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一、几种常见协议差别

在日常工作中我们总是会听到提到socket、tcp/ip协议、modbus tcp协议、HTTP协议等常用通讯协议，下面我们了解一下这些通讯协议的关系和区别，TCP/IP协议族通常分为‌四层：

TCP/IP协议族包含网络层（IP协议）和传输层（TCP/UDP协议），而应用层协议（如HTTP、Modbus TCP）运行在传输层之上。‌Socket‌是更底层的编程接口，支持TCP和UDP等协议。在C#中，Socket类提供了更灵活的控制，但需要处理更多底层细节，如连接管理、数据发送和接收‌，用于实现进程间网络通信‌。
下面这张图更加清楚的表明了这种关系。

二、C# HTTP通讯协议代码示例

下面代码展示了C# 使用HTTP协议通讯的整个过程。
下面是服务端伪代码：

HttpListener listener = new HttpListener();
listener.Prefixes.Add("http://127.0.0.1:5088/");
listener.Start();// 等待请求
HttpListenerContext context = listener.GetContext();
HttpListenerRequest request = context.Request;
HttpListenerResponse response = context.Response;// 读取请求体中的JSON数据
string jsonContent;
using (var reader = new StreamReader(request.InputStream, request.ContentEncoding))
{jsonContent = reader.ReadToEnd();Dictionary<string, object> dictionary = JsonConvert.DeserializeObject<Dictionary<string, object>>(jsonContent);
}

下面是客户端伪代码：

private static readonly HttpClient client = new HttpClient();
var values = new Dictionary<string, string> {{ "imgPath"," "}};
var content = new FormUrlEncodedContent(values);
HttpResponseMessage response = await client.PostAsync(url, content);
response.EnsureSuccessStatusCode();
pythonResult=await response.Content.ReadAsStringAsync();

三、C# Modbus TCP通讯协议代码示例

ModbusTCP modbusTCP = new ModbusTCP("192.168.3.1", 502);
modbusTCP.ConnectExecute();string strReadValue = modbusTCP.ReadExecute("real", byte.Parse("1"), ushort.Parse("24"));
modbusTCP.WriteExecute("real", "0", byte.Parse("1"), ushort.Parse("16"));public class ModbusTCP
{private ModbusFactory modbusFactory;private IModbusMaster master;private TcpClient tcpClient;public string IPAdress { get; set; }public int Port { get; set; }public bool Connected{get => tcpClient.Connected;}public ModbusTCP(string ip, int port){IPAdress = ip;Port = port;}public void WriteExecute(string VariableType, string WriteValue, byte SlaveID, ushort WriteAddress){try{if (VariableType == "real"){ushort[] buff = new ushort[2];float value = float.Parse(WriteValue);MODBUS.SetReal(buff, 0, value);WriteMultipleRegisters(SlaveID, WriteAddress, buff);}else if (VariableType == "string"){ushort[] buff = new ushort[10];MODBUS.SetString(buff, 0, WriteValue);WriteMultipleRegisters(SlaveID, WriteAddress, buff);}else if (VariableType == "Int16"){ushort[] buff = new ushort[1];short value = short.Parse(WriteValue);MODBUS.SetShort(buff, 0, value);WriteMultipleRegisters(SlaveID, WriteAddress, buff);}}catch (Exception ex){//Msg.Info(ex.Message);}}public string ReadExecute(string VariableType, byte SlaveID, ushort ReadAddress){string ReadValue = string.Empty;if (VariableType == "real"){ushort[] buff = ReadHoldingRegisters(SlaveID, ReadAddress, 2);float value = MODBUS.GetReal(buff, 0);ReadValue = value.ToString();}else if (VariableType == "string"){ushort[] buff = ReadHoldingRegisters(SlaveID, ReadAddress, 10);ReadValue = MODBUS.GetString(buff, 0, 10);}else if (VariableType == "Int16"){ushort[] buff = ReadHoldingRegisters(SlaveID, ReadAddress, 1);short value = MODBUS.GetShort(buff, 0);ReadValue = value.ToString();}return ReadValue;}public void ConnectExecute(){modbusFactory = new ModbusFactory();tcpClient = new TcpClient();tcpClient.Connect(IPAdress, Port);master = modbusFactory.CreateMaster(tcpClient);master.Transport.ReadTimeout = 2000;master.Transport.Retries = 5;}   

四、C# Socket通讯协议代码示例

Socket ClientSocket;
IPAddress ip = IPAddress.Parse("192.168.2.25");  //将IP地址字符串转换成IPAddress实例
int port = 2001;
IPEndPoint endPoint = new IPEndPoint(ip, port); //用指定的ip和端口号初始化IPEndPoint实例
//使用指定的地址簇协议、套接字类型和通信协议
ClientSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
ClientSocket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReceiveTimeout, true);     //必须先启用接收超时选项，设置接收超时才有用。   
ClientSocket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.SendTimeout, true);
ClientSocket.ReceiveTimeout = 3000;
ClientSocket.SendTimeout = 1000;
ClientSocket.Connect(endPoint);//上面是ClientSocket初始化，下面是发送和接受的过程
byte[] byteArray = System.Text.Encoding.Default.GetBytes("start");
int W = ClientSocket.Send(byteArray, byteArray.Length, SocketFlags.None);
while (true)
{byte[] recv_buffer = new byte[1024];int real_recv = ClientSocket.Receive(recv_buffer);  //接收浏览器的请求数据if (real_recv > 0){qrcodeContent = Encoding.UTF8.GetString(recv_buffer, 0, real_recv);qrcodeContent = qrcodeContent.Trim();break;}}