import time import string import zlib import struct import __builtin__ # implements a python function that reads and writes a gzipped file # 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 FTEXT, FHCRC, FEXTRA, FNAME, FCOMMENT = 1, 2, 4, 8, 16 READ, WRITE = 1, 2 def write32(output, value): output.write(struct.pack("' 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)) write32(self.fileobj, int(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) ) def writelines(self,lines): self.write(string.join(lines)) def read(self, size=None): if self.extrasize <= 0 and self.fileobj is None: return '' readsize = 1024 if not size: # 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 return chunk def _unread(self, buf): self.extrabuf = buf + self.extrabuf self.extrasize = len(buf) + self.extrasize 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 # # 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(): self.fileobj = None return 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.fileobj = None 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 != self.crc: 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 flush(self): self.fileobj.flush() def seek(self): raise IOError, 'Random access not allowed in gzip files' def tell(self): raise IOError, 'I won\'t tell() you for gzip files' def isatty(self): return 0 def readline(self): bufs = [] readsize = 100 while 1: c = self.read(readsize) i = string.find(c, '\n') if i >= 0 or c == '': bufs.append(c[:i+1]) self._unread(c[i+1:]) return string.join(bufs, '') bufs.append(c) readsize = readsize * 2 def readlines(self): buf = self.read() lines = string.split(buf, '\n') for i in range(len(lines)-1): lines[i] = lines[i] + '\n' if lines and not lines[-1]: del lines[-1] return lines 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. import sys 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()