chore: cleanup the patch code

dns/system_common.go

@@ -0,0 +1,71 @@
+//go:build !(android && cmfa)
+
+package dns
+
+import (
+	"net"
+	"time"
+
+	"github.com/metacubex/mihomo/component/resolver"
+	"github.com/metacubex/mihomo/log"
+
+	"golang.org/x/exp/slices"
+)
+
+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
+}