cpython-withatomic / Lib / gzip.py

The branch '2.2' does not exist.
"""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
import zlib
import __builtin__

__all__ = ["GzipFile","open"]

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

READ, WRITE = 1, 2

def write32(output, value):
    output.write(struct.pack("<l", value))

def write32u(output, value):
    if value < 0:
        value = value + 0x100000000L
    output.write(struct.pack("<L", value))

def read32(input):
    return struct.unpack("<l", input.read(4))[0]

def open(filename, mode="rb", compresslevel=9):
    return GzipFile(filename, mode, compresslevel)

class GzipFile:

    myfileobj = None

    def __init__(self, filename=None, mode=None,
                 compresslevel=9, fileobj=None):
        if fileobj is None:
            fileobj = self.myfileobj = __builtin__.open(filename, mode or 'rb')
        if filename is None:
            if hasattr(fileobj, 'name'): filename = fileobj.name
            else: filename = ''
        if mode is None:
            if hasattr(fileobj, 'mode'): mode = fileobj.mode
            else: mode = 'rb'

        if mode[0:1] == 'r':
            self.mode = READ
            # Set flag indicating start of a new member
            self._new_member = 1
            self.extrabuf = ""
            self.extrasize = 0
            self.filename = filename

        elif mode[0:1] == 'w' or mode[0:1] == '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, "Mode " + mode + " not supported"

        self.fileobj = fileobj
        self.offset = 0

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

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

    def _init_write(self, filename):
        if filename[-3:] != '.gz':
            filename = filename + '.gz'
        self.filename = filename
        self.crc = zlib.crc32("")
        self.size = 0
        self.writebuf = []
        self.bufsize = 0

    def _write_gzip_header(self):
        self.fileobj.write('\037\213')             # magic header
        self.fileobj.write('\010')                 # compression method
        fname = self.filename[:-3]
        flags = 0
        if fname:
            flags = FNAME
        self.fileobj.write(chr(flags))
        write32u(self.fileobj, long(time.time()))
        self.fileobj.write('\002')
        self.fileobj.write('\377')
        if fname:
            self.fileobj.write(fname + '\000')

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

    def _read_gzip_header(self):
        magic = self.fileobj.read(2)
        if magic != '\037\213':
            raise IOError, 'Not a gzipped file'
        method = ord( self.fileobj.read(1) )
        if method != 8:
            raise IOError, 'Unknown compression method'
        flag = ord( self.fileobj.read(1) )
        # modtime = self.fileobj.read(4)
        # extraflag = self.fileobj.read(1)
        # os = self.fileobj.read(1)
        self.fileobj.read(6)

        if flag & FEXTRA:
            # Read & discard the extra field, if present
            xlen=ord(self.fileobj.read(1))
            xlen=xlen+256*ord(self.fileobj.read(1))
            self.fileobj.read(xlen)
        if flag & FNAME:
            # Read and discard a null-terminated string containing the filename
            while (1):
                s=self.fileobj.read(1)
                if not s or s=='\000': break
        if flag & FCOMMENT:
            # Read and discard a null-terminated string containing a comment
            while (1):
                s=self.fileobj.read(1)
                if not s or s=='\000': break
        if flag & FHCRC:
            self.fileobj.read(2)     # Read & discard the 16-bit header CRC


    def write(self,data):
        if self.fileobj is None:
            raise ValueError, "write() on closed GzipFile object"
        if len(data) > 0:
            self.size = self.size + len(data)
            self.crc = zlib.crc32(data, self.crc)
            self.fileobj.write( self.compress.compress(data) )
            self.offset += len(data)

    def read(self, size=-1):
        if self.extrasize <= 0 and self.fileobj is None:
            return ''

        readsize = 1024
        if size < 0:        # get the whole thing
            try:
                while 1:
                    self._read(readsize)
                    readsize = readsize * 2
            except EOFError:
                size = self.extrasize
        else:               # just get some more of it
            try:
                while size > self.extrasize:
                    self._read(readsize)
                    readsize = readsize * 2
            except EOFError:
                if size > self.extrasize:
                    size = self.extrasize

        chunk = self.extrabuf[:size]
        self.extrabuf = self.extrabuf[size:]
        self.extrasize = self.extrasize - size

        self.offset += size
        return chunk

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

    def _read(self, size=1024):
        if self.fileobj is None: raise EOFError, "Reached EOF"

        if self._new_member:
            # If the _new_member flag is set, we have to
            # jump to the next member, if there is one.
            #
            # First, check if we're at the end of the file;
            # if so, it's time to stop; no more members to read.
            pos = self.fileobj.tell()   # Save current position
            self.fileobj.seek(0, 2)     # Seek to end of file
            if pos == self.fileobj.tell():
                raise EOFError, "Reached EOF"
            else:
                self.fileobj.seek( pos ) # Return to original position

            self._init_read()
            self._read_gzip_header()
            self.decompress = zlib.decompressobj(-zlib.MAX_WBITS)
            self._new_member = 0

        # 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 == "":
            uncompress = self.decompress.flush()
            self._read_eof()
            self._add_read_data( uncompress )
            raise EOFError, 'Reached EOF'

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

        if self.decompress.unused_data != "":
            # 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.
            # (The number of bytes to seek back is the length of the unused
            # data, minus 8 because _read_eof() will rewind a further 8 bytes)
            self.fileobj.seek( -len(self.decompress.unused_data)+8, 1)

            # 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 = 1

    def _add_read_data(self, data):
        self.crc = zlib.crc32(data, self.crc)
        self.extrabuf = self.extrabuf + data
        self.extrasize = self.extrasize + len(data)
        self.size = self.size + len(data)

    def _read_eof(self):
        # We've read to the end of the file, so we have to rewind in order
        # to reread the 8 bytes containing the CRC and the file size.
        # We check the that the computed CRC and size of the
        # uncompressed data matches the stored values.
        self.fileobj.seek(-8, 1)
        crc32 = read32(self.fileobj)
        isize = read32(self.fileobj)
        if crc32%0x100000000L != self.crc%0x100000000L:
            raise ValueError, "CRC check failed"
        elif isize != self.size:
            raise ValueError, "Incorrect length of data produced"

    def close(self):
        if self.mode == WRITE:
            self.fileobj.write(self.compress.flush())
            write32(self.fileobj, self.crc)
            write32(self.fileobj, self.size)
            self.fileobj = None
        elif self.mode == READ:
            self.fileobj = None
        if self.myfileobj:
            self.myfileobj.close()
            self.myfileobj = None

    def __del__(self):
        try:
            if (self.myfileobj is None and
                self.fileobj is None):
                return
        except AttributeError:
            return
        self.close()

    def flush(self):
        self.fileobj.flush()

    def isatty(self):
        return 0

    def tell(self):
        return self.offset

    def rewind(self):
        '''Return the uncompressed stream file position indicator to the
        beginning of the file'''
        if self.mode != READ:
            raise IOError("Can't rewind in write mode")
        self.fileobj.seek(0)
        self._new_member = 1
        self.extrabuf = ""
        self.extrasize = 0
        self.offset = 0

    def seek(self, offset):
        if self.mode == WRITE:
            if offset < self.offset:
                raise IOError('Negative seek in write mode')
            count = offset - self.offset
            for i in range(count/1024):
                self.write(1024*'\0')
            self.write((count%1024)*'\0')
        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)

    def readline(self, size=-1):
        if size < 0: size = sys.maxint
        bufs = []
        readsize = min(100, size)    # Read from the file in small chunks
        while 1:
            if size == 0:
                return "".join(bufs) # Return resulting line

            c = self.read(readsize)
            i = c.find('\n')
            if size is not None:
                # 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 i==-1 and len(c) > size: i=size-1
                elif size <= i: i = size -1

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

            # Append chunk to list, decrease 'size',
            bufs.append(c)
            size = size - len(c)
            readsize = min(size, readsize * 2)

    def readlines(self, sizehint=0):
        # Negative numbers result in reading all the lines
        if sizehint <= 0: sizehint = sys.maxint
        L = []
        while sizehint > 0:
            line = self.readline()
            if line == "": break
            L.append( line )
            sizehint = sizehint - len(line)

        return L

    def writelines(self, L):
        for line in L:
            self.write(line)


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)
                g = sys.stdout
            else:
                if arg[-3:] != ".gz":
                    print "filename doesn't end in .gz:", `arg`
                    continue
                f = open(arg, "rb")
                g = __builtin__.open(arg[:-3], "wb")
        else:
            if arg == "-":
                f = sys.stdin
                g = GzipFile(filename="", mode="wb", fileobj=sys.stdout)
            else:
                f = __builtin__.open(arg, "rb")
                g = open(arg + ".gz", "wb")
        while 1:
            chunk = f.read(1024)
            if not chunk:
                break
            g.write(chunk)
        if g is not sys.stdout:
            g.close()
        if f is not sys.stdin:
            f.close()

if __name__ == '__main__':
    _test()
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