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

__all__ = ["GzipFile", "open", "compress", "decompress"]

FTEXT, FHCRC, FEXTRA, FNAME, FCOMMENT = 1, 2, 4, 8, 16

READ, WRITE = 1, 2

def open(filename, mode="rb", compresslevel=9,
         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", "a" or "ab" for binary mode,
    or "rt", "wt" 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)):
        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:
        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'', readprevious=False):
        if self._read is None:
            self._buffer = prepend
        elif readprevious and len(prepend) <= self._read:
            self._read -= len(prepend)
            return
        else:
            self._buffer = self._buffer[read:] + prepend
        self._length = len(self._buffer)
        self._read = 0

    def unused(self):
        if self._read is None:
            return b''
        return self._buffer[self._read:]

    def seek(self, offset, whence=0):
        # This is only ever called with offset=whence=0
        if whence == 1 and self._read is not None:
            if 0 <= offset + self._read <= self._length:
                self._read += offset
                return
            else:
                offset += self._length - self._read
        self._read = None
        self._buffer = None
        return self.file.seek(offset, whence)

    def __getattr__(self, name):
        return getattr(self.file, name)


class GzipFile(io.BufferedIOBase):
    """The GzipFile class simulates most of the methods of a file object with
    the exception of the readinto() and truncate() methods.

    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.

    """

    myfileobj = None
    max_read_chunk = 10 * 1024 * 1024   # 10Mb

    def __init__(self, filename=None, mode=None,
                 compresslevel=9, 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, a StringIO 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 includes 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', or 'wb',
        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', and 'a' and 'ab'.

        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 stream when compressing.  All gzip compressed streams
        are required to contain a timestamp.  If omitted or None, the
        current time is used.  This module ignores the timestamp when
        decompressing; however, some programs, such as gunzip, make use
        of it.  The format of the timestamp is the same as that of the
        return value of time.time() and of the st_mtime member of the
        object returned by os.stat().

        """

        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 = ''
        if mode is None:
            mode = getattr(fileobj, 'mode', 'rb')

        if mode.startswith('r'):
            self.mode = READ
            # Set flag indicating start of a new member
            self._new_member = True
            # Buffer data read from gzip file. extrastart is offset in
            # stream where buffer starts. extrasize is number of
            # bytes remaining in buffer from current stream position.
            self.extrabuf = b""
            self.extrasize = 0
            self.extrastart = 0
            self.name = filename
            # Starts small, scales exponentially
            self.min_readsize = 100
            fileobj = _PaddedFile(fileobj)

        elif mode.startswith(('w', 'a')):
            self.mode = WRITE
            self._init_write(filename)
            self.compress = zlib.compressobj(compresslevel,
                                             zlib.DEFLATED,
                                             -zlib.MAX_WBITS,
                                             zlib.DEF_MEM_LEVEL,
                                             0)
        else:
            raise ValueError("Invalid mode: {!r}".format(mode))

        self.fileobj = fileobj
        self.offset = 0
        self.mtime = mtime

        if self.mode == WRITE:
            self._write_gzip_header()

    @property
    def filename(self):
        import warnings
        warnings.warn("use the name attribute", DeprecationWarning, 2)
        if self.mode == WRITE and self.name[-3:] != ".gz":
            return self.name + ".gz"
        return self.name

    def __repr__(self):
        fileobj = self.fileobj
        if isinstance(fileobj, _PaddedFile):
            fileobj = fileobj.file
        s = repr(fileobj)
        return '<gzip ' + s[1:-1] + ' ' + hex(id(self)) + '>'

    def _check_closed(self):
        """Raises a ValueError if the underlying file object has been closed.

        """
        if self.closed:
            raise ValueError('I/O operation on closed file.')

    def _init_write(self, filename):
        self.name = filename
        self.crc = zlib.crc32(b"") & 0xffffffff
        self.size = 0
        self.writebuf = []
        self.bufsize = 0

    def _write_gzip_header(self):
        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.mtime
        if mtime is None:
            mtime = time.time()
        write32u(self.fileobj, int(mtime))
        self.fileobj.write(b'\002')
        self.fileobj.write(b'\377')
        if fname:
            self.fileobj.write(fname + b'\000')

    def _init_read(self):
        self.crc = zlib.crc32(b"") & 0xffffffff
        self.size = 0

    def _read_exact(self, n):
        data = self.fileobj.read(n)
        while len(data) < n:
            b = self.fileobj.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(self):
        magic = self.fileobj.read(2)
        if magic == b'':
            return False

        if magic != b'\037\213':
            raise OSError('Not a gzipped file')

        method, flag, self.mtime = struct.unpack("<BBIxx", self._read_exact(8))
        if method != 8:
            raise OSError('Unknown compression method')

        if flag & FEXTRA:
            # Read & discard the extra field, if present
            self._read_exact(struct.unpack("<H", self._read_exact(2)))
        if flag & FNAME:
            # Read and discard a null-terminated string containing the filename
            while True:
                s = self.fileobj.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 = self.fileobj.read(1)
                if not s or s==b'\000':
                    break
        if flag & FHCRC:
            self._read_exact(2)     # Read & discard the 16-bit header CRC

        unused = self.fileobj.unused()
        if unused:
            uncompress = self.decompress.decompress(unused)
            self._add_read_data(uncompress)
        return True

    def write(self,data):
        self._check_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")

        # Convert data type if called by io.BufferedWriter.
        if isinstance(data, memoryview):
            data = data.tobytes()

        if len(data) > 0:
            self.size = self.size + len(data)
            self.crc = zlib.crc32(data, self.crc) & 0xffffffff
            self.fileobj.write( self.compress.compress(data) )
            self.offset += len(data)

        return len(data)

    def read(self, size=-1):
        self._check_closed()
        if self.mode != READ:
            import errno
            raise OSError(errno.EBADF, "read() on write-only GzipFile object")

        if self.extrasize <= 0 and self.fileobj is None:
            return b''

        readsize = 1024
        if size < 0:        # get the whole thing
            while self._read(readsize):
                readsize = min(self.max_read_chunk, readsize * 2)
            size = self.extrasize
        else:               # just get some more of it
            while size > self.extrasize:
                if not self._read(readsize):
                    if size > self.extrasize:
                        size = self.extrasize
                    break
                readsize = min(self.max_read_chunk, readsize * 2)

        offset = self.offset - self.extrastart
        chunk = self.extrabuf[offset: offset + size]
        self.extrasize = self.extrasize - size

        self.offset += size
        return chunk

    def read1(self, size=-1):
        self._check_closed()
        if self.mode != READ:
            import errno
            raise OSError(errno.EBADF, "read1() on write-only GzipFile object")

        if self.extrasize <= 0 and self.fileobj is None:
            return b''

        # For certain input data, a single call to _read() may not return
        # any data. In this case, retry until we get some data or reach EOF.
        while self.extrasize <= 0 and self._read():
            pass
        if size < 0 or size > self.extrasize:
            size = self.extrasize

        offset = self.offset - self.extrastart
        chunk = self.extrabuf[offset: offset + size]
        self.extrasize -= size
        self.offset += size
        return chunk

    def peek(self, n):
        if self.mode != READ:
            import errno
            raise OSError(errno.EBADF, "peek() on write-only GzipFile object")

        # Do not return ridiculously small buffers, for one common idiom
        # is to call peek(1) and expect more bytes in return.
        if n < 100:
            n = 100
        if self.extrasize == 0:
            if self.fileobj is None:
                return b''
            # Ensure that we don't return b"" if we haven't reached EOF.
            # 1024 is the same buffering heuristic used in read()
            while self.extrasize == 0 and self._read(max(n, 1024)):
                pass
        offset = self.offset - self.extrastart
        remaining = self.extrasize
        assert remaining == len(self.extrabuf) - offset
        return self.extrabuf[offset:offset + n]

    def _unread(self, buf):
        self.extrasize = len(buf) + self.extrasize
        self.offset -= len(buf)

    def _read(self, size=1024):
        if self.fileobj is None:
            return False

        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():
                return False
            self.decompress = zlib.decompressobj(-zlib.MAX_WBITS)
            self._new_member = False

        # Read a chunk of data from the file
        buf = self.fileobj.read(size)

        # If the EOF has been reached, flush the decompression object
        # and mark this object as finished.

        if buf == b"":
            uncompress = self.decompress.flush()
            # Prepend the already read bytes to the fileobj to they can be
            # seen by _read_eof()
            self.fileobj.prepend(self.decompress.unused_data, True)
            self._read_eof()
            self._add_read_data( uncompress )
            return False

        uncompress = self.decompress.decompress(buf)
        self._add_read_data( uncompress )

        if self.decompress.unused_data != b"":
            # Ending case: we've come to the end of a member in the file,
            # so seek back to the start of the unused data, finish up
            # this member, and read a new gzip header.
            # Prepend the already read bytes to the fileobj to they can be
            # seen by _read_eof() and _read_gzip_header()
            self.fileobj.prepend(self.decompress.unused_data, True)
            # Check the CRC and file size, and set the flag so we read
            # a new member on the next call
            self._read_eof()
            self._new_member = True
        return True

    def _add_read_data(self, data):
        self.crc = zlib.crc32(data, self.crc) & 0xffffffff
        offset = self.offset - self.extrastart
        self.extrabuf = self.extrabuf[offset:] + data
        self.extrasize = self.extrasize + len(data)
        self.extrastart = self.offset
        self.size = self.size + len(data)

    def _read_eof(self):
        # We've read to the end of the file
        # We check the 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", self._read_exact(8))
        if crc32 != self.crc:
            raise OSError("CRC check failed %s != %s" % (hex(crc32),
                                                         hex(self.crc)))
        elif isize != (self.size & 0xffffffff):
            raise OSError("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.fileobj.read(1)
        if c:
            self.fileobj.prepend(c, True)

    @property
    def closed(self):
        return self.fileobj is None

    def close(self):
        if self.fileobj is None:
            return
        if self.mode == WRITE:
            self.fileobj.write(self.compress.flush())
            write32u(self.fileobj, self.crc)
            # self.size may exceed 2GB, or even 4GB
            write32u(self.fileobj, self.size & 0xffffffff)
            self.fileobj = None
        elif self.mode == READ:
            self.fileobj = None
        if self.myfileobj:
            self.myfileobj.close()
            self.myfileobj = None

    def flush(self,zlib_mode=zlib.Z_SYNC_FLUSH):
        self._check_closed()
        if self.mode == WRITE:
            # 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.fileobj.seek(0)
        self._new_member = True
        self.extrabuf = b""
        self.extrasize = 0
        self.extrastart = 0
        self.offset = 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=0):
        if whence:
            if whence == 1:
                offset = self.offset + offset
            else:
                raise ValueError('Seek from end not supported')
        if self.mode == WRITE:
            if offset < self.offset:
                raise OSError('Negative seek in write mode')
            count = offset - self.offset
            chunk = bytes(1024)
            for i in range(count // 1024):
                self.write(chunk)
            self.write(bytes(count % 1024))
        elif self.mode == READ:
            if offset < self.offset:
                # for negative seek, rewind and do positive seek
                self.rewind()
            count = offset - self.offset
            for i in range(count // 1024):
                self.read(1024)
            self.read(count % 1024)

        return self.offset

    def readline(self, size=-1):
        if size < 0:
            # Shortcut common case - newline found in buffer.
            offset = self.offset - self.extrastart
            i = self.extrabuf.find(b'\n', offset) + 1
            if i > 0:
                self.extrasize -= i - offset
                self.offset += i - offset
                return self.extrabuf[offset: i]

            size = sys.maxsize
            readsize = self.min_readsize
        else:
            readsize = size
        bufs = []
        while size != 0:
            c = self.read(readsize)
            i = c.find(b'\n')

            # We set i=size to break out of the loop under two
            # conditions: 1) there's no newline, and the chunk is
            # larger than size, or 2) there is a newline, but the
            # resulting line would be longer than 'size'.
            if (size <= i) or (i == -1 and len(c) > size):
                i = size - 1

            if i >= 0 or c == b'':
                bufs.append(c[:i + 1])    # Add portion of last chunk
                self._unread(c[i + 1:])   # Push back rest of chunk
                break

            # Append chunk to list, decrease 'size',
            bufs.append(c)
            size = size - len(c)
            readsize = min(size, readsize * 2)
        if readsize > self.min_readsize:
            self.min_readsize = min(readsize, self.min_readsize * 2, 512)
        return b''.join(bufs) # Return resulting line


def compress(data, compresslevel=9):
    """Compress data in one shot and return the compressed string.
    Optional argument is the compression level, in range of 0-9.
    """
    buf = io.BytesIO()
    with GzipFile(fileobj=buf, mode='wb', compresslevel=compresslevel) as f:
        f.write(data)
    return buf.getvalue()

def decompress(data):
    """Decompress a gzip compressed string in one shot.
    Return the decompressed string.
    """
    with GzipFile(fileobj=io.BytesIO(data)) as f:
        return f.read()


def _test():
    # Act like gzip; with -d, act like gunzip.
    # The input file is not deleted, however, nor are any other gzip
    # options or features supported.
    args = sys.argv[1:]
    decompress = args and args[0] == "-d"
    if decompress:
        args = args[1:]
    if not args:
        args = ["-"]
    for arg in args:
        if decompress:
            if arg == "-":
                f = GzipFile(filename="", mode="rb", fileobj=sys.stdin.buffer)
                g = sys.stdout.buffer
            else:
                if arg[-3:] != ".gz":
                    print("filename doesn't end in .gz:", repr(arg))
                    continue
                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)
            else:
                f = builtins.open(arg, "rb")
                g = open(arg + ".gz", "wb")
        while True:
            chunk = f.read(1024)
            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__':
    _test()