Doh: put in pkg/doh (#1946)

* DoH: put in pkg/doh

Factor out the DoH stuff into its own package, add function to request
a DoH response. This can be used by forward (and maybe proxy) to
implement DoH client support.

Signed-off-by: Miek Gieben <miek@miek.nl>

* lint

Signed-off-by: Miek Gieben <miek@miek.nl>

* ... and make it compile

Signed-off-by: Miek Gieben <miek@miek.nl>

plugin/pkg/doh/doh_test.go

@@ -0,0 +1,52 @@
+package doh
+
+import (
+	"net/http"
+	"testing"
+
+	"github.com/miekg/dns"
+)
+
+func TestPostRequest(t *testing.T) {
+	m := new(dns.Msg)
+	m.SetQuestion("example.org.", dns.TypeDNSKEY)
+
+	req, err := NewRequest(http.MethodPost, "https://example.org:443", m)
+	if err != nil {
+		t.Errorf("Failure to make request: %s", err)
+	}
+
+	m, err = RequestToMsg(req)
+	if err != nil {
+		t.Fatalf("Failure to get message from request: %s", err)
+	}
+
+	if x := m.Question[0].Name; x != "example.org." {
+		t.Errorf("Qname expected %s, got %s", "example.org.", x)
+	}
+	if x := m.Question[0].Qtype; x != dns.TypeDNSKEY {
+		t.Errorf("Qname expected %d, got %d", x, dns.TypeDNSKEY)
+	}
+}
+
+func TestGetRequest(t *testing.T) {
+	m := new(dns.Msg)
+	m.SetQuestion("example.org.", dns.TypeDNSKEY)
+
+	req, err := NewRequest(http.MethodGet, "https://example.org:443", m)
+	if err != nil {
+		t.Errorf("Failure to make request: %s", err)
+	}
+
+	m, err = RequestToMsg(req)
+	if err != nil {
+		t.Fatalf("Failure to get message from request: %s", err)
+	}
+
+	if x := m.Question[0].Name; x != "example.org." {
+		t.Errorf("Qname expected %s, got %s", "example.org.", x)
+	}
+	if x := m.Question[0].Qtype; x != dns.TypeDNSKEY {
+		t.Errorf("Qname expected %d, got %d", x, dns.TypeDNSKEY)
+	}
+}