fix: 纯IPv6环境的一些问题

dnsresolver/resolver.go

@@ -3,37 +3,63 @@ package dnsresolver
 import (
 	"context"
 	"fmt"
+	"log"
 	"net"
 	"net/http"
+	"sort"
 	"strings"
+	"sync"
 	"time"
 )
 
 var (
-	// DNS服务器列表，按优先级排序
 	DNSServers = []string{
+		"[2606:4700:4700::1111]:53", // Cloudflare IPv6
+		"[2606:4700:4700::1001]:53", // Cloudflare IPv6 备用
+		"[2001:4860:4860::8888]:53", // Google IPv6
+		"[2001:4860:4860::8844]:53", // Google IPv6 备用
+
 		"114.114.114.114:53", // 114DNS，中国大陆
-		"8.8.8.8:53",         // Google DNS，全球
-		"8.8.4.4:53",         // Google DNS备用，全球
-		"1.1.1.1:53",         // Cloudflare DNS，全球
+		"1.1.1.1:53",         // Cloudflare IPv4
+		"8.8.8.8:53",         // Google IPv4
+		"8.8.4.4:53",         // Google IPv4 备用
 		"223.5.5.5:53",       // 阿里DNS，中国大陆
 		"119.29.29.29:53",    // DNSPod，中国大陆
-
 	}
 
 	// CustomDNSServer 自定义DNS服务器，可以通过命令行参数设置
 	CustomDNSServer string
+
+	preferV4Once sync.Once
+	hasIPv4      bool
 )
 
 // SetCustomDNSServer 设置自定义DNS服务器
 func SetCustomDNSServer(dnsServer string) {
-	if dnsServer != "" {
-		// 检查是否已包含端口，如果没有则添加默认端口53
-		if !strings.Contains(dnsServer, ":") {
-			dnsServer = dnsServer + ":53"
-		}
-		CustomDNSServer = dnsServer
+	if dnsServer == "" {
+		return
 	}
+	CustomDNSServer = normalizeDNSServer(dnsServer)
+}
+
+// normalizeDNSServer 将输入的 DNS 服务器字符串规范化为 host:port 形式：
+// - IPv6 地址自动加方括号并补全端口 :53（若未提供）
+// - IPv4/域名未提供端口时补全 :53
+func normalizeDNSServer(s string) string {
+	s = strings.TrimSpace(s)
+	// 已是 [ipv6]:port 或 host:port 形式
+	if (strings.HasPrefix(s, "[") && strings.Contains(s, "]:")) || (strings.Count(s, ":") == 1 && !strings.Contains(s, "]")) {
+		return s
+	}
+	// 纯 IPv6（未加端口/括号）
+	if strings.Count(s, ":") >= 2 && !strings.Contains(s, "]") {
+		return "[" + s + "]:53"
+	}
+	// 其它情况：若未包含端口则补 53
+	if !strings.Contains(s, ":") {
+		return s + ":53"
+	}
+	return s
 }
 
 // getCurrentDNSServer 获取当前要使用的DNS服务器
@@ -67,7 +93,7 @@ func GetCustomResolver() *net.Resolver {
 					return conn, nil
 				}
 			}
-
+			log.Printf("Custom DNS server %s is unreachable, trying fallback servers", dnsServer)
 			// 如果自定义DNS不可用，则尝试内置列表作为兜底
 			for _, server := range DNSServers {
 				if server == dnsServer {
@@ -103,6 +129,20 @@ func GetHTTPClient(timeout time.Duration) *http.Client {
 				if err != nil {
 					return nil, err
 				}
+				// 根据本机是否具备 IPv4 动态排序
+				preferIPv4 := preferIPv4First()
+				sort.SliceStable(ips, func(i, j int) bool {
+					ip1 := net.ParseIP(ips[i])
+					ip2 := net.ParseIP(ips[j])
+					if ip1 == nil || ip2 == nil {
+						return false
+					}
+					if preferIPv4 {
+						return ip1.To4() != nil && ip2.To4() == nil
+					}
+					// IPv6 优先
+					return ip1.To4() == nil && ip2.To4() != nil
+				})
 				for _, ip := range ips {
 					dialer := &net.Dialer{
 						Timeout:   30 * time.Second,
@@ -137,3 +177,91 @@ func GetNetDialer(timeout time.Duration) *net.Dialer {
 		Resolver:  GetCustomResolver(),
 	}
 }
+
+// GetDialContext 返回一个自定义 DialContext：
+// - 使用自定义解析器解析主机名
+// - 优先尝试 IPv4，再尝试 IPv6
+// - 逐个 IP 进行连接尝试，直到成功或全部失败
+func GetDialContext(timeout time.Duration) func(ctx context.Context, network, addr string) (net.Conn, error) {
+	if timeout <= 0 {
+		timeout = 15 * time.Second
+	}
+
+	resolver := GetCustomResolver()
+
+	return func(ctx context.Context, network, addr string) (net.Conn, error) {
+		host, port, err := net.SplitHostPort(addr)
+		if err != nil {
+			return nil, err
+		}
+
+		// 为解析设置一个带超时的子 context，避免整体拨号过快超时
+		lookupCtx, cancel := context.WithTimeout(ctx, timeout)
+		defer cancel()
+
+		ips, err := resolver.LookupHost(lookupCtx, host)
+		if err != nil {
+			return nil, err
+		}
+
+		// 根据本机是否具备 IPv4 动态排序
+		preferIPv4 := preferIPv4First()
+		sort.SliceStable(ips, func(i, j int) bool {
+			ip1 := net.ParseIP(ips[i])
+			ip2 := net.ParseIP(ips[j])
+			if ip1 == nil || ip2 == nil {
+				return false
+			}
+			if preferIPv4 {
+				return ip1.To4() != nil && ip2.To4() == nil
+			}
+			// IPv6 优先
+			return ip1.To4() == nil && ip2.To4() != nil
+		})
+
+		// 逐个 IP 尝试连接
+		for _, ip := range ips {
+			d := &net.Dialer{
+				Timeout:   timeout,
+				KeepAlive: 30 * time.Second,
+				DualStack: true,
+			}
+			c, err := d.DialContext(ctx, network, net.JoinHostPort(ip, port))
+			if err == nil {
+				return c, nil
+			}
+		}
+		return nil, fmt.Errorf("failed to dial to any of the resolved IPs")
+	}
+}
+
+// preferIPv4First 检测本机是否存在可用的 IPv4 地址，若没有则在连接尝试中优先 IPv6
+func preferIPv4First() bool {
+	preferV4Once.Do(func() {
+		ifaces, _ := net.Interfaces()
+		for _, iface := range ifaces {
+			if (iface.Flags&net.FlagUp) == 0 || (iface.Flags&net.FlagLoopback) != 0 {
+				continue
+			}
+			addrs, _ := iface.Addrs()
+			for _, a := range addrs {
+				var ip net.IP
+				switch v := a.(type) {
+				case *net.IPNet:
+					ip = v.IP
+				case *net.IPAddr:
+					ip = v.IP
+				}
+				if ip == nil || ip.IsLoopback() {
+					continue
+				}
+				if ip.To4() != nil {
+					hasIPv4 = true
+					return
+				}
+			}
+		}
+		hasIPv4 = false
+	})
+	return hasIPv4
+}