C# UDP套接字无法接收消息

Question

我无法从 UDP 套接字接收消息。我制作了运行良好的 C++ 服务器和客户端应用程序。服务器从客户端接收消息然后发回响应，客户端接收消息然后他们都关闭套接字并退出。现在我尝试用 C# 创建客户端程序，但我无法从服务器接收消息。客户端 C# 应用程序发送消息，然后 C++ 服务器正确接收它，但是当服务器发回他的响应时，客户端无法接收它。我已经在本地虚拟机和 VPS 上测试了我的服务器，结果是一样的。有什么想法吗？

服务器代码 C++：

#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <stdio.h>
#include <pthread.h>

#define MSG "Hi i'm server"
#define SERVERPORT "8642"
#define MAXBUFLEN 100


// Get sockaddr, IPv4 or IPv6.
void *get_in_addr(struct sockaddr *sa)
{
    if (sa->sa_family == AF_INET)
    {
        return &(((struct sockaddr_in*)sa)->sin_addr);
    }

    return &(((struct sockaddr_in6*)sa)->sin6_addr);
}

int LoginUser()
{
    int locUserId = 0;

    // Call DB.

    return 0;
}

int main(int argc, char *argv[])
{
    // Load up address structs.
    struct addrinfo hints, *res;

    memset(&hints, 0, sizeof hints);
    hints.ai_family = AF_UNSPEC; // Use IPv4 or IPv6, whichever.
    hints.ai_socktype = SOCK_DGRAM; // UDP.
    hints.ai_flags = AI_PASSIVE; // Fill in my IP for me.

    int locInitAddrInfo = getaddrinfo(NULL, SERVERPORT, &hints, &res);

    if (locInitAddrInfo != 0)
    {
        printf("Error initialize address info: %s\n", gai_strerror(locInitAddrInfo));
        return 1;
    }

    printf("Address info initialized: %i\n", locInitAddrInfo);

    // Initialize the socket.
    int locInitSocket = socket(res->ai_family, res->ai_socktype, res->ai_protocol);

    if (locInitSocket == -1)
    {
        printf("Error initialize socket: %s\n", strerror(errno));
        freeaddrinfo(res);
        return 2;
    }

    printf("Socket initialized: %i\n", locInitSocket);

    // Bind a name to a socket.
    int locInitBind = bind(locInitSocket, res->ai_addr, res->ai_addrlen);

    if (locInitBind == -1)
    {
        printf("Error bind socket: %s\n", strerror(errno));
        freeaddrinfo(res);
        close(locInitSocket);
        return 3;
    }

    printf("Socket binded: %i\n", locInitBind);

    // Receive message from client.
    char buf[MAXBUFLEN];
    struct sockaddr_storage their_addr;
    socklen_t addr_len = sizeof their_addr;

    int locNumByteRecv = recvfrom(locInitSocket, buf, MAXBUFLEN, 0, (struct sockaddr *)&their_addr, &addr_len);

    if (locNumByteRecv == -1)
    {
        printf("Error receive from: %s\n", strerror(errno));
        freeaddrinfo(res);
        close(locInitSocket);
        return 4;
    }

    // -----------------------------------------
    char s[INET6_ADDRSTRLEN];

    printf("Server: got packet from %s\n", inet_ntop(their_addr.ss_family, get_in_addr((struct sockaddr *)&their_addr), s, sizeof s));
    printf("Server: packet is %d bytes long\n", locNumByteRecv);
    buf[locNumByteRecv] = '[=10=]';
    printf("Server: packet contains \"%s\"\n", buf);
    // -----------------------------------------

    sleep(2);

    // Send to client.
    int locNumByteSend = sendto(locInitSocket, MSG, strlen(MSG), 0, (struct sockaddr *)&their_addr, addr_len);

    if (locNumByteSend == -1)
    {
        printf("Error send to: %s\n", strerror(errno));
        freeaddrinfo(res);
        close(locInitSocket);
        return 5;
    }

    printf("Server: sent %d bytes to %s:%s\n", locNumByteSend, inet_ntop(their_addr.ss_family, get_in_addr((struct sockaddr *)&their_addr), s, sizeof s), SERVERPORT);

    // Free the linked-list.
    freeaddrinfo(res);

    // Close the socket.
    close(locInitSocket);

    printf("Socket closed.\nHave a nice day :)\n");

    return 0;
}

客户端代码 C++：

#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netdb.h>

#define MSG "Hi i'm client"
#define SERVERIP "192.168.1.33"
#define SERVERPORT "8642"
#define MAXBUFLEN 100

// Get sockaddr, IPv4 or IPv6.
void *get_in_addr(struct sockaddr *sa)
{
    if (sa->sa_family == AF_INET)
    {
        return &(((struct sockaddr_in*)sa)->sin_addr);
    }

    return &(((struct sockaddr_in6*)sa)->sin6_addr);
}

int main(int argc, char *argv[])
{
    // Load up address structs.
    struct addrinfo hints, *res;

    memset(&hints, 0, sizeof hints);
    hints.ai_family = AF_UNSPEC; // Use IPv4 or IPv6, whichever.
    hints.ai_socktype = SOCK_DGRAM; // UDP.

    int locInitAddrInfo = getaddrinfo(SERVERIP, SERVERPORT, &hints, &res);

    if (locInitAddrInfo != 0)
    {
        printf("Error initialize address info: %s\n", gai_strerror(locInitAddrInfo));
        return 1;
    }

    printf("Address info initialized: %i\n", locInitAddrInfo);

    // Initialize the socket.
    int locInitSocket = socket(res->ai_family, res->ai_socktype, res->ai_protocol);

    if (locInitSocket == -1)
    {
        printf("Error initialize socket: %s\n", strerror(errno));
        freeaddrinfo(res);
        return 2;
    }

    printf("Socket initialized: %i\n", locInitSocket);

    // Send to server.
    int locNumByteSend = sendto(locInitSocket, MSG, strlen(MSG), 0, res->ai_addr, res->ai_addrlen);

    if (locNumByteSend == -1)
    {
        printf("Error send to: %s\n", strerror(errno));
        freeaddrinfo(res);
        close(locInitSocket);
        return 3;
    }

    printf("Client: sent %d bytes to %s:%s\n", locNumByteSend, SERVERIP, SERVERPORT);

    // Receive message from server.
    char buf[MAXBUFLEN];
    struct sockaddr_storage their_addr;
    socklen_t addr_len = sizeof their_addr;

    int locNumByteRecv = recvfrom(locInitSocket, buf, MAXBUFLEN, 0, (struct sockaddr *)&their_addr, &addr_len);

    if (locNumByteRecv == -1)
    {
        printf("Error receive from: %s\n", strerror(errno));
        freeaddrinfo(res);
        close(locInitSocket);
        return 4;
    }

    // -----------------------------------------
    char s[INET6_ADDRSTRLEN];

    printf("Client: got packet from %s\n", inet_ntop(their_addr.ss_family, get_in_addr((struct sockaddr *)&their_addr), s, sizeof s));
    printf("Client: packet is %d bytes long\n", locNumByteRecv);
    buf[locNumByteRecv] = '[=11=]';
    printf("Client: packet contains \"%s\"\n", buf);
    // -----------------------------------------

    // Free the linked-list.
    freeaddrinfo(res);

    // Close the socket.
    close(locInitSocket);

    printf("Socket closed.\nHave a nice day :)\n");

    return 0;
}

这是我的 C# 代码不起作用：

using System;
using System.Net;
using System.Net.Sockets;
using System.Text;

namespace TestCSharpSocket
{
    class Program
    {
        static void Main(string[] args)
        {
            try
            {
                // This work fine  ----------------------------
                IPEndPoint RemoteEndPoint = new IPEndPoint(IPAddress.Parse("192.168.1.33"), 8642);
                Socket server = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
                string welcome = "Welcome";
                byte[] data = Encoding.ASCII.GetBytes(welcome);
                server.SendTo(data, data.Length, SocketFlags.None, RemoteEndPoint);
                server.Close();

                Console.WriteLine("Welcome send");

                // End This work fine  ----------------------------

                IPHostEntry hostEntry = Dns.GetHostEntry(Dns.GetHostName());
                IPEndPoint ServerEndPoint = new IPEndPoint(IPAddress.Any, 8642);
                Socket WinSocket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
                WinSocket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReceiveTimeout, 5000);


                IPEndPoint sender = new IPEndPoint(IPAddress.Any, 8642);
                EndPoint Remote = (EndPoint)(sender);

                WinSocket.Bind(ServerEndPoint);

                data = new byte[256];
                int recv = WinSocket.ReceiveFrom(data, ref Remote);
                WinSocket.Close();


                Console.WriteLine(Encoding.ASCII.GetString(data, 0, recv));
            }
            catch (SocketException sex)
            {
                Console.WriteLine("Time Out: " + sex.ToString());
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.ToString());
            }

            Console.ReadLine();
        }
    }
}

这是另一个不起作用的 C# 代码：

using System;
using System.Net;
using System.Net.Sockets;
using System.Text;

namespace TestCSharpSocket
{
    class Program
    {
        static void Main(string[] args)
        {
            try
            {
                // This work fine  ----------------------------
                IPEndPoint RemoteEndPoint = new IPEndPoint(IPAddress.Parse("192.168.1.33"), 8642);
                Socket server = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
                string welcome = "Welcome";
                byte[] data = Encoding.ASCII.GetBytes(welcome);
                server.SendTo(data, data.Length, SocketFlags.None, RemoteEndPoint);
                server.Close();

                Console.WriteLine("Welcome send");

                // End This work fine  ----------------------------

                UdpClient listener = new UdpClient(8642);
                listener.Client.ReceiveTimeout = 5000;
                IPEndPoint endpoint = new IPEndPoint(IPAddress.Any, 8642);

                byte[] receivebytes;
                receivebytes = listener.Receive(ref endpoint);

                Console.WriteLine(Encoding.ASCII.GetString(receivebytes, 0, receivebytes.Length));
            }
            catch (SocketException sex)
            {
                Console.WriteLine("Time Out: " + sex.ToString());
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.ToString());
            }

            Console.ReadLine();
        }
    }
}

Answer 1

谢谢@Peter！在我检查我的代码后，这里是解决方案：

using System;
using System.Net;
using System.Net.Sockets;
using System.Text;

namespace TestCSharpSocket
{
  class Program
  {
    static void Main(string[] args)
    {
        try
        {
            // This work fine  ----------------------------
            IPEndPoint RemoteEndPoint = new IPEndPoint(IPAddress.Parse("192.168.1.33"), 8642);
            Socket server = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
            string welcome = "Welcome";
            byte[] data = Encoding.ASCII.GetBytes(welcome);
            server.SendTo(data, data.Length, SocketFlags.None, RemoteEndPoint);

            Console.WriteLine("Welcome send");

            IPEndPoint sender = new IPEndPoint(IPAddress.Any, 0);
            EndPoint Remote = (EndPoint)(sender);

            data = new byte[256];
            int recv = server.ReceiveFrom(data, ref Remote);
            server.Close();

            Console.WriteLine(Encoding.ASCII.GetString(data, 0, recv));
        }
        catch (SocketException sex)
        {
            Console.WriteLine("Time Out: " + sex.ToString());
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.ToString());
        }

        Console.ReadLine();
    }
  }
}

C# UDP套接字无法接收消息

C# UDP socket unable to receive message

c#

c++

sockets

udp

server