Fixes #72

- Using custom DNS internally (without TLS) to download Unbound files
- Using then Unbound with DNS over TLS internally and system wide
- Works even if you host system DNS is broken
- Waits a few milliseconds for Unbound to start up

internal/dns/nameserver.go

@@ -0,0 +1,47 @@
+package dns
+
+import (
+	"context"
+	"net"
+	"strings"
+
+	"github.com/qdm12/private-internet-access-docker/internal/constants"
+)
+
+// UseDNSInternally is to change the Go program DNS only
+func (c *configurator) UseDNSInternally(IP net.IP) {
+	c.logger.Info("%s: using DNS address %s internally", logPrefix, IP.String())
+	net.DefaultResolver = &net.Resolver{
+		PreferGo: true,
+		Dial: func(ctx context.Context, network, address string) (net.Conn, error) {
+			d := net.Dialer{}
+			return d.DialContext(ctx, "udp", net.JoinHostPort(IP.String(), "53"))
+		},
+	}
+}
+
+// UseDNSSystemWide changes the nameserver to use for DNS system wide
+func (c *configurator) UseDNSSystemWide(IP net.IP) error {
+	c.logger.Info("%s: using DNS address %s system wide", logPrefix, IP.String())
+	data, err := c.fileManager.ReadFile(string(constants.ResolvConf))
+	if err != nil {
+		return err
+	}
+	s := strings.TrimSuffix(string(data), "\n")
+	lines := strings.Split(s, "\n")
+	if len(lines) == 1 && lines[0] == "" {
+		lines = nil
+	}
+	found := false
+	for i := range lines {
+		if strings.HasPrefix(lines[i], "nameserver ") {
+			lines[i] = "nameserver " + IP.String()
+			found = true
+		}
+	}
+	if !found {
+		lines = append(lines, "nameserver "+IP.String())
+	}
+	data = []byte(strings.Join(lines, "\n"))
+	return c.fileManager.WriteToFile(string(constants.ResolvConf), data)
+}