On Windows, GetAddrInfoW is a syscall and the Go resolver does
not attempt to map errors beyond WSA_HOST_NOT_FOUND, which becomes
"no such host", which we map to "dns_nxdomain_error".
See https://github.com/golang/go/blob/go1.17.1/src/net/lookup_windows.go#L16.
To map more GetAddrInfoW errors, thus, we need to enhance our
error classifier to have system specific errors.
Then, we need to filter for the WSA errors that are most likely
to pop up and map them to OONI failures. Those are three:
- WSANO_DATA which we have from our own UDP resolver as well
and which we can map to `dns_no_answer`
- WSANO_RECOVERY which we don't have but existed for MK so
we will use `dns_non_recoverable_failure`, which was an MK error
- WSATRY_AGAIN which likewise we map to the error that MK
used to emit, so `dns_temporary_failure`
This diff should address https://github.com/ooni/probe/issues/1467.
I need to run test on Windows and I just discovered that:
1. the `errno_unix.go` filename does not mean anything because
`unix` is not a valid platform, so we need a filename for
each platform that we care about;
2. on Windows we need to use WSA prefixed names;
3. `i/e/session_psiphon.go` was not building because of the
migration from `netxlite/iox` to `netxlite`.
This diff attempts to fix all three issues.
The reference issue is https://github.com/ooni/probe/issues/1733,
because I was working on such an issue.
