为什么我的 c++ Winsock 服务器无法从客户端接收数据？

Question

我尝试运行一个简单的客户端和服务器程序。 Therin，我试图从客户端向服务器发送一条消息，并让服务器回显该消息。问题是每次我都会收到 10057 错误。我不知道为什么。

这是服务器代码

#include <stdio.h>
#include <winsock2.h>
#include <stdlib.h>

#define MYBUFSIZE   128


void shutdown_close(SOCKET s)
{

    // Tell the operating system the socket is
    // about to be closed   
    shutdown(s, SD_BOTH); 

    // close the socket….
    closesocket(s); 
}

void shutdown_close_and_exit(SOCKET s)
{
    shutdown_close(s);
    exit(1);
}

void main(int argc, char *argv[])
{
    SOCKET srvr_socket;
    struct sockaddr_in srvr_addr;
    struct sockaddr_in clnt_addr; // Client address
    int addr_len = 0;
    WSADATA wsaData;
    char recv_buf[MYBUFSIZE];
    int recv_msg_len;
    short portnum;


    if (argc == 2)
    {
        portnum = atoi(argv[1]);
        printf("Setting port number to %d\n", portnum);

    } else
    {
        fprintf(stderr, "Usage: %s port_num_to_listen_at\n",
                argv[0]);
        exit(1);
    }

    // Init Winsock
    if (WSAStartup(MAKEWORD(2, 0), &wsaData) != 0)
    {
        fprintf(stderr, "Error: WSAStartup() failed");
        exit(1);
    }

    // Create UDP datagram socket for incoming connections
    if ((srvr_socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) == SOCKET_ERROR)
    {
        fprintf(stderr, "Error: socket() failed with error %d\n", WSAGetLastError());
        shutdown_close_and_exit(srvr_socket);
    }

    // Construct local address structure
    memset(&srvr_addr, 0, sizeof(srvr_addr));
    srvr_addr.sin_family = AF_INET;
    srvr_addr.sin_addr.s_addr = inet_addr("127.0.0.1");  // Accept messages on any network interface.
    srvr_addr.sin_port = htons(portnum);     // Bind the port number specified on the command line.

    /* Bind to the local address */
    if (bind(srvr_socket, (struct sockaddr *) &srvr_addr, sizeof(srvr_addr)) == SOCKET_ERROR)
    {
        fprintf(stderr, "Error: socket() failed with error %d", WSAGetLastError());
        shutdown_close_and_exit(srvr_socket);
    }

    listen(srvr_socket, SOMAXCONN);

    // Loop forever
    for (;;)
    {
        // Set the size of the in-out parameter, where the client address
        // and port number will be stored by the OS
        addr_len = sizeof(clnt_addr);

        if(accept(srvr_socket,(SOCKADDR *) &srvr_addr, &addr_len) == SOCKET_ERROR)
        {
            fprintf(stderr, "Error: accept() failed with error %d\n", WSAGetLastError());
            shutdown_close_and_exit(srvr_socket);
        }

        // Receive message from client
        if ((recv_msg_len = recvfrom(srvr_socket, recv_buf, MYBUFSIZE, 0,
            (struct sockaddr *) &clnt_addr, &addr_len )) == SOCKET_ERROR) {

            fprintf(stderr, "Error: recvfrom() failed with error %d\n", WSAGetLastError());
            shutdown_close_and_exit(srvr_socket);
        } else {
            printf("Received message of size %d: %s\n from client %s:%d\n", 
                    recv_msg_len, recv_buf, inet_ntoa(clnt_addr.sin_addr),
                    ntohs(clnt_addr.sin_port));
        }


        // 'echo' message back to client
        if ((recv_msg_len = sendto(srvr_socket, recv_buf, recv_msg_len, 0,
            (struct sockaddr *) &clnt_addr, addr_len )) == SOCKET_ERROR) {

            fprintf(stderr, "Error: sendto() failed with error %d\n", WSAGetLastError());
            shutdown_close_and_exit(srvr_socket);
        } else {
            printf("Echo'd message %s to client %s:%d\n", 
                    recv_buf, inet_ntoa(clnt_addr.sin_addr),
                    ntohs(clnt_addr.sin_port));
        }
    }
}

这是客户端代码：

#include <stdio.h>
#include <winsock2.h>
#include <stdlib.h>

#define BUFSIZE 128  /* Size of receive buffer */


void shutdown_close(SOCKET s)
{

    // Tell the operating system the socket is
    // about to be closed   
    shutdown(s, SD_BOTH); 

    // close the socket….
    closesocket(s); 
}

void shutdown_close_and_exit(SOCKET s)
{
    shutdown_close(s);
    exit(1);
}

void main(int argc, char *argv[])
{
    SOCKET servSock;
    struct sockaddr_in srvr_addr;
    struct sockaddr_in recv_addr;
    int addr_len = 0; 
    WSADATA wsaData;
    char mesg_buf[BUFSIZE];
    char *mesg_to_send;
    long server_IP;
    short portnum;


    if (argc == 4)
    {
        portnum = atoi(argv[1]);
        printf("Setting port number to %d\n", portnum);

        server_IP = inet_addr(argv[2]);
        printf("Target server IP address is %s\n", argv[2]);

        mesg_to_send = argv[3];

    } else
    {
        fprintf(stderr, "Usage: %s server_port_num server_IP_address message_to_send\n",
                argv[0]);
        exit(1);
    }

    // Init Winsock
    if (WSAStartup(MAKEWORD(2, 0), &wsaData) != 0)
    {
        fprintf(stderr, "Error: WSAStartup() failed with error %d\n", WSAGetLastError());
        exit(1);
    }

    // Create socket for incoming connections
    if ((servSock = socket(AF_INET,SOCK_STREAM, IPPROTO_TCP)) == SOCKET_ERROR)
    {
        fprintf(stderr, "Error: socket() failed with error %d\n", WSAGetLastError());
        shutdown_close_and_exit(servSock);
    }

    // Construct local address structure
    // with server address.  This is like
    // addressing the envelope of a letter.
    memset(&srvr_addr, 0, sizeof(srvr_addr));
    srvr_addr.sin_family = AF_INET;
    srvr_addr.sin_addr.s_addr = server_IP;
    srvr_addr.sin_port = htons(portnum);

    if ( connect(servSock, (SOCKADDR*) &srvr_addr, sizeof(srvr_addr)) == SOCKET_ERROR)
    {
        fprintf(stderr, "Error: connect() failed with error %d\n", WSAGetLastError());
        shutdown_close_and_exit(servSock);
    }

    // Set the size of the in-out parameter
    addr_len = sizeof(recv_addr);

    if (sendto(servSock, mesg_to_send, strlen(mesg_to_send) + 1, 0,
                (sockaddr *) &srvr_addr, addr_len) == SOCKET_ERROR)
    {
        fprintf(stderr, "Error: sendto() failed with error %d\n", WSAGetLastError());
        shutdown_close_and_exit(servSock);
    }

    printf("Send message %s to server at %s:%d\n", argv[3], argv[2], portnum);

    // Sleep 1 full second to allow message  to get to server and be sent back...
    Sleep(1000);

    addr_len = sizeof(recv_addr);

    if (recvfrom(servSock, mesg_buf, BUFSIZE, 0,
                (sockaddr *) &recv_addr, &addr_len) == SOCKET_ERROR)
    {
        fprintf(stderr, "Error: recvfrom() failed with error %d\n", WSAGetLastError());
        shutdown_close_and_exit(servSock);
    }

    printf("Received message %s from %s:%d\n", mesg_buf, 
            inet_ntoa(recv_addr.sin_addr), ntohs(recv_addr.sin_port));

    // close socket gracefully
    shutdown_close(servSock);

}

有人能看出代码有什么问题吗？

Answer 1

您应该将recv 用于SOCK_STREAM 套接字，而不是recvfrom。

（但那是一大堆代码，没有明显的迹象表明故障在哪里，所以可能还有其他问题。）

Answer 2

使用send() 代替sendto()，使用recv() 代替recvfrom()。此外，您在服务器端将错误的sockaddr_in 传递给accept()。

Answer 3

我知道出了什么问题。我的服务器从未建立连接，因为我从未与接受功能建立连接。换句话说，我正在接受连接但不记得它。我应该创建一个用于接受连接的套接字并将其设置为等于接受函数，如下所示：

Socket acceptSocket;

...

AcceptSocket = accept(srvr_socket,(SOCKADDR *) &clnt_addr, &addr_len) ;

        if(AcceptSocket == INVALID_SOCKET)
        {
            fprintf(stderr, "Error: accept() failed with error %d\n", WSAGetLastError());
            shutdown_close_and_exit(srvr_socket);
        }

我也应该使用 recv() 和 send() 而不是像 RichieHindle 提到的 sendto() 和 recvfrom() 因为它们是为 UDP 无连接套接字而不是 TCP 连接套接字设计的

Answer 4

当我从 recvfrom() 收到错误 10057 时，我的初始代码段如下：

if (listen(s, SOMAXCONN) == SOCKET_ERROR) {
printf("Error in Listening .. ErroR Code: %d \n", WSAGetLastError());
exit(EXIT_FAILURE);
}
else
printf("Listening\n");

//Accept and incoming connection
puts("Waiting for incoming connections...");

c = sizeof(struct sockaddr_in);
new_socket = accept(s, (struct sockaddr *)&client, &c);

if (new_socket == INVALID_SOCKET)
{
printf("accept failed with error code : %d", WSAGetLastError());
return 1;
}
else
puts("Connection accepted");
recv_size = recvfrom(s , client_msg, sizeof(client_msg), 0,
(SOCKADDR *)&recv_from, &addrlen);

我试图在我正在监听的同一个套接字上接收来自客户端的数据，即“s”，而不是我接受客户端连接的新套接字，即“new_socket”。

    After making the following changes:
recv_size = recvfrom(new_socket , client_msg, sizeof(client_msg), 0, (SOCKADDR 
*)&recv_from, &addrlen);

我可以完美地接收来自客户端应用程序的数据。