# 實作通訊&定位app
###### tags: `自主學習`

## 概念 & 規劃
:::success
- 採用**公鑰加密 私鑰解密**
- 每個使用者有一個專屬自己的頻道
:::

## 程式碼
### Main

public MainPage()
{
    // 初始化頁面
    InitializeComponent();

    // 建立 user list
    userList = new List<string>();

    // 創建使用者的 client
    Client();

}

### 建立 MQTT Client

public async void Client()
{
    Console.WriteLine("Into");
    try
    {
        //客戶端初始值設定
        var configuration = new MqttConfiguration
        {
            BufferSize = 128 * 1024,
            Port = 1883,
            KeepAliveSecs = 60000,
            WaitTimeoutSecs = 2,
            MaximumQualityOfService = MqttQualityOfService.AtMostOnce,
            AllowWildcardsInTopicFilters = true
        };
        Console.WriteLine("Basic Infom");

        configuration.MaximumQualityOfService = MqttQualityOfService.ExactlyOnce; //?
        Console.WriteLine("Config");

        //創建客戶端
        client = await MqttClient.CreateAsync("163.22.17.72", configuration);    //主機: 163.22.17.72
        Console.WriteLine("Create");

        //Client端連線
        await client.ConnectAsync(new MqttClientCredentials(clientId: username));
        Console.WriteLine("User");

        //Subscribe訂閱主題
        await client.SubscribeAsync("key", MqttQualityOfService.AtMostOnce);
        Console.WriteLine("Subscribe");

        //收到來自 "個人頻道" 的消息(訊息內容) 
        //接收訊息後，drawPin(msg)
        client.MessageStream
            .Where(msg => msg.Topic == username)
            .Subscribe(msg => drawPin(msg));

        // 收到來自 "key頻道" 的消息(public key)
        //接收訊息後，GetPublicKey(msg)
        client.MessageStream
        .Where(msg => msg.Topic == "key")
        .Subscribe(msg => GetPublicKey(msg));
    }
    catch (Exception ex)
    {
        Console.WriteLine("error" + ex);
    }
}

### 產生 & 傳送鑰匙

public async void produce()
{
    RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
    privatekey = rsa.ToXmlString(true);         //私鑰
    string publickey = rsa.ToXmlString(false);  //公鑰

    User me = new User
    {
        name = username,
        publicKey = publickey
    };

    //序列化 (object to string)
    string jsonString = JsonSerializer.Serialize(me);
    //傳送公鑰
    var key = new MqttApplicationMessage("key", Encoding.UTF8.GetBytes(jsonString));
    await client.PublishAsync(key, MqttQualityOfService.AtMostOnce, false);
    Console.WriteLine("send the key");
}
public void SendKey(object sender, EventArgs e)
{
    produce();
}

### 接收鑰匙

public async void GetPublicKey(MqttApplicationMessage msg)
{
    string oherKey = Encoding.UTF8.GetString(msg.Payload);
    //轉成物件(User)
    var options = new JsonSerializerOptions
    {
        IncludeFields = true,
    };
    //反序列化
    User getKey = JsonSerializer.Deserialize<User>(oherKey, options);
    //檢查有沒有重複的使用者
    for (int i = 0; i < allkey.Count; i++)
    {
        //使用者之前有傳過->覆蓋
        if (allkey[i].name == getKey.name)
        {
            allkey[i].publicKey = getKey.publicKey;
            return;
        }
    }
    //沒有紀錄過就新增在list
    allkey.Add(getKey);
    //訂閱他的頻道
    await client.SubscribeAsync(getKey.name, MqttQualityOfService.AtMostOnce);
}

### 加密

public static byte[] Encode(string publicKey, string content)
{
    RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
    rsa.FromXmlString(publicKey);

    byte[] encryptString = rsa.Encrypt(Encoding.UTF8.GetBytes(content), false);

    return encryptString;
}

### 解密

public static string Decode(string privateKey, byte[] encryptedContent)
{
    RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
    rsa.FromXmlString(privateKey);

    string decryptString = Encoding.UTF8.GetString(rsa.Decrypt(encryptedContent, false));

    return decryptString;
}

### 發訊息

private async void Publish(object sender, EventArgs e)
{
    // 把位置資訊存成 string: "名字 緯度 經度"(用空格隔開)
    var location = await Geolocation.GetLastKnownLocationAsync();
    string msg = username
                + " " + Math.Round(location.Latitude,3)
                + " " + Math.Round(location.Longitude,3)
                + " " + DateTime.Now.ToLongTimeString()
                + " " + PublishText.Text;

    //加密
    for (int i = 0; i < allkey.Count; i++)
    {
        byte[] encryptString = Encode(allkey[i].publicKey, msg);
        //發送訊息到頻道
        var message = new MqttApplicationMessage(allkey[i].name, encryptString);
        await client.PublishAsync(message, MqttQualityOfService.AtMostOnce, false);
        Console.WriteLine("Send Message");
    }
    PublishText.Text = "";
}

### 收訊息 & 在地圖上更新Pin

public void drawPin(MqttApplicationMessage msg)
{
    // 轉換收到的訊息型態(string)
    byte[] msgByte = msg.Payload;
    Console.Write("~~received: ");
    Console.WriteLine(msgByte);

    //解密
    string encryptString = Decode(privatekey, msgByte);

    // 從 msgSting 切出資料: 名字, 經度, 緯度
    string[] data = encryptString.Split(' ');
    string name = data[0];

    // 看清單上是否已經有該使用者的資料
    // 如果沒有，新增到 userList 並畫 Pin
    if (userList.IndexOf(name) == -1)
    {
        userList.Add(name);
        Pin newLocation = AddPin(data);
        map.Pins.Add(newLocation);

    }
    // 如果有，覆蓋原本的 Pin
    else
    {
        Pin newLocation = AddPin(data);
        map.Pins[userList.IndexOf(name)] = newLocation;
    }

    // 移動地圖至最新接收到訊息的位置
    Device.InvokeOnMainThreadAsync(() =>
    {
         map.MoveToRegion(MapSpan.FromCenterAndRadius(map.Pins[userList.IndexOf(name)].Position, Distance.FromMiles(10)));
    });
}

// AddPin(): 產生一個 Pin 
public Pin AddPin(string[] data)
{
    string name = data[0];
    float latitude = float.Parse(data[1]);
    float longitude = float.Parse(data[2]);
    string time = data[3] + data[4];
    string messenge = data[5];


    Pin newLocation = new Pin
    {
        Label = name + ":" + messenge,
        Address = "(" + data[1] + ", " + data[2] + "), " + time,
        Type = PinType.Generic,
        Position = new Position(latitude, longitude)
    };

    return newLocation;
}

:::spoiler 完整程式碼

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Xamarin.Forms;
using Xamarin.Forms.Maps;
using Xamarin.Essentials;
using System.Timers;
using System.Net.Mqtt;
using System.Reactive.Linq;
using System.Text.Json;
using System.Security.Cryptography;//加密

namespace Maps2
{
    public partial class MainPage : ContentPage
    {
        public IMqttClient client;    // 
        public System.Timers.Timer timer;    // 計時器
        public List<string> userList;     // 紀錄所有使用者名稱
        public int count = 0;    // 秒數
                                 // 使用者名稱
        public string username = "Amber";

        string privatekey; //自己的私鑰
        List<User> allkey = new List<User>();//記錄所有人的公key

        //使用者的公鑰匙
        public class User
        {
            public string name { get; set; }   //名字
            public string publicKey { get; set; }    //公鑰
        }


        // AddPin(): 產生一個 Pin 
        public Pin AddPin(string[] data)
        {
            // 加 Pin
            string name = data[0];
            float latitude = float.Parse(data[1]);
            float longitude = float.Parse(data[2]);
            string time = data[3] + data[4];
            string messenge = data[5];


            Pin newLocation = new Pin
            {
                Label = name + ":" + messenge,
                Address = "(" + data[1] + ", " + data[2] + "), " + time,
                Type = PinType.Generic,
                Position = new Position(latitude, longitude)
            };

            return newLocation;
        }
        // drawPin(): 接收訊息&畫 Pin
        // msg: 收到的訊息
        public void drawPin(MqttApplicationMessage msg)
        {
            // 轉換收到的訊息型態(string)
            byte[] msgByte = msg.Payload;
            Console.Write("~~received: ");
            Console.WriteLine(msgByte);

            //解密
            string encryptString = Decode(privatekey, msgByte);

            // 從 msgSting 切出資料: 名字, 經度, 緯度
            string[] data = encryptString.Split(' ');
            string name = data[0];

            // 看清單上是否已經有該使用者的資料
            // 如果沒有，新增到 userList 並畫 Pin
            if (userList.IndexOf(name) == -1)
            {
                userList.Add(name);
                Pin newLocation = AddPin(data);
                map.Pins.Add(newLocation);

            }
            // 如果有，覆蓋原本的 Pin
            else
            {
                Pin newLocation = AddPin(data);
                map.Pins[userList.IndexOf(name)] = newLocation;
            }
            Device.InvokeOnMainThreadAsync(() =>
            {
                移動地圖 map.MoveToRegion(MapSpan.FromCenterAndRadius(map.Pins[userList.IndexOf(name)].Position, Distance.FromMiles(10)));
            });

        }
        // Publish(): 發布訊息
        // userLocation: 位置資訊
        private async void Publish(object sender, EventArgs e)
        {
            // 把位置資訊存成 string: "名字 緯度 經度"(用空格隔開)
            var location = await Geolocation.GetLastKnownLocationAsync();
            string msg = username
                        + " " + Math.Round(location.Latitude,3)
                        + " " + Math.Round(location.Longitude,3)
                        + " " + DateTime.Now.ToLongTimeString()
                        + " " + PublishText.Text;

            //加密
            for (int i = 0; i < allkey.Count; i++)
            {
                byte[] encryptString = Encode(allkey[i].publicKey, msg);
                //發送訊息到頻道
                var message = new MqttApplicationMessage(allkey[i].name, encryptString);
                await client.PublishAsync(message, MqttQualityOfService.AtMostOnce, false);
                Console.WriteLine("Send Message");
            }
            PublishText.Text = "";

        }
        //加密
        public static byte[] Encode(string publicKey, string content)
        {
            RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
            rsa.FromXmlString(publicKey);

            byte[] encryptString = rsa.Encrypt(Encoding.UTF8.GetBytes(content), false);

            return encryptString;
        }
        //解密(公鑰)
        public static string Decode(string privateKey, byte[] encryptedContent)
        {
            RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
            rsa.FromXmlString(privateKey);

            string decryptString = Encoding.UTF8.GetString(rsa.Decrypt(encryptedContent, false));

            return decryptString;
        }

        // 接收鑰匙
        public async void GetPublicKey(MqttApplicationMessage msg)
        {
            string oherKey = Encoding.UTF8.GetString(msg.Payload);
            //轉成物件(User)
            var options = new JsonSerializerOptions
            {
                IncludeFields = true,
            };
            //反序列化
            User getKey = JsonSerializer.Deserialize<User>(oherKey, options);
            //檢查有沒有重複的使用者
            for (int i = 0; i < allkey.Count; i++)
            {
                //使用者之前有傳過->覆蓋
                if (allkey[i].name == getKey.name)
                {
                    allkey[i].publicKey = getKey.publicKey;
                    return;
                }
            }
            //沒有紀錄過就新增在list
            allkey.Add(getKey);
            //訂閱他的頻道
            await client.SubscribeAsync(getKey.name, MqttQualityOfService.AtMostOnce);
        }
        //產生鑰匙
        public async void produce()
        {
            RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
            privatekey = rsa.ToXmlString(true);         //私鑰
            string publickey = rsa.ToXmlString(false);  //公鑰

            User me = new User
            {
                name = username,
                publicKey = publickey
            };

            //序列化 (object to string)
            string jsonString = JsonSerializer.Serialize(me);
            //傳送公鑰
            var key = new MqttApplicationMessage("key", Encoding.UTF8.GetBytes(jsonString));
            await client.PublishAsync(key, MqttQualityOfService.AtMostOnce, false);
            Console.WriteLine("send the key");
        }
        public void SendKey(object sender, EventArgs e)
        {
            produce();
        }
        // Client(): 創建客戶、連線、訂閱
        // userName: 使用者名
        public async void Client()
        {
            Console.WriteLine("Into");
            try
            {
                //客戶端初始值設定
                var configuration = new MqttConfiguration
                {
                    BufferSize = 128 * 1024,
                    Port = 1883,
                    KeepAliveSecs = 60000,
                    WaitTimeoutSecs = 2,
                    MaximumQualityOfService = MqttQualityOfService.AtMostOnce,
                    AllowWildcardsInTopicFilters = true
                };
                Console.WriteLine("Basic Infom");

                configuration.MaximumQualityOfService = MqttQualityOfService.ExactlyOnce; //?
                Console.WriteLine("Config");

                //創建客戶端
                client = await MqttClient.CreateAsync("163.22.17.72", configuration);    //主機: 163.22.17.72
                Console.WriteLine("Create");

                //Client端連線
                await client.ConnectAsync(new MqttClientCredentials(clientId: username));
                Console.WriteLine("User");

                //Subscribe訂閱主題: maps2
                await client.SubscribeAsync("maps2", MqttQualityOfService.AtMostOnce);
                await client.SubscribeAsync("key", MqttQualityOfService.AtMostOnce);
                Console.WriteLine("Subscribe");

                //收到來自訂閱主題的消息 
                //接收訊息，畫ping
                client.MessageStream
                    .Where(msg => msg.Topic == username)
                    .Subscribe(msg => drawPin(msg));

                // 接收public key
                client.MessageStream
                .Where(msg => msg.Topic == "key")
                .Subscribe(msg => GetPublicKey(msg));
            }
            catch (Exception ex)
            {
                Console.WriteLine("error" + ex);
            }
        }
        public MainPage()
        {
            InitializeComponent();

            // 把使用者加到 usersList
            userList = new List<string>();

            // 創建使用者的 client
            Client();

        }

    }
}

:::

### 顯示結果