Notes

Building a Command Line Tool that can View Minecraft Data

This week's blog post is about creating a command line tool to view Minecraft NBT files. You will learn:



Named Binary Tag (NBT) files contain information about Minecraft in a simple binary file format. These documents provide more details about the NBT format.



"NBT format" via Minecraft Wiki. "NBT" via Minecraft.vg. "Named Binary Tag specification” via Minecraft.net (WebArchive).



Script source code



view-nbt



Use the script to look at an NBT-file



I have an NBT file, level.dat, that contains details about a Minecraft level that I play on:



To look at the data in a readable format, I use view-nbt



(level.dat files can be compressed, and I use --gzip.



How the script functions



NBT files have tags of many different kinds, so I used an enum.Enum Tag to represent the tags.



To help with the parsing process, I created various data structures that are auxiliary to the main one:



Scalar_fmt is an fmt dictionary that maps some Tag objects to format strings usable by the struct module. This is for simple tags like Tag.Int and Tag.Byte. array_fmt is a dictionary which converts Tag objects to format strings that can be used by the struct module (but, missing a length prefix). This is for simple array tags like Tag.Int_Array. The dictionary byte tag maps bytes to the appropriate tags. This information was derived from the NBT specification for file formats.



The struct module is used by the parser to decompress binary data into various numbers (like short double, int, and short).
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The parser is recursive.



It directly parses Tag.String in addition to the tags in array_fmt or scalar_fmt. It recursively parses Tag.List and Tag.Compound.



The parsing creates a Node object, which is a collections.namedtuple that holds:



The tag type. - The tag name (optional). The value of the tag.



To make it easier to read data, I created an application called json_friendly which converts Node objects into data structures.



To allow NBT files that are compressed using Python's Gzip module, I use it.



To convert JSON-friendly data into a string, I use Python's JSON function from Python.



Let's conclude...



In this week's blog you'll learn how to build an application that runs on command line to display Minecraft NBT files. You learned:



How to decode binary data with the struct module. - How to write a recursive parser for the NBT file format. How do you convert the parsed data to a JSON-friendly file format



My challenge to you is:



Create a tool, view-region, that turns Region files into readable JSON.



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