Vapour started off as an attempt to fix the case-sensitivity issues of Valve's
Steam content-distribution system by intercepting open() syscalls and
attempting to adjust the capitalisation of paths which aren't accessible.
However, during the short development process a major steam update was made
available which blocked the ability to dtruss the Steam process (and so see
the ways in which it is broken) and also to prevent the use of
DYLD_INSERT_LIBRARIES mechanism to inject the updated functions - presumably
to protect Steam's DRM mechanism.
Even with this being the case, libc_hook_open remains a useful demonstration
of how to cleanly hook functions on Mac OS X/macOS.
Build with:
clang -Wall -arch x86_64 -arch i386 -dynamiclib -o libc_hook_open.dylib libc_hook_open.c
Run a static analysis (using a third-party LLVM/clang build, since Apple don't appear to supply scan-build with Xcode):
scan-build clang -Wall -arch x86_64 -arch i386 -dynamiclib -o libc_hook_open.dylib libc_hook_open.c
Execute as:
DYLD_INSERT_LIBRARIES="/path/to/vapour/libc_hook_open.dylib" cat /dev/null
Please note the values of:
#define DEBUG 1
... and:
#define HOOK_IMPLEMENTATION 1
... where the former constant outputs additional debugging information when
performing path-mangling operations, and the latter hooks all of OS X's open()
functions, including _nocancel variants, at the cost of losing the ability to
recursively call open() or to use any function which internally calls open()
itself from within the hook functions.