Windows may raise WSAEHOSTUNREACH instead WSAENETUNREACH in case of
network not available when resuming from sleep or switching network, so
checkUpstream is never kicked in for this type of error.
Generating nextdns config must happen after stopping current ctrld
process. Otherwise, config processing may pick wrong IP+Port.
While at it, also making logging better when updating listener config:
- Change warn to info, prevent confusing that "something is wrong".
- Do not emit info when generating working default config, which may
cause duplicated messages printed.
Otherwise, network changes may not be seen on some platforms, causing
ctrld failed to recover and failing all requests.
While at it, also doing the check DNS in separate goroutine, prevent it
from blocking ctrld from notifying others that it "started". The issue
was seen when ctrld is configured as direct listener, requests are
flooded before ctrld started, causing the healtch process failed.
Some users mentioned that when there is an Internet outage, ctrld fails
to recover, crashing or locks up the router. When requests start
failing, this results in the clients emitting more queries, creating a
resource spiral of death that can brick the device entirely.
To guard against this case, this commit implement an upstream monitor
approach:
- Marking upstream as down after 100 consecutive failed queries.
- Start a goroutine to check when the upstream is back again.
- When upstream is down, answer all queries with SERVFAIL.
- The checking process uses backoff retry to reduce high requests rate.
- As long as the query succeeded, marking the upstream as alive then
start operate normally.
The current approach to get default route IP is finding the LAN
interface with the same MAC address. However, there could be multiple
interfaces like that, making ctrld confused.
This commit fixes this issue, by listing all possible private IPs, then
sorting them and use the smallest one for router self queries.
For reporting router queries, ctrld uses private IP of the default route
interface. However, when the default route is conntected directly to
ISP, the interface will have a public IP, and another interface with the
same MAC address will be created for LAN ip. So when no private IP found
for default route interface, ctrld must look at the other interface to
find the corret LAN ip.
