Implemented + tested dna.Struct.field_get

.gitignore

@@ -2,4 +2,5 @@
 __pycache__
 /*.egg-info/
 /.cache
+/.pytest_cache
 /.coverage

blender_asset_tracer/blendfile/__init__.py

@@ -29,7 +29,7 @@ import pathlib
 import tempfile
 import typing
 
-from . import exceptions, dna_io, dna
+from . import exceptions, dna_io, dna, header
 
 log = logging.getLogger(__name__)
 
@@ -94,7 +94,7 @@ class BlendFile:
         elif magic != BLENDFILE_MAGIC:
             raise exceptions.BlendFileError("File is not a blend file", path)
 
-        self.header = BlendFileHeader(self.fileobj, self.raw_filepath)
+        self.header = header.BlendFileHeader(self.fileobj, self.raw_filepath)
         self.block_header_struct = self.header.create_block_header_struct()
         self.blocks = []
         self.code_index = collections.defaultdict(list)
@@ -171,9 +171,10 @@ class BlendFile:
         DNACatalog is a catalog of all information in the DNA1 file-block
         """
         self.log.debug("building DNA catalog")
-        shortstruct = self.header.types.USHORT
+        endian = self.header.endian
-        shortstruct2 = self.header.types.USHORT2
+        shortstruct = endian.USHORT
-        intstruct = self.header.types.UINT
+        shortstruct2 = endian.USHORT2
+        intstruct = endian.UINT
         assert intstruct.size == 4
 
         data = self.fileobj.read(block.size)
@@ -188,7 +189,7 @@ class BlendFile:
 
         self.log.debug("building #%d names" % names_len)
         for _ in range(names_len):
-            typename = dna_io.read_data0_offset(data, offset)
+            typename = endian.read_data0_offset(data, offset)
             offset = offset + len(typename) + 1
             typenames.append(dna.Name(typename))
 
@@ -198,7 +199,7 @@ class BlendFile:
         offset += 4
         self.log.debug("building #%d types" % types_len)
         for _ in range(types_len):
-            dna_type_id = dna_io.read_data0_offset(data, offset)
+            dna_type_id = endian.read_data0_offset(data, offset)
             types.append(dna.Struct(dna_type_id))
             offset += len(dna_type_id) + 1
 
@@ -246,54 +247,6 @@ class BlendFile:
         return structs, sdna_index_from_id
 
 
-class BlendFileHeader:
-    """
-    BlendFileHeader represents the first 12 bytes of a blend file.
-
-    it contains information about the hardware architecture, which is relevant
-    to the structure of the rest of the file.
-    """
-    log = log.getChild('BlendFileHeader')
-    structure = struct.Struct(b'7s1s1s3s')
-
-    def __init__(self, fileobj: typing.BinaryIO, path: pathlib.Path):
-        self.log.debug("reading blend-file-header %s", path)
-        header = fileobj.read(self.structure.size)
-        values = self.structure.unpack(header)
-
-        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:
-            raise exceptions.BlendFileError('invalid pointer size %r' % pointer_size_id, path)
-
-        endian_id = values[2]
-        if endian_id == b'v':
-            self.types = dna_io.LittleEndianTypes
-            self.endian_str = b'<'  # indication for struct.Struct()
-        elif endian_id == b'V':
-            self.types = dna_io.BigEndianTypes
-            self.endian_str = b'>'  # indication for struct.Struct()
-        else:
-            raise exceptions.BlendFileError('invalid endian indicator %r' % endian_id, path)
-
-        version_id = values[3]
-        self.version = int(version_id)
-
-    def create_block_header_struct(self) -> struct.Struct:
-        """Create a Struct instance for parsing data block headers."""
-        return struct.Struct(b''.join((
-            self.endian_str,
-            b'4sI',
-            b'I' if self.pointer_size == 4 else b'Q',
-            b'II',
-        )))
-
-
 class BlendFileBlock:
     """
     Instance of a struct.
@@ -421,7 +374,7 @@ class BlendFileBlock:
         return dna_struct.field_get(
             self.file.header, self.file.handle, path,
             default=default,
-            use_nil=use_nil, use_str=use_str,
+            nil_terminated=use_nil, as_str=use_str,
         )
 
     def get_recursive_iter(self, path, path_root=b"",

blender_asset_tracer/blendfile/dna.py

@@ -1,6 +1,12 @@
-import os
 import typing
 
+import os
+
+from . import dna_io, header
+
+# Either a simple path b'propname', or a tuple (b'parentprop', b'actualprop', arrayindex)
+FieldPath = typing.Union[bytes, typing.Iterable[typing.Union[bytes, int]]]
+
 
 class Name:
     """dna.Name is a C-type name stored in the DNA as bytes."""
@@ -74,29 +80,52 @@ class Field:
 class Struct:
     """dna.Struct is a C-type structure stored in the DNA."""
 
-    def __init__(self, dna_type_id: bytes):
+    def __init__(self, dna_type_id: bytes, size: int = None):
+        """
+        :param dna_type_id: name of the struct in C, like b'AlembicObjectPath'.
+        :param size: only for unit tests; typically set after construction by
+            BlendFile.decode_structs(). If not set, it is calculated on the fly
+            when struct.size is evaluated, based on the available fields.
+        """
         self.dna_type_id = dna_type_id
+        self._size = size
         self._fields = []
         self._fields_by_name = {}
 
     def __repr__(self):
         return '%s(%r)' % (type(self).__qualname__, self.dna_type_id)
 
+    @property
+    def size(self) -> int:
+        if self._size is None:
+            if not self._fields:
+                raise ValueError('Unable to determine size of fieldless %r' % self)
+            last_field = max(self._fields, key=lambda f: f.offset)
+            self._size = last_field.offset + last_field.size
+        return self._size
+
+    @size.setter
+    def size(self, new_size: int):
+        self._size = new_size
+
     def append_field(self, field: Field):
         self._fields.append(field)
         self._fields_by_name[field.name.name_only] = field
 
     def field_from_path(self,
                         pointer_size: int,
-                        path: typing.Union[bytes, typing.Iterable[typing.Union[bytes, int]]]) \
+                        path: FieldPath) \
-            -> typing.Tuple[typing.Optional[Field], int]:
+            -> typing.Tuple[Field, int]:
         """
         Support lookups as bytes or a tuple of bytes and optional index.
 
         C style 'id.name'   -->  (b'id', b'name')
         C style 'array[4]'  -->  (b'array', 4)
 
-        :returns: the field itself, and its offset taking into account the optional index.
+        :returns: the field itself, and its offset taking into account the
+            optional index. The offset is relative to the start of the struct,
+            i.e. relative to the BlendFileBlock containing the data.
+        :raises KeyError: if the field does not exist.
         """
         if isinstance(path, (tuple, list)):
             name = path[0]
@@ -124,72 +153,77 @@ class Struct:
             return field.dna_type.field_from_path(pointer_size, name_tail)
 
         offset = field.offset
-        # fileobj.seek(field.offset, os.SEEK_CUR)
         if index:
             if field.name.is_pointer:
                 index_offset = pointer_size * index
             else:
                 index_offset = field.dna_type.size * index
             if index_offset >= field.size:
-                raise OverflowError('path %r is out of bounds of its DNA type' % path)
+                raise OverflowError('path %r is out of bounds of its DNA type %s' %
-            # fileobj.seek(index_offset, os.SEEK_CUR)
+                                    (path, field.dna_type))
             offset += index_offset
+
         return field, offset
 
-    def field_get(self, header, handle, path,
+    def field_get(self,
+                  file_header: header.BlendFileHeader,
+                  fileobj: typing.BinaryIO,
+                  path: FieldPath,
                   default=...,
-                  use_nil=True, use_str=True,
+                  nil_terminated=True,
+                  as_str=True,
                   ):
-        field = self.field_from_path(header, handle, path)
+        """Read the value of the field from the blend file.
-        if field is None:
+
-            if default is not ...:
+        Assumes the file pointer of `fileobj` is seek()ed to the start of the
+        struct on disk (e.g. the start of the BlendFileBlock containing the
+        data).
+        """
+        try:
+            field, offset = self.field_from_path(file_header.pointer_size, path)
+        except KeyError:
+            if default is ...:
+                raise
             return default
-            else:
+
-                raise KeyError("%r not found in %r (%r)" %
+        fileobj.seek(offset, os.SEEK_CUR)
-                               (
-                                   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
+        dna_name = field.name
-        dna_size = field.dna_size
+        types = file_header.endian
 
+        # Some special cases (pointers, strings/bytes)
         if dna_name.is_pointer:
-            return DNA_IO.read_pointer(handle, header)
+            return types.read_pointer(fileobj, file_header.pointer_size)
-        elif dna_type.dna_type_id == b'int':
+        if dna_type.dna_type_id == b'char':
-            if dna_name.array_size > 1:
+            if field.size == 1:
-                return [DNA_IO.read_int(handle, header) for i in range(dna_name.array_size)]
-            return DNA_IO.read_int(handle, header)
-        elif dna_type.dna_type_id == b'short':
-            if dna_name.array_size > 1:
-                return [DNA_IO.read_short(handle, header) for i in range(dna_name.array_size)]
-            return DNA_IO.read_short(handle, header)
-        elif dna_type.dna_type_id == b'uint64_t':
-            if dna_name.array_size > 1:
-                return [DNA_IO.read_ulong(handle, header) for i in range(dna_name.array_size)]
-            return DNA_IO.read_ulong(handle, header)
-        elif dna_type.dna_type_id == b'float':
-            if dna_name.array_size > 1:
-                return [DNA_IO.read_float(handle, header) for i in range(dna_name.array_size)]
-            return DNA_IO.read_float(handle, header)
-        elif dna_type.dna_type_id == b'char':
-            if dna_size == 1:
                 # Single char, assume it's bitflag or int value, and not a string/bytes data...
-                return DNA_IO.read_char(handle, header)
+                return types.read_char(fileobj)
-            if use_str:
+            if nil_terminated:
-                if use_nil:
+                data = types.read_bytes0(fileobj, dna_name.array_size)
-                    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:
+                data = fileobj.read(dna_name.array_size)
+
+            if as_str:
+                return data.decode('utf8')
+            return data
+
+        simple_readers = {
+            b'int': types.read_int,
+            b'short': types.read_short,
+            b'uint64_t': types.read_ulong,
+            b'float': types.read_float,
+        }
+        try:
+            simple_reader = simple_readers[dna_type.dna_type_id]
+        except KeyError:
             raise NotImplementedError("%r exists but isn't pointer, can't resolve field %r" %
                                       (path, dna_name.name_only), dna_name, dna_type)
 
+        if dna_name.array_size > 1:
+            return [simple_reader(fileobj) for _ in range(dna_name.array_size)]
+        return simple_reader(fileobj)
+
     def field_set(self, header, handle, path, value):
         assert (type(path) == bytes)
 

blender_asset_tracer/blendfile/dna_io.py

@@ -5,7 +5,7 @@ import typing
 
 
 class EndianIO:
-    UCHAR = struct.Struct(b'<b')
+    UCHAR = struct.Struct(b'<B')
     USHORT = struct.Struct(b'<H')
     USHORT2 = struct.Struct(b'<HH')  # two shorts in a row
     SSHORT = struct.Struct(b'<h')
@@ -48,40 +48,23 @@ class EndianIO:
         return cls._read(fileobj, cls.ULONG)
 
     @classmethod
-    def read_pointer(cls, fileobj: typing.BinaryIO, fileheader):
+    def read_pointer(cls, fileobj: typing.BinaryIO, pointer_size: int):
-        """Read a pointer from a file.
+        """Read a pointer from a file."""
 
-        The pointer size is given by the header (BlendFileHeader).
+        if pointer_size == 4:
-        """
-
-        if fileheader.pointer_size == 4:
             return cls.read_uint(fileobj)
-        if fileheader.pointer_size == 8:
+        if pointer_size == 8:
             return cls.read_ulong(fileobj)
-        raise ValueError('unsupported pointer size %d' % fileheader.pointer_size)
+        raise ValueError('unsupported pointer size %d' % pointer_size)
 
-
+    @classmethod
-class LittleEndianTypes(EndianIO):
+    def write_string(cls, fileobj: typing.BinaryIO, astring: str, fieldlen: int):
-    pass
-
-
-class BigEndianTypes(LittleEndianTypes):
-    UCHAR = struct.Struct(b'>b')
-    USHORT = struct.Struct(b'>H')
-    USHORT2 = struct.Struct(b'>HH')  # two shorts in a row
-    SSHORT = struct.Struct(b'>h')
-    UINT = struct.Struct(b'>I')
-    SINT = struct.Struct(b'>i')
-    FLOAT = struct.Struct(b'>f')
-    ULONG = struct.Struct(b'>Q')
-
-
-def write_string(fileobj: typing.BinaryIO, astring: str, fieldlen: int):
         assert isinstance(astring, str)
-    write_bytes(fileobj, astring.encode('utf-8'), fieldlen)
+        # TODO: truncate the string on a UTF-8 character boundary to avoid creating invalid UTF-8.
+        cls.write_bytes(fileobj, astring.encode('utf-8'), fieldlen)
 
-
+    @classmethod
-def write_bytes(fileobj: typing.BinaryIO, data: bytes, fieldlen: int):
+    def write_bytes(cls, fileobj: typing.BinaryIO, data: bytes, fieldlen: int):
         assert isinstance(data, (bytes, bytearray))
         if len(data) >= fieldlen:
             to_write = data[0:fieldlen]
@@ -90,25 +73,34 @@ def write_bytes(fileobj: typing.BinaryIO, data: bytes, fieldlen: int):
 
         fileobj.write(to_write)
 
-
+    @classmethod
-def read_bytes0(fileobj, length):
+    def read_bytes0(cls, fileobj, length):
         data = fileobj.read(length)
-    return read_data0(data)
+        return cls.read_data0(data)
 
-
+    @classmethod
-def read_string(fileobj, length):
+    def read_data0_offset(cls, data, offset):
-    return fileobj.read(length).decode('utf-8')
-
-
-def read_string0(fileobj, length):
-    return read_bytes0(fileobj, length).decode('utf-8')
-
-
-def read_data0_offset(data, offset):
         add = data.find(b'\0', offset) - offset
         return data[offset:offset + add]
 
-
+    @classmethod
-def read_data0(data):
+    def read_data0(cls, data):
         add = data.find(b'\0')
+        if add < 0:
+            return data
         return data[:add]
+
+
+class LittleEndianTypes(EndianIO):
+    pass
+
+
+class BigEndianTypes(LittleEndianTypes):
+    UCHAR = struct.Struct(b'>B')
+    USHORT = struct.Struct(b'>H')
+    USHORT2 = struct.Struct(b'>HH')  # two shorts in a row
+    SSHORT = struct.Struct(b'>h')
+    UINT = struct.Struct(b'>I')
+    SINT = struct.Struct(b'>i')
+    FLOAT = struct.Struct(b'>f')
+    ULONG = struct.Struct(b'>Q')

blender_asset_tracer/blendfile/header.py

@@ -0,0 +1,55 @@
+import logging
+import pathlib
+import struct
+import typing
+
+from . import dna_io, exceptions
+
+log = logging.getLogger(__name__)
+
+
+class BlendFileHeader:
+    """
+    BlendFileHeader represents the first 12 bytes of a blend file.
+
+    it contains information about the hardware architecture, which is relevant
+    to the structure of the rest of the file.
+    """
+    structure = struct.Struct(b'7s1s1s3s')
+
+    def __init__(self, fileobj: typing.BinaryIO, path: pathlib.Path):
+        log.debug("reading blend-file-header %s", path)
+        header = fileobj.read(self.structure.size)
+        values = self.structure.unpack(header)
+
+        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:
+            raise exceptions.BlendFileError('invalid pointer size %r' % pointer_size_id, path)
+
+        endian_id = values[2]
+        if endian_id == b'v':
+            self.endian = dna_io.LittleEndianTypes
+            self.endian_str = b'<'  # indication for struct.Struct()
+        elif endian_id == b'V':
+            self.endian = dna_io.BigEndianTypes
+            self.endian_str = b'>'  # indication for struct.Struct()
+        else:
+            raise exceptions.BlendFileError('invalid endian indicator %r' % endian_id, path)
+
+        version_id = values[3]
+        self.version = int(version_id)
+
+    def create_block_header_struct(self) -> struct.Struct:
+        """Create a Struct instance for parsing data block headers."""
+        return struct.Struct(b''.join((
+            self.endian_str,
+            b'4sI',
+            b'I' if self.pointer_size == 4 else b'Q',
+            b'II',
+        )))

tests/test_blendfile_dna.py

@@ -1,6 +1,9 @@
+import io
+import os
 import unittest
+from unittest import mock
 
-from blender_asset_tracer.blendfile import dna
+from blender_asset_tracer.blendfile import dna, dna_io
 
 
 class NameTest(unittest.TestCase):
@@ -68,18 +71,161 @@ class NameTest(unittest.TestCase):
 
 
 class StructTest(unittest.TestCase):
-    def test_field_from_path(self):
+    class FakeHeader:
+        pointer_size = 8
+        endian = dna_io.BigEndianTypes
+
+    def setUp(self):
+        self.s = dna.Struct(b'AlembicObjectPath')
+        self.s_char = dna.Struct(b'char', 1)
+        self.s_float = dna.Struct(b'float', 4)
+        self.s_uint64 = dna.Struct(b'uint64_t', 8)
+        self.s_uint128 = dna.Struct(b'uint128_t', 16)  # non-supported type
+
+        self.f_next = dna.Field(self.s, dna.Name(b'*next'), 8, 0)
+        self.f_prev = dna.Field(self.s, dna.Name(b'*prev'), 8, 8)
+        self.f_path = dna.Field(self.s_char, dna.Name(b'path[4096]'), 4096, 16)
+        self.f_pointer = dna.Field(self.s_char, dna.Name(b'*ptr'), 3 * 8, 4112)
+        self.f_number = dna.Field(self.s_uint64, dna.Name(b'numbah'), 8, 4136)
+        self.f_floaty = dna.Field(self.s_float, dna.Name(b'floaty[2]'), 2 * 4, 4144)
+        self.f_flag = dna.Field(self.s_char, dna.Name(b'bitflag'), 1, 4152)
+        self.f_bignum = dna.Field(self.s_uint128, dna.Name(b'bignum'), 16, 4153)
+
+        self.s.append_field(self.f_next)
+        self.s.append_field(self.f_prev)
+        self.s.append_field(self.f_path)
+        self.s.append_field(self.f_pointer)
+        self.s.append_field(self.f_number)
+        self.s.append_field(self.f_floaty)
+        self.s.append_field(self.f_flag)
+        self.s.append_field(self.f_bignum)
+
+    def test_autosize(self):
+        with self.assertRaises(ValueError):
+            # Maybe it would be better to just return 0 on empty structs.
+            # They are actually used in Blendfiles (for example
+            # AbcArchiveHandle), but when actually loading from a blendfile
+            # the size property is explicitly set anyway. The situation we
+            # test here is for manually created Struct instances that don't
+            # have any fields.
+            dna.Struct(b'EmptyStruct').size
+
+        # Create AlebicObjectPath as it is actually used in Blender 2.79a
         s = dna.Struct(b'AlembicObjectPath')
         f_next = dna.Field(s, dna.Name(b'*next'), 8, 0)
         f_prev = dna.Field(s, dna.Name(b'*prev'), 8, 8)
-        f_path = dna.Field(dna.Struct(b'char'), dna.Name(b'path[4096]'), 4096, 16)
+        f_path = dna.Field(self.s_char, dna.Name(b'path[4096]'), 4096, 16)
-        f_pointer = dna.Field(dna.Struct(b'char'), dna.Name(b'*ptr'), 3 * 8, 16 + 4096)
         s.append_field(f_next)
         s.append_field(f_prev)
         s.append_field(f_path)
-        s.append_field(f_pointer)
 
+        self.assertEqual(s.size, 4112)
+
+    def test_field_from_path(self):
         psize = 8
-        self.assertEqual(s.field_from_path(psize, b'path'), (f_path, 16))
+        self.assertEqual(self.s.field_from_path(psize, b'path'),
-        self.assertEqual(s.field_from_path(psize, (b'prev', b'path')), (f_path, 16))
+                         (self.f_path, 16))
-        self.assertEqual(s.field_from_path(psize, (b'ptr', 2)), (f_pointer, 16 + 4096 + 2 * psize))
+        self.assertEqual(self.s.field_from_path(psize, (b'prev', b'path')),
+                         (self.f_path, 16))
+        self.assertEqual(self.s.field_from_path(psize, (b'ptr', 2)),
+                         (self.f_pointer, 16 + 4096 + 2 * psize))
+        self.assertEqual(self.s.field_from_path(psize, (b'floaty', 1)),
+                         (self.f_floaty, 4144 + self.s_float.size))
+
+        with self.assertRaises(OverflowError):
+            self.s.field_from_path(psize, (b'floaty', 2))
+
+        with self.assertRaises(KeyError):
+            self.s.field_from_path(psize, b'non-existant')
+
+        with self.assertRaises(TypeError):
+            self.s.field_from_path(psize, 'path')
+
+    def test_simple_field_get(self):
+        fileobj = mock.MagicMock(io.BufferedReader)
+        fileobj.read.return_value = b'\x01\x02\x03\x04\xff\xfe\xfd\xfa'
+        val = self.s.field_get(self.FakeHeader(), fileobj, b'numbah')
+
+        self.assertEqual(val, 0x1020304fffefdfa)
+        fileobj.seek.assert_called_with(4136, os.SEEK_CUR)
+
+    def test_field_get_default(self):
+        fileobj = mock.MagicMock(io.BufferedReader)
+        fileobj.read.side_effect = RuntimeError
+        val = self.s.field_get(self.FakeHeader(), fileobj, b'nonexistant', default=519871531)
+
+        self.assertEqual(val, 519871531)
+        fileobj.seek.assert_not_called()
+
+    def test_field_get_nonexistant(self):
+        fileobj = mock.MagicMock(io.BufferedReader)
+        fileobj.read.side_effect = RuntimeError
+
+        with self.assertRaises(KeyError):
+            self.s.field_get(self.FakeHeader(), fileobj, b'nonexistant')
+        fileobj.seek.assert_not_called()
+
+    def test_field_get_unsupported_type(self):
+        fileobj = mock.MagicMock(io.BufferedReader)
+        fileobj.read.side_effect = RuntimeError
+
+        with self.assertRaises(NotImplementedError):
+            self.s.field_get(self.FakeHeader(), fileobj, b'bignum')
+        fileobj.seek.assert_called_with(4153, os.SEEK_CUR)
+
+    def test_pointer_field_get(self):
+        fileobj = mock.MagicMock(io.BufferedReader)
+        fileobj.read.return_value = b'\xf0\x9f\xa6\x87\x00dum'
+        val = self.s.field_get(self.FakeHeader(), fileobj, b'ptr')
+
+        self.assertEqual(0xf09fa6870064756d, val)
+        fileobj.seek.assert_called_with(4112, os.SEEK_CUR)
+
+    def test_string_field_get(self):
+        fileobj = mock.MagicMock(io.BufferedReader)
+        fileobj.read.return_value = b'\xf0\x9f\xa6\x87\x00dummydata'
+        val = self.s.field_get(self.FakeHeader(), fileobj, b'path', as_str=True)
+
+        self.assertEqual('🦇', val)
+        fileobj.seek.assert_called_with(16, os.SEEK_CUR)
+
+    def test_string_field_get_single_char(self):
+        fileobj = mock.MagicMock(io.BufferedReader)
+        fileobj.read.return_value = b'\xf0'
+        val = self.s.field_get(self.FakeHeader(), fileobj, b'bitflag')
+
+        self.assertEqual(0xf0, val)
+        fileobj.seek.assert_called_with(4152, os.SEEK_CUR)
+
+    def test_string_field_get_invalid_utf8(self):
+        fileobj = mock.MagicMock(io.BufferedReader)
+        fileobj.read.return_value = b'\x01\x02\x03\x04\xff\xfe\xfd\xfa'
+
+        with self.assertRaises(UnicodeDecodeError):
+            self.s.field_get(self.FakeHeader(), fileobj, b'path', as_str=True)
+
+    def test_string_field_get_bytes_null_terminated(self):
+        fileobj = mock.MagicMock(io.BufferedReader)
+        fileobj.read.return_value = b'\x01\x02\x03\x04\xff\xfe\xfd\xfa\x00dummydata'
+
+        val = self.s.field_get(self.FakeHeader(), fileobj, b'path', as_str=False)
+        self.assertEqual(b'\x01\x02\x03\x04\xff\xfe\xfd\xfa', val)
+        fileobj.seek.assert_called_with(16, os.SEEK_CUR)
+
+    def test_string_field_get_bytes(self):
+        fileobj = mock.MagicMock(io.BufferedReader)
+        fileobj.read.return_value = b'\x01\x02\x03\x04\xff\xfe\xfd\xfa\x00dummydata'
+
+        val = self.s.field_get(self.FakeHeader(), fileobj, b'path', as_str=False,
+                               nil_terminated=False)
+        self.assertEqual(b'\x01\x02\x03\x04\xff\xfe\xfd\xfa\x00dummydata', val)
+        fileobj.seek.assert_called_with(16, os.SEEK_CUR)
+
+    def test_string_field_get_float_array(self):
+        fileobj = mock.MagicMock(io.BufferedReader)
+        fileobj.read.side_effect = (b'@333', b'@2\x8f\\')
+
+        val = self.s.field_get(self.FakeHeader(), fileobj, b'floaty')
+        self.assertAlmostEqual(2.8, val[0])
+        self.assertAlmostEqual(2.79, val[1])
+        fileobj.seek.assert_called_with(4144, os.SEEK_CUR)