Classes which contain calls to platform specific methods cause
problems, because the dexer will go looking for that method even
if you put a guard condition checking the build number. However,
if you lazily load a class depdending on the version number, then
older API devices wont try and load it, and no VerifyError occurs.
* Android-21 introduced an API for symlinking.
* Android-19 has an API which can be used via reflection.
* Earlier versions use Runtime.exec('/system/bin/ln')
This also extends the SanitizedFile stuff so that the android < 19 can
safely use Runtime.exec() with less fear of command injection vulnerabilities.
Finally, some tests for the SanitizedFile and symlink stuff was added.
This prevents an app with "write external storage" permission from
being able to switch the legit app with a dodgey one between F-Droid
requesting an install, and the package manager actually showing the
install dialog to the user.
In order to make the file in private internal storage readable by
the package manager, its parent directories need to be world-executable,
and the file itself needs to be world-readable. It seems that the
"/data/data/org.fdroid.fdroid/cache" dir provided by the Context is
already world executable, but the "apks" subdirectory does not default
to this.
Also, to be compatible with android-8, a Runtime.getRuntime().exec()
call was added for such devices, which invokes /system/bin/chmod.
The effect of this was to require some level of file sanitization to
be made available using the Java type system to prevent command injection
attacks from weird apk names (as people are free to download metadata
from random internet people).
Also, start using String[] like Android's SUPPORTED_ABIS instead of
Set<String>. Said list of ABIs will always be very short, at most containing a
handful of elements.
