套接字编程 - 简单的客户端/服务器应用程序 [英] Socket Programming - Simple Client/Server Application
问题描述
我在这里有一个简单的客户端/服务器应用程序的代码.工作原理:客户端输入获取时间"，服务器以时间响应.
问题是客户端成功连接服务器后抛出NullReferenceException.为什么会这样?
代码:
客户:
使用系统；使用 System.Collections.Generic;使用 System.Linq；使用 System.Text;使用 System.Net；使用 System.Net.Sockets；命名空间 Time_Client{课程计划{私有静态 Socket clientSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);static void Main(string[] args){Console.Title = "客户端";循环连接()；发送循环()；Console.ReadLine();}私有静态无效 SendLoop(){而(真){Console.Write("输入请求:");string req = Console.ReadLine();byte[] buffer = Encoding.ASCII.GetBytes(req);clientSocket.Send(buffer);byte[] receivedBuf = 新字节 [1024];int rec = clientSocket.Receive(receivedBuf);字节 [] 数据 = 新字节 [rec];Array.Copy(receivedBuf, data, rec);Console.WriteLine("收到:" + Encoding.ASCII.GetString(data));}}私有静态无效 LoopConnect(){int 尝试 = 0;while (!clientSocket.Connected){尝试{尝试++；clientSocket.Connect(IPAddress.Loopback, 100);}捕获(套接字异常){Console.WriteLine("连接尝试次数:" + 尝试次数);}}Console.Clear();Console.WriteLine("已连接");}}}服务器:
使用系统；使用 System.Collections.Generic;使用 System.Linq；使用 System.Text;使用 System.Threading.Tasks;使用 System.Net；使用 System.Net.Sockets；命名空间 Time_Server{课程计划{私有静态字节[]缓冲区=新字节[1024]；私有静态列表<套接字>clientSockets = new List();私有静态 Socket serverSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);static void Main(string[] args){Console.Title = "服务器";设置服务器();Console.ReadLine();}私有静态无效 SetupServer(){Console.WriteLine("正在设置服务器...");serverSocket.Bind(new IPEndPoint(IPAddress.Any, 100));serverSocket.Listen(5);serverSocket.BeginAccept(new AsyncCallback(RecieveCallback), null);}私有静态无效 AcceptCallback(IAsyncResult AR){套接字套接字 = serverSocket.EndAccept(AR);clientSockets.Add(socket);Console.WriteLine("客户端连接");socket.BeginReceive(buffer, 0, buffer.Length, SocketFlags.None, new AsyncCallback(RecieveCallback), socket);serverSocket.BeginAccept(new AsyncCallback(AcceptCallback), null);}私有静态无效接收回调(IAsyncResult AR){Socket socket = (Socket)AR.AsyncState;int 接收 = socket.EndReceive(AR);//这里抛出异常字节[] dataBuf = 新字节[接收];Array.Copy(buffer, dataBuf, 收到);字符串文本 = Encoding.ASCII.GetString(dataBuf);Console.WriteLine("收到的文本:" + text);字符串响应 = "";if (text.ToLower() != "get time"){response = "无效请求";}别的{response = DateTime.Now.ToLongTimeString();}byte[] data = Encoding.ASCII.GetBytes(response);socket.BeginSend(data, 0, data.Length, SocketFlags.None, new AsyncCallback(RecieveCallback), socket);socket.BeginReceive(buffer, 0, buffer.Length, SocketFlags.None, new AsyncCallback(RecieveCallback), socket);}私有静态无效 SendCallback(IAsyncResult AR){Socket socket = (Socket)AR.AsyncState;socket.EndSend(AR);}}} 我该如何解决这个问题?
啊，我搞错了什么.这就是问题所在.
serverSocket.BeginAccept(new AsyncCallback(RecieveCallback), null);请注意，您使用的是 RecieveCallback 而不是 AcceptCallback.所以你最终进入 RecieveCallback(顺便说一下，它应该是 ReceiveCallback)，此时你会找到异步状态 - 为空 - 并调用 EndReceive... 但这不是 Receive 操作的回调，而是 Accept 操作的回调.
上面这行应该是:
serverSocket.BeginAccept(new AsyncCallback(AcceptCallback), null);但是，如果您正在尝试编写一个简单客户端/服务器程序，我会完全避免使用异步 IO，而只是开始进行同步操作.当您确实想要使用异步操作时，请使用 C# 5 中的 async/await - 它会让您的生活更轻松.
我还建议使用 TcpClient 和 TcpListener 类使事情变得更简单.它们是套接字周围的包装器.
I've have this code here of a simple Client/Server application. How it works: The client enters "get time", and the server responds with the time.
The problem is that a NullReferenceException is thrown after the client successfully connects to the server. Why does that happen?
Codes:
Client:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net;
using System.Net.Sockets;
namespace Time_Client
{
class Program
{
private static Socket clientSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
static void Main(string[] args)
{
Console.Title = "Client";
LoopConnect();
SendLoop();
Console.ReadLine();
}
private static void SendLoop()
{
while (true)
{
Console.Write("Enter a request: ");
string req = Console.ReadLine();
byte[] buffer = Encoding.ASCII.GetBytes(req);
clientSocket.Send(buffer);
byte[] receivedBuf = new byte[1024];
int rec = clientSocket.Receive(receivedBuf);
byte[] data = new byte[rec];
Array.Copy(receivedBuf, data, rec);
Console.WriteLine("Received: " + Encoding.ASCII.GetString(data));
}
}
private static void LoopConnect()
{
int attempts = 0;
while (!clientSocket.Connected)
{
try
{
attempts++;
clientSocket.Connect(IPAddress.Loopback, 100);
}
catch (SocketException)
{
Console.WriteLine("Connection attempts: " + attempts);
}
}
Console.Clear();
Console.WriteLine("Connected");
}
}
}
Server:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Net;
using System.Net.Sockets;
namespace Time_Server
{
class Program
{
private static byte[] buffer = new byte[1024];
private static List<Socket> clientSockets = new List<Socket>();
private static Socket serverSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
static void Main(string[] args)
{
Console.Title = "Server";
SetupServer();
Console.ReadLine();
}
private static void SetupServer()
{
Console.WriteLine("Setting up server...");
serverSocket.Bind(new IPEndPoint(IPAddress.Any, 100));
serverSocket.Listen(5);
serverSocket.BeginAccept(new AsyncCallback(RecieveCallback), null);
}
private static void AcceptCallback(IAsyncResult AR)
{
Socket socket = serverSocket.EndAccept(AR);
clientSockets.Add(socket);
Console.WriteLine("Client Connected");
socket.BeginReceive(buffer, 0, buffer.Length, SocketFlags.None, new AsyncCallback(RecieveCallback), socket);
serverSocket.BeginAccept(new AsyncCallback(AcceptCallback), null);
}
private static void RecieveCallback(IAsyncResult AR)
{
Socket socket = (Socket)AR.AsyncState;
int received = socket.EndReceive(AR); // the exception is thrown here
byte[] dataBuf = new byte[received];
Array.Copy(buffer, dataBuf, received);
string text = Encoding.ASCII.GetString(dataBuf);
Console.WriteLine("Text received: " + text);
string response = "";
if (text.ToLower() != "get time")
{
response = "Invalid Request";
}
else
{
response = DateTime.Now.ToLongTimeString();
}
byte[] data = Encoding.ASCII.GetBytes(response);
socket.BeginSend(data, 0, data.Length, SocketFlags.None, new AsyncCallback(RecieveCallback), socket);
socket.BeginReceive(buffer, 0, buffer.Length, SocketFlags.None, new AsyncCallback(RecieveCallback), socket);
}
private static void SendCallback(IAsyncResult AR)
{
Socket socket = (Socket)AR.AsyncState;
socket.EndSend(AR);
}
}
}
How can I solve this?
EDIT: Ah, I was mistaken in what was wrong. This is the problem.
serverSocket.BeginAccept(new AsyncCallback(RecieveCallback), null);
Note that you're using RecieveCallback instead of AcceptCallback. So you end up in RecieveCallback (which should be ReceiveCallback, by the way) at which point you find the async state - which is null - and call EndReceive... but this isn't the callback for Receive operation, it's a callback for an Accept operation.
The line above should be:
serverSocket.BeginAccept(new AsyncCallback(AcceptCallback), null);
However, if you're trying to write a simple client/server program, I would avoid using async IO at all, and just go for synchronous operations, to start with. When you do want to use asynchronous operations, use async / await from C# 5 - it'll make your life a lot easier.
I'd also recommend using the TcpClient and TcpListener classes to make things simpler. They're wrappers around the sockets.
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