Upstream plugin prototype

upstream/https_upstream.go

@@ -0,0 +1,109 @@
+package upstream
+
+import (
+	"bytes"
+	"crypto/tls"
+	"fmt"
+	"github.com/miekg/dns"
+	"github.com/pkg/errors"
+	"golang.org/x/net/context"
+	"golang.org/x/net/http2"
+	"io/ioutil"
+	"log"
+	"net/http"
+	"net/url"
+)
+
+const (
+	dnsMessageContentType = "application/dns-message"
+)
+
+// HttpsUpstream is the upstream implementation for DNS-over-HTTPS
+type HttpsUpstream struct {
+	client   *http.Client
+	endpoint *url.URL
+}
+
+// NewHttpsUpstream creates a new DNS-over-HTTPS upstream from hostname
+func NewHttpsUpstream(endpoint string) (Upstream, error) {
+	u, err := url.Parse(endpoint)
+	if err != nil {
+		return nil, err
+	}
+
+	// Update TLS and HTTP client configuration
+	tlsConfig := &tls.Config{ServerName: u.Hostname()}
+	transport := &http.Transport{
+		TLSClientConfig:    tlsConfig,
+		DisableCompression: true,
+		MaxIdleConns:       1,
+	}
+	http2.ConfigureTransport(transport)
+
+	client := &http.Client{
+		Timeout:   defaultTimeout,
+		Transport: transport,
+	}
+
+	return &HttpsUpstream{client: client, endpoint: u}, nil
+}
+
+// Exchange provides an implementation for the Upstream interface
+func (u *HttpsUpstream) Exchange(ctx context.Context, query *dns.Msg) (*dns.Msg, error) {
+	queryBuf, err := query.Pack()
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to pack DNS query")
+	}
+
+	// No content negotiation for now, use DNS wire format
+	buf, backendErr := u.exchangeWireformat(queryBuf)
+	if backendErr == nil {
+		response := &dns.Msg{}
+		if err := response.Unpack(buf); err != nil {
+			return nil, errors.Wrap(err, "failed to unpack DNS response from body")
+		}
+
+		response.Id = query.Id
+		return response, nil
+	}
+
+	log.Printf("failed to connect to an HTTPS backend %q due to %s", u.endpoint, backendErr)
+	return nil, backendErr
+}
+
+// Perform message exchange with the default UDP wireformat defined in current draft
+// https://tools.ietf.org/html/draft-ietf-doh-dns-over-https-10
+func (u *HttpsUpstream) exchangeWireformat(msg []byte) ([]byte, error) {
+	req, err := http.NewRequest("POST", u.endpoint.String(), bytes.NewBuffer(msg))
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to create an HTTPS request")
+	}
+
+	req.Header.Add("Content-Type", dnsMessageContentType)
+	req.Header.Add("Accept", dnsMessageContentType)
+	req.Host = u.endpoint.Hostname()
+
+	resp, err := u.client.Do(req)
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to perform an HTTPS request")
+	}
+
+	// Check response status code
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("returned status code %d", resp.StatusCode)
+	}
+
+	contentType := resp.Header.Get("Content-Type")
+	if contentType != dnsMessageContentType {
+		return nil, fmt.Errorf("return wrong content type %s", contentType)
+	}
+
+	// Read application/dns-message response from the body
+	buf, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to read the response body")
+	}
+
+	return buf, nil
+}