So we don't have to worry about network stack changes causes an upstream
to be broken. Just send requests to all nameservers concurrently, and
get the first success response.
For better recovery and dealing with network stack changes, this commit
change the request flow to:
failure of any kind -> recreate transport/re-bootstrap -> retry once
That would make ctrld recover from all scenarios in theory.
At startup, ctrld gathers bootstrap IP information and use this
bootstrap IP for connecting to upstream. However, in case the network
stack changed, for example, dues to VPN connection, ctrld will still use
this old (maybe invalid) bootstrap IP for the current network stack.
This commit rework the discovering process, and re-initializing the
bootstrap IP if connecting to upstream failed.
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.
This commit adds the ability to start `ctrld` without config file. All
necessary information can be provided via command line flags, either in
base64 encoded config or launch arguments.
