chore: cleanup the patch code

dns/system.go

@@ -3,16 +3,11 @@ package dns
 import (
 	"context"
 	"fmt"
-	"net"
 	"strings"
 	"sync"
 	"time"
 
-	"github.com/metacubex/mihomo/component/resolver"
-	"github.com/metacubex/mihomo/log"
-
 	D "github.com/miekg/dns"
-	"golang.org/x/exp/slices"
 )
 
 const (
@@ -31,64 +26,6 @@ type systemClient struct {
 	lastFlush  time.Time
 }
 
-func (c *systemClient) getDnsClients() ([]dnsClient, error) {
-	c.mu.Lock()
-	defer c.mu.Unlock()
-	var err error
-	if time.Since(c.lastFlush) > SystemDnsFlushTime {
-		var nameservers []string
-		if nameservers, err = dnsReadConfig(); err == nil {
-			log.Debugln("[DNS] system dns update to %s", nameservers)
-			for _, addr := range nameservers {
-				if resolver.IsSystemDnsBlacklisted(addr) {
-					continue
-				}
-				if _, ok := c.dnsClients[addr]; !ok {
-					clients := transform(
-						[]NameServer{{
-							Addr: net.JoinHostPort(addr, "53"),
-							Net:  "udp",
-						}},
-						nil,
-					)
-					if len(clients) > 0 {
-						c.dnsClients[addr] = &systemDnsClient{
-							disableTimes: 0,
-							dnsClient:    clients[0],
-						}
-					}
-				}
-			}
-			available := 0
-			for nameserver, sdc := range c.dnsClients {
-				if slices.Contains(nameservers, nameserver) {
-					sdc.disableTimes = 0 // enable
-					available++
-				} else {
-					if sdc.disableTimes > SystemDnsDeleteTimes {
-						delete(c.dnsClients, nameserver) // drop too old dnsClient
-					} else {
-						sdc.disableTimes++
-					}
-				}
-			}
-			if available > 0 {
-				c.lastFlush = time.Now()
-			}
-		}
-	}
-	dnsClients := make([]dnsClient, 0, len(c.dnsClients))
-	for _, sdc := range c.dnsClients {
-		if sdc.disableTimes == 0 {
-			dnsClients = append(dnsClients, sdc.dnsClient)
-		}
-	}
-	if len(dnsClients) > 0 {
-		return dnsClients, nil
-	}
-	return nil, err
-}
-
 func (c *systemClient) ExchangeContext(ctx context.Context, m *D.Msg) (msg *D.Msg, err error) {
 	dnsClients, err := c.getDnsClients()
 	if err != nil {