Fix single instance lock for macOS sandbox app (#3029)

* fix single instance lock for sandbox app

* fix single instance lock for sandbox app

v2/internal/frontend/desktop/darwin/AppDelegate.h

@@ -28,4 +28,6 @@ extern void HandleSecondInstanceData(char * message);
 
 void SendDataToFirstInstance(char * singleInstanceUniqueId, char * text);
 
+char* GetMacOsNativeTempDir();
+
 #endif /* AppDelegate_h */

v2/internal/frontend/desktop/darwin/AppDelegate.m

@@ -48,17 +48,26 @@
 }
 
 void SendDataToFirstInstance(char * singleInstanceUniqueId, char * message) {
+    // we pass message in object because otherwise sandboxing will prevent us from sending it https://developer.apple.com/forums/thread/129437
+    NSString * myString = [NSString stringWithUTF8String:message];
     [[NSDistributedNotificationCenter defaultCenter]
         postNotificationName:[NSString stringWithUTF8String:singleInstanceUniqueId]
-        object:nil
-        userInfo:@{@"message": [NSString stringWithUTF8String:message]}
+        object:(__bridge const void *)(myString)
+        userInfo:nil
         deliverImmediately:YES];
 }
 
+char* GetMacOsNativeTempDir() {
+    NSString *tempDir = NSTemporaryDirectory();
+    char *copy = strdup([tempDir UTF8String]);
+
+    return copy;
+}
+
 - (void)handleSecondInstanceNotification:(NSNotification *)note;
 {
-    if (note.userInfo[@"message"] != nil) {
-        NSString *message = note.userInfo[@"message"];
+    if (note.object != nil) {
+        NSString * message = (__bridge NSString *)note.object;
         const char* utf8Message = message.UTF8String;
         HandleSecondInstanceData((char*)utf8Message);
     }

v2/internal/frontend/desktop/darwin/single_instance.go

@@ -12,13 +12,16 @@ package darwin
 import "C"
 import (
 	"encoding/json"
+	"fmt"
 	"github.com/wailsapp/wails/v2/pkg/options"
 	"os"
+	"strings"
 	"syscall"
+	"unsafe"
 )
 
 func SetupSingleInstance(uniqueID string) {
-	lockFilePath := os.TempDir()
+	lockFilePath := getTempDir()
 	lockFileName := uniqueID + ".lock"
 	_, err := createLockFile(lockFilePath + "/" + lockFileName)
 
@@ -62,14 +65,28 @@ func HandleSecondInstanceData(secondInstanceMessage *C.char) {
 func createLockFile(filename string) (*os.File, error) {
 	file, err := os.OpenFile(filename, os.O_WRONLY|os.O_CREATE, 0600)
 	if err != nil {
+		fmt.Printf("Failed to open lockfile %s: %s", filename, err)
 		return nil, err
 	}
 
 	err = syscall.Flock(int(file.Fd()), syscall.LOCK_EX|syscall.LOCK_NB)
 	if err != nil {
+		// Flock failed for some other reason than other instance already lock it. Print it in logs for possible debugging.
+		if !strings.Contains(err.Error(), "resource temporarily unavailable") {
+			fmt.Printf("Failed to lock lockfile %s: %s", filename, err)
+		}
 		file.Close()
 		return nil, err
 	}
 
 	return file, nil
 }
+
+// If app is sandboxed, golang os.TempDir() will return path that will not be accessible. So use native macOS temp dir function.
+func getTempDir() string {
+	cstring := C.GetMacOsNativeTempDir()
+	path := C.GoString(cstring)
+	C.free(unsafe.Pointer(cstring))
+
+	return path
+}