Firebase React Native Share Extension Credentials Syncer

FirebaseAuthSync.m

// see https://github.com/firebase/firebase-ios-sdk/issues/2179
//
// this is a hack workaround that periodically copies the Firebase credentials
// between your main app and your share extension,
// thus allowing the extension to authenticate using the same creds
// 
// make sure you've created an app group beforehand so they can share that storage

#import <Foundation/Foundation.h>
#import "FirebaseAuthSync.h"


#define RCT_DIR (@"RCTAsyncLocalStorage_V1")  // as of 8/17/2019. idk if this'll change. Hacky.
#define APP_GROUP (@"YOUR.GROUP.ID.HERE")  // TODO change to e.g. (@"group.com.foo.bar")

@interface FirebaseAuthSync : NSObject
+ (void) sync: (BOOL) mainApp;
+ (void) timer: (BOOL) mainApp;
@end


@implementation FirebaseAuthSync

+ (void) sync: (BOOL) mainApp {
  NSURL* url = [[NSFileManager defaultManager] containerURLForSecurityApplicationGroupIdentifier: APP_GROUP];
  NSString* sharedDir = [NSString stringWithFormat:@"%@/%@", [url path], RCT_DIR];
  NSString* docsDir = [NSString stringWithFormat:@"%@/%@", NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES)[0], RCT_DIR];
  
  NSString* src = NULL;
  NSString* dst = NULL;
  if (mainApp) {
    src = docsDir;
    dst = sharedDir;
  } else {
    src = sharedDir;
    dst = docsDir;
  }
  
  NSError* error;
  [[NSFileManager defaultManager] removeItemAtPath:dst error:&error];
  NSLog(@"Deleted item %@, error (ok if null): %@", dst, error);
  [[NSFileManager defaultManager] copyItemAtURL: [NSURL fileURLWithPath:src] toURL: [NSURL fileURLWithPath:dst] error: &error];
  NSLog(@"Copying from %@ to %@, error (ok if null): %@", src, dst, error);
}

+ (void) timer: (BOOL) mainApp {
  [FirebaseAuthSync sync: mainApp];
  dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 60 * NSEC_PER_SEC), dispatch_get_main_queue(), ^{
    NSLog(@"Timer for FirebaseAuthSync firing");
    [FirebaseAuthSync timer: mainApp];
  });
}

@end

in your AppDelegate.m:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
  [FirebaseAuthSync timer: true];

in your share extension's .m, if you're using react-native-share-extension's instructions:

- (UIView*) shareView {
  [FirebaseAuthSync sync: false];