The program mpq is used for unpacking Diablo 1 mpq files
go get github.com/sanctuary/mpq
mpq -m=/path/to/mpq/diabdat.mpq
If the mpq file is named diabdat.mpq and is in current directory, just run mpq without parameters to unpack all files.
Big thanks to the StormLib project and the TTDecomp project for providing lots of good information and code that has helpt us a lot!
The source code and any original content of this repository is hereby released into the public domain.