C++ Winsock 客户端不会从服务器接收数据，但使用 Putty 客户端它可以工作

Question

我需要向设备发送一些数据。为此，我正在尝试使用 WinSock 套接字客户端。主要连接有效，但我没有得到任何数据，只有ACK。我用 Putty 客户端尝试了同样的测试，我在那里接收数据。我正在查看 Wireshark，我看到我的 WinSock 客户端在传输数据后正在发送FIN。腻子不是这种情况。我知道FIN 会因为shutdown(SD_SEND) 而被发送，但我该如何以另一种方式处理呢？您可以在下面的图片中看到这一点。

用于 WinSock 的 Wireshark：

用于腻子的 Wireshark：

这是我的客户端代码：

#define WIN32_LEAN_AND_MEAN

#include <windows.h>
#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdlib.h>
#include <stdio.h>


// Need to link with Ws2_32.lib, Mswsock.lib, and Advapi32.lib
#pragma comment (lib, "Ws2_32.lib")
#pragma comment (lib, "Mswsock.lib")
#pragma comment (lib, "AdvApi32.lib")


#define DEFAULT_BUFLEN 512
#define DEFAULT_PORT "8000"
#define DEFAULT_IP "127.0.0.1"

//int __cdecl main(int argc, char** argv)
int __cdecl main()
{
    WSADATA wsaData;
    SOCKET ConnectSocket = INVALID_SOCKET;
    struct addrinfo* result = NULL,
        * ptr = NULL,
        hints;
    const char* sendbuf = "M:UA 111111 SEP1,00000";
    char recvbuf[DEFAULT_BUFLEN];
    int iResult;
    int recvbuflen = DEFAULT_BUFLEN;

    // Validate the parameters
   // if (argc != 2) {
   //     printf("usage: %s server-name\n", argv[0]);
   //     return 1;
   // }

    // Initialize Winsock
    iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
    if (iResult != 0) {
        printf("WSAStartup failed with error: %d\n", iResult);
        return 1;
    }

    ZeroMemory(&hints, sizeof(hints));
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_protocol = IPPROTO_TCP;

    // Resolve the server address and port
   // iResult = getaddrinfo(argv[1], DEFAULT_PORT, &hints, &result);
    iResult = getaddrinfo(DEFAULT_IP, DEFAULT_PORT, &hints, &result);

    if (iResult != 0) {
        printf("getaddrinfo failed with error: %d\n", iResult);
        WSACleanup();
        return 1;
    }

    // Attempt to connect to an address until one succeeds
    for (ptr = result; ptr != NULL; ptr = ptr->ai_next) {

        // Create a SOCKET for connecting to server
        ConnectSocket = socket(ptr->ai_family, ptr->ai_socktype,
            ptr->ai_protocol);
        if (ConnectSocket == INVALID_SOCKET) {
            printf("socket failed with error: %ld\n", WSAGetLastError());
            WSACleanup();
            return 1;
        }

        // Connect to server.
        iResult = connect(ConnectSocket, ptr->ai_addr, (int)ptr->ai_addrlen);
        if (iResult == SOCKET_ERROR) {
            closesocket(ConnectSocket);
            ConnectSocket = INVALID_SOCKET;
            continue;
        }
        break;
    }

    freeaddrinfo(result);

    if (ConnectSocket == INVALID_SOCKET) {
        printf("Unable to connect to server!\n");
        WSACleanup();
        return 1;
    }

    // Send an initial buffer
    iResult = send(ConnectSocket, sendbuf, (int)strlen(sendbuf), 0);
   
    if (iResult == SOCKET_ERROR) {
        printf("send failed with error: %d\n", WSAGetLastError());
        closesocket(ConnectSocket);
        WSACleanup();
        return 1;
    }

    printf("Bytes Sent: %ld\n", iResult);
    

    // shutdown the connection since no more data will be sent
    iResult = shutdown(ConnectSocket, SD_SEND);
   
    if (iResult == SOCKET_ERROR) {
        printf("shutdown failed with error: %d\n", WSAGetLastError());
        closesocket(ConnectSocket);
        WSACleanup();
        return 1;
    }

    // Receive until the peer closes the connection
    do {

        iResult = recv(ConnectSocket, recvbuf, recvbuflen, 0);
        if (iResult > 0)
            printf("Bytes received: %d\n", iResult);
        else if (iResult == 0)
            printf("Connection closed\n");
        else
            printf("recv failed with error: %d\n", WSAGetLastError());

    } while (iResult > 0);

    // cleanup
    closesocket(ConnectSocket);
    WSACleanup();

    return 0;
}

Answer 1

Putty 在每个文本之后发送 2 个额外字节。大概是 CRLF 行结尾。您的 Winsock 代码没有发送这 2 个字节。很可能，服务器在将数据发送回客户端之前预计会出现换行符。

尝试改变这个：

const char* sendbuf = "M:UA 111111 SEP1,00000";

到这里：

const char* sendbuf = "M:UA 111111 SEP1,00000\r\n";

不，Putty 没有发送FIN，因为它是一个用户控制的终端，用户（你）没有向它表明不会输入更多文本，所以它只是坐在那里等待发送更多文本。

Answer 2

感谢您的快速响应。我试过这个，但它不起作用。我还研究了 Wireshark 的 Putty 包，最后没有两个额外的字节。