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>

2 files changed, 171 insertions, 0 deletions

diff --git a/plugin/pkg/doh/doh.go b/plugin/pkg/doh/doh.go
new file mode 100644
index 000000000..e0a398e9c
--- /dev/null
+++ b/plugin/pkg/doh/doh.go
@@ -0,0 +1,119 @@
+package doh
+
+import (
+	"bytes"
+	"encoding/base64"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"net/http"
+
+	"github.com/miekg/dns"
+)
+
+// MimeType is the DoH mimetype that should be used.
+const MimeType = "application/dns-message"
+
+// Path is the URL path that should be used.
+const Path = "/dns-query"
+
+// NewRequest returns a new DoH request given a method, URL (without any paths, so exclude /dns-query) and dns.Msg.
+func NewRequest(method, url string, m *dns.Msg) (*http.Request, error) {
+	buf, err := m.Pack()
+	if err != nil {
+		return nil, err
+	}
+
+	switch method {
+	case http.MethodGet:
+		b64 := base64.RawURLEncoding.EncodeToString(buf)
+
+		req, err := http.NewRequest(http.MethodGet, "https://"+url+Path+"?dns="+b64, nil)
+		if err != nil {
+			return req, err
+		}
+
+		req.Header.Set("content-type", MimeType)
+		req.Header.Set("accept", MimeType)
+		return req, nil
+
+	case http.MethodPost:
+		req, err := http.NewRequest(http.MethodPost, "https://"+url+Path+"?bla=foo:443", bytes.NewReader(buf))
+		if err != nil {
+			return req, err
+		}
+
+		req.Header.Set("content-type", MimeType)
+		req.Header.Set("accept", MimeType)
+		return req, nil
+
+	default:
+		return nil, fmt.Errorf("method not allowed: %s", method)
+	}
+
+}
+
+// ResponseToMsg converts a http.Repsonse to a dns message.
+func ResponseToMsg(resp *http.Response) (*dns.Msg, error) {
+	defer resp.Body.Close()
+
+	return toMsg(resp.Body)
+}
+
+// RequestToMsg converts a http.Request to a dns message.
+func RequestToMsg(req *http.Request) (*dns.Msg, error) {
+	switch req.Method {
+	case http.MethodGet:
+		return requestToMsgGet(req)
+
+	case http.MethodPost:
+		return requestToMsgPost(req)
+
+	default:
+		return nil, fmt.Errorf("method not allowed: %s", req.Method)
+	}
+
+}
+
+// requestToMsgPost extracts the dns message from the request body.
+func requestToMsgPost(req *http.Request) (*dns.Msg, error) {
+	defer req.Body.Close()
+	return toMsg(req.Body)
+}
+
+// requestToMsgGet extract the dns message from the GET request.
+func requestToMsgGet(req *http.Request) (*dns.Msg, error) {
+	values := req.URL.Query()
+	b64, ok := values["dns"]
+	if !ok {
+		return nil, fmt.Errorf("no 'dns' query parameter found")
+	}
+	if len(b64) != 1 {
+		return nil, fmt.Errorf("multiple 'dns' query values found")
+	}
+	return base64ToMsg(b64[0])
+}
+
+func toMsg(r io.ReadCloser) (*dns.Msg, error) {
+	buf, err := ioutil.ReadAll(r)
+	if err != nil {
+		return nil, err
+	}
+	m := new(dns.Msg)
+	err = m.Unpack(buf)
+	return m, err
+}
+
+func base64ToMsg(b64 string) (*dns.Msg, error) {
+	buf, err := b64Enc.DecodeString(b64)
+	if err != nil {
+		return nil, err
+	}
+
+	m := new(dns.Msg)
+	err = m.Unpack(buf)
+
+	return m, err
+}
+
+var b64Enc = base64.RawURLEncoding
diff --git a/plugin/pkg/doh/doh_test.go b/plugin/pkg/doh/doh_test.go
new file mode 100644
index 000000000..449166151
--- /dev/null
+++ b/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)
+	}
+}