In this tutorial I’ll be detailing the process used to develop a Peach Pit for the RAR file format. I’ll also be discussing the use of Fixups and the steps required to implement your own custom Fixup. This article is intended to build upon the skills described in my first article so if you haven’t read it, I highly recommend doing so before continuing. You can find that article here. With that said, the following will assume that you have working level knowledge of the Peach Pit format.
A quick update, after posting this article I realized that Mike also has a very informative section on extending peach with custom fixups. You can find that article here.
To begin, let’s grab a copy of the most recent RAR tech note available here. Please note that since the tech note does not fully describe the specification, some of the information contained in this Pit has been enumerated from the UnRAR source, 010 RAR Binary Template, and other sources.
Moving right along we see that the specification is defined as a series of block-like structures, each of which contains several recurring elements. As we are unable to tell which order some of these blocks will occur, we will wrap all blocks in a choice element. Let’s first begin by creating the block structure for the “Marker Block”.