[cupertino_http] CupertinoClient requests hang and fail to complete

[martyfuhry]

I've been using IOClient in my Flutter application. When I switched to using CupertinoClient, my requests fail to complete. I have inspected the network traffic from my iOS app through a proxy. The requests are being properly sent by the application and the web server is responding with the correct data. But the future from client.get is never resolved in the Flutter application. No errors show up, the request simply hangs.

Here is my code for initializing the CupertinoClient

Client getHttpClient() {
  if (UniversalPlatform.isAndroid) {
    return CronetClient.defaultCronetEngine();
  } else if (UniversalPlatform.isIOS) {
    return CupertinoClient.defaultSessionConfiguration();
  } else {
    throw UnsupportedError('Platform not supported');
  }
}

Here is an example of our code sending a request:

    return client
        .get(
          url,
          headers: headers,
        );

I've also tried using UrlSessionConfiguration.ephemeralSessionConfiguration() and it does not change the result. If I change the above code to return IOClient instead of the CupertinoClient, the application works.

Finally, it would seem that every network request hangs, not just those to my own webserver. In particular, this get request hangs:

return client.get(Uri.parse('https://google.com'));

I do not see any errors in my console. The responses simply fail to resolve the future and the code hangs forever.

This was all tested on a physical iOS 17.6.1 device (iPhone 11 Pro Max).

[brianquinlan]

@martyfuhry What version of cupertino_http are you using. This issue may have been resolved in the 2.0.2. release.

[martyfuhry]

Ah, that would be great! I am only running 2.0.1 so I will try updating and seeing if that resolves the issue. Thank you!

[brianquinlan]

OK, let me know how it goes.

[martyfuhry]

Unfortunately, the behavior persists in version 2.0.2.

[brianquinlan]

@liamappelbe

@martyfuhry Did you ever use cuperinto_http before 2.0? If not, could you try testing your app with cupertino_http 1.5.1? If you are only using the Client interface then it should be enough to just change your pubspec.yaml

[chenfisher]

@brianquinlan downgrading to 1.5.1 solves the issue.

[martyfuhry]

It does indeed work with 1.5.1. Thank you for the help.

[brianquinlan]

It does indeed work with 1.5.1. Thank you for the help.

That's not good. I don't have an explanation for this regression in 2.0.2.

[liamappelbe]

Do we know what sort of callback this code path is using? The only thing I know of that could deadlock is a blocking callback.

jnigen has a similar issue. If there's a reliable repro here I can investigate it and see if it'll be fixed by the fix we're working on for that. In the meantime it might be a good idea to remove blocking callbacks from cupertino_http.

EDIT: Actually I guess this isn't deadlocking, but just not receiving a listener callback.

[brianquinlan]

@liamappelbe

The listener is installed here:

http/pkgs/cupertino_http/lib/src/cupertino_api.dart

Line 853 in 6d99ff5

ncb.NSURLSessionDataDelegate.URLSession_task_didCompleteWithError_

Presumably the request is waiting here:

http/pkgs/cupertino_http/lib/src/cupertino_client.dart

Line 348 in 6d99ff5

result = await taskTracker.responseCompleter.future;

I don't see a path through here that doesn't complete the future:

http/pkgs/cupertino_http/lib/src/cupertino_client.dart

Line 167 in 6d99ff5

static void _onComplete(

[brianquinlan]

@chenfisher @martyfuhry (and possibly others):

Could you tell me a bit more about the environments where you can reproduce this issue? I take it that you can only produce the issue on a physical device? Do you see this issue with flutter run or only after building the application (e.g. with flutter build ipa)? Are you setting any flags?

[brianquinlan]

I tried running the demo application on a real device using both --release and --debug on a real iPhone 16 running iOS 18.1.1 and it worked fine.

$ flutter doctor -v
[!] Flutter (Channel stable, 3.27.3, on macOS 15.2 24C101 darwin-arm64, locale en)
    • Flutter version 3.27.3 on channel stable at /Users/bquinlan/flutter
    ! Warning: `dart` on your path resolves to /opt/homebrew/Cellar/dart/3.6.0/libexec/bin/dart, which is not inside your current Flutter SDK checkout at
      /Users/bquinlan/flutter. Consider adding /Users/bquinlan/flutter/bin to the front of your path.
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision c519ee916e (8 days ago), 2025-01-21 10:32:23 -0800
    • Engine revision e672b006cb
    • Dart version 3.6.1
    • DevTools version 2.40.2
    • If those were intentional, you can disregard the above warnings; however it is recommended to use "git" directly to perform update checks and upgrades.

[!] Android toolchain - develop for Android devices (Android SDK version 35.0.0)
    • Android SDK at /Users/bquinlan/Library/Android/sdk
    ✗ cmdline-tools component is missing
      Run `path/to/sdkmanager --install "cmdline-tools;latest"`
      See https://developer.android.com/studio/command-line for more details.
    ✗ Android license status unknown.
      Run `flutter doctor --android-licenses` to accept the SDK licenses.
      See https://flutter.dev/to/macos-android-setup for more details.

[✓] Xcode - develop for iOS and macOS (Xcode 16.1)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Build 16B40
    • CocoaPods version 1.16.2

[✓] Chrome - develop for the web
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 2024.2)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 21.0.3+-79915917-b509.11)

[✓] VS Code (version 1.96.4)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.102.0

[✓] Connected device (5 available)
    • Brian’s iPhone (mobile)         • 00008140-0000795E2093C01C            • ios            • iOS 18.1.1 22B91
    • iPhone 15 (mobile)              • 1E351645-1116-4E39-B2C9-BB705CCF3E44 • ios            • com.apple.CoreSimulator.SimRuntime.iOS-17-0 (simulator)
    • macOS (desktop)                 • macos                                • darwin-arm64   • macOS 15.2 24C101 darwin-arm64
    • Mac Designed for iPad (desktop) • mac-designed-for-ipad                • darwin         • macOS 15.2 24C101 darwin-arm64
    • Chrome (web)                    • chrome                               • web-javascript • Google Chrome 132.0.6834.112

[✓] Network resources
    • All expected network resources are available.

! Doctor found issues in 2 categories.

@chenfisher and @martyfuhry - could you include the output of flutter doctor -v? Maybe there is an issue with different Flutter versions.