support http proxy on DOH

upstream.go

@@ -1,12 +1,16 @@
 package main
 
 import (
+	"bufio"
 	"context"
 	"crypto/tls"
 	"errors"
+	"fmt"
 	"net"
 	"net/http"
 	"net/url"
+	"os"
+	"strings"
 	"time"
 
 	log "github.com/fangdingjun/go-log"
@@ -147,8 +151,42 @@ func initDNSClient(c *conf) {
 			Transport: &http2.Transport{
 				DialTLS: func(network, addr string, cfg *tls.Config) (net.Conn, error) {
 					log.Debugln("dial to", network, addr)
-					conn, err := tls.DialWithDialer(dialer, network, addr, cfg)
+					p := os.Getenv("https_proxy")
-					return conn, err
+					if p == "" {
+						p = os.Getenv("http_proxy")
+					}
+					if p == "" {
+						conn, err := tls.DialWithDialer(dialer, network, addr, cfg)
+						return conn, err
+					}
+					u, _ := url.Parse(p)
+					log.Debugf("dial to proxy %s", u.Host)
+					conn, err := net.Dial(network, u.Host)
+					if err != nil {
+						return nil, err
+					}
+					fmt.Fprintf(conn, "CONNECT %s HTTP/1.1\r\nHost: %s\r\n\r\n", addr, addr)
+					r := bufio.NewReader(conn)
+					line, err := r.ReadString('\n')
+					ss := strings.Fields(line)
+					if ss[1] != "200" {
+						return nil, fmt.Errorf("http code %s", ss[1])
+					}
+					for {
+						line, err := r.ReadString('\n')
+						if err != nil {
+							return nil, err
+						}
+						line = strings.Trim(line, "\r\n")
+						if line == "" {
+							break
+						}
+					}
+					tlsconn := tls.Client(conn, cfg)
+					if err = tlsconn.Handshake(); err != nil {
+						return nil, err
+					}
+					return tlsconn, nil
 				},
 				TLSClientConfig: &tls.Config{
 					InsecureSkipVerify: c.UpstreamInsecure,