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A replacement Chunk class that allows both reading and writing IFF chunks.

Project description

An IFF chunk, as defined in the EA IFF 85 standard, consists of a 4-byte ID field, a 4-byte length field, and the data content of the chunk, and optionally followed by a single padding null byte if required to make the total number of bytes even.

Chunk ID 4 bytes
Length 4 bytes
Data n bytes
Padding 0 or 1 byte
  • The Chunk ID is a 4-character string that identifies the type of chunk.
  • The Length is a 4-byte integer (generally in big-endian format) indicating how long the data field is.

The Chunk class allows for either reading a chunk from a file-like object or creating a chunk and writing it into a file-like object, but not both.

For reading, the Chunk class reads a single chunk from the file-like object, and is in turn a read-only file-like object for reading the contents of the chunk.

Chunk tries to determine if the underlying file-like object is seekable by via the tell operation; if that does not raise an exception, then the file-like object presented by Chunk is itself seekable.

When the Chunk is closed, the underlying file-like object is positioned to read immediately following the Chunk (and after the padding byte, if any).

For writing, the Chunk class presents a write-only file-like object for creating the contents of the chunk, as well as the setname method for assigning the Chunk ID.

For writable chunks whose underlying file-like object is not seekable, an in-memory file object is created to hold the chunk’s data; only when the chunk is closed is the in-memory file object is flushed to the underlying file-like object.

IFF files can consist of multiple top-level chunks; “container” chunk types (FORM, CAT ``, and ``LIST) contain other chunks. The Chunk class is designed to be instantiated multiple times, one after the other, for either reading or writing multiple chunks from or to a file, or from or to the content of a “container” chunk.

The parse_chunk and parse_iff_file helper methods assist in reading IFF files by automating the parsing of container chunks. parse_iff_file returns a list of chunk tuples consisting of the chunk name and chunk content; for container chunks, the chunk content is itself a list of chunk tuples.


To Do

  • Rewrite from scratch to remove original Python code, if possible
  • Modify to work with both Python 2 and Python 3, if possible

License

Original code base copied from Python 2.7 library, then modified to support write functionality.

Original chunk.py is Copyright (c) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017 Python Software Foundation; All Rights Reserved; licensed under the Python Software Foundation License Version 2 <https://docs.python.org/2.7/license.html>

Derived portions are Copyright (c) 2017 Johnson Earls; All Rights Reserved; licensed as follows:

Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted, provided that the above copyright notice and this permission notice appear in all copies.

THE SOFTWARE IS PROVIDED “AS IS” AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

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