GoBackend: default MTU is 1280

This sucks, but it works with mobile networks. Later we can do something
sophisticated like we do with wg-quick.c, but not now.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

3 files changed, 16 insertions, 7 deletions

diff --git a/app/src/main/java/com/wireguard/android/backend/GoBackend.java b/app/src/main/java/com/wireguard/android/backend/GoBackend.java
index 7b397f05..28ce7a5e 100644
--- a/app/src/main/java/com/wireguard/android/backend/GoBackend.java
+++ b/app/src/main/java/com/wireguard/android/backend/GoBackend.java
@@ -72,7 +72,7 @@ public final class GoBackend implements Backend {
 
     private static native void wgTurnOff(int handle);
 
-    private static native int wgTurnOn(String ifName, int tunFd, String settings);
+    private static native int wgTurnOn(String ifName, int tunFd, int mtu, String settings);
 
     @Override
     public Config applyConfig(final Tunnel tunnel, final Config config) throws Exception {
@@ -244,12 +244,21 @@ public final class GoBackend implements Backend {
                 }
             }
 
+            int mtu = -1;
+            try {
+                mtu = Integer.parseInt(config.getInterface().getMtu(), 10);
+            } catch (Exception e) {
+            }
+            if (mtu < 0)
+                mtu = 1280;
+            builder.setMtu(mtu);
+
             builder.setBlocking(true);
             ParcelFileDescriptor tun = builder.establish();
             if (tun == null)
                 throw new Exception("Unable to create tun device");
 
-            currentTunnelHandle = wgTurnOn(tunnel.getName(), tun.detachFd(), fmt.toString());
+            currentTunnelHandle = wgTurnOn(tunnel.getName(), tun.detachFd(), mtu, fmt.toString());
             if (currentTunnelHandle < 0)
                 throw new Exception("Unable to turn tunnel on (wgTurnOn return " + currentTunnelHandle + ")");
 
diff --git a/app/tools/libwg-go/api-android.go b/app/tools/libwg-go/api-android.go
index b283d3ad..08367b9c 100644
--- a/app/tools/libwg-go/api-android.go
+++ b/app/tools/libwg-go/api-android.go
@@ -30,7 +30,7 @@ func init() {
 }
 
 //export wgTurnOn
-func wgTurnOn(ifnameRef string, tun_fd int32, settings string) int32 {
+func wgTurnOn(ifnameRef string, tun_fd int32, mtu int32, settings string) int32 {
 	interfaceName := string([]byte(ifnameRef))
 
 	logger := &Logger{
@@ -48,7 +48,7 @@ func wgTurnOn(ifnameRef string, tun_fd int32, settings string) int32 {
 		nopi:   true,
 	}
 	device := NewDevice(tun, logger)
-	device.tun.mtu = DefaultMTU //TODO: make dynamic
+	device.tun.mtu = mtu
 
 	bufferedSettings := bufio.NewReadWriter(bufio.NewReader(strings.NewReader(settings)), bufio.NewWriter(ioutil.Discard))
 	setError := ipcSetOperation(device, bufferedSettings)
diff --git a/app/tools/libwg-go/jni.c b/app/tools/libwg-go/jni.c
index 1476dab7..d32d64c4 100644
--- a/app/tools/libwg-go/jni.c
+++ b/app/tools/libwg-go/jni.c
@@ -1,12 +1,12 @@
 #include <jni.h>
 
 struct go_string { const char *str; long n; };
-extern int wgTurnOn(struct go_string ifname, int tun_fd, struct go_string settings);
+extern int wgTurnOn(struct go_string ifname, int tun_fd, int mtu, struct go_string settings);
 extern void wgTurnOff(int handle);
 extern int wgGetSocketV4(int handle);
 extern int wgGetSocketV6(int handle);
 
-JNIEXPORT jint JNICALL Java_com_wireguard_android_backend_GoBackend_wgTurnOn(JNIEnv *env, jclass c, jstring ifname, jint tun_fd, jstring settings)
+JNIEXPORT jint JNICALL Java_com_wireguard_android_backend_GoBackend_wgTurnOn(JNIEnv *env, jclass c, jstring ifname, jint tun_fd, jint mtu, jstring settings)
 {
 	const char *ifname_str = (*env)->GetStringUTFChars(env, ifname, 0);
 	size_t ifname_len = (*env)->GetStringUTFLength(env, ifname);
@@ -15,7 +15,7 @@ JNIEXPORT jint JNICALL Java_com_wireguard_android_backend_GoBackend_wgTurnOn(JNI
 	int ret = wgTurnOn((struct go_string){
 		.str = ifname_str,
 		.n = ifname_len
-	}, tun_fd, (struct go_string){
+	}, tun_fd, mtu, (struct go_string){
 		.str = settings_str,
 		.n = settings_len
 	});