When calling PR_GetAddrInfoByName we should be able to differentiate between NXDOMAIN and a network failure.

We should check the PR_SetError result to see if they show up as different codes.

I've tested what PR_GetOSError returns for NXDOMAIN vs when the network is unreachable.

On Linux we get -2 (EAI_NONAME) for NXDOMAIN, and -3 (EAI_AGAIN) when the network is down.
However, on Windows, we always get 11001 (WSAHOST_NOT_FOUND) for both NXDOMAIN and network failure.

I don't think we have an easy way to fix this.
Dragana, what do you think?

This error is coming from the system call? I am asking because I know cases where (nspr transforms some errors )

Yes, it comes from the system call to getaddrinfo here

We've determined that this impossible to differentiate given how the current DNS API works.
In the next iteration we might have a better way to do this, or if we end up implementing a Do53 resolver.