How to open and work with unknown archives?

Question

Data archiving

Tell me, how do programmers approach working with unknown archives?
Let's say there is a file from the game https://fex.net/#!928034132041 in the .arc format which, in theory, contains text files. How to extract/pack such archives? Are programmers looking for some libraries or write themselves? If by yourself, how does it happen?

Answer 1

Doesn't look like an arc archive. It cannot be opened by archivers with arc support and also the file contains quite a lot of null bytes, which is not allowed for archivers.
And the file is still an archive. Only at me it was not defined by any software.
To determine unknown file types (MIME type), there are programs that can determine the type by its header in the first bytes of the file, as well as by some other features in the file body.
www.forensicswiki.org/wiki/File_Format_Identification