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Core: extract blendfile_header.py as common utility for parsing .blend files

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This new file can parse the file header (first few bytes) as well as the block
headers.

Right now, this is used by two places:
* `blendfile.py` which is used by `blend2json.py`
* `blend_render_info.py`

This new module is shipped with Blender because it's needed for
`blend_render_info.py` which is shipped with Blender too. This makes using it in
`blendfile.py` (which is not shipped with Blender) a bit more annoying. However,
this is already not ideal, because e.g. `blend2json` also has to add to
`sys.path` already to be able to import `blendfile.py`.

This new file could also be used by blender-asset-tracer (BAT).

The new `BlendFileHeader` and `BlockHeader` types may be subclassed by code
using it, because it wants to store additional derived data (`blendfile.py` and
BAT need this).

New tests have been added that check that the file and block header is parsed
correctly for different kinds of .blend files.

Pull Request: https://projects.blender.org/blender/blender/pulls/140341
This commit is contained in:
Jacques Lucke
2025-06-23 12:53:55 +02:00
parent a5399af388
commit f0c7e52ff2
10 changed files with 468 additions and 220 deletions
Download Patch File Download Diff File Expand all files Collapse all files

174
tools/modules/blendfile.py
View File

@@ -18,11 +18,13 @@ __all__ = (
"BlendFileRaw",
)
import os
import sys
sys.path.append(os.path.join(os.path.dirname(__file__), "..", "..", "scripts", "modules"))
from collections import namedtuple
import blendfile_header
import gzip
import logging
import os
import struct
import tempfile
import zstandard as zstd
@@ -55,10 +57,8 @@ class BlendFile:
"filepath_orig",
# BlendFileHeader
"header",
# struct.Struct
# blendfile_header.BlockHeaderStruct
"block_header_struct",
# namedtuple
"block_header_fields",
# BlendFileBlock
"blocks",
# [DNAStruct, ...]
@@ -80,7 +80,7 @@ class BlendFile:
log.debug("initializing reading blend-file")
self.handle = handle
self.header = BlendFileHeader(handle)
self.block_header_struct, self.block_header_fields = self.header.create_block_header_struct()
self.block_header_struct = self.header.create_block_header_struct()
self.blocks = []
self.code_index = {}
self.structs = []
@@ -245,18 +245,13 @@ class BlendFile:
return structs, sdna_index_from_id
class BlendFileBlock:
class BlendFileBlock(blendfile_header.BlockHeader):
"""
Instance of a struct.
"""
__slots__ = (
# BlendFile
"file",
"code",
"size",
"addr_old",
"sdna_index",
"count",
"file_offset",
"user_data",
)
@@ -273,46 +268,10 @@ class BlendFileBlock:
))
def __init__(self, handle, bfile):
super().__init__(handle, bfile.block_header_struct)
self.file = bfile
self.user_data = None
data = handle.read(bfile.block_header_struct.size)
if len(data) != bfile.block_header_struct.size:
print("WARNING! Blend file seems to be badly truncated!")
self.code = b'ENDB'
self.size = 0
self.addr_old = 0
self.sdna_index = 0
self.count = 0
self.file_offset = 0
return
# Header can be just 8 byte because of ENDB block in old .blend files.
if len(data) > 8:
blockheader = bfile.block_header_fields(*bfile.block_header_struct.unpack(data))
self.code = blockheader[0].partition(b'\0')[0]
if self.code != b'ENDB':
self.size = blockheader.len
self.addr_old = blockheader.old
self.sdna_index = blockheader.SDNAnr
self.count = blockheader.nr
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:
OLDBLOCK = struct.Struct(b'4sI')
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
self.file_offset = handle.tell()
@property
def dna_type(self):
@@ -744,74 +703,12 @@ class BlendFileBlockRaw:
# Read Magic
class BlendFileHeader:
"""
BlendFileHeader allocates the first 12-17 bytes (depending on the file version) of a blend file
it contains information about the hardware architecture
"""
__slots__ = (
# str
"magic",
# int
"file_format_version",
# 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",
)
class BlendFileHeader(blendfile_header.BlendFileHeader):
endian_index: int
endian_str: bytes
def __init__(self, handle):
log.debug("reading blend-file-header")
bytes_0_6 = handle.read(7)
if bytes_0_6 != b'BLENDER':
raise BlendFileError("invalid first bytes")
self.magic = bytes_0_6
byte_7 = handle.read(1)
is_legacy_header = byte_7 in (b'_', b'-')
if is_legacy_header:
self.file_format_version = 0
if byte_7 == b'_':
self.pointer_size = 4
elif byte_7 == b'-':
self.pointer_size = 8
else:
raise BlendFileError("invalid file header")
byte_8 = handle.read(1)
if byte_8 == b'v':
self.is_little_endian = True
elif byte_8 == b'V':
self.is_little_endian = False
else:
raise BlendFileError("invalid file header")
bytes_9_11 = handle.read(3)
self.version = int(bytes_9_11)
else:
byte_8 = handle.read(1)
header_size = int(byte_7 + byte_8)
if header_size != 17:
raise BlendFileError("invalid file header")
byte_9 = handle.read(1)
if byte_9 != b'-':
raise BlendFileError("invalid file header")
self.pointer_size = 8
byte_10_11 = handle.read(2)
self.file_format_version = int(byte_10_11)
if self.file_format_version != 1:
raise BlendFileError("unsupported file format version")
byte_12 = handle.read(1)
if byte_12 != b'v':
raise BlendFileError("invalid file header")
self.is_little_endian = True
byte_13_16 = handle.read(4)
self.version = int(byte_13_16)
super().__init__(handle)
if self.is_little_endian:
self.endian_str = b'<'
@@ -820,51 +717,6 @@ class BlendFileHeader:
self.endian_index = 1
self.endian_str = b'>'
def create_block_header_struct(self):
if self.file_format_version == 0:
if self.pointer_size == 4:
return struct.Struct(b''.join((
self.endian_str,
# BHead4.code
b'4s',
# BHead4.len
b'i',
# BHead4.old
b'I',
# BHead4.SDNAnr
b'i',
# BHead4.nr
b'i',
))), namedtuple('BHead4', ('code', 'len', 'old', 'SDNAnr', 'nr'))
else:
return struct.Struct(b''.join((
self.endian_str,
# SmallBHead8.code
b'4s',
# SmallBHead8.len
b'i',
# SmallBHead8.old
b'Q',
# SmallBHead8.SDNAnr
b'i',
# SmallBHead8.nr
b'i',
))), namedtuple('SmallBHead8', ('code', 'len', 'old', 'SDNAnr', 'nr'))
else:
return struct.Struct(b''.join((
self.endian_str,
# LargeBHead8.code
b'4s',
# LargeBHead8.SDNAnr
b'i',
# LargeBHead8.old
b'Q',
# LargeBHead8.len
b'q',
# LargeBHead8.nr
b'q',
))), namedtuple('LargeBHead8', ('code', 'SDNAnr', 'old', 'len', 'nr'))
class DNAName:
"""