Implemented + tested dna.Struct.field_get

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',
+        )))