Allow customizing MTU

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

wireguard-go-bridge/example.c

@@ -14,14 +14,14 @@ static struct {
 
 static bool is_closed = false;
 
-ssize_t do_read(const void *ctx, const unsigned char *buf, size_t len)
+ssize_t do_read(void *ctx, unsigned char *buf, size_t len)
 {
 	printf("Reading from instance with ctx %p into buffer %p of length %zu\n", ctx, buf, len);
 	sleep(1);
 	return is_closed ? -1 : 0;
 }
 
-ssize_t do_write(const void *ctx, const unsigned char *buf, size_t len)
+ssize_t do_write(void *ctx, unsigned char *buf, size_t len)
 {
 	printf("Writing from instance with ctx %p into buffer %p of length %zu\n", ctx, buf, len);
 	return len;
@@ -38,7 +38,7 @@ int main(int argc, char *argv[])
 
 	printf("WireGuard Go Version %s\n", wgVersion());
 	wgSetLogger(do_log);
-	handle = wgTurnOn((gostring_t){ .p = "test", .n = 4 }, (gostring_t){ .p = "", .n = 0 }, do_read, do_write, &ctx);
+	handle = wgTurnOn((gostring_t){ .p = "test", .n = 4 }, (gostring_t){ .p = "", .n = 0 }, 0, do_read, do_write, &ctx);
 	sleep(5);
 	is_closed = true;
 	wgTurnOff(handle);

wireguard-go-bridge/src/api-ios.go

@@ -79,7 +79,7 @@ func wgSetLogger(loggerFn uintptr) {
 }
 
 //export wgTurnOn
-func wgTurnOn(ifnameRef string, settings string, readFn uintptr, writeFn uintptr, ctx uintptr) int32 {
+func wgTurnOn(ifnameRef string, settings string, mtu uint16, readFn uintptr, writeFn uintptr, ctx uintptr) int32 {
 	interfaceName := string([]byte(ifnameRef))
 
 	logger := &Logger{
@@ -90,7 +90,7 @@ func wgTurnOn(ifnameRef string, settings string, readFn uintptr, writeFn uintptr
 
 	logger.Debug.Println("Debug log enabled")
 
-	tun := tun.CreateTUN(1280, unsafe.Pointer(readFn), unsafe.Pointer(writeFn), unsafe.Pointer(ctx))
+	tun := tun.CreateTUN(mtu, unsafe.Pointer(readFn), unsafe.Pointer(writeFn), unsafe.Pointer(ctx))
 	logger.Info.Println("Attaching to interface")
 	device := NewDevice(tun, logger)
 

wireguard-go-bridge/src/tun/tun_ios.go

@@ -26,10 +26,17 @@ type nativeTun struct {
 	ctx     unsafe.Pointer
 }
 
-func CreateTUN(mtu int, readFn unsafe.Pointer, writeFn unsafe.Pointer, ctx unsafe.Pointer) TUNDevice {
+func CreateTUN(mtu uint16, readFn unsafe.Pointer, writeFn unsafe.Pointer, ctx unsafe.Pointer) TUNDevice {
+	if mtu == 0 {
+		/* 0 means automatic MTU, which iOS makes outerMTU-80-15. The 80 is for
+		 * WireGuard and the 15 ensures our padding will work. Therefore, it's
+		 * safe to have this code assume a massive MTU.
+		 */
+		mtu = ^mtu
+	}
 	tun := &nativeTun{
 		events:  make(chan TUNEvent, 10),
-		mtu:     mtu,
+		mtu:     int(mtu),
 		readFn:  readFn,
 		writeFn: writeFn,
 		ctx:     ctx,

wireguard-go-bridge/wireguard.h

@@ -7,12 +7,13 @@
 #define WIREGUARD_H
 
 #include <sys/types.h>
+#include <stdint.h>
 
 typedef struct { const char *p; size_t n; } gostring_t;
 typedef ssize_t(*read_write_fn_t)(void *ctx, unsigned char *buf, size_t len);
 typedef void(*logger_fn_t)(int level, const char *tag, const char *msg);
 extern void wgSetLogger(logger_fn_t logger_fn);
-extern int wgTurnOn(gostring_t ifname, gostring_t settings, read_write_fn_t read_fn, read_write_fn_t write_fn, void *ctx);
+extern int wgTurnOn(gostring_t ifname, gostring_t settings, uint16_t mtu, read_write_fn_t read_fn, read_write_fn_t write_fn, void *ctx);
 extern void wgTurnOff(int handle);
 extern char *wgVersion();