Is it possible to view the source of a mac app?

Question

Would be usefull to see how things work but not sure on the legality of it

Answer 1

Is it possible to view the source of a mac app?

Realistically, no. Sure, you might be a able to use a decompiler to get a peek, but the kind of output you'll get won't be easy to read. If you're asking this question, this route probably isn't going to be helpful to you.

Specifically interested in GUI and how the steam app for mac works

It's a good bet that it works about the same way that most other applications work. It might use custom controls to look different from a typical application that mostly uses the standard Cocoa controls. But underneath, just about any GUI application written for MacOS X will use the run loops, responder chain, and view hierarchy that Cocoa provide. The main exceptions would be applications that are built mostly using an alternate framework like OpenGL or WebKit.

Figure out what, specifically, the Steam application does that you'd like to do. Take a look at the tools that Cocoa provides to see if you can figure it out yourself; if not, ask about it here.

Answer 2

By far, the best Mac OS X disassembler I've used is Hopper available here: http://www.hopperapp.com/

It will also convert the assembly to C pseudo code as best it can. It will generate code flow diagrams with blue lines (true blue, love it) for true and red for false paths.

It's The Mac OS reverse engineering tool. There are even Youtube videos that will show you how to use it.

Answer 3

Most Mac apps are written using Cocoa in Objective-C; which, while it is a compiled language, means that there is a fair bit of information left over that could be used by a decompiler.

I'm not sure if there are a lot of decompilers out there that leverages this information, at least I haven't heard of any.

However, there are also another option; F-Script.

F-Script can be used to attach to an executable and explore its interfaces, while not as good as source, it can give you a pretty clear idea of how the executable is built, and how it operates.

As for the legality issue:

IANAL, but as far as I know, reverse-engineering for the purposes of compatibility is legal in many jurisdictions, and I can't imagine that decompiling an executable to look at its code is illegal, unless the specific EULA specifically prohibits it.

Edit: WRT Steam specifically, it is probably NOT written in Cocoa, but C# with some manner of .NET compatibility layer; and it's probably not a good place to start if you want to learn how to make applications for Mac OS X.

Answer 4

If it's an open-source app, yes. Otherwise it's possible through decompilation but the output will be a real pain in the ass to look at. If you just want the protocols and the interfaces of categories and classes, have a look at class-dump.

I'm not aware of a nib decompiler.

Whether decompilation is legal: ask a lawyer. This may (and probably does) differ per jurisdiction.