How to get device user agent information in Flutter

I done it by calling native methods in flutter. First you have to add method channel in android Main Activity

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    GeneratedPluginRegistrant.registerWith(this);

    new MethodChannel(getFlutterView(), CHANNEL).setMethodCallHandler(
            new MethodChannel.MethodCallHandler() {
                @Override
                public void onMethodCall(MethodCall call, MethodChannel.Result result) {
                    if (call.method.equals("getUserAgent")) {
                        result.success(System.getProperty("http.agent"));
                    } else {
                        result.notImplemented();
                    }
                }
            });
}

Then getUserAgent() method can be called in flutter like below

Future<String> _getUserAgent() async {
  try {
    return await platform.invokeMethod('getUserAgent');
  } catch (e) {
    return 'Unknown';
  }
}

You can get it in a cross-platform way by using the flutter_user_agent library: https://pub.dev/packages/flutter_user_agent.

import 'package:flutter_user_agent/flutter_user_agent.dart';

...

    String ua = await FlutterUserAgent.getPropertyAsync('userAgent');

this worked for me by using flutter_user_agent library: https://pub.dev/packages/flutter_user_agent as mentioned above

String _userAgent = await FlutterUserAgent.getPropertyAsync('userAgent');

    final _response = await http.get(_url, headers: {
      'Content-Type': 'application/json',
      'Accept-Charset': 'utf-8',
      'User-Agent': '${_userAgent.toLowerCase()}',
    });

Found a library that does it. It would be interesting to look at what the library does, i don't think it's needed to implement a library for that.

https://pub.dartlang.org/packages/user_agent

An example on how you would use it:

main() async {
    app.get('/', (req, res) async {
        var ua = new UserAgent(req.headers.value('user-agent'));

        if (ua.isChrome) {
            res.redirect('/upgrade-your-browser');
            return;
        } else {
            // ...
        }
    });
}

Alternatively, if you want to add a user-agent to the http client, you can do it this way:

Future<http.Response> fetchPost() {
  return http.get(your_url,
    // Send user-agent header to your backend
    headers: {HttpHeaders.userAgentHeader: "your_user_agent"},
  );
}

You can look at HttpHeadersto see the full list of predefined headers, although headers take a map, you could create your own header if you want.