ooni-probe-cli/internal/engine/geolocate/resolverlookup.go

package geolocate

import (
	"context"
	"errors"
	"net"
)

var (
	// ErrNoIPAddressReturned indicates that no IP address was
	// returned by a specific DNS resolver.
	ErrNoIPAddressReturned = errors.New("geolocate: no IP address returned")
)

type dnsResolver interface {
	LookupHost(ctx context.Context, host string) (addrs []string, err error)
}

type resolverLookupClient struct{}

func (rlc resolverLookupClient) do(ctx context.Context, r dnsResolver) (string, error) {
	var ips []string
	ips, err := r.LookupHost(ctx, "whoami.v4.powerdns.org")
	if err != nil {
		return "", err
	}
	if len(ips) < 1 {
		return "", ErrNoIPAddressReturned
	}
	return ips[0], nil
}

func (rlc resolverLookupClient) LookupResolverIP(ctx context.Context) (ip string, err error) {
	return rlc.do(ctx, &net.Resolver{})
}