syncthing-android/patches/golang/all/dns.patch

--- /net/dnsconfig_unix.go	2016-08-20 08:14:05.763235602 -0400
+++ /net/dnsconfig_unix.go	2016-08-20 08:14:05.763235602 -0400
@@ -9,16 +9,59 @@
 package net
 
 import (
+	"fmt"
 	"os"
+	"os/exec"
+	"strings"
 	"sync/atomic"
 	"time"
 )
 
 var (
-	defaultNS   = []string{"127.0.0.1:53", "[::1]:53"}
+	currentNS   []string
 	getHostname = os.Hostname // variable for testing
 )
 
+func getDefaultNS() []string {
+	var servers []string
+	for _, prop := range []string{"net.dns1", "net.dns2"} {
+		cmd := exec.Command("getprop", prop)
+		outputBytes, err := cmd.Output()
+		if err != nil {
+			continue
+		}
+		output := strings.Trim(string(outputBytes), "\n")
+		if ParseIP(output) != nil {
+			servers = append(servers, JoinHostPort(output, "53"))
+		}
+	}
+
+	if len(servers) == 0 {
+		servers = []string{"8.8.8.8:53", "8.8.4.4:53", "4.2.2.1:53"}
+	}
+
+	if !slicesEqual(currentNS, servers) {
+		fmt.Println("Using DNS servers:", servers)
+		currentNS = servers
+	}
+
+	return currentNS
+}
+
+func slicesEqual(a, b []string) bool {
+	if len(a) != len(b) {
+		return false
+	}
+
+	for i := range a {
+		if a[i] != b[i] {
+			return false
+		}
+	}
+
+	return true
+}
+
 type dnsConfig struct {
 	servers    []string      // server addresses (in host:port form) to use
 	search     []string      // rooted suffixes to append to local name
@@ -42,7 +85,7 @@ func dnsReadConfig(filename string) *dnsConfig {
 	}
 	file, err := open(filename)
 	if err != nil {
-		conf.servers = defaultNS
+		conf.servers = getDefaultNS()
 		conf.search = dnsDefaultSearch()
 		conf.err = err
 		return conf
@@ -51,7 +94,7 @@ func dnsReadConfig(filename string) *dnsConfig {
 	if fi, err := file.file.Stat(); err == nil {
 		conf.mtime = fi.ModTime()
 	} else {
-		conf.servers = defaultNS
+		conf.servers = getDefaultNS()
 		conf.search = dnsDefaultSearch()
 		conf.err = err
 		return conf
@@ -130,7 +173,7 @@ func dnsReadConfig(filename string) *dnsConfig {
 		}
 	}
 	if len(conf.servers) == 0 {
-		conf.servers = defaultNS
+		conf.servers = getDefaultNS()
 	}
 	if len(conf.search) == 0 {
 		conf.search = dnsDefaultSearch()