Await future for a specific time

Question

How would you wait for future response for a specific amount of time?

Say, we make a http post request and await for its response before we close the http request, but, we wait for only 3 secs, else we close the request.

How would you achieve that?

Something like

Future makePostReq() async{
  .... 

  await http response for 3 secs

  .... 

 if(response) {
  ... Do something with it
 }

 Http.close

} 

Answer 1

You can use Future.any constructor to make a race condition

final result = await Future.any([
  Future.value(42),
  Future.delayed(const Duration(seconds: 3))
]);

You can also use Future.timeout method

final result = await Future.value(42).timeout(const Duration(seconds: 3));

Answer 2

You can do it very easily

try {
       var response = await Http.get("YourUrl").timeout(const Duration(seconds: 3));
       if(response.statusCode == 200){
          print("Success");
       }else{
          print("Something wrong");
       }
 } on TimeoutException catch (e) {
     print('Timeout');
 } on Error catch (e) {
     print('Error: $e');
 }

This example sets timeout to 3 second. If it has been 3 seconds and no response received, it will throw TimeoutException

Import this :

import 'package:http/http.dart' as Http;
import 'dart:async';

Answer 3

Future.any([asyncfunc, ...])

Here's an example of using Remi's Future.any solution where the future that returns first, will be used. The other is discarded.

So, the first future is your data-gathering/slow function and the other is a fallback when your call is taking too long.

    dynamic result = await Future.any([
      getData(fakeDelay: seconds), // ← hope this returns first
      timeoutAfter(sec: timeout, onTimeout: () => 'Timed Out!', ) // ← waited too long, do this
    ]);

Example in Flutter Page

Here's a copy/paste example for a Flutter page:

(look at your debug/run output window for messages)

import 'package:flutter/material.dart';

class FutureTimeoutPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Future or Timeout Page'),
      ),
      body: FutureAnyExample(),
    );
  }
}

class FutureAnyExample extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: [
        Text('Complete before timeout or timeout:'),
        SizedBox(height: 30,),
        Row(
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
          children: [
            ElevatedButton(onPressed: () => getDataOrTimeout(seconds: 1, timeout: 3),
                child: Text('In Time')),
            ElevatedButton(onPressed: () => getDataOrTimeout(seconds: 5, timeout: 3),
                child: Text('Too Slow'))
          ],
        )
      ],
    );
  }

  Future<void> getDataOrTimeout({int seconds, int timeout}) async {
    /// In Future.any, put as many async functions as you need.
    /// Whichever completes first, will be returned. All others are discarded
    dynamic result = await Future.any([
      getData(fakeDelay: seconds), // ← hope this returns first
      timeoutAfter(sec: timeout, onTimeout: () => 'Timed Out!', ) // ← waited too long, do this
    ]);

    print(result);
  }

  /// Mock of a long-running operation like getting DB data, or API call
  Future<String> getData({int fakeDelay}) async {
    return Future.delayed(Duration(seconds: fakeDelay), () => 'Data returned!');
  }

  /// Do this in case my long-running op takes too long
  /// Can run a function or just return some message
  Future<dynamic> timeoutAfter({int sec, Function() onTimeout}) async {
    return Future.delayed(Duration(seconds: sec), onTimeout);
  }
}