Include CRC32 in FileInfo

[myers]

Is your feature request related to a problem? Please describe.
I would like to get the crc32 of a file without having to extract it.

Describe the solution you'd like
Add crc32 as a field on FileInfo

Describe alternatives you've considered
I suspect this is already in some deeper structure of py7zr, but I don't understand enough to find it. I know it is listed when doing 7z l -slt file.7z.

[miurahr]

There are several CRC value in 7zip archive. Which one should be included?

• startheadercrc
• nextheadercrc
• each archive file crcs[] (optional)
• each folders(lzma containers) crc[] (optional)

Mandatory CRC is header crc and it may not be good for FileInfo field

[miurahr]

Oh,

** the crc32 of a file **

If a file means '*.7z' file, there is no value in the archive.

[myers]

Have you ever used the built in python module zipfile or https://pypi.org/project/rarfile/ ? Both of these allow you to get the crc32 of the files in the archive, as they are in the metadata of the archive.

I was able to find what I needed:

        self._zf = py7zr.SevenZipFile(self.filepath, "r")
        # later in the class
        for fi in self._zf.list():
            if fi.is_directory:
                assert fi.uncompressed == 0
                continue

            fnfo = dict(filepath=fi.filename, size=fi.uncompressed)
            for ff in self._zf.header.files_info.files:
                if ff["filename"] != fi.filename:
                    continue
                crc32_uint32 = ctypes.c_uint32(0)
                crc32_uint32.value = ff["digest"]
                fnfo["crc32"] = f"{crc32_uint32.value:08X}"

[myers]

Very odd, the code above gives me the CRC32 of the file in the archive. If it's not in the metadata of the archive, where is it getting it from?

[miurahr]

You may mean

each archive file crcs[] (optional)

[myers]

You may mean

each archive file crcs[] (optional)

Yes, sorry. That is what I'm looking for.

[miurahr]

Sorry, just now, I cannot find a place where is a filed of CRC for each Files info in header.files_info.files.

Here is a header decode block for files_info

py7zr/py7zr/archiveinfo.py

Lines 682 to 736 in a2971e4

	def _read(self, fp: BinaryIO):
	numfiles = read_uint64(fp)
	self.files = [{'emptystream': False} for _ in range(numfiles)]
	numemptystreams = 0
	while True:
	prop = fp.read(1)
	if prop == Property.END:
	break
	size = read_uint64(fp)
	if prop == Property.DUMMY:
	# Added by newer versions of 7z to adjust padding.
	fp.seek(size, os.SEEK_CUR)
	continue
	buffer = io.BytesIO(fp.read(size))
	if prop == Property.EMPTY_STREAM:
	isempty = read_boolean(buffer, numfiles, checkall=False)
	list(map(lambda x, y: x.update({'emptystream': y}), self.files, isempty)) # type: ignore
	numemptystreams += isempty.count(True)
	elif prop == Property.EMPTY_FILE:
	self.emptyfiles = read_boolean(buffer, numemptystreams, checkall=False)
	elif prop == Property.ANTI:
	self.antifiles = read_boolean(buffer, numemptystreams, checkall=False)
	elif prop == Property.NAME:
	external = buffer.read(1)
	if external == b'\x00':
	self._read_name(buffer)
	else:
	dataindex = read_uint64(buffer)
	current_pos = fp.tell()
	fp.seek(dataindex, 0)
	self._read_name(fp)
	fp.seek(current_pos, 0)
	elif prop == Property.CREATION_TIME:
	self._read_times(buffer, 'creationtime')
	elif prop == Property.LAST_ACCESS_TIME:
	self._read_times(buffer, 'lastaccesstime')
	elif prop == Property.LAST_WRITE_TIME:
	self._read_times(buffer, 'lastwritetime')
	elif prop == Property.ATTRIBUTES:
	defined = read_boolean(buffer, numfiles, checkall=True)
	external = buffer.read(1)
	if external == b'\x00':
	self._read_attributes(buffer, defined)
	else:
	dataindex = read_uint64(buffer)
	# try to read external data
	current_pos = fp.tell()
	fp.seek(dataindex, 0)
	self._read_attributes(fp, defined)
	fp.seek(current_pos, 0)
	elif prop == Property.START_POS:
	self._read_start_pos(buffer)
	else:
	raise Bad7zFile('invalid type %r' % prop)

[miurahr]

Maybe around L463.

py7zr/py7zr/py7zr.py

Lines 458 to 467 in a2971e4

	file_info['folder'] = folder
	file_info['maxsize'] = maxsize
	file_info['compressed'] = compressed
	file_info['uncompressed'] = uncompressed
	file_info['packsizes'] = packsize
	if subinfo.digestsdefined[pstat.outstreams]:
	file_info['digest'] = subinfo.digests[pstat.outstreams]
	if folder is None:
	pstat.src_pos += file_info['compressed']
	else:

[miurahr]

Try to implement in #136
Could you test it and give me a feedback?

[myers]

This looks good to me!