As part of v1.4.0 release, reading DNS from /etc/resolv.conf file is
only available for Macos. However, there's no reason to prevent this
function from working on other *nix systems.
This commit unify the function to *nix, so it could be added as DNS
source for Linux and Freebsd.
The bootstrap process has two issues that can make ctrld stop resolving
after restarting machine host.
ctrld uses bootstrap DNS and os nameservers for resolving upstream. On
unix, /etc/resolv.conf content is used to get available nameservers.
This works well when installing ctrld. However, after being installed,
ctrld may modify the content of /etc/resolv.conf itself, to make other
apps use its listener as DNS resolver. So when ctrld starts after OS
restart, it ends up using [bootstrap DNS + ctrld's listener], for
resolving upstream. At this moment, if ctrld could not contact bootstrap
DNS for any reason, upstream domain will not be resolved.
For above reason, an upstream may not have bootstrap IPs after ctrld
starts. When re-bootstrapping, if there's no bootstrap IPs, ctrld should
call the setup bootstrap process again. Currently, it does not, causing
all queries failed.
This commit fixes above issue by adding mechanism for retrieving OS
nameservers properly, by querying routing table information:
- Parsing /proc/net subsystem on Linux.
- For BSD variants, just fetching routing information base from OS.
- On Windows, just include the gateway information when reading iface.
The fixing for second issue is trivial, just kickoff a bootstrap process
if there's no bootstrap IPs when re-boostrapping.
While at it, also ensure that fetching resolver information from
ControlD API is also used the same approach.
Fixes#34
Currently, os resolver not only handle A and AAAA records, but also does
it wrongly, since when it packs AAAA record to a dns.A record.
This commit reworks os resolver to make it works with all supported
record types.
