Pigeon : Support for asynchronous methods/Functions

[xsahil03x]

Fixes: flutter/flutter#64810

Usage: Just add an async annotation above methods to make them asynchronous.

@FlutterApi()
abstractclassTestFlutterApi {
@asyncUserResultgetUser();
}

This code here generates

abstractclassTestFlutterApi {
Future<UserResult> getUser();
staticvoidsetup(TestFlutterApiapi) {
{
constBasicMessageChannel<dynamic> channel =
BasicMessageChannel<dynamic>('dev.flutter.pigeon.TestFlutterApi.getUser', StandardMessageCodec());
channel.setMessageHandler((dynamicmessage) async {
finalUserResultoutput = awaitapi.getUser();
returnoutput._toMap();
});
}
}
}

[gaaclarke]

This is a great start. You have a few broken tests and need to add some tests that exercise the code. You should also implement @HostApi, right now you are only supporting @FlutterApi. We can't really land support of one without the other.

For tests, at a minimum you should have some unit tests for the generators and add a compilation test. You can see how to add that in run_tests.sh.

[gaaclarke]

Can you switch this so that it is reading in the async keyword instead of using a using @async metadata?

[xsahil03x]

@gaaclarke by adding an async keyword to the method

@HostApiabstractclassApi {
Future<Foo> doit() async;
}

will look more like a broken code as it won't compile. Maybe we can try reading Future<> instead ?

@HostApiabstractclassApi {
Future<Foo> doit();
}

[gaaclarke]

Why do you think that looks like broken code? It looks correct to me.

[xsahil03x]

Because this doesn't compile. It needs a function body. (Due to async keyword)

@HostApi()
abstractclassApi {
Future<Foo> doit() async;
}

[xsahil03x]

@gaaclarke I'm trying something like this for @HostApi. Might need some help for Objective C as I don't have a Mac to test.

@HostApi()
abstractclassHostPlatformApi {
@asyncStartDayResulttriggerStartDay();
}

publicinterfaceHostPlatformApi {
voidtriggerStartDay(Result<StartDayResult> result);
/** * Sets up an instance of `HostPlatformApi` to handle messages through the `binaryMessenger` */staticvoidsetup(BinaryMessengerbinaryMessenger, HostPlatformApiapi) {
{
BasicMessageChannel<Object> channel =
newBasicMessageChannel<>(binaryMessenger, "dev.flutter.pigeon.HostPlatformApi.triggerStartDay", newStandardMessageCodec());
if (api != null) {
channel.setMessageHandler((message, reply) -> {
HashMap<String, HashMap> wrapped = newHashMap<>();
try {
api.triggerStartDay(result -> {
wrapped.put("result", result.toMap());
reply.reply(wrapped);
});
} catch (Exceptionexception) {
wrapped.put("error", wrapError(exception));
reply.reply(wrapped);
}
});
} else {
channel.setMessageHandler(null);
}
}
}
}

[gaaclarke]

@xsahil03x There are some people in this thread that are interested in helping: flutter/flutter#60399

FWIW the 'local_tests' CI step is running on a mac so that can help validate your objc work. That said, if you get as far as implementing HostApi for java and we are happy with it I can fill in the objc if needed.

[fzyzcjy]

Great work! IMHO this is useful in many places! Thanks friends!

[xsahil03x]

@gaaclarkejava version of HostApi is done from my end. You might want to have a look at the codebase and review it. It would be great if you can do the objC part.

Also, can you guide me on why local_tests are failing? It says ->

Analyzing/var/folders/3y/l0z1x3693dl_8n0qybp4dqwh0000gn/T/pigeon.L80yAjJZ/pigeon.dart...
error • Undefinedclass'Uint8List'. • /var/folders/3y/l0z1x3693dl_8n0qybp4dqwh0000gn/T/pigeon.L80yAjJZ/pigeon.dart:12:3 • undefined_class
error • Undefinedclass'Int32List'. • /var/folders/3y/l0z1x3693dl_8n0qybp4dqwh0000gn/T/pigeon.L80yAjJZ/pigeon.dart:13:3 • undefined_class
error • Undefinedclass'Int64List'. • /var/folders/3y/l0z1x3693dl_8n0qybp4dqwh0000gn/T/pigeon.L80yAjJZ/pigeon.dart:14:3 • undefined_class
error • Undefinedclass'Float64List'. • /var/folders/3y/l0z1x3693dl_8n0qybp4dqwh0000gn/T/pigeon.L80yAjJZ/pigeon.dart:15:3 • undefined_class
4 errors found.

[gaaclarke]

@xsahil03x That is the result of the compilation test for ./pigeons/all_datatypes.dart It seems like maybe you are missing

indent.writeln(
'import \'dart:typed_data\' show Uint8List, Int32List, Int64List, Float64List;');

If you rebase on master that should go away.

Give me some time to look into the objc stuff. I might have some android unit tests soon which would be nice to have for this too.

[gaaclarke]

I haven't forgotten about this. I'm getting pulled into some higher priority problems.

[gaaclarke]

Here is the java output of the pigeon I added. There are a few places where there should be spaces in the java output. I had just a few other nits but otherwise LGTM. Let's land this for now and I can get around to the objective-c code in a different PR. Once the objective-c code is written we can update the change log and advertise the change.

aaclarke-macbookpro2:pigeonaaclarke$pubrunpigeon --inputpigeons/async_handlers.dart --java_outstdout --dart_out /dev/null// Autogenerated from Pigeon (v0.1.7), do not edit directly.// See also: https://pub.dev/packages/pigeonimportio.flutter.plugin.common.BasicMessageChannel;
importio.flutter.plugin.common.BinaryMessenger;
importio.flutter.plugin.common.StandardMessageCodec;
importjava.util.ArrayList;
importjava.util.HashMap;
/** Generated class from Pigeon. */@SuppressWarnings("unused")
publicclassstdout {
/** Generated class from Pigeon that represents data sent in messages. */publicstaticclassValue {
privateLongnumber;
publicLonggetNumber() { returnnumber; }
publicvoidsetNumber(LongsetterArg) { this.number = setterArg; }
HashMaptoMap() {
HashMap<String, Object> toMapResult = newHashMap<>();
toMapResult.put("number", number);
returntoMapResult;
}
staticValuefromMap(HashMapmap) {
ValuefromMapResult = newValue();
Objectnumber = map.get("number");
fromMapResult.number = (number == null) ? null : ((numberinstanceofInteger) ? (Integer)number : (Long)number);
returnfromMapResult;
}
}
/** Generated class from Pigeon that represents Flutter messages that can be called from Java.*/publicstaticclassApi2Flutter {
privatefinalBinaryMessengerbinaryMessenger;
publicApi2Flutter(BinaryMessengerargBinaryMessenger){
this.binaryMessenger = argBinaryMessenger;
}
publicinterfaceReply<T> {
voidreply(Treply);
}
publicvoidcalculate(ValueargInput, Reply<Value> callback) {
BasicMessageChannel<Object> channel =
newBasicMessageChannel<>(binaryMessenger, "dev.flutter.pigeon.Api2Flutter.calculate", newStandardMessageCodec());
HashMapinputMap = argInput.toMap();
channel.send(inputMap, channelReply -> {
HashMapoutputMap = (HashMap)channelReply;
@SuppressWarnings("ConstantConditions")
Valueoutput = Value.fromMap(outputMap);
callback.reply(output);
});
}
}
publicinterfaceResult<T> {
voidsuccess(Tresult);
}
/** Generated interface from Pigeon that represents a handler of messages from Flutter.*/publicinterfaceApi2Host {
voidcalculate(Valuearg,Result<Value> result);
/** Sets up an instance of `Api2Host` to handle messages through the `binaryMessenger` */staticvoidsetup(BinaryMessengerbinaryMessenger, Api2Hostapi) {
{
BasicMessageChannel<Object> channel =
newBasicMessageChannel<>(binaryMessenger, "dev.flutter.pigeon.Api2Host.calculate", newStandardMessageCodec());
if (api != null) {
channel.setMessageHandler((message, reply) -> {
HashMap<String, HashMap> wrapped = newHashMap<>();
try {
@SuppressWarnings("ConstantConditions")
Valueinput = Value.fromMap((HashMap)message);
api.calculate(input,result -> {wrapped.put("result", result.toMap());reply.reply(wrapped);});
}
catch (Exceptionexception) {
wrapped.put("error", wrapError(exception));
reply.reply(wrapped);
}
});
} else {
channel.setMessageHandler(null);
}
}
}
}
privatestaticHashMapwrapError(Exceptionexception) {
HashMap<String, Object> errorMap = newHashMap<>();
errorMap.put("message", exception.toString());
errorMap.put("code", null);
errorMap.put("details", null);
returnerrorMap;
}
}

[gaaclarke]

/// Whether the receiver of this method is expected to return synchronously or not.

[gaaclarke]

Done.

[gaaclarke]

nit: argSignature.join(', ')

[gaaclarke]

Done.

[gaaclarke]

Is there no way to do equality checks on the type directly instead of resorting to string checks?

[dreadjr]

@gaaclarke Why does Result not have an error() method? I have an async android method and it executes in an executor, but there is no way to return the error, since the outer try catch has already returned execution.

[gaaclarke]

That's being tracked here: flutter/flutter#83244 There is a workaround and it will be added.