Feature: support DoH

dns/doh.go

@@ -0,0 +1,75 @@
+package dns
+
+import (
+	"bytes"
+	"context"
+	"crypto/tls"
+	"io/ioutil"
+	"net/http"
+
+	D "github.com/miekg/dns"
+)
+
+const (
+	// dotMimeType is the DoH mimetype that should be used.
+	dotMimeType = "application/dns-message"
+
+	// dotPath is the URL path that should be used.
+	dotPath = "/dns-query"
+)
+
+var dohTransport = &http.Transport{
+	TLSClientConfig: &tls.Config{ClientSessionCache: globalSessionCache},
+}
+
+type dohClient struct {
+	url string
+}
+
+func (dc *dohClient) Exchange(m *D.Msg) (msg *D.Msg, err error) {
+	return dc.ExchangeContext(context.Background(), m)
+}
+
+func (dc *dohClient) ExchangeContext(ctx context.Context, m *D.Msg) (msg *D.Msg, err error) {
+	req, err := dc.newRequest(m)
+	if err != nil {
+		return nil, err
+	}
+
+	req = req.WithContext(ctx)
+	return dc.doRequest(req)
+}
+
+// newRequest returns a new DoH request given a dns.Msg.
+func (dc *dohClient) newRequest(m *D.Msg) (*http.Request, error) {
+	buf, err := m.Pack()
+	if err != nil {
+		return nil, err
+	}
+
+	req, err := http.NewRequest(http.MethodPost, dc.url+"?bla=foo:443", bytes.NewReader(buf))
+	if err != nil {
+		return req, err
+	}
+
+	req.Header.Set("content-type", dotMimeType)
+	req.Header.Set("accept", dotMimeType)
+	return req, nil
+}
+
+func (dc *dohClient) doRequest(req *http.Request) (msg *D.Msg, err error) {
+	client := &http.Client{Transport: dohTransport}
+	resp, err := client.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+
+	buf, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		return nil, err
+	}
+	msg = &D.Msg{}
+	err = msg.Unpack(buf)
+	return msg, err
+}