Embed Zipped data into ELF, Windows PE, or Generic Binaries
This is a separate repository kept for tests and tracking issues of the Ren-C encap script:
https://github.com/metaeducation/ren-c/blob/master/scripts/encap.reb
Because de-encapping needs to be baked into the executable itself, the whole script is currently turned into C constant data and compiled in. For this reason, the script itself is not kept in this repository at this time. This makes it easier to keep in sync with the rest of the code.
Encapping grafts data into an already-compiled executable, to add resources to it "after the fact". Note that there are different executable formats used on different operating systems, each with a header that tells the operating system how to interpret the file:
- Linux: https://en.wikipedia.org/wiki/Executable_and_Linkable_Format
- Windows: https://en.wikipedia.org/wiki/Portable_Executable
- OS X: https://en.wikipedia.org/wiki/Mach-O
A "naive" form of adding data into an executable is to append the data at the tail, which generally does not affect operation:
http://stackoverflow.com/a/5801598/
This is a common approach, yet it has some flaws. e.g. on Linux, running the
strip command will see the added data as irrelevant, and remove it. Other
manipulations like adding an icon resource may add the icon resource data to
the end. There are other things, like executable compression (although some
executable compressors are aware of this well-known embedding tactic, and
account for it).
It may be reasonable to say that it is the burden of those doing executable manipulations to de-encap it, do the modification, and then re-encap the executable. But all things being equal, it's desirable to find ways to slipstream the information into the "valid/known" resource logic of the OS.
This can be done with OS-specific tools or system calls, but the advantage of writing it standalone in Ren-C is that it reduces the dependencies. It allows encapping of executables built on a platform different than the one you are running on. So attempts are made here to manipulate the published formats with usermode code itself.
For formats not supported currently by the encapper, the simple appending strategy is used.