feat: preshared key, client port and DoH

Closes #2, Closes #3

internal/resolver/resolver_test.go

@@ -0,0 +1,39 @@
+package resolver
+
+import (
+	"net"
+	"testing"
+)
+
+func TestResolve(t *testing.T) {
+	if testing.Short() {
+		t.Skip()
+	}
+
+	for _, server := range []string{
+		"",
+		"223.5.5.5",
+		"223.5.5.5:53",
+		"tcp://223.5.5.5",
+		"tcp://223.5.5.5:53",
+		"udp://223.5.5.5",
+		"udp://223.5.5.5:53",
+		"tls://223.5.5.5",
+		"tls://223.5.5.5:853",
+		"https://223.5.5.5",
+		"https://223.5.5.5:443",
+		"https://223.5.5.5:443/dns-query",
+	} {
+		t.Run(server, func(t *testing.T) {
+			d := &net.Dialer{
+				Resolver: New(server),
+			}
+			c, err := d.Dial("tcp4", "www.example.com:80")
+			if err != nil {
+				t.Error(err)
+			} else {
+				t.Logf("got %s", c.RemoteAddr())
+			}
+		})
+	}
+}