diff -r ffa851df0825 -r 2fb8b9db1c86 symbian-qemu-0.9.1-12/python-win32-2.6.1/lib/chunk.py --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/symbian-qemu-0.9.1-12/python-win32-2.6.1/lib/chunk.py Fri Jul 31 15:01:17 2009 +0100 @@ -0,0 +1,167 @@ +"""Simple class to read IFF chunks. + +An IFF chunk (used in formats such as AIFF, TIFF, RMFF (RealMedia File +Format)) has the following structure: + ++----------------+ +| ID (4 bytes) | ++----------------+ +| size (4 bytes) | ++----------------+ +| data | +| ... | ++----------------+ + +The ID is a 4-byte string which identifies the type of chunk. + +The size field (a 32-bit value, encoded using big-endian byte order) +gives the size of the whole chunk, including the 8-byte header. + +Usually an IFF-type file consists of one or more chunks. The proposed +usage of the Chunk class defined here is to instantiate an instance at +the start of each chunk and read from the instance until it reaches +the end, after which a new instance can be instantiated. At the end +of the file, creating a new instance will fail with a EOFError +exception. + +Usage: +while True: + try: + chunk = Chunk(file) + except EOFError: + break + chunktype = chunk.getname() + while True: + data = chunk.read(nbytes) + if not data: + pass + # do something with data + +The interface is file-like. The implemented methods are: +read, close, seek, tell, isatty. +Extra methods are: skip() (called by close, skips to the end of the chunk), +getname() (returns the name (ID) of the chunk) + +The __init__ method has one required argument, a file-like object +(including a chunk instance), and one optional argument, a flag which +specifies whether or not chunks are aligned on 2-byte boundaries. The +default is 1, i.e. aligned. +""" + +class Chunk: + def __init__(self, file, align=True, bigendian=True, inclheader=False): + import struct + self.closed = False + self.align = align # whether to align to word (2-byte) boundaries + if bigendian: + strflag = '>' + else: + strflag = '<' + self.file = file + self.chunkname = file.read(4) + if len(self.chunkname) < 4: + raise EOFError + try: + self.chunksize = struct.unpack(strflag+'L', file.read(4))[0] + except struct.error: + raise EOFError + if inclheader: + self.chunksize = self.chunksize - 8 # subtract header + self.size_read = 0 + try: + self.offset = self.file.tell() + except (AttributeError, IOError): + self.seekable = False + else: + self.seekable = True + + def getname(self): + """Return the name (ID) of the current chunk.""" + return self.chunkname + + def getsize(self): + """Return the size of the current chunk.""" + return self.chunksize + + def close(self): + if not self.closed: + self.skip() + self.closed = True + + def isatty(self): + if self.closed: + raise ValueError, "I/O operation on closed file" + return False + + def seek(self, pos, whence=0): + """Seek to specified position into the chunk. + Default position is 0 (start of chunk). + If the file is not seekable, this will result in an error. + """ + + if self.closed: + raise ValueError, "I/O operation on closed file" + if not self.seekable: + raise IOError, "cannot seek" + if whence == 1: + pos = pos + self.size_read + elif whence == 2: + pos = pos + self.chunksize + if pos < 0 or pos > self.chunksize: + raise RuntimeError + self.file.seek(self.offset + pos, 0) + self.size_read = pos + + def tell(self): + if self.closed: + raise ValueError, "I/O operation on closed file" + return self.size_read + + def read(self, size=-1): + """Read at most size bytes from the chunk. + If size is omitted or negative, read until the end + of the chunk. + """ + + if self.closed: + raise ValueError, "I/O operation on closed file" + if self.size_read >= self.chunksize: + return '' + if size < 0: + size = self.chunksize - self.size_read + if size > self.chunksize - self.size_read: + size = self.chunksize - self.size_read + data = self.file.read(size) + self.size_read = self.size_read + len(data) + if self.size_read == self.chunksize and \ + self.align and \ + (self.chunksize & 1): + dummy = self.file.read(1) + self.size_read = self.size_read + len(dummy) + return data + + def skip(self): + """Skip the rest of the chunk. + If you are not interested in the contents of the chunk, + this method should be called so that the file points to + the start of the next chunk. + """ + + if self.closed: + raise ValueError, "I/O operation on closed file" + if self.seekable: + try: + n = self.chunksize - self.size_read + # maybe fix alignment + if self.align and (self.chunksize & 1): + n = n + 1 + self.file.seek(n, 1) + self.size_read = self.size_read + n + return + except IOError: + pass + while self.size_read < self.chunksize: + n = min(8192, self.chunksize - self.size_read) + dummy = self.read(n) + if not dummy: + raise EOFError