cs8425 · March 5, 2025 08:30 · Mar 21, 2019 · Mar 21, 2019 · Mar 21, 2019 · Mar 21, 2019
diff --git a/setDefaultNS.go b/setDefaultNS.go
@@ -46,16 +46,30 @@ type resolverConfig struct {
 	dnsConfig *dnsConfig   // parsed resolv.conf structure used in lookups
 }
 
-func setDefaultNS(addrs []string) {
-	now := time.Now()
-	resolvConf.dnsConfig.mtime = now
-	resolvConf.lastChecked = now
+
+//go:linkname (*resolverConfig).tryUpdate net.(*resolverConfig).tryUpdate
+func (conf *resolverConfig) tryUpdate(name string)
+// need to put a empty .s file
+
+
+func setDefaultNS(addrs []string, loadFromSystem bool) {
+	if resolvConf.dnsConfig == nil {
+		resolvConf.tryUpdate("")
+	}
+
+	if loadFromSystem {
+		now := time.Now()
+		resolvConf.lastChecked = now.Add(-6 * time.Second)
+		resolvConf.dnsConfig.mtime = now
+	}
+
 	resolvConf.dnsConfig.servers = addrs
 	defaultNS = addrs
 }
 
 // --------------
 
+
 func test() {
 	ips, err := net.LookupIP("google.com")
 	if err != nil {
@@ -66,15 +80,22 @@ func test() {
 }
 
 func main() {
-	// test default
-	test()
+	// force use a non-exist DNS server
+	setDefaultNS([]string{"127.0.0.1:5300"}, false)
+	test() // error
+	fmt.Println("------------------")
+
+
+	// force use a list of DNS server
+	setDefaultNS([]string{"8.8.8.8:53", "1.1.1.1:53"}, false)
+	test() // ok
 	fmt.Println("------------------")
 
-	// set DNS
-	setDefaultNS([]string{"8.8.8.8:53", "1.1.1.1:53"})
+
+	// set DNS & try reload from system config
+	setDefaultNS([]string{"127.0.0.1:5300"}, true)
 
 	// check & test net.defaultNS
-	fmt.Println("use DNS", defaultNS)
-	test()
+	test() // ok
 	fmt.Println("------------------")
 }
diff --git a/setDefaultNS.go b/setDefaultNS.go
@@ -11,6 +11,8 @@ import (
 
 // DNS resolve workaround for android in pure go
 
+//go:linkname defaultNS net.defaultNS
+var defaultNS []string
 
 // need to keep sync with go version
 //go:linkname resolvConf net.resolvConf
@@ -54,7 +56,6 @@ func setDefaultNS(addrs []string) {
 
 // --------------
 
-
 func test() {
 	ips, err := net.LookupIP("google.com")
 	if err != nil {
@@ -77,29 +78,3 @@ func main() {
 	test()
 	fmt.Println("------------------")
 }
-
-
-// --------------
-
-// this only work before any Lookup call and net.dnsReadConfig() failed
-//go:linkname defaultNS net.defaultNS
-var defaultNS []string
-
-func setDefaultNS2(addrs []string) {
-	defaultNS = addrs
-}
-
-func main2() {
-	// print net.defaultNS
-	fmt.Println("use DNS", defaultNS)
-	//test() // should setup before any call!!
-	fmt.Println("------------------")
-
-	// set net.defaultNS
-	setDefaultNS2([]string{"8.8.8.8:53", "1.1.1.1:53"})
-
-	// check & test net.defaultNS
-	fmt.Println("use DNS", defaultNS)
-	test()
-	fmt.Println("------------------")
-}
diff --git a/setDefaultNS2.go b/setDefaultNS2.go
@@ -0,0 +1,44 @@
+package main
+
+import (
+	"fmt"
+
+	"net"
+	_ "unsafe"
+)
+
+// DNS resolve workaround for android in pure go
+
+// this only work before any Lookup call and net.dnsReadConfig() failed
+//go:linkname defaultNS net.defaultNS
+var defaultNS []string
+
+func setDefaultNS2(addrs []string) {
+	defaultNS = addrs
+}
+
+// --------------
+
+func test() {
+	ips, err := net.LookupIP("google.com")
+	if err != nil {
+		fmt.Printf("Could not get IPs: %v\n", err)
+		return
+	}
+	fmt.Println("IPs:", ips)
+}
+
+func main() {
+	// print net.defaultNS
+	fmt.Println("use DNS", defaultNS)
+	//test() // should setup before any call!!
+	fmt.Println("------------------")
+
+	// set net.defaultNS
+	setDefaultNS2([]string{"8.8.8.8:53", "1.1.1.1:53"})
+
+	// check & test net.defaultNS
+	fmt.Println("use DNS", defaultNS)
+	test()
+	fmt.Println("------------------")
+}
diff --git a/setDefaultNS.go b/setDefaultNS.go
@@ -4,18 +4,57 @@ import (
 	"fmt"
 
 	"net"
+	"sync"
+	"time"
 	_ "unsafe"
 )
 
 // DNS resolve workaround for android in pure go
 
-//go:linkname defaultNS net.defaultNS
-var defaultNS []string
+
+// need to keep sync with go version
+//go:linkname resolvConf net.resolvConf
+var resolvConf resolverConfig
+
+// copy from /src/net/dnsconfig_unix.go
+type dnsConfig struct {
+	servers    []string      // server addresses (in host:port form) to use
+	search     []string      // rooted suffixes to append to local name
+	ndots      int           // number of dots in name to trigger absolute lookup
+	timeout    time.Duration // wait before giving up on a query, including retries
+	attempts   int           // lost packets before giving up on server
+	rotate     bool          // round robin among servers
+	unknownOpt bool          // anything unknown was encountered
+	lookup     []string      // OpenBSD top-level database "lookup" order
+	err        error         // any error that occurs during open of resolv.conf
+	mtime      time.Time     // time of resolv.conf modification
+	soffset    uint32        // used by serverOffset
+}
+
+// copy from /src/net/dnsclient_unix.go
+type resolverConfig struct {
+	initOnce sync.Once // guards init of resolverConfig
+
+	// ch is used as a semaphore that only allows one lookup at a
+	// time to recheck resolv.conf.
+	ch          chan struct{} // guards lastChecked and modTime
+	lastChecked time.Time     // last time resolv.conf was checked
+
+	mu        sync.RWMutex // protects dnsConfig
+	dnsConfig *dnsConfig   // parsed resolv.conf structure used in lookups
+}
 
 func setDefaultNS(addrs []string) {
+	now := time.Now()
+	resolvConf.dnsConfig.mtime = now
+	resolvConf.lastChecked = now
+	resolvConf.dnsConfig.servers = addrs
 	defaultNS = addrs
 }
 
+// --------------
+
+
 func test() {
 	ips, err := net.LookupIP("google.com")
 	if err != nil {
@@ -26,16 +65,41 @@ func test() {
 }
 
 func main() {
+	// test default
+	test()
+	fmt.Println("------------------")
+
+	// set DNS
+	setDefaultNS([]string{"8.8.8.8:53", "1.1.1.1:53"})
+
+	// check & test net.defaultNS
+	fmt.Println("use DNS", defaultNS)
+	test()
+	fmt.Println("------------------")
+}
+
+
+// --------------
+
+// this only work before any Lookup call and net.dnsReadConfig() failed
+//go:linkname defaultNS net.defaultNS
+var defaultNS []string
+
+func setDefaultNS2(addrs []string) {
+	defaultNS = addrs
+}
+
+func main2() {
 	// print net.defaultNS
-	fmt.Println(defaultNS)
+	fmt.Println("use DNS", defaultNS)
 	//test() // should setup before any call!!
 	fmt.Println("------------------")
 
 	// set net.defaultNS
-	setDefaultNS([]string{"8.8.8.8:53", "1.1.1.1:53"})
+	setDefaultNS2([]string{"8.8.8.8:53", "1.1.1.1:53"})
 
 	// check & test net.defaultNS
-	fmt.Println(defaultNS)
+	fmt.Println("use DNS", defaultNS)
 	test()
 	fmt.Println("------------------")
 }
diff --git a/setDefaultNS.go b/setDefaultNS.go
@@ -4,7 +4,6 @@ import (
 	"fmt"
 
 	"net"
-	"reflect"
 	_ "unsafe"
 )
 
@@ -14,13 +13,7 @@ import (
 var defaultNS []string
 
 func setDefaultNS(addrs []string) {
-	valuePtr := reflect.ValueOf(&defaultNS)
-	v := valuePtr.Elem()
-
-	v.Set(reflect.MakeSlice(v.Type(), len(addrs), len(addrs)))
-	for i, w := range addrs {
-		v.Index(i).Set(reflect.ValueOf(w))
-	}
+	defaultNS = addrs
 }
 
 func test() {

diff --git a/setDefaultNS.go b/setDefaultNS.go
@@ -13,8 +13,8 @@ import (
 //go:linkname defaultNS net.defaultNS
 var defaultNS []string
 
-func setSlice(arrPtr interface{}, addrs []string) {
-	valuePtr := reflect.ValueOf(arrPtr)
+func setDefaultNS(addrs []string) {
+	valuePtr := reflect.ValueOf(&defaultNS)
 	v := valuePtr.Elem()
 
 	v.Set(reflect.MakeSlice(v.Type(), len(addrs), len(addrs)))
@@ -39,9 +39,9 @@ func main() {
 	fmt.Println("------------------")
 
 	// set net.defaultNS
-	setSlice(&defaultNS, []string{"8.8.8.8:53", "1.1.1.1:53"})
+	setDefaultNS([]string{"8.8.8.8:53", "1.1.1.1:53"})
 
-	// check net.defaultNS
+	// check & test net.defaultNS
 	fmt.Println(defaultNS)
 	test()
 	fmt.Println("------------------")

diff --git a/setDefaultNS.go b/setDefaultNS.go
@@ -8,7 +8,7 @@ import (
 	_ "unsafe"
 )
 
-// DNS resolve work around for android in pure go
+// DNS resolve workaround for android in pure go
 
 //go:linkname defaultNS net.defaultNS
 var defaultNS []string

diff --git a/setDefaultNS.go b/setDefaultNS.go
@@ -3,9 +3,9 @@ package main
 import (
 	"fmt"
 
+	"net"
 	"reflect"
 	_ "unsafe"
-	_ "net"
 )
 
 // DNS resolve work around for android in pure go
@@ -23,15 +23,26 @@ func setSlice(arrPtr interface{}, addrs []string) {
 	}
 }
 
+func test() {
+	ips, err := net.LookupIP("google.com")
+	if err != nil {
+		fmt.Printf("Could not get IPs: %v\n", err)
+		return
+	}
+	fmt.Println("IPs:", ips)
+}
+
 func main() {
 	// print net.defaultNS
 	fmt.Println(defaultNS)
+	//test() // should setup before any call!!
 	fmt.Println("------------------")
 
 	// set net.defaultNS
 	setSlice(&defaultNS, []string{"8.8.8.8:53", "1.1.1.1:53"})
 
 	// check net.defaultNS
 	fmt.Println(defaultNS)
+	test()
 	fmt.Println("------------------")
 }
diff --git a/setDefaultNS.go b/setDefaultNS.go
@@ -0,0 +1,37 @@
+package main
+
+import (
+	"fmt"
+
+	"reflect"
+	_ "unsafe"
+	_ "net"
+)
+
+// DNS resolve work around for android in pure go
+
+//go:linkname defaultNS net.defaultNS
+var defaultNS []string
+
+func setSlice(arrPtr interface{}, addrs []string) {
+	valuePtr := reflect.ValueOf(arrPtr)
+	v := valuePtr.Elem()
+
+	v.Set(reflect.MakeSlice(v.Type(), len(addrs), len(addrs)))
+	for i, w := range addrs {
+		v.Index(i).Set(reflect.ValueOf(w))
+	}
+}
+
+func main() {
+	// print net.defaultNS
+	fmt.Println(defaultNS)
+	fmt.Println("------------------")
+
+	// set net.defaultNS
+	setSlice(&defaultNS, []string{"8.8.8.8:53", "1.1.1.1:53"})
+
+	// check net.defaultNS
+	fmt.Println(defaultNS)
+	fmt.Println("------------------")
+}