project.dart

===============
//main.dart 

import 'package:flutter/material.dart';
import './chat.dart';

void main() {
  runApp(ChatApp());
}

class ChatApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: chat(),
    );
  }
}

=============
// chat.dart

import 'dart:convert';
import 'package:flutter/material.dart';
import 'package:flutter_socket_io/flutter_socket_io.dart';
import 'package:flutter_socket_io/socket_io_manager.dart';

class chat extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    _chatState createState(){
      _chatState();
    }
  }
}

class _chatState extends State<chat> {
  static SocketIO _socketIO;
  static List<String> _messages;
  static double _height, _width;
  static TextEditingController _textController;
  static ScrollController _scrollController;

  @override
  void initState() {
    // Start the message list :
    _messages = List<String>();
    // Initializing the TextEditingController and ScrollController:
    _textController = TextEditingController();
    _scrollController = ScrollController();
    // Magic out the socket
    _socketIO = SocketIOManager().createSocketIO("https://monjochattest.herokuapp.com", "/");
    // Call init before doing anything with the socket
    _socketIO.init();
    // listen to an event: {must be must with "index.js"}
    _socketIO.subscribe('receive_message', (jsonData) {
      // Convert the Json data into native Map:
      Map<String, dynamic> data = json.decode(jsonData);
      // honestly I hate widgets: :(
      this.setState(() => _messages.add(data["message"]));
      _scrollController.animateTo(_scrollController.position.maxScrollExtent,
          duration: Duration(milliseconds: 600), curve: Curves.ease);
    });
    // Now Finally connect to the socket
    _socketIO.connect();
    super.initState();
  }

  Widget _buildSingleMessage(int _index) {
    return Container(
      alignment: Alignment.centerLeft,
      child: Container(
        padding: const EdgeInsets.all(20.0),
        margin: const EdgeInsets.only(bottom: 20.0, left: 20.0),
        decoration: BoxDecoration(
          color: Colors.deepPurple,
          borderRadius: BorderRadius.circular(20.0),
        ),
        child: Text(
          _messages[_index],
          style: TextStyle(color: Colors.white, fontSize: 15.0),
        ),
      ),
    );
  }

  Widget _buildMessageList() {
    return Container(
      height: _height * 0.8,
      width: _width,
      child: ListView.builder(
        controller: _scrollController,
        itemCount: _messages.length,
        itemBuilder: (BuildContext context, int index) {
          return _buildSingleMessage(index);
        },
      ),
    );
  }

  Widget _buildChatInput() {
    return Container(
      width: _width * 0.7,
      padding: const EdgeInsets.all(2.0),
      margin: const EdgeInsets.only(left: 40.0),
      child: TextField(
        decoration: InputDecoration.collapsed(
          hintText: 'Send a message...',
        ),
        controller: _textController,
      ),
    );
  }

  Widget _buildSendButton() {
    return FloatingActionButton(
      backgroundColor: Colors.deepPurple,
      onPressed: () {
        //Check if the textfield has text or not
        if (_textController.text.isNotEmpty) {
          //Send the message as JSON data to send_message event
          _socketIO.sendMessage(
              'send_message', json.encode({'message': _textController.text}));
          //Add the message to the list
          this.setState(() => _messages.add(_textController.text));
          _textController.text = '';
          //Scrolldown the list to show the latest message
          _scrollController.animateTo(
            _scrollController.position.maxScrollExtent,
            duration: Duration(milliseconds: 600),
            curve: Curves.ease,
          );
        }
      },
      child: Icon(
        Icons.send,
        size: 30,
      ),
    );
  }

  Widget _buildInputArea() {
    return Container(
      height: _height * 0.1,
      width: _width,
      child: Row(
        children: <Widget>[
          _buildChatInput(),
          _buildSendButton(),
        ],
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    _height = MediaQuery.of(context).size.height;
    _width = MediaQuery.of(context).size.width;
    return Scaffold(
      body: SingleChildScrollView(
        child: Column(
          children: <Widget>[
            SizedBox(height: _height * 0.1),
            _buildMessageList(),
            _buildInputArea(),
          ],
        ),
      ),
    );
  }
}

=== server side : nodejs

/**
 * This is @Prototype
 * This is A server Side using Nodejs
 * @Written By John Melody
 */

 const app = require("express") ()
 const http = require("http").createServer(app);
 const socketio = require("socket.io")(http)

 /**
  * @param 
  * @note I created a test server and using Heroku cli
  * just to get the feeling how it work , where Can I encryption and 
  * push the $hashes to the server 
  * @url https://monjochattest.herokuapp.com/
  * @global https://git.heroku.com/monjochattest.git
  */

 app.get("/", (req, res) => {
       res.send("Test");
 });

socketio.on("connection", (userSocket) => {
      userSocket.on("send_message", (data) => {
            userSocket.broadcast.emit("receive_message", data);
      });
});

//  http.listen(8080);
// Deployment to heroku:
http.listen(process.env.PORT);



///////////////////error I got :


An Observatory debugger and profiler on SM G530H is available at: http://127.0.0.1:57654/wZm5c2IebL8=/
I/flutter ( 4069): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter ( 4069): The following NoSuchMethodError was thrown building Builder:
I/flutter ( 4069): The method '_debugTypesAreRight' was called on null.
I/flutter ( 4069): Receiver: null
I/flutter ( 4069): Tried calling: _debugTypesAreRight(Instance of 'chat')
I/flutter ( 4069): The relevant error-causing widget was:
I/flutter ( 4069):   MaterialApp
I/flutter ( 4069):   file:///D:/Mynapse/MobileApplication/Documents/Design/Research/Encryption/encryption_test_app/lib/main.dart:11:12
I/flutter ( 4069): When the exception was thrown, this was the stack:
I/flutter ( 4069): #0      Object.noSuchMethod (dart:core-patch/object_patch.dart:53:5)
I/flutter ( 4069): #1      new StatefulElement.<anonymous closure> (package:flutter/src/widgets/framework.dart:4594:19)
I/flutter ( 4069): #2      new StatefulElement (package:flutter/src/widgets/framework.dart:4605:6)
I/flutter ( 4069): #3      StatefulWidget.createElement (package:flutter/src/widgets/framework.dart:894:38)
I/flutter ( 4069): ...     Normal element mounting (115 frames)
I/flutter ( 4069): #118    Element.inflateWidget (package:flutter/src/widgets/framework.dart:3446:14)
I/flutter ( 4069): #119    MultiChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5947:32)
I/flutter ( 4069): ...     Normal element mounting (238 frames)
I/flutter ( 4069): #357    Element.inflateWidget (package:flutter/src/widgets/framework.dart:3446:14)
I/flutter ( 4069): #358    Element.updateChild (package:flutter/src/widgets/framework.dart:3214:18)
I/flutter ( 4069): #359    RenderObjectToWidgetElement._rebuild (package:flutter/src/widgets/binding.dart:1148:16)
I/flutter ( 4069): #360    RenderObjectToWidgetElement.mount (package:flutter/src/widgets/binding.dart:1119:5)
I/flutter ( 4069): #361    RenderObjectToWidgetAdapter.attachToRenderTree.<anonymous closure> (package:flutter/src/widgets/binding.dart:1061:17)
I/flutter ( 4069): #362    BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2607:19)
I/flutter ( 4069): #363    RenderObjectToWidgetAdapter.attachToRenderTree (package:flutter/src/widgets/binding.dart:1060:13)
I/flutter ( 4069): #364    WidgetsBinding.attachRootWidget (package:flutter/src/widgets/binding.dart:941:7)
I/flutter ( 4069): #365    WidgetsBinding.scheduleAttachRootWidget.<anonymous closure> (package:flutter/src/widgets/binding.dart:922:7)
I/flutter ( 4069): (elided 11 frames from class _RawReceivePortImpl, class _Timer, dart:async, and dart:async-patch)