Retry Http Get request if there is no response in Flutter - flutter

Question

getData() async {
http.Response response = await http.get('https://www.example.com/);
print(response.body);
}
The above function works to get the HTML code of a page but it fails in some cases. The function is sometimes never completed and it waits forever to get response( For example, if the app is opened while internet is off and even when its turned on, it never connects). In such situations is there any way to retry ?
I tried the http retry package but it gives me 15+ errors.

Answer 1

Example code for how this could be done:
import 'package:http/http.dart' as http;
import 'dart:convert';
Future<List> loadData() async {
bool loadRemoteDatatSucceed = false;
var data;
try {
http.Response response = await http.post("https://www.example.com",
body: <String, String>{"username": "test"});
data = json.decode(response.body);
if (data.containsKey("success")) {
loadRemoteDatatSucceed = true;
}
} catch (e) {
if (loadRemoteDatatSucceed == false) retryFuture(loadData, 2000);
}
return data;
}
retryFuture(future, delay) {
Future.delayed(Duration(milliseconds: delay), () {
future();
});
}

Answer 2

You can use RetryPolicy from http package to retry your connection, just create your own class and inherit form RetryPolicy and override these function like the following example, then create a Client using HttpClientWithInterceptor.build and add your custom retryPolicy as a parameter, this will retry your request for a number of times until a condition is met, if not, it'll just stop retrying.
import 'package:http/http.dart';
class MyRetryPolicy extends RetryPolicy {
final url = 'https://www.example.com/';
#override
// how many times you want to retry your request.
int maxRetryAttempts = 5;
#override
Future<bool> shouldAttemptRetryOnResponse(ResponseData response) async {
//You can check if you got your response after certain timeout,
//or if you want to retry your request based on the status code,
//usually this is used for refreshing your expired token but you can check for what ever you want
//your should write a condition here so it won't execute this code on every request
//for example if(response == null)
// a very basic solution is that you can check
// for internet connection, for example
try {
final result = await InternetAddress.lookup('google.com');
if (result.isNotEmpty && result[0].rawAddress.isNotEmpty) {
return true;
}
return false;
} on SocketException catch (_) {
return false;
}
}
}
then create and use a client to make your requests.
it will automatically retry the request if the condition you wrote is met.
Client client = HttpClientWithInterceptor.build(
retryPolicy: ExpiredTokenRetryPolicy(),
);
final response = await client.get('https://www.example.com/);
there is also a package to check for internet connection if that your problem, see connectivity

Answer 3

You can use try-catch blocks inside async functions like you would in synchronous code. Perhaps you'd be able to add some sort of error handling mechanism in the function, and retry the function on error? Here's some documentation on that one.
Example from the docs:
try {
var order = await getUserOrder();
print('Awaiting user order...');
} catch (err) {
print('Caught error: $err');
}
You can also catch specific Exceptions, per this github issue.
doLogin(String username, String password) async {
try {
var user = await api.login(username, password);
_view.onLoginSuccess(user);
} on Exception catch(error) {
_view.onLoginError(error.toString());
}
}
EDIT: This may also help.
While we're at it, look here for a function that reattempts an async operation however many times you need.