优化DoH请求处理，使用HTTP POST发送DNS消息并解析响应

internal/dns/dns.go

@@ -1,9 +1,11 @@
 package dns
 
 import (
+	"bytes"
 	"context"
 	"crypto/tls"
 	"fmt"
+	"io"
 	"net/http"
 	"sync"
 	"time"
@@ -142,17 +144,46 @@ func (s *DNSServer) forwardDoH(req *dns.Msg) (*dns.Msg, error) {
 	ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
 	defer cancel()
 
-	// 使用 DNS-over-HTTPS 客户端
-	client := &dns.Client{
-		Net: "https",
-		TLSConfig: &tls.Config{
-			InsecureSkipVerify: false,
-		},
-		Timeout: 3 * time.Second,
+	// 将 DNS 消息打包
+	packed, err := req.Pack()
+	if err != nil {
+		return nil, err
 	}
 
-	resp, _, err := client.ExchangeContext(ctx, req, s.DoHURL)
-	return resp, err
+	// 创建 HTTP POST 请求
+	httpReq, err := http.NewRequestWithContext(ctx, "POST", s.DoHURL, bytes.NewReader(packed))
+	if err != nil {
+		return nil, err
+	}
+
+	// 设置 DoH 请求头
+	httpReq.Header.Set("Content-Type", "application/dns-message")
+	httpReq.Header.Set("Accept", "application/dns-message")
+
+	// 发送请求
+	resp, err := s.httpClient.Do(httpReq)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("DoH server returned status %d", resp.StatusCode)
+	}
+
+	// 读取响应
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, err
+	}
+
+	// 解析 DNS 响应
+	dnsResp := new(dns.Msg)
+	if err := dnsResp.Unpack(body); err != nil {
+		return nil, err
+	}
+
+	return dnsResp, nil
 }
 
 // recordQuery 记录DNS查询