else:
+            return None
+
+    # ----------------------
+    # Python convenience API
+
+    # dict like access
+    def __getitem__(self, item):
+        return self.get(item, use_str=False)
+
+    def __setitem__(self, item, value):
+        self.set(item, value)
+
+    def keys(self):
+        return (f.dna_name.name_only for f in self.dna_type.fields)
+
+    def values(self):
+        for k in self.keys():
+            try:
+                yield self[k]
+            except NotImplementedError as err:
+                yield ...
+
+    def items(self):
+        for k in self.keys():
+            try:
+                yield (k, self[k])
+            except NotImplementedError as err:
+                yield (k, ...)
+
+
+# -----------------------------------------------------------------------------
+# Read Magic
+#
+# magic = str
+# pointer_size = int
+# is_little_endian = bool
+# version = int
+
+
+class BlendFileHeader:
+    """
+    BlendFileHeader allocates the first 12 bytes of a blend file
+    it contains information about the hardware architecture
+    """
+    __slots__ = (
+        # str
+        "magic",
+        # int 4/8
+        "pointer_size",
+        # bool
+        "is_little_endian",
+        # int
+        "version",
+        # str, used to pass to 'struct'
+        "endian_str",
+        # int, used to index common types
+        "endian_index",
+        )
+
+    def __init__(self, handle):
+        FILEHEADER = struct.Struct(b'7s1s1s3s')
+
+        log.debug("reading blend-file-header")
+        values = FILEHEADER.unpack(handle.read(FILEHEADER.size))
+        self.magic = values[0]
+        pointer_size_id = values[1]
+        if pointer_size_id == b'-':
+            self.pointer_size = 8
+        elif pointer_size_id == b'_':
+            self.pointer_size = 4
+        else:
+            assert(0)
+        endian_id = values[2]
+        if endian_id == b'v':
+            self.is_little_endian = True
+            self.endian_str = b'<'
+            self.endian_index = 0
+        elif endian_id == b'V':
+            self.is_little_endian = False
+            self.endian_index = 1
+            self.endian_str = b'>'
+        else:
+            assert(0)
+
+        version_id = values[3]
+        self.version = int(version_id)
+
+    def create_block_header_struct(self):
+        return struct.Struct(b''.join((
+                self.endian_str,
+                b'4sI',
+                b'I' if self.pointer_size == 4 else b'Q',
+                b'II',
+                )))
+
+
+class DNAName:
+    """
+    DNAName is a C-type name stored in the DNA
+    """
+    __slots__ = (
+        "name_full",
+        "name_only",
+        "is_pointer",
+        "is_method_pointer",
+        "array_size",
+        )
+
+    def __init__(self, name_full):
+        self.name_full = name_full
+        self.name_only = self.calc_name_only()
+        self.is_pointer = self.calc_is_pointer()
+        self.is_method_pointer = self.calc_is_method_pointer()
+        self.array_size = self.calc_array_size()
+
+    def as_reference(self, parent):
+        if parent is None:
+            result = b''
+        else:
+            result = parent + b'.'
+
+        result = result + self.name_only
+        return result
+
+    def calc_name_only(self):
+        result = self.name_full.strip(b'*()')
+        index = result.find(b'[')
+        if index != -1:
+            result = result[:index]
+        return result
+
+    def calc_is_pointer(self):
+        return (b'*' in self.name_full)
+
+    def calc_is_method_pointer(self):
+        return (b'(*' in self.name_full)
+
+    def calc_array_size(self):
+        result = 1
+        temp = self.name_full
+        index = temp.find(b'[')
+
+        while index != -1:
+            index_2 = temp.find(b']')
+            result *= int(temp[index + 1:index_2])
+            temp = temp[index_2 + 1:]
+            index = temp.find(b'[')
+
+        return result
+
+
+class DNAField:
+    """
+    DNAField is a coupled DNAStruct and DNAName
+    and cache offset for reuse
+    """
+    __slots__ = (
+        # DNAName
+        "dna_name",
+        # tuple of 3 items
+        # [bytes (struct name), int (struct size), DNAStruct]
+        "dna_type",
+        # size on-disk
+        "dna_size",
+        # cached info (avoid looping over fields each time)
+        "dna_offset",
+        )
+
+    def __init__(self, dna_type, dna_name, dna_size, dna_offset):
+        self.dna_type = dna_type
+        self.dna_name = dna_name
+        self.dna_size = dna_size
+        self.dna_offset = dna_offset
+
+
+class DNAStruct:
+    """
+    DNAStruct is a C-type structure stored in the DNA
+    """
+    __slots__ = (
+        "dna_type_id",
+        "size",
+        "fields",
+        "field_from_name",
+        "user_data",
+        )
+
+    def __init__(self, dna_type_id):
+        self.dna_type_id = dna_type_id
+        self.fields = []
+        self.field_from_name = {}
+        self.user_data = None
+
+    def field_from_path(self, header, handle, path):
+        assert(type(path) == bytes)
+        # support 'id.name'
+        name, _, name_tail = path.partition(b'.')
+
+        # support 'mtex[1].tex'
+        # note, multi-dimensional arrays not supported
+        # FIXME: 'mtex[1]' works, but not 'mtex[1].tex', why is this???
+        if name.endswith(b']'):
+            name, _, index = name[:-1].partition(b'[')
+            index = int(index)
+        else:
+            index = 0
+
+        field = self.field_from_name.get(name)
+
+        if field is not None:
+            handle.seek(field.dna_offset, os.SEEK_CUR)
+            if index != 0:
+                if field.dna_name.is_pointer:
+                    index_offset = header.pointer_size * index
+                else:
+                    index_offset = field.dna_type.size * index
+                assert(index_offset < field.dna_size)
+                handle.seek(index_offset, os.SEEK_CUR)
+            if name_tail == b'':
+                return field
+            else:
+                return field.dna_type.field_from_path(header, handle, name_tail)
+
+    def field_get(self, header, handle, path,
+                  default=...,
+                  use_nil=True, use_str=True,
+                  ):
+        assert(type(path) == bytes)
+
+        field = self.field_from_path(header, handle, path)
+        if field is None:
+            if default is not ...:
+                return default
+            else:
+                raise KeyError("%r not found in %r (%r)" % (path, [f.dna_name.name_only for f in self.fields], self.dna_type_id))
+
+        dna_type = field.dna_type
+        dna_name = field.dna_name
+
+        if dna_name.is_pointer:
+            return DNA_IO.read_pointer(handle, header)
+        elif dna_type.dna_type_id == b'int':
+            return DNA_IO.read_int(handle, header)
+        elif dna_type.dna_type_id == b'short':
+            return DNA_IO.read_short(handle, header)
+        elif dna_type.dna_type_id == b'float':
+            return DNA_IO.read_float(handle, header)
+        elif dna_type.dna_type_id == b'char':
+            if use_str:
+                if use_nil:
+                    return DNA_IO.read_string0(handle, dna_name.array_size)
+                else:
+                    return DNA_IO.read_string(handle, dna_name.array_size)
+            else:
+                if use_nil:
+                    return DNA_IO.read_bytes0(handle, dna_name.array_size)
+                else:
+                    return DNA_IO.read_bytes(handle, dna_name.array_size)
+        else:
+            raise NotImplementedError("%r exists but isn't pointer, can't resolve field %r" % (path, dna_name.name_only))
+
+    def field_set(self, header, handle, path, value):
+        assert(type(path) == bytes)
+
+        field = self.field_from_path(header, handle, path)
+        if field is None:
+            raise KeyError("%r not found in %r" % (path, [f.dna_name.name_only for f in self.fields]))
+
+        dna_type = field.dna_type
+        dna_name = field.dna_name
+
+        if dna_type.dna_type_id == b'char':
+            if type(value) is str:
+                return DNA_IO.write_string(handle, value, dna_name.array_size)
+            else:
+                return DNA_IO.write_bytes(handle, value, dna_name.array_size)
+        else:
+            raise NotImplementedError("Setting %r is not yet supported" % dna_type[0])
+
+
+class DNA_IO:
+    """
+    Module like class, for read-write utility functions.
+
+    Only stores static methods & constants.
+    """
+
+    __slots__ = ()
+
+    def __new__(cls, *args, **kwargs):
+        raise RuntimeError("%s should not be instantiated" % cls)
+
+    @staticmethod
+    def write_string(handle, astring, fieldlen):
+        assert(isinstance(astring, str))
+        if len(astring) >= fieldlen:
+            stringw = astring[0:fieldlen]
+        else:
+            stringw = astring + '\0'
+        handle.write(stringw.encode('utf-8'))
+
+    @staticmethod
+    def write_bytes(handle, astring, fieldlen):
+        assert(isinstance(astring, (bytes, bytearray)))
+        if len(astring) >= fieldlen:
+            stringw = astring[0:fieldlen]
+        else:
+            stringw = astring + b'\0'
+
+        handle.write(stringw)
+
+    @staticmethod
+    def read_bytes(handle, length):
+        data = handle.read(length)
+        return data
+
+    @staticmethod
+    def read_bytes0(handle, length):
+        data = handle.read(length)
+        return DNA_IO.read_data0(data)
+
+    @staticmethod
+    def read_string(handle, length):
+        return DNA_IO.read_bytes(handle, length).decode('utf-8')
+
+    @staticmethod
+    def read_string0(handle, length):
+        return DNA_IO.read_bytes0(handle, length).decode('utf-8')
+
+    @staticmethod
+    def read_data0_offset(data, offset):
+        add = data.find(b'\0', offset) - offset
+        return data[offset:offset + add]
+
+    @staticmethod
+    def read_data0(data):
+        add = data.find(b'\0')
+        return data[:add]
+
+    USHORT = struct.Struct(b'<H'), struct.Struct(b'>H')
+
+    @staticmethod
+    def read_ushort(handle, fileheader):
+        st = DNA_IO.USHORT[fileheader.endian_index]
+        return st.unpack(handle.read(st.size))[0]
+
+    UINT = struct.Struct(b'<I'), struct.Struct(b'>I')
+
+    @staticmethod
+    def read_uint(handle, fileheader):
+        st = DNA_IO.UINT[fileheader.endian_index]
+        return st.unpack(handle.read(st.size))[0]
+
+    SINT = struct.Struct(b'<i'), struct.Struct(b'>i')
+
+    @staticmethod
+    def read_int(handle, fileheader):
+        st = DNA_IO.SINT[fileheader.endian_index]
+        return st.unpack(handle.read(st.size))[0]
+
+    @staticmethod
+    def read_float(handle, fileheader):
+        return struct.unpack(fileheader.endian_str + b'f', handle.read(4))[0]
+
+    SSHORT = struct.Struct(b'<h'), struct.Struct(b'>h')
+
+    @staticmethod
+    def read_short(handle, fileheader):
+        st = DNA_IO.SSHORT[fileheader.endian_index]
+        return st.unpack(handle.read(st.size))[0]
+
+    ULONG = struct.Struct(b'<Q'), struct.Struct(b'>Q')
+
+    @staticmethod
+    def read_ulong(handle, fileheader):
+        st = DNA_IO.ULONG[fileheader.endian_index]
+        return st.unpack(handle.read(st.size))[0]
+
+    @staticmethod
+    def read_pointer(handle, header):
+        """
+        reads an pointer from a file handle
+        the pointer size is given by the header (BlendFileHeader)
+        """
+        if header.pointer_size == 4:
+            st = DNA_IO.UINT[header.endian_index]
+            return st.unpack(handle.read(st.size))[0]
+        if header.pointer_size == 8:
+            st = DNA_IO.ULONG[header.endian_index]
+            return st.unpack(handle.read(st.size))[0]