fix: Adds support for SharedPreferencesAsync

[romaingyh]

What kind of change does this PR introduce?

It's both a bug fix and feature.

9 months ago with version 2.3.0, shared_preferences package added SharedPreferencesAsync and SharedPreferencesWithCache to replace the legacy (and deprecated in future) SharedPreferences. See here

Supabase flutter uses by default the legacy one with SharedPreferencesLocalStorage.

Problem is that on some platform like Windows, the legacy one and new one are not compatible. If the developer made the migration to SharedPreferencesAsync then the supabase's local storage is broken.

Example :
I'm using SharedPreferencesAsync in my app. After sign in, the sb-x-auth-token is saved in saved-preferences.json by supabase's SharedPreferences. After that, any call to my app's SharedPreferencesAsync will overwrite the token and user have to sign in on next app launch. In practice it can lead to sign in every time he opens the app if you use shared preferences frequently in your code.

What is the new behavior?

I added a boolean flag useSharedPreferencesAsync to SharedPreferencesLocalStorage. There wasn't very much changes as every methods are already async in LocalStorage interface.

If you prefer two distinct classes SharedPreferencesLocalStorage and SharedPreferencesAsyncLocalStorage I can do this

[Vinzent03]

I can confirm that this issue exists, as I encountered this as well in a recent project, but didn't have the time to investigate more and come up with a pr. At that time, I solved it by manually providing my own storage implementation using the async shared preferences.
But I'm really unsure about the current design of the solution and will have to think about it a bit.

[coveralls]

Pull Request Test Coverage Report for Build 14823893141

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
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• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 18 (0.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.2%) to 75.138%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
packages/supabase_flutter/lib/src/local_storage.dart	0	18	0.0%

Totals
Change from base Build 14730510657:	-0.2%
Covered Lines:	2868
Relevant Lines:	3817

---

💛 - Coveralls

[romaingyh]

I can confirm that this issue exists, as I encountered this as well in a recent project, but didn't have the time to investigate more and come up with a pr. At that time, I solved it by manually providing my own storage implementation using the async shared preferences. But I'm really unsure about the current design of the solution and will have to think about it a bit.

I thought of another solution like this :

Code

/// A [LocalStorage] implementation that implements SharedPreferences as the
/// storage method.
class SharedPreferencesLocalStorage extends LocalStorage {
  late final SharedPreferences _prefs;

  SharedPreferencesLocalStorage({required this.persistSessionKey});

  final String persistSessionKey;

  static const _useWebLocalStorage =
      kIsWeb && bool.fromEnvironment("dart.library.js_interop");

  @override
  Future<void> initialize() async {
    if (!_useWebLocalStorage) {
      WidgetsFlutterBinding.ensureInitialized();
      _prefs = await SharedPreferences.getInstance();
    }
  }

  @override
  Future<bool> hasAccessToken() async {
    if (_useWebLocalStorage) {
      return web.hasAccessToken(persistSessionKey);
    }
    return _prefs.containsKey(persistSessionKey);
  }

  @override
  Future<String?> accessToken() async {
    if (_useWebLocalStorage) {
      return web.accessToken(persistSessionKey);
    }
    return _prefs.getString(persistSessionKey);
  }

  @override
  Future<void> removePersistedSession() async {
    if (_useWebLocalStorage) {
      web.removePersistedSession(persistSessionKey);
    } else {
      await _prefs.remove(persistSessionKey);
    }
  }

  @override
  Future<void> persistSession(String persistSessionString) {
    if (_useWebLocalStorage) {
      return web.persistSession(persistSessionKey, persistSessionString);
    }
    return _prefs.setString(persistSessionKey, persistSessionString);
  }
}

/// A [LocalStorage] implementation that implements SharedPreferencesAsync as the
/// storage method.
class SharedPreferencesAsyncLocalStorage extends LocalStorage {
  late final SharedPreferencesAsync _prefs;

  SharedPreferencesAsyncLocalStorage({required this.persistSessionKey});

  final String persistSessionKey;

  static const _useWebLocalStorage =
      kIsWeb && bool.fromEnvironment("dart.library.js_interop");

  @override
  Future<void> initialize() async {
    if (!_useWebLocalStorage) {
      WidgetsFlutterBinding.ensureInitialized();
      _prefs = SharedPreferencesAsync();
    }
  }

  @override
  Future<bool> hasAccessToken() async {
    if (_useWebLocalStorage) {
      return web.hasAccessToken(persistSessionKey);
    }
    return _prefs.containsKey(persistSessionKey);
  }

  @override
  Future<String?> accessToken() async {
    if (_useWebLocalStorage) {
      return web.accessToken(persistSessionKey);
    }
    return _prefs.getString(persistSessionKey);
  }

  @override
  Future<void> removePersistedSession() async {
    if (_useWebLocalStorage) {
      web.removePersistedSession(persistSessionKey);
    } else {
      await _prefs.remove(persistSessionKey);
    }
  }

  @override
  Future<void> persistSession(String persistSessionString) {
    if (_useWebLocalStorage) {
      return web.persistSession(persistSessionKey, persistSessionString);
    }
    return _prefs.setString(persistSessionKey, persistSessionString);
  }
}

where the dev has to opt-in for SharedPreferencesAsyncLocalStorage when he initializes supabase.

I didn't choose this implementation in my PR because the two classes are pretty much the same except for shared prefs init.

[romaingyh]

I think CI test fails because with Flutter 3.19 the resolvable shared_preferences package version is < 2.3.0 but not sure about this