[pigeon][video_player] Support for asynchronous generators on iOS

@gaaclarke

Is it possible to generate async return values in pigeon? If not, is this a feature that could be added? This could be useful for several native plugins I'm working on.

In particular, the video_player plugin defines the create pigeon method as follows:

// messages.dart
TextureMessage create(CreateMessage msg);

The Obj-C implementation becomes:

- (FLTTextureMessage*)create:(FLTCreateMessage*)input error:(FlutterError**)error {
         ...
         return textureMessage;
}

I maintain a video_player fork which adds support for PHAsset videos. My implementation creates a TextureMessage within a callback in the create method which in turn makes the TextureMessage instance unreachable when the create function returns.

I'm looking for something like the following:

// messages.dart
Future<TextureMessage> create(CreateMessage msg);

Which would generate the following code on iOS:

- (void)create:(FLTCreateMessage*)input
                       error:(FlutterError* __strong*)error
                    callback:(FlutterReplyForFLTTextureMessage)callback {
         ...
         callback(textureMessage, *error));
         ...
}

For now, I have manually edited the pigeon generated files to overcome this limitation in my video_player fork: recastrodiaz/plugins@c228f21#diff-8e327466253211b3b37c9a42a44ba65dR230

Manually edited create method: https://github.com/recastrodiaz/plugins/blob/c228f21229c870fb01ea1e0ae4d137b146744084/packages/video_player/video_player/ios/Classes/FLTVideoPlayerPlugin.m#L884

@gaaclarke Let me know if this is possible to do or if this is something that you may consider adding.

Thanks!

It's definitely on the roadmap. The chances of me getting to it soon are slim. Here is what I had in mind, if the pigeon file declared the method async the generated methods would be async:

class Foo {
  String bar;
}

@HostApi
abstract class Api {
  Future<Foo> doit() async;
}

- (void)doit:(FooReplyCallback)callback {
         ...
         callback(foo, error));
         ...
}

That would work for my use cases. I'm looking forward to this feature.

Not passing the ** error pointer as parameter to doit is a good choice. The code in my previous message did not actually work in release mode (it was ok in debug mode). Setting the parameter as __strong seemed to have had no effect and by the time the callback function was called, the error variable pointed to an invalid address:

Crashed: com.apple.main-thread
EXC_BAD_ACCESS KERN_INVALID_ADDRESS 0x0000000ef41820a0

My work around was to declare error within the block scope: recastrodiaz/plugins@a31d0ec#diff-b8b3fa6c990e0fc6b09b10abac5904caR886

@recastrodiaz

@recastrodiaz you should check out the Pigeon repo https://github.com/flutter/packages/tree/master/packages/pigeon, it might be something you'd want to implement ;) I'm a bit biased but I think it's pretty fun to work on.

Alright, I'll check your code out and I'll try to come up with a proof of concept :). What should the Java Generated API interface/implementaion look like?

void doit(FooReplyCallback callback) {
    ...
    callback(foo, error);
    ...
}

@recastrodiaz

@recastrodiaz Yea, check out how MethodChannel's do it to get an idea since they use async methods by default: https://api.flutter.dev/javadoc/io/flutter/plugin/common/MethodChannel.html#invokeMethod-java.lang.String-java.lang.Object-io.flutter.plugin.common.MethodChannel.Result-

Thanks. Will check that out.

@recastrodiaz

@recastrodiaz I forgot to mention that you can implement asynchronous functions by creating 2 APIs as a workaround:

class Query {
  String keyword;
}

class Task {
  int id;
}

class Result {
  Query query;
  Task task;
}

@HostApi
abstract class HostApi {
  Task search(Query query);
}

@FlutterApi
abstract class FlutterApi {
  Result onSearchResult();
}

That might be a hint to how we could easily implement the feature, too, but I haven't thought that far.

+1 for this feature!

@gaaclarke

@gaaclarke Hi it has been another 1 month... Any updates? Thanks!

@fzyzcjy

Hi @fzyzcjy I got busy with work. It might still take me another month before getting to this. If someone would like to give it a go in the meantime, feel free.

@recastrodiaz

@recastrodiaz Thanks very much! I will also try to do it when having some time. (By the way, will the official flutter team do it?)

This PR started working on it: flutter/packages#201 It still doesn't handle @HostApi. I didn't look closely at the approach yet since it is half implemented.

@gaaclarke

@gaaclarke Thanks!

@xsahil03x

I've created a doc that lays out potential future investments in Pigeon to help the company understand the long term vision. Even though we are in the middle of implementing async callbacks, it's on the list. You might be interested in the doc and have some feedback:

https://docs.google.com/document/d/1R-jjZnYUIwpG7Y5EkoHODmlvVeN1zz2Y-lCjTOku9Y0/edit#

cc @xsahil03x

@gaaclarke

@gaaclarke 🎉 🎉 🎉 The merge PR looks wonderful! And the features in doc also looks appealing!

@gaaclarke

@gaaclarke Any updates for @hostapi? Thanks!

any updates?

@gaaclak

This PR started working on it: flutter/packages#201 It still doesn't handle @HostApi. I didn't look closely at the approach yet since it is half implemented.

This mr only work for android platfrom . The synchronization code is still generated on iOS. Thanks!

Implemented for ios in flutter/packages#282

This thread has been automatically locked since there has not been any recent activity after it was closed. If you are still experiencing a similar issue, please open a new bug, including the output of flutter doctor -v and a minimal reproduction of the issue.

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[pigeon][video_player] Support for asynchronous generators on iOS #60399

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[pigeon][video_player] Support for asynchronous generators on iOS #60399

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gaaclarke commented on Jun 29, 2020

recastrodiaz commented on Jun 29, 2020

gaaclarke commented on Jun 29, 2020

recastrodiaz commented on Jun 29, 2020

gaaclarke commented on Jun 29, 2020

recastrodiaz commented on Jun 29, 2020

gaaclarke commented on Jul 1, 2020

fzyzcjy commented on Aug 16, 2020

fzyzcjy commented on Sep 17, 2020

recastrodiaz commented on Sep 17, 2020

fzyzcjy commented on Sep 17, 2020

gaaclarke commented on Sep 17, 2020

fzyzcjy commented on Sep 17, 2020

gaaclarke commented on Sep 29, 2020

fzyzcjy commented on Sep 30, 2020

nslogx commented on Nov 12, 2020

vexorsis commented on Dec 10, 2020

caikaidev commented on Dec 10, 2020

gaaclarke commented on Feb 17, 2021

github-actions commented on Aug 5, 2021

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