iOS doesn't let you run subprocesses,
which means we can't use netstat to get routing information.
Instead, use syscalls and grub around in the results.
We keep the old netstat version around,
both for use in non-cgo builds,
and for use testing the syscall-based version.
Note that iOS doesn't ship route.h,
so we include a copy here from the macOS 10.15 SDK
(which is itself unchanged from the 10.14 SDK).
I have tested manually that this yields the correct
gateway IP address on my own macOS and iOS devices.
More coverage would be most welcome.
Signed-off-by: Josh Bleecher Snyder <josharian@gmail.com>
Also:
* add -verbose flag to cmd/tailscale netcheck
* remove some API from the interfaces package
* convert some of the interfaces package to netaddr.IP
* don't even send IPv4 probes on machines with no IPv4 (or only v4
loopback)
* and once three regions have replied, stop waiting for other probes
at 2x the slowest duration.
Updates #376
Basically, don't trust the OS-level link monitor to only tell you
interesting things. Sanity check it.
Also, move the interfaces package into the net directory now that we
have it.
