new DoH client

miekg/dns dropped DoH support in v1.0.15,
so use my own DoH client

client_https.go

@@ -0,0 +1,59 @@
+package main
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"time"
+
+	"github.com/miekg/dns"
+)
+
+type httpclient struct {
+	Net        string
+	Timeout    time.Duration
+	HTTPClient *http.Client
+}
+
+func (c *httpclient) Exchange(msg *dns.Msg, upstream string) (*dns.Msg, int, error) {
+	data, err := msg.Pack()
+	if err != nil {
+		return nil, 0, err
+	}
+
+	req, err := http.NewRequest("POST", upstream, bytes.NewReader(data))
+	if err != nil {
+		return nil, 0, err
+	}
+
+	req.Header.Set("Content-Type", dnsMsgType)
+
+	ctx, cancel := context.WithTimeout(context.Background(), c.Timeout)
+	defer cancel()
+
+	req = req.WithContext(ctx)
+
+	resp, err := c.HTTPClient.Do(req)
+	if err != nil {
+		return nil, 0, err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return nil, 0, fmt.Errorf("http error %d", resp.StatusCode)
+	}
+
+	data, err = ioutil.ReadAll(resp.Body)
+	if err != nil {
+		return nil, 0, err
+	}
+
+	m := new(dns.Msg)
+	if err = m.Unpack(data); err != nil {
+		return nil, 0, err
+	}
+
+	return m, 0, nil
+}

upstream.go

@@ -9,15 +9,15 @@ import (
 	"net/url"
 	"time"
 
-	"github.com/fangdingjun/go-log"
+	log "github.com/fangdingjun/go-log"
 	"github.com/miekg/dns"
 	"golang.org/x/net/http2"
 )
 
 var dnsClientTCP *dns.Client
-var dnsClientHTTPS *dns.Client
 var dnsClientUDP *dns.Client
 var dnsClientTLS *dns.Client
+var dnsClientHTTPS *httpclient
 
 func getResponseFromUpstream(msg *dns.Msg, upstreams []*url.URL) (*dns.Msg, error) {
 	ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
@@ -129,7 +129,7 @@ func initDNSClient(c *conf) {
 		Net:     "tcp",
 		Timeout: time.Duration(c.UpstreamTimeout) * time.Second,
 	}
-	dnsClientHTTPS = &dns.Client{
+	dnsClientHTTPS = &httpclient{
 		Net:     "https",
 		Timeout: time.Duration(c.UpstreamTimeout) * time.Second,
 		HTTPClient: &http.Client{