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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 io import __builtin__ __all__ = ["GzipFile","open"] FTEXT, FHCRC, FEXTRA, FNAME, FCOMMENT = 1, 2, 4, 8, 16 READ, WRITE = 1, 2 def write32u(output, value): # The L format writes the bit pattern correctly whether signed # or unsigned. output.write(struct.pack("<L", value)) def read32(input): return struct.unpack("<I", input.read(4))[0] def open(filename, mode="rb", compresslevel=9): """Shorthand for GzipFile(filename, mode, compresslevel). The filename argument is required; mode defaults to 'rb' and compresslevel defaults to 9. """ return GzipFile(filename, mode, compresslevel) 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. """ 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 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', 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'. Be aware that only the 'rb', 'ab', and 'wb' values should be used for cross-platform portability. 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(). """ # Make sure we don't inadvertently enable universal newlines on the # underlying file object - in read mode, this causes data corruption. if mode: mode = mode.replace('U', '') # guarantee the file is opened in binary mode on platforms # that care about that sort of thing if mode and 'b' not in mode: mode += 'b' if fileobj is None: fileobj = self.myfileobj = __builtin__.open(filename, mode or 'rb') if filename is None: # Issue #13781: os.fdopen() creates a fileobj with a bogus name # attribute. Avoid saving this in the gzip header's filename field. filename = getattr(fileobj, 'name', '') if not isinstance(filename, basestring) or filename == '<fdopen>': 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 = 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 = "" self.extrasize = 0 self.extrastart = 0 self.name = filename # Starts small, scales exponentially self.min_readsize = 100 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 IOError, "Mode " + mode + " not supported" 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): s = repr(self.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("") & 0xffffffffL 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 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, str): fname = fname.encode('latin-1') if fname.endswith('.gz'): fname = fname[:-3] except UnicodeEncodeError: fname = '' flags = 0 if fname: flags = FNAME self.fileobj.write(chr(flags)) mtime = self.mtime if mtime is None: mtime = time.time() write32u(self.fileobj, long(mtime)) self.fileobj.write('\002') self.fileobj.write('\377') if fname: self.fileobj.write(fname + '\000') def _init_read(self): self.crc = zlib.crc32("") & 0xffffffffL 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) ) self.mtime = read32(self.fileobj) # extraflag = self.fileobj.read(1) # os = self.fileobj.read(1) self.fileobj.read(2) 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 True: 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 True: 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): self._check_closed() if self.mode != WRITE: import errno raise IOError(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.fileobj.write(self.compress.compress(data)) self.size += len(data) self.crc = zlib.crc32(data, self.crc) & 0xffffffffL self.offset += len(data) return len(data) def read(self, size=-1): self._check_closed() if self.mode != READ: import errno raise IOError(errno.EBADF, "read() on write-only GzipFile object") if self.extrasize <= 0 and self.fileobj is None: return '' readsize = 1024 if size < 0: # get the whole thing try: while True: self._read(readsize) readsize = min(self.max_read_chunk, readsize * 2) except EOFError: size = self.extrasize else: # just get some more of it try: while size > self.extrasize: self._read(readsize) readsize = min(self.max_read_chunk, readsize * 2) except EOFError: if size > self.extrasize: size = self.extrasize offset = self.offset - self.extrastart chunk = self.extrabuf[offset: offset + size] self.extrasize = self.extrasize - size self.offset += size return chunk def _unread(self, buf): 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 = 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 == "": 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 = True def _add_read_data(self, data): self.crc = zlib.crc32(data, self.crc) & 0xffffffffL 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, 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. Note that the size # stored is the true file size mod 2**32. self.fileobj.seek(-8, 1) crc32 = read32(self.fileobj) isize = read32(self.fileobj) # may exceed 2GB if crc32 != self.crc: raise IOError("CRC check failed %s != %s" % (hex(crc32), hex(self.crc))) elif isize != (self.size & 0xffffffffL): raise IOError, "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 = "\x00" while c == "\x00": c = self.fileobj.read(1) if c: self.fileobj.seek(-1, 1) @property def closed(self): return self.fileobj is None def close(self): fileobj = self.fileobj if fileobj is None: return self.fileobj = None try: if self.mode == WRITE: fileobj.write(self.compress.flush()) write32u(fileobj, self.crc) # self.size may exceed 2GB, or even 4GB write32u(fileobj, self.size & 0xffffffffL) finally: myfileobj = self.myfileobj if myfileobj: self.myfileobj = None myfileobj.close() 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 IOError("Can't rewind in write mode") self.fileobj.seek(0) self._new_member = True self.extrabuf = "" 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 IOError('Negative seek in write mode') count = offset - self.offset for i in xrange(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 xrange(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('\n', offset) + 1 if i > 0: self.extrasize -= i - offset self.offset += i - offset return self.extrabuf[offset: i] size = sys.maxint readsize = self.min_readsize else: readsize = size bufs = [] while size != 0: c = self.read(readsize) i = c.find('\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 == '': 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 ''.join(bufs) # Return resulting 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:", repr(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 True: 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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