Add the default() method back in (#55)

Author: Schamper

dissect/cstruct/types/base.py

@@ -54,6 +54,10 @@ def __len__(cls) -> int:
 
         return cls.size
 
+    def default(cls) -> BaseType:
+        """Return the default value of this type."""
+        return cls()
+
     def reads(cls, data: bytes) -> BaseType:
         """Parse the given data from a bytes-like object.
 
@@ -196,6 +200,9 @@ def _read(cls, stream: BinaryIO, context: dict[str, Any] = None) -> Array:
 
         return cls.type._read_array(stream, num, context)
 
+    def default(cls) -> BaseType:
+        return [cls.type.default() for _ in range(0 if cls.dynamic or cls.null_terminated else cls.num_entries)]
+
 
 class Array(list, BaseType, metaclass=ArrayMetaType):
     """Implements a fixed or dynamically sized array type.

dissect/cstruct/types/char.py

@@ -48,6 +48,10 @@ def _write(cls, stream: BinaryIO, data: Union[bytes, int, str]) -> int:
 
         return stream.write(data)
 
+    @classmethod
+    def default(cls) -> Char:
+        return type.__call__(cls, b"\x00")
+
 
 class CharArray(bytes, BaseType, metaclass=ArrayMetaType):
     """Character array type for reading and writing byte strings."""
@@ -67,3 +71,7 @@ def _write(cls, stream: BinaryIO, data: bytes) -> int:
         if cls.null_terminated:
             return stream.write(data + b"\x00")
         return stream.write(data)
+
+    @classmethod
+    def default(cls) -> CharArray:
+        return type.__call__(cls, b"\x00" * (0 if cls.dynamic or cls.null_terminated else cls.num_entries))

dissect/cstruct/types/structure.py

@@ -63,7 +63,7 @@ def __call__(cls, *args, **kwargs) -> Structure:
             # Shortcut for single char/bytes type
             return type.__call__(cls, *args, **kwargs)
         elif not args and not kwargs:
-            obj = cls(**{field.name: field.type() for field in cls.__fields__})
+            obj = cls(**{field.name: field.type.default() for field in cls.__fields__})
             object.__setattr__(obj, "_values", {})
             object.__setattr__(obj, "_sizes", {})
             return obj

dissect/cstruct/types/wchar.py

@@ -54,6 +54,10 @@ def _read_0(cls, stream: BinaryIO, context: dict[str, Any] = None) -> Wchar:
     def _write(cls, stream: BinaryIO, data: str) -> int:
         return stream.write(data.encode(cls.__encoding_map__[cls.cs.endian]))
 
+    @classmethod
+    def default(cls) -> Wchar:
+        return type.__call__(cls, "\x00")
+
 
 class WcharArray(str, BaseType, metaclass=ArrayMetaType):
     """Wide-character array type for reading and writing UTF-16 strings."""
@@ -67,3 +71,7 @@ def _write(cls, stream: BinaryIO, data: str) -> int:
         if cls.null_terminated:
             data += "\x00"
         return stream.write(data.encode(Wchar.__encoding_map__[cls.cs.endian]))
+
+    @classmethod
+    def default(cls) -> WcharArray:
+        return type.__call__(cls, "\x00" * (0 if cls.dynamic or cls.null_terminated else cls.num_entries))

tests/test_basic.py

@@ -107,95 +107,93 @@ def test_lookups(cs: cstruct, compiled: bool):
     assert cs.lookups["a"] == {1: 3, 2: 4}
 
 
-# TODO:
-# def test_default_constructors(cs: cstruct, compiled: bool):
-#     cdef = """
-#     enum Enum {
-#         a = 0,
-#         b = 1
-#     };
-
-#     flag Flag {
-#         a = 0,
-#         b = 1
-#     };
-
-#     struct test {
-#         uint32  t_int;
-#         uint32  t_int_array[2];
-#         uint24  t_bytesint;
-#         uint24  t_bytesint_array[2];
-#         char    t_char;
-#         char    t_char_array[2];
-#         wchar   t_wchar;
-#         wchar   t_wchar_array[2];
-#         Enum    t_enum;
-#         Enum    t_enum_array[2];
-#         Flag    t_flag;
-#         Flag    t_flag_array[2];
-#     };
-#     """
-#     cs.load(cdef, compiled=compiled)
-
-#     assert verify_compiled(cs.test, compiled)
-
-#     obj = cs.test()
-#     assert obj.t_int == 0
-#     assert obj.t_int_array == [0, 0]
-#     assert obj.t_bytesint == 0
-#     assert obj.t_bytesint_array == [0, 0]
-#     assert obj.t_char == b"\x00"
-#     assert obj.t_char_array == b"\x00\x00"
-#     assert obj.t_wchar == "\x00"
-#     assert obj.t_wchar_array == "\x00\x00"
-#     assert obj.t_enum == cs.Enum(0)
-#     assert obj.t_enum_array == [cs.Enum(0), cs.Enum(0)]
-#     assert obj.t_flag == cs.Flag(0)
-#     assert obj.t_flag_array == [cs.Flag(0), cs.Flag(0)]
-
-#     assert obj.dumps() == b"\x00" * 54
-
-
-# TODO:
-# def test_default_constructors_dynamic(cs: cstruct, compiled: bool):
-#     cdef = """
-#     enum Enum {
-#         a = 0,
-#         b = 1
-#     };
-#     flag Flag {
-#         a = 0,
-#         b = 1
-#     };
-#     struct test {
-#         uint8   x;
-#         uint32  t_int_array_n[];
-#         uint32  t_int_array_d[x];
-#         uint24  t_bytesint_array_n[];
-#         uint24  t_bytesint_array_d[x];
-#         char    t_char_array_n[];
-#         char    t_char_array_d[x];
-#         wchar   t_wchar_array_n[];
-#         wchar   t_wchar_array_d[x];
-#         Enum    t_enum_array_n[];
-#         Enum    t_enum_array_d[x];
-#         Flag    t_flag_array_n[];
-#         Flag    t_flag_array_d[x];
-#     };
-#     """
-#     cs.load(cdef, compiled=compiled)
-
-#     assert verify_compiled(cs.test, compiled)
-
-#     obj = cs.test()
-
-#     assert obj.t_int_array_n == obj.t_int_array_d == []
-#     assert obj.t_bytesint_array_n == obj.t_bytesint_array_d == []
-#     assert obj.t_char_array_n == obj.t_char_array_d == b""
-#     assert obj.t_wchar_array_n == obj.t_wchar_array_d == ""
-#     assert obj.t_enum_array_n == obj.t_enum_array_d == []
-#     assert obj.t_flag_array_n == obj.t_flag_array_d == []
-#     assert obj.dumps() == b"\x00" * 19
+def test_default_constructors(cs: cstruct, compiled: bool):
+    cdef = """
+    enum Enum {
+        a = 0,
+        b = 1
+    };
+
+    flag Flag {
+        a = 0,
+        b = 1
+    };
+
+    struct test {
+        uint32  t_int;
+        uint32  t_int_array[2];
+        uint24  t_bytesint;
+        uint24  t_bytesint_array[2];
+        char    t_char;
+        char    t_char_array[2];
+        wchar   t_wchar;
+        wchar   t_wchar_array[2];
+        Enum    t_enum;
+        Enum    t_enum_array[2];
+        Flag    t_flag;
+        Flag    t_flag_array[2];
+    };
+    """
+    cs.load(cdef, compiled=compiled)
+
+    assert verify_compiled(cs.test, compiled)
+
+    obj = cs.test()
+    assert obj.t_int == 0
+    assert obj.t_int_array == [0, 0]
+    assert obj.t_bytesint == 0
+    assert obj.t_bytesint_array == [0, 0]
+    assert obj.t_char == b"\x00"
+    assert obj.t_char_array == b"\x00\x00"
+    assert obj.t_wchar == "\x00"
+    assert obj.t_wchar_array == "\x00\x00"
+    assert obj.t_enum == cs.Enum(0)
+    assert obj.t_enum_array == [cs.Enum(0), cs.Enum(0)]
+    assert obj.t_flag == cs.Flag(0)
+    assert obj.t_flag_array == [cs.Flag(0), cs.Flag(0)]
+
+    assert obj.dumps() == b"\x00" * 54
+
+
+def test_default_constructors_dynamic(cs: cstruct, compiled: bool):
+    cdef = """
+    enum Enum {
+        a = 0,
+        b = 1
+    };
+    flag Flag {
+        a = 0,
+        b = 1
+    };
+    struct test {
+        uint8   x;
+        uint32  t_int_array_n[];
+        uint32  t_int_array_d[x];
+        uint24  t_bytesint_array_n[];
+        uint24  t_bytesint_array_d[x];
+        char    t_char_array_n[];
+        char    t_char_array_d[x];
+        wchar   t_wchar_array_n[];
+        wchar   t_wchar_array_d[x];
+        Enum    t_enum_array_n[];
+        Enum    t_enum_array_d[x];
+        Flag    t_flag_array_n[];
+        Flag    t_flag_array_d[x];
+    };
+    """
+    cs.load(cdef, compiled=compiled)
+
+    assert verify_compiled(cs.test, compiled)
+
+    obj = cs.test()
+
+    assert obj.t_int_array_n == obj.t_int_array_d == []
+    assert obj.t_bytesint_array_n == obj.t_bytesint_array_d == []
+    assert obj.t_char_array_n == obj.t_char_array_d == b""
+    assert obj.t_wchar_array_n == obj.t_wchar_array_d == ""
+    assert obj.t_enum_array_n == obj.t_enum_array_d == []
+    assert obj.t_flag_array_n == obj.t_flag_array_d == []
+    assert obj.dumps() == b"\x00" * 19
 
 
 def test_config_flag_nocompile(cs: cstruct, compiled: bool):