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

diff --git a/net/dnsconfig_unix.go b/net/dnsconfig_unix.go
index 6073fdb..9df3cec 100644
--- a/net/dnsconfig_unix.go
+++ b/net/dnsconfig_unix.go
@@ -8,18 +8,57 @@
 
 package net
 
-var defaultNS = []string{"127.0.0.1", "::1"}
+import (
+	"fmt"
+	"os/exec"
+	"strings"
+	"sync"
+	"time"
+)
+
+var (
+	logOnce sync.Once
+)
+
+func getDefaultNS() []string {
+	var servers []string
+	for _, prop := range []string{"net.dns", "net.dns1", "net.dns2", "net.dns3", "net.dns4"} {
+		cmd := exec.Command("getprop", prop)
+		if cmd.Run() == nil {
+			outputBytes, err := cmd.Output()
+			if err != nil {
+				continue
+			}
+
+			output := strings.Trim(string(outputBytes), "\n")
+			if ParseIP(output) != nil {
+				servers = append(servers, output)
+			}
+		}
+	}
+
+	if servers == nil {
+		servers = []string{"8.8.8.8", "8.8.4.4", "4.2.2.1"}
+	}
+
+	logOnce.Do(func() {
+		fmt.Println("Using the following DNS servers", servers)
+	})
+
+	return servers
+}
 
 type dnsConfig struct {
-	servers    []string // servers to use
-	search     []string // suffixes to append to local name
-	ndots      int      // number of dots in name to trigger absolute lookup
-	timeout    int      // seconds before giving up on packet
-	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
+	servers    []string  // servers to use
+	search     []string  // suffixes to append to local name
+	ndots      int       // number of dots in name to trigger absolute lookup
+	timeout    int       // seconds before giving up on packet
+	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
 }
 
 // See resolv.conf(5) on a Linux machine.
@@ -33,11 +72,20 @@ func dnsReadConfig(filename string) *dnsConfig {
 	}
 	file, err := open(filename)
 	if err != nil {
-		conf.servers = defaultNS
+		conf.servers = getDefaultNS()
+		conf.mtime = time.Now()
 		conf.err = err
 		return conf
 	}
 	defer file.close()
+	if fi, err := file.file.Stat(); err == nil {
+		conf.mtime = fi.ModTime()
+	} else {
+		conf.mtime = time.Now()
+		conf.servers = getDefaultNS()
+		conf.err = err
+		return conf
+	}
 	for line, ok := file.readLine(); ok; line, ok = file.readLine() {
 		if len(line) > 0 && (line[0] == ';' || line[0] == '#') {
 			// comment.
@@ -51,7 +99,7 @@ func dnsReadConfig(filename string) *dnsConfig {
 		case "nameserver": // add one name server
 			if len(f) > 1 && len(conf.servers) < 3 { // small, but the standard limit
 				// One more check: make sure server name is
-				// just an IP address.  Otherwise we need DNS
+				// just an IP address. Otherwise we need DNS
 				// to look it up.
 				if parseIPv4(f[1]) != nil {
 					conf.servers = append(conf.servers, f[1])
@@ -110,7 +158,7 @@ func dnsReadConfig(filename string) *dnsConfig {
 		}
 	}
 	if len(conf.servers) == 0 {
-		conf.servers = defaultNS
+		conf.servers = getDefaultNS()
 	}
 	return conf
 }
@@ -118,3 +166,4 @@ func dnsReadConfig(filename string) *dnsConfig {
 func hasPrefix(s, prefix string) bool {
 	return len(s) >= len(prefix) && s[:len(prefix)] == prefix
 }
+