Unsupported Operation at ServerSocket.bind using HttpServer in Flutter - sockets

Question

Inconsistent behavior of HttpServer in Flutter/Dart ! The following code runs fine if executed as a desktop application but returns an error as Unsupported Operation at ServerSocket.bind if executed as a web server or through browser !
import 'package:flutter/material.dart';
import 'dart:io';
void main()
{
runApp(MaterialApp(home: Home(),));
}
class Home extends StatefulWidget {
#override
_HomeState createState() => _HomeState();
}
class _HomeState extends State<Home> {
String statusText = "Start Server";
startServer()
async{
setState(() {
statusText = "Starting server on Port : 8088";
});
print("Attempting bind");
// other attempts with same result
// var server = await HttpServer.bind(InternetAddress.loopbackIPv4, 8088, shared: true);
// var server = await HttpServer.bind(InternetAddress.loopbackIPv4, 8089, shared: true);
// var server = await HttpServer.bind(InternetAddress.anyIPv4, 0, shared: true);
// var server = await HttpServer.bind("0.0.0.0", 35568, shared: true);
var serverSocket = await ServerSocket.bind("0.0.0.0", 0);
var server = HttpServer.listenOn(serverSocket);
setState(() {
statusText = "Server running on IP : "+server.address.toString()+" On Port : "+server.port.toString();
});
print("Server running on IP : "+server.address.toString()+" On Port : "+server.port.toString());
await for (var request in server) {
setState(() {
statusText = request.requestedUri.toString();
});
request.response.headers.contentType = new ContentType("text", "plain", charset: "utf-8");
request.response.write("hello world");
request.response.close();
print("Response served\n");
}
}
#override
Widget build(BuildContext context) {
return Scaffold(
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.center,
children: <Widget>[
RaisedButton(
onPressed: (){startServer();},
child: Text(statusText),)],),));
}
}
Testing on
Ubuntu 16.04 lts
Tested with and without firewall
Need this to host a web service
Any other methods available within Flutter are welcome
Haven't yet tried with threading

Answer 1

First, dart:io are not supported in web browsers so that explain your problem with running the code in browsers:
Important: Browser-based applications can't use this library. Only servers, command-line scripts, and Flutter mobile apps can import and use dart:io.
https://api.dart.dev/stable/2.8.4/dart-io/dart-io-library.html
Second, your code is very complicated if the purpose is to create a simple HTTP server running on a headless server. I have simplified your code so it does no longer depend on Flutter and can just be executed with dart:
import 'dart:io';
void main() {
startServer();
}
Future<void> startServer() async {
print("Starting server on Port : 8088");
print("Attempting bind");
final server = await HttpServer.bind("0.0.0.0", 8080);
print("Server running on IP : ${server.address} On Port : ${server.port}");
await for (final request in server) {
print(request.requestedUri);
request.response
..headers.contentType = ContentType("text", "plain", charset: "utf-8")
..write("hello world");
await request.response.flush();
await request.response.close();
print("Response served\n");
}
}