tree 573423e19a755e60e5fc7e534625ab02fe438819
parent 288ed55dd75ec89b3d56efca198ee7c0be98906d
author Jon Gjengset <jon@thesquareplanet.com> 1493260792 -0400
committer Jon Gjengset <jon@thesquareplanet.com> 1493391505 -0400
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Add binding for res_init.

Some notes about the particularities of the changes:

res_init has been deprecated in favor of res_ninit, and many (but not
all) targets have therefore renamed the link name to __res_init. For
example, this happened in glibc in version 2.2:
https://bugzilla.redhat.com/show_bug.cgi?id=43822#c6
In these systems, res_init is #defined to __res_init in resolv.h, which
lets existing C programs continue to be compiled.

Unfortunately, this define doesn't automatically apply to our Rust code.
We therefore need to manually map the link name of res_init as
appropriate for each target:

macOS and iOS use res_9_init: https://github.com/practicalswift/osx/blob/3908694d6328baa293f0d7fc337348c01d13ed8f/src/libresolv/resolv.h#L316
Solaris uses res_init: https://java.net/projects/solaris/sources/on-src/content/usr/src/head/resolv.h
OpenBSD uses __res_init: https://github.com/openbsd/src/blob/f3b3b7c7ca9a921db3a5650eed40f2b2e4d731d8/include/resolv.h#L268
FreeBSD uses __res_init: https://github.com/freebsd/freebsd/blob/6911f4a88c9832e5985b788f5e84010424f9e020/include/resolv.h#L290
NetBSD uses __res_init: http://ftp.netbsd.org/pub/NetBSD/NetBSD-current/src/include/resolv.h
glibc uses __res_init: https://github.com/lattera/glibc/blob/a2f34833b1042d5d8eeb263b4cf4caaea138c4ad/resolv/resolv.h#L259
eglibc uses __res_init: https://github.com/Xilinx/eglibc/blob/7f0bcce417c47aefad06ddfec7cd4ced3a4e10ff/resolv/resolv.h#L259
musl uses res_init: https://github.com/runtimejs/musl-libc/blob/0a11d7cb13e243782da36e2e5747b8b151933cca/include/resolv.h#L128
Android uses res_init: https://github.com/android/platform_bionic/blob/306ea559528255e19a5bcd68cc2a9b1afc2cfb27/libc/include/resolv.h#L57

One caveat here is that NetBSD doesn't seem to use the symbol name
__res_init yet, despite the redefine being present in resolv.h. At least
Travis fails for the netbsd target if __res_init is used. This may
change in the future.

iOS and macOS both unfortunately require linking with libresolv, despite
the symbols technically being available without libresolv:
resolv: http://blog.achernya.com/2013/03/os-x-has-silly-libsystem.html
Android and OpenBSD fall in the same category.