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gzip.py
"""Functions that read and write gzipped files. The user of the file doesn't have to worry about the compression, but random access is not allowed.""" # based on Andrew Kuchling's minigzip.py distributed with the zlib module import struct, sys, time, os import zlib import builtins import io import _compression __all__ = ["BadGzipFile", "GzipFile", "open", "compress", "decompress"] FTEXT, FHCRC, FEXTRA, FNAME, FCOMMENT = 1, 2, 4, 8, 16 READ, WRITE = 1, 2 _COMPRESS_LEVEL_FAST = 1 _COMPRESS_LEVEL_TRADEOFF = 6 _COMPRESS_LEVEL_BEST = 9 READ_BUFFER_SIZE = 128 * 1024 _WRITE_BUFFER_SIZE = 4 * io.DEFAULT_BUFFER_SIZE def open(filename, mode="rb", compresslevel=_COMPRESS_LEVEL_BEST, encoding=None, errors=None, newline=None): """Open a gzip-compressed file in binary or text mode. The filename argument can be an actual filename (a str or bytes object), or an existing file object to read from or write to. The mode argument can be "r", "rb", "w", "wb", "x", "xb", "a" or "ab" for binary mode, or "rt", "wt", "xt" or "at" for text mode. The default mode is "rb", and the default compresslevel is 9. For binary mode, this function is equivalent to the GzipFile constructor: GzipFile(filename, mode, compresslevel). In this case, the encoding, errors and newline arguments must not be provided. For text mode, a GzipFile object is created, and wrapped in an io.TextIOWrapper instance with the specified encoding, error handling behavior, and line ending(s). """ if "t" in mode: if "b" in mode: raise ValueError("Invalid mode: %r" % (mode,)) else: if encoding is not None: raise ValueError("Argument 'encoding' not supported in binary mode") if errors is not None: raise ValueError("Argument 'errors' not supported in binary mode") if newline is not None: raise ValueError("Argument 'newline' not supported in binary mode") gz_mode = mode.replace("t", "") if isinstance(filename, (str, bytes, os.PathLike)): binary_file = GzipFile(filename, gz_mode, compresslevel) elif hasattr(filename, "read") or hasattr(filename, "write"): binary_file = GzipFile(None, gz_mode, compresslevel, filename) else: raise TypeError("filename must be a str or bytes object, or a file") if "t" in mode: encoding = io.text_encoding(encoding) return io.TextIOWrapper(binary_file, encoding, errors, newline) else: return binary_file def write32u(output, value): # The L format writes the bit pattern correctly whether signed # or unsigned. output.write(struct.pack("<L", value)) class _PaddedFile: """Minimal read-only file object that prepends a string to the contents of an actual file. Shouldn't be used outside of gzip.py, as it lacks essential functionality.""" def __init__(self, f, prepend=b''): self._buffer = prepend self._length = len(prepend) self.file = f self._read = 0 def read(self, size): if self._read is None: return self.file.read(size) if self._read + size <= self._length: read = self._read self._read += size return self._buffer[read:self._read] else: read = self._read self._read = None return self._buffer[read:] + \ self.file.read(size-self._length+read) def prepend(self, prepend=b''): if self._read is None: self._buffer = prepend else: # Assume data was read since the last prepend() call self._read -= len(prepend) return self._length = len(self._buffer) self._read = 0 def seek(self, off): self._read = None self._buffer = None return self.file.seek(off) def seekable(self): return True # Allows fast-forwarding even in unseekable streams class BadGzipFile(OSError): """Exception raised in some cases for invalid gzip files.""" class _WriteBufferStream(io.RawIOBase): """Minimal object to pass WriteBuffer flushes into GzipFile""" def __init__(self, gzip_file): self.gzip_file = gzip_file def write(self, data): return self.gzip_file._write_raw(data) def seekable(self): return False def writable(self): return True class GzipFile(_compression.BaseStream): """The GzipFile class simulates most of the methods of a file object with the exception of the truncate() method. This class only supports opening files in binary mode. If you need to open a compressed file in text mode, use the gzip.open() function. """ # Overridden with internal file object to be closed, if only a filename # is passed in myfileobj = None def __init__(self, filename=None, mode=None, compresslevel=_COMPRESS_LEVEL_BEST, fileobj=None, mtime=None): """Constructor for the GzipFile class. At least one of fileobj and filename must be given a non-trivial value. The new class instance is based on fileobj, which can be a regular file, an io.BytesIO object, or any other object which simulates a file. It defaults to None, in which case filename is opened to provide a file object. When fileobj is not None, the filename argument is only used to be included in the gzip file header, which may include the original filename of the uncompressed file. It defaults to the filename of fileobj, if discernible; otherwise, it defaults to the empty string, and in this case the original filename is not included in the header. The mode argument can be any of 'r', 'rb', 'a', 'ab', 'w', 'wb', 'x', or 'xb' depending on whether the file will be read or written. The default is the mode of fileobj if discernible; otherwise, the default is 'rb'. A mode of 'r' is equivalent to one of 'rb', and similarly for 'w' and 'wb', 'a' and 'ab', and 'x' and 'xb'. The compresslevel argument is an integer from 0 to 9 controlling the level of compression; 1 is fastest and produces the least compression, and 9 is slowest and produces the most compression. 0 is no compression at all. The default is 9. The mtime argument is an optional numeric timestamp to be written to the last modification time field in the stream when compressing. If omitted or None, the current time is used. """ if mode and ('t' in mode or 'U' in mode): raise ValueError("Invalid mode: {!r}".format(mode)) if mode and 'b' not in mode: mode += 'b' if fileobj is None: fileobj = self.myfileobj = builtins.open(filename, mode or 'rb') if filename is None: filename = getattr(fileobj, 'name', '') if not isinstance(filename, (str, bytes)): filename = '' else: filename = os.fspath(filename) origmode = mode if mode is None: mode = getattr(fileobj, 'mode', 'rb') if mode.startswith('r'): self.mode = READ raw = _GzipReader(fileobj) self._buffer = io.BufferedReader(raw) self.name = filename elif mode.startswith(('w', 'a', 'x')): if origmode is None: import warnings warnings.warn( "GzipFile was opened for writing, but this will " "change in future Python releases. " "Specify the mode argument for opening it for writing.", FutureWarning, 2) self.mode = WRITE self._init_write(filename) self.compress = zlib.compressobj(compresslevel, zlib.DEFLATED, -zlib.MAX_WBITS, zlib.DEF_MEM_LEVEL, 0) self._write_mtime = mtime self._buffer_size = _WRITE_BUFFER_SIZE self._buffer = io.BufferedWriter(_WriteBufferStream(self), buffer_size=self._buffer_size) else: raise ValueError("Invalid mode: {!r}".format(mode)) self.fileobj = fileobj if self.mode == WRITE: self._write_gzip_header(compresslevel) @property def mtime(self): """Last modification time read from stream, or None""" return self._buffer.raw._last_mtime def __repr__(self): s = repr(self.fileobj) return '<gzip ' + s[1:-1] + ' ' + hex(id(self)) + '>' def _init_write(self, filename): self.name = filename self.crc = zlib.crc32(b"") self.size = 0 self.writebuf = [] self.bufsize = 0 self.offset = 0 # Current file offset for seek(), tell(), etc def tell(self): self._check_not_closed() self._buffer.flush() return super().tell() def _write_gzip_header(self, compresslevel): self.fileobj.write(b'\037\213') # magic header self.fileobj.write(b'\010') # compression method try: # RFC 1952 requires the FNAME field to be Latin-1. Do not # include filenames that cannot be represented that way. fname = os.path.basename(self.name) if not isinstance(fname, bytes): fname = fname.encode('latin-1') if fname.endswith(b'.gz'): fname = fname[:-3] except UnicodeEncodeError: fname = b'' flags = 0 if fname: flags = FNAME self.fileobj.write(chr(flags).encode('latin-1')) mtime = self._write_mtime if mtime is None: mtime = time.time() write32u(self.fileobj, int(mtime)) if compresslevel == _COMPRESS_LEVEL_BEST: xfl = b'\002' elif compresslevel == _COMPRESS_LEVEL_FAST: xfl = b'\004' else: xfl = b'\000' self.fileobj.write(xfl) self.fileobj.write(b'\377') if fname: self.fileobj.write(fname + b'\000') def write(self,data): self._check_not_closed() if self.mode != WRITE: import errno raise OSError(errno.EBADF, "write() on read-only GzipFile object") if self.fileobj is None: raise ValueError("write() on closed GzipFile object") return self._buffer.write(data) def _write_raw(self, data): # Called by our self._buffer underlying WriteBufferStream. if isinstance(data, (bytes, bytearray)): length = len(data) else: # accept any data that supports the buffer protocol data = memoryview(data) length = data.nbytes if length > 0: self.fileobj.write(self.compress.compress(data)) self.size += length self.crc = zlib.crc32(data, self.crc) self.offset += length return length def read(self, size=-1): self._check_not_closed() if self.mode != READ: import errno raise OSError(errno.EBADF, "read() on write-only GzipFile object") return self._buffer.read(size) def read1(self, size=-1): """Implements BufferedIOBase.read1() Reads up to a buffer's worth of data if size is negative.""" self._check_not_closed() if self.mode != READ: import errno raise OSError(errno.EBADF, "read1() on write-only GzipFile object") if size < 0: size = io.DEFAULT_BUFFER_SIZE return self._buffer.read1(size) def peek(self, n): self._check_not_closed() if self.mode != READ: import errno raise OSError(errno.EBADF, "peek() on write-only GzipFile object") return self._buffer.peek(n) @property def closed(self): return self.fileobj is None def close(self): fileobj = self.fileobj if fileobj is None: return try: if self.mode == WRITE: self._buffer.flush() fileobj.write(self.compress.flush()) write32u(fileobj, self.crc) # self.size may exceed 2 GiB, or even 4 GiB write32u(fileobj, self.size & 0xffffffff) elif self.mode == READ: self._buffer.close() finally: self.fileobj = None myfileobj = self.myfileobj if myfileobj: self.myfileobj = None myfileobj.close() def flush(self,zlib_mode=zlib.Z_SYNC_FLUSH): self._check_not_closed() if self.mode == WRITE: self._buffer.flush() # Ensure the compressor's buffer is flushed self.fileobj.write(self.compress.flush(zlib_mode)) self.fileobj.flush() def fileno(self): """Invoke the underlying file object's fileno() method. This will raise AttributeError if the underlying file object doesn't support fileno(). """ return self.fileobj.fileno() def rewind(self): '''Return the uncompressed stream file position indicator to the beginning of the file''' if self.mode != READ: raise OSError("Can't rewind in write mode") self._buffer.seek(0) def readable(self): return self.mode == READ def writable(self): return self.mode == WRITE def seekable(self): return True def seek(self, offset, whence=io.SEEK_SET): if self.mode == WRITE: self._check_not_closed() # Flush buffer to ensure validity of self.offset self._buffer.flush() if whence != io.SEEK_SET: if whence == io.SEEK_CUR: offset = self.offset + offset else: raise ValueError('Seek from end not supported') if offset < self.offset: raise OSError('Negative seek in write mode') count = offset - self.offset chunk = b'\0' * self._buffer_size for i in range(count // self._buffer_size): self.write(chunk) self.write(b'\0' * (count % self._buffer_size)) elif self.mode == READ: self._check_not_closed() return self._buffer.seek(offset, whence) return self.offset def readline(self, size=-1): self._check_not_closed() return self._buffer.readline(size) def _read_exact(fp, n): '''Read exactly *n* bytes from `fp` This method is required because fp may be unbuffered, i.e. return short reads. ''' data = fp.read(n) while len(data) < n: b = fp.read(n - len(data)) if not b: raise EOFError("Compressed file ended before the " "end-of-stream marker was reached") data += b return data def _read_gzip_header(fp): '''Read a gzip header from `fp` and progress to the end of the header. Returns last mtime if header was present or None otherwise. ''' magic = fp.read(2) if magic == b'': return None if magic != b'\037\213': raise BadGzipFile('Not a gzipped file (%r)' % magic) (method, flag, last_mtime) = struct.unpack("<BBIxx", _read_exact(fp, 8)) if method != 8: raise BadGzipFile('Unknown compression method') if flag & FEXTRA: # Read & discard the extra field, if present extra_len, = struct.unpack("<H", _read_exact(fp, 2)) _read_exact(fp, extra_len) if flag & FNAME: # Read and discard a null-terminated string containing the filename while True: s = fp.read(1) if not s or s==b'\000': break if flag & FCOMMENT: # Read and discard a null-terminated string containing a comment while True: s = fp.read(1) if not s or s==b'\000': break if flag & FHCRC: _read_exact(fp, 2) # Read & discard the 16-bit header CRC return last_mtime class _GzipReader(_compression.DecompressReader): def __init__(self, fp): super().__init__(_PaddedFile(fp), zlib._ZlibDecompressor, wbits=-zlib.MAX_WBITS) # Set flag indicating start of a new member self._new_member = True self._last_mtime = None def _init_read(self): self._crc = zlib.crc32(b"") self._stream_size = 0 # Decompressed size of unconcatenated stream def _read_gzip_header(self): last_mtime = _read_gzip_header(self._fp) if last_mtime is None: return False self._last_mtime = last_mtime return True def read(self, size=-1): if size < 0: return self.readall() # size=0 is special because decompress(max_length=0) is not supported if not size: return b"" # For certain input data, a single # call to decompress() may not return # any data. In this case, retry until we get some data or reach EOF. while True: if self._decompressor.eof: # Ending case: we've come to the end of a member in the file, # so finish up this member, and read a new gzip header. # Check the CRC and file size, and set the flag so we read # a new member self._read_eof() self._new_member = True self._decompressor = self._decomp_factory( **self._decomp_args) if self._new_member: # If the _new_member flag is set, we have to # jump to the next member, if there is one. self._init_read() if not self._read_gzip_header(): self._size = self._pos return b"" self._new_member = False # Read a chunk of data from the file if self._decompressor.needs_input: buf = self._fp.read(READ_BUFFER_SIZE) uncompress = self._decompressor.decompress(buf, size) else: uncompress = self._decompressor.decompress(b"", size) if self._decompressor.unused_data != b"": # Prepend the already read bytes to the fileobj so they can # be seen by _read_eof() and _read_gzip_header() self._fp.prepend(self._decompressor.unused_data) if uncompress != b"": break if buf == b"": raise EOFError("Compressed file ended before the " "end-of-stream marker was reached") self._crc = zlib.crc32(uncompress, self._crc) self._stream_size += len(uncompress) self._pos += len(uncompress) return uncompress def _read_eof(self): # We've read to the end of the file # We check that the computed CRC and size of the # uncompressed data matches the stored values. Note that the size # stored is the true file size mod 2**32. crc32, isize = struct.unpack("<II", _read_exact(self._fp, 8)) if crc32 != self._crc: raise BadGzipFile("CRC check failed %s != %s" % (hex(crc32), hex(self._crc))) elif isize != (self._stream_size & 0xffffffff): raise BadGzipFile("Incorrect length of data produced") # Gzip files can be padded with zeroes and still have archives. # Consume all zero bytes and set the file position to the first # non-zero byte. See http://www.gzip.org/#faq8 c = b"\x00" while c == b"\x00": c = self._fp.read(1) if c: self._fp.prepend(c) def _rewind(self): super()._rewind() self._new_member = True def _create_simple_gzip_header(compresslevel: int, mtime = None) -> bytes: """ Write a simple gzip header with no extra fields. :param compresslevel: Compresslevel used to determine the xfl bytes. :param mtime: The mtime (must support conversion to a 32-bit integer). :return: A bytes object representing the gzip header. """ if mtime is None: mtime = time.time() if compresslevel == _COMPRESS_LEVEL_BEST: xfl = 2 elif compresslevel == _COMPRESS_LEVEL_FAST: xfl = 4 else: xfl = 0 # Pack ID1 and ID2 magic bytes, method (8=deflate), header flags (no extra # fields added to header), mtime, xfl and os (255 for unknown OS). return struct.pack("<BBBBLBB", 0x1f, 0x8b, 8, 0, int(mtime), xfl, 255) def compress(data, compresslevel=_COMPRESS_LEVEL_BEST, *, mtime=None): """Compress data in one shot and return the compressed string. compresslevel sets the compression level in range of 0-9. mtime can be used to set the modification time. The modification time is set to the current time by default. """ if mtime == 0: # Use zlib as it creates the header with 0 mtime by default. # This is faster and with less overhead. return zlib.compress(data, level=compresslevel, wbits=31) header = _create_simple_gzip_header(compresslevel, mtime) trailer = struct.pack("<LL", zlib.crc32(data), (len(data) & 0xffffffff)) # Wbits=-15 creates a raw deflate block. return (header + zlib.compress(data, level=compresslevel, wbits=-15) + trailer) def decompress(data): """Decompress a gzip compressed string in one shot. Return the decompressed string. """ decompressed_members = [] while True: fp = io.BytesIO(data) if _read_gzip_header(fp) is None: return b"".join(decompressed_members) # Use a zlib raw deflate compressor do = zlib.decompressobj(wbits=-zlib.MAX_WBITS) # Read all the data except the header decompressed = do.decompress(data[fp.tell():]) if not do.eof or len(do.unused_data) < 8: raise EOFError("Compressed file ended before the end-of-stream " "marker was reached") crc, length = struct.unpack("<II", do.unused_data[:8]) if crc != zlib.crc32(decompressed): raise BadGzipFile("CRC check failed") if length != (len(decompressed) & 0xffffffff): raise BadGzipFile("Incorrect length of data produced") decompressed_members.append(decompressed) data = do.unused_data[8:].lstrip(b"\x00") def main(): from argparse import ArgumentParser parser = ArgumentParser(description= "A simple command line interface for the gzip module: act like gzip, " "but do not delete the input file.") group = parser.add_mutually_exclusive_group() group.add_argument('--fast', action='store_true', help='compress faster') group.add_argument('--best', action='store_true', help='compress better') group.add_argument("-d", "--decompress", action="store_true", help="act like gunzip instead of gzip") parser.add_argument("args", nargs="*", default=["-"], metavar='file') args = parser.parse_args() compresslevel = _COMPRESS_LEVEL_TRADEOFF if args.fast: compresslevel = _COMPRESS_LEVEL_FAST elif args.best: compresslevel = _COMPRESS_LEVEL_BEST for arg in args.args: if args.decompress: if arg == "-": f = GzipFile(filename="", mode="rb", fileobj=sys.stdin.buffer) g = sys.stdout.buffer else: if arg[-3:] != ".gz": sys.exit(f"filename doesn't end in .gz: {arg!r}") f = open(arg, "rb") g = builtins.open(arg[:-3], "wb") else: if arg == "-": f = sys.stdin.buffer g = GzipFile(filename="", mode="wb", fileobj=sys.stdout.buffer, compresslevel=compresslevel) else: f = builtins.open(arg, "rb") g = open(arg + ".gz", "wb") while True: chunk = f.read(READ_BUFFER_SIZE) if not chunk: break g.write(chunk) if g is not sys.stdout.buffer: g.close() if f is not sys.stdin.buffer: f.close() if __name__ == '__main__': main()
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