The Android sparse format is a format to more efficiently store files for for example firmware updates to save on bandwidth. Files in sparse format first have to be converted back to their original format.
A tool to create images for testing can be found in the Android source code tree:
https://android.googlesource.com/platform/system/core/+/e8d02c50d7/libsparse - img2simg.c
Note: this is not the same as the Android sparse data image format.
This page hosts a formal specification of Android sparse image using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.
All parsing code for Python generated by Kaitai Struct depends on the Python runtime library. You have to install it before you can parse data.
The Python runtime library can be installed from PyPI:
python3 -m pip install kaitaistructParse a local file and get structure in memory:
data = AndroidSparse.from_file("path/to/local/file.img")
Or parse structure from a bytes:
from kaitaistruct import KaitaiStream, BytesIO
raw = b"\x00\x01\x02..."
data = AndroidSparse(KaitaiStream(BytesIO(raw)))
After that, one can get various attributes from the structure by invoking getter methods like:
data.header_prefix # => internal; access `_root.header` instead
# This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild
# type: ignore
import kaitaistruct
from kaitaistruct import KaitaiStruct, KaitaiStream, BytesIO
from enum import IntEnum
if getattr(kaitaistruct, 'API_VERSION', (0, 9)) < (0, 11):
raise Exception("Incompatible Kaitai Struct Python API: 0.11 or later is required, but you have %s" % (kaitaistruct.__version__))
class AndroidSparse(KaitaiStruct):
"""The Android sparse format is a format to more efficiently store files
for for example firmware updates to save on bandwidth. Files in sparse
format first have to be converted back to their original format.
A tool to create images for testing can be found in the Android source code tree:
<https://android.googlesource.com/platform/system/core/+/e8d02c50d7/libsparse> - `img2simg.c`
Note: this is not the same as the Android sparse data image format.
.. seealso::
Source - https://android.googlesource.com/platform/system/core/+/e8d02c50d7/libsparse/sparse_format.h
.. seealso::
Source - https://web.archive.org/web/20220322054458/https://source.android.com/devices/bootloader/images#sparse-image-format
"""
class ChunkTypes(IntEnum):
raw = 51905
fill = 51906
dont_care = 51907
crc32 = 51908
def __init__(self, _io, _parent=None, _root=None):
super(AndroidSparse, self).__init__(_io)
self._parent = _parent
self._root = _root or self
self._read()
def _read(self):
self.header_prefix = AndroidSparse.FileHeaderPrefix(self._io, self, self._root)
self._raw_header = self._io.read_bytes(self.header_prefix.len_header - 10)
_io__raw_header = KaitaiStream(BytesIO(self._raw_header))
self.header = AndroidSparse.FileHeader(_io__raw_header, self, self._root)
self.chunks = []
for i in range(self.header.num_chunks):
self.chunks.append(AndroidSparse.Chunk(self._io, self, self._root))
def _fetch_instances(self):
pass
self.header_prefix._fetch_instances()
self.header._fetch_instances()
for i in range(len(self.chunks)):
pass
self.chunks[i]._fetch_instances()
class Chunk(KaitaiStruct):
def __init__(self, _io, _parent=None, _root=None):
super(AndroidSparse.Chunk, self).__init__(_io)
self._parent = _parent
self._root = _root
self._read()
def _read(self):
self._raw_header = self._io.read_bytes(self._root.header.len_chunk_header)
_io__raw_header = KaitaiStream(BytesIO(self._raw_header))
self.header = AndroidSparse.Chunk.ChunkHeader(_io__raw_header, self, self._root)
_on = self.header.chunk_type
if _on == AndroidSparse.ChunkTypes.crc32:
pass
self.body = self._io.read_u4le()
else:
pass
self.body = self._io.read_bytes(self.header.len_body)
def _fetch_instances(self):
pass
self.header._fetch_instances()
_on = self.header.chunk_type
if _on == AndroidSparse.ChunkTypes.crc32:
pass
else:
pass
class ChunkHeader(KaitaiStruct):
def __init__(self, _io, _parent=None, _root=None):
super(AndroidSparse.Chunk.ChunkHeader, self).__init__(_io)
self._parent = _parent
self._root = _root
self._read()
def _read(self):
self.chunk_type = KaitaiStream.resolve_enum(AndroidSparse.ChunkTypes, self._io.read_u2le())
self.reserved1 = self._io.read_u2le()
self.num_body_blocks = self._io.read_u4le()
self.len_chunk = self._io.read_u4le()
if not self.len_chunk == (self._root.header.len_chunk_header + self.len_body_expected if self.len_body_expected != -1 else self.len_chunk):
raise kaitaistruct.ValidationNotEqualError((self._root.header.len_chunk_header + self.len_body_expected if self.len_body_expected != -1 else self.len_chunk), self.len_chunk, self._io, u"/types/chunk/types/chunk_header/seq/3")
def _fetch_instances(self):
pass
@property
def len_body(self):
if hasattr(self, '_m_len_body'):
return self._m_len_body
self._m_len_body = self.len_chunk - self._root.header.len_chunk_header
return getattr(self, '_m_len_body', None)
@property
def len_body_expected(self):
"""
.. seealso::
Source - https://android.googlesource.com/platform/system/core/+/e8d02c50d7/libsparse/sparse_read.cpp#184
.. seealso::
Source - https://android.googlesource.com/platform/system/core/+/e8d02c50d7/libsparse/sparse_read.cpp#215
.. seealso::
Source - https://android.googlesource.com/platform/system/core/+/e8d02c50d7/libsparse/sparse_read.cpp#249
.. seealso::
Source - https://android.googlesource.com/platform/system/core/+/e8d02c50d7/libsparse/sparse_read.cpp#270
"""
if hasattr(self, '_m_len_body_expected'):
return self._m_len_body_expected
self._m_len_body_expected = (self._root.header.block_size * self.num_body_blocks if self.chunk_type == AndroidSparse.ChunkTypes.raw else (4 if self.chunk_type == AndroidSparse.ChunkTypes.fill else (0 if self.chunk_type == AndroidSparse.ChunkTypes.dont_care else (4 if self.chunk_type == AndroidSparse.ChunkTypes.crc32 else -1))))
return getattr(self, '_m_len_body_expected', None)
class FileHeader(KaitaiStruct):
def __init__(self, _io, _parent=None, _root=None):
super(AndroidSparse.FileHeader, self).__init__(_io)
self._parent = _parent
self._root = _root
self._read()
def _read(self):
self.len_chunk_header = self._io.read_u2le()
self.block_size = self._io.read_u4le()
_ = self.block_size
if not _ % 4 == 0:
raise kaitaistruct.ValidationExprError(self.block_size, self._io, u"/types/file_header/seq/1")
self.num_blocks = self._io.read_u4le()
self.num_chunks = self._io.read_u4le()
self.checksum = self._io.read_u4le()
def _fetch_instances(self):
pass
@property
def len_header(self):
"""size of file header, should be 28."""
if hasattr(self, '_m_len_header'):
return self._m_len_header
self._m_len_header = self._root.header_prefix.len_header
return getattr(self, '_m_len_header', None)
@property
def version(self):
if hasattr(self, '_m_version'):
return self._m_version
self._m_version = self._root.header_prefix.version
return getattr(self, '_m_version', None)
class FileHeaderPrefix(KaitaiStruct):
def __init__(self, _io, _parent=None, _root=None):
super(AndroidSparse.FileHeaderPrefix, self).__init__(_io)
self._parent = _parent
self._root = _root
self._read()
def _read(self):
self.magic = self._io.read_bytes(4)
if not self.magic == b"\x3A\xFF\x26\xED":
raise kaitaistruct.ValidationNotEqualError(b"\x3A\xFF\x26\xED", self.magic, self._io, u"/types/file_header_prefix/seq/0")
self.version = AndroidSparse.Version(self._io, self, self._root)
self.len_header = self._io.read_u2le()
def _fetch_instances(self):
pass
self.version._fetch_instances()
class Version(KaitaiStruct):
def __init__(self, _io, _parent=None, _root=None):
super(AndroidSparse.Version, self).__init__(_io)
self._parent = _parent
self._root = _root
self._read()
def _read(self):
self.major = self._io.read_u2le()
if not self.major == 1:
raise kaitaistruct.ValidationNotEqualError(1, self.major, self._io, u"/types/version/seq/0")
self.minor = self._io.read_u2le()
def _fetch_instances(self):
pass