make CoreDNS DoH Server (#1619)

* WIP: make CoreDNS DoH Server

* It works

* Fix tests

* Review from Tom - on diff. PR

* correct mime type

* Cleanups and use the pkg/nonwriter

* rename and updates

* implement get

* implement GET

* Code review comments

* correct context

* tweaks

* code review

core/dnsserver/https_test.go

@@ -0,0 +1,66 @@
+package dnsserver
+
+import (
+	"bytes"
+	"encoding/base64"
+	"net/http"
+	"testing"
+
+	"github.com/miekg/dns"
+)
+
+func TestPostRequest(t *testing.T) {
+	const ex = "example.org."
+
+	m := new(dns.Msg)
+	m.SetQuestion(ex, dns.TypeDNSKEY)
+
+	out, _ := m.Pack()
+	req, err := http.NewRequest(http.MethodPost, "https://"+ex+pathDOH+"?bla=foo:443", bytes.NewReader(out))
+	if err != nil {
+		t.Errorf("Failure to make request: %s", err)
+	}
+	req.Header.Set("content-type", mimeTypeDOH)
+	req.Header.Set("accept", mimeTypeDOH)
+
+	m, err = postRequestToMsg(req)
+	if err != nil {
+		t.Fatalf("Failure to get message from request: %s", err)
+	}
+
+	if x := m.Question[0].Name; x != ex {
+		t.Errorf("Qname expected %s, got %s", ex, 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) {
+	const ex = "example.org."
+
+	m := new(dns.Msg)
+	m.SetQuestion(ex, dns.TypeDNSKEY)
+
+	out, _ := m.Pack()
+	b64 := base64.RawURLEncoding.EncodeToString(out)
+
+	req, err := http.NewRequest(http.MethodGet, "https://"+ex+pathDOH+"?dns="+b64, nil)
+	if err != nil {
+		t.Errorf("Failure to make request: %s", err)
+	}
+	req.Header.Set("content-type", mimeTypeDOH)
+	req.Header.Set("accept", mimeTypeDOH)
+
+	m, err = getRequestToMsg(req)
+	if err != nil {
+		t.Fatalf("Failure to get message from request: %s", err)
+	}
+
+	if x := m.Question[0].Name; x != ex {
+		t.Errorf("Qname expected %s, got %s", ex, x)
+	}
+	if x := m.Question[0].Qtype; x != dns.TypeDNSKEY {
+		t.Errorf("Qname expected %d, got %d", x, dns.TypeDNSKEY)
+	}
+}