binconvert 0.1.2

Converts byte ordering in binary files from one platform to another

binconvert

A CLI utility for converting byte orders in binary files from one platform to another.

Introduction and Motivation

binconvert is a program that was born out of the author’s need to read old files that were written in a binary format on a SPARC system. Because SPARC’s native byte-ordering is big endian (ie, most significant byte first), this caused comptatability issues when porting these files over to an x86 Linux machine (which has little endian, or least significant byte first native byte-ordering). In an ideal world where the binary files are unstructured and every data value stored in the file has the same type, one could easily get around this problem by either recompiling their program with special compiler flags or using some existing CLI solutions like dd conv=swab.

Unfortunately there are many binary files which are structured, ie the variables stored in the file are of different lengths and types, and so it becomes necessary to know the internal structure of the file beforehand. Thankfully, python provides an easy to use struct module which allows for users to express the structure and byte-ordering of the data as a format string. For example, “f6s” would imply that the first 4 bytes in the file represent a floating point number, while the remaining 6 bytes designate a 6 character string.

Although this is a much nicer alternative than forcing the user to manually perform the byte-swapping by hand, it can still break down when needing to process larger binary files with more complex structures. As an example, consider a binary file named a.bin which represents the following table:

Name	Age(yr)	Weight(lb)	Height(ft)
Alex	26	170.5	6.0

Now imagine if this table had hundreds of additional entries. The format string required by struct can easily become very long. However, we know that it can be generalized as a header which labels each column in the table (“4s7s10s10s”) followed by the actual entries of the table (“4si2f”), so it should be possible to generate the format string for an arbitrary number of entries. Using binconvert, without even knowing the total size of the file beforehand, we can easily convert its byte-ordering from big to little-endian on an x86 machine using:

bconv a.bin -f 4s7s10s10s 4si2f:#

In summary, binconvert’s main purpose is to extend the functionality of the python struct module for these use cases by doing the following:

1. Make it easier to generate format strings for larger files.

2. Provide a simple CLI interface for performing the endianness conversion.

Installation and Usage

To install binconvert from the current codebase, you may use

git clone https://github.com/agoodm/binconvert.git
cd binconvert
python setup.py install

If all goes well, you should be able to execute the program with:

bconv -h

In the near future, installation methods using conda will be provided.