Question

我正在尝试使用Winsock2 API学习网络编程的基础知识。我已经成功地通过LAN IP地址进行了连接，但是在过去的一天中，我一直在努力使客户端通过其公共IP连接到我的服务器。

我已经在路由器上设置了端口转发，甚至还使用Wireshark来监视客户端连接请求。我在Wireshark中看到了请求，但是它从未连接到服务器，最终出现了超时错误。

我很茫然，我感谢任何能为我指出正确方向的人！

这是客户端实现：

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

#pragma comment(lib, "Ws2_32.lib")



#define DEFAULT_PORT //MY PORT
#define DEFAULT_BUFLEN 512
#define SERVER_IPV4 //"MY PUBLIC IP STRING"


int main(int argc, char **argv)
{

    //wsaData to hold Winsock dll information
    WSADATA wsaData;
    WORD wVersionRequired = MAKEWORD(2, 2);

    //Attempts to load winsock dll matching required version and fills WSADATA object
    int wsaInit = WSAStartup(wVersionRequired, &wsaData);
    if(wsaInit != 0)
    {
        printf("WSAStartup failed with error code: %d\n", wsaInit);
    }

    //If dll fails to load correct version free winsock dll resources
    if(wsaData.wHighVersion != wVersionRequired)
    {
        printf("No usable version of Winsock.dll found\n");
        WSACleanup();
        return 1;
    }
    else
    {
        printf("Winsock dll 2.2 loaded correctly\n");
    }


    /**********************Socket Code Here**********************/

    SOCKADDR_IN SockAddrIP4;
    SockAddrIP4.sin_family = AF_INET;
    SockAddrIP4.sin_addr.s_addr = inet_addr(SERVER_IPV4);
    SockAddrIP4.sin_port = htons(DEFAULT_PORT);

    /**************Create Socket****************/

    //INVALID_SOCKET used like NULL
    SOCKET ConnectSocket = INVALID_SOCKET;

    // TODO(baruch): Only supporting IP_V4
    ConnectSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

    if(ConnectSocket == INVALID_SOCKET)
    {
        printf("socket() error: %ld\n", WSAGetLastError());
        //clean up address info after getaddrinfo function when socket fails
        WSACleanup();
        return 1;
    }

    /*****************Connect to socket**************/

    int connectResult = connect(ConnectSocket, (SOCKADDR*)&SockAddrIP4, sizeof(SOCKADDR_IN));
    if(connectResult == SOCKET_ERROR)
    {
        printf("Connect failed with error: %d\n", WSAGetLastError());
        closesocket(ConnectSocket);
        ConnectSocket = INVALID_SOCKET;
    }
    else
    {
        printf("Connected with server: %s\n", SERVER_IPV4);
    }

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

    /*************END of Socket CODE CLEANUP********/

    // TODO(baruch): close socket
    WSACleanup();

}

这是服务器：

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

#pragma comment(lib, "Ws2_32.lib")

// TODO(baruch): Only supporting ascii consider Unicode later
#undef UNICODE

#define DEFAULT_PORT //My Port
#define DEFAULT_BUFLEN 512

int main(int argc, char **argv)
{

    //wsaData to hold Winsock dll information
    WSADATA wsaData;
    WORD wVersionRequired = MAKEWORD(2, 2);


    int wsaInit = WSAStartup(wVersionRequired, &wsaData);
    if(wsaInit != 0)
    {
        printf("WSAStartup failed with error code: %d\n", wsaInit);
    }

    //If dll fails to load correct version free winsock dll resources
    if(wsaData.wHighVersion != wVersionRequired)
    {
        printf("No usable version of Winsock.dll found\n");
        WSACleanup();
        return 1;
    }
    else
    {
        printf("Winsock dll 2.2 loaded correctly\n");
    }

    /**********************Socket Code Here**********************/


    /**************Create Socket****************/
    SOCKADDR_IN SockAddrIP4;
    SockAddrIP4.sin_family = AF_INET;
    SockAddrIP4.sin_addr.s_addr = INADDR_ANY;
    SockAddrIP4.sin_port = htons(DEFAULT_PORT);

    //INVALID_SOCKET used like NULL
    SOCKET ListenSocket = INVALID_SOCKET;

    // TODO(baruch): Only supporting IP_V4
    // Socket for server to listen on for client connections
    ListenSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

    if(ListenSocket == INVALID_SOCKET)
    {
        printf("socket() error: %ld\n", WSAGetLastError());
        //clean up address info after getaddrinfo function when socket fails
        WSACleanup();
        return 1;
    }

    /**************Bind Socket******************/
    int bindResult = bind(ListenSocket, (SOCKADDR*)&SockAddrIP4, sizeof(SOCKADDR_IN));
    if(bindResult == SOCKET_ERROR)
    {
        printf("failed to bind with error: %d\n", WSAGetLastError());
        closesocket(ListenSocket);
        WSACleanup();
        return 1;
    }

    /************Listen for Connections**********/
    int listenResult = listen(ListenSocket, SOMAXCONN);
    if(listenResult == SOCKET_ERROR)
    {
        printf("Listen failed, error: %d\n", WSAGetLastError() );
        WSACleanup();
        return 1;
    }
    else
    {
        printf("Now listening for client connections...\n");
    }
    /************Accept and Handle CLient Connections***********/
    // TODO(baruch): For testing, only allowing a single client. Eventually need to create a loop to handle all client connections.
    SOCKET ClientSocket;
    SOCKADDR_IN connectedAddress;
    int addressLength = sizeof(connectedAddress);
    ClientSocket = accept(ListenSocket, (SOCKADDR *) &connectedAddress, &addressLength);
    if(ClientSocket == SOCKET_ERROR)
    {
        printf("Accept failed, error: %d\n", WSAGetLastError());
        closesocket(ListenSocket);
        WSACleanup();
        return 1;
    }
    else
    {
        //inet_ntoa converts ip address to binary format.
        char *clientIp = inet_ntoa(connectedAddress.sin_addr);
        // TODO(baruch): Make sure this string correctly prints address
        printf("Client connection from: %s accepted\n", clientIp);
    }

    /**********Handle inbound and outbound data**********/

    char inBuf[DEFAULT_BUFLEN];
    int dataBufLen = DEFAULT_BUFLEN;
    int inDataResult, outDataResult;

    do
    {
        inDataResult = recv(ClientSocket, inBuf, dataBufLen, 0);
        if(inDataResult > 0)
        {
            printf("Number of bytes received: %d", inDataResult);

            //Confirm to client message received
            char confirmReceipt[] = "\nMessage received!\n";
            outDataResult =
                send(ClientSocket, confirmReceipt, sizeof(confirmReceipt), 0);
            if(outDataResult == SOCKET_ERROR)
            {
                printf("Confirmation message failed with error: %d\n", WSAGetLastError());
                closesocket(ClientSocket);
                WSACleanup();
                return 1;
            }
            else
            {
                printf("Confirmation message sent\n");
            }
        }
        else if(inDataResult == 0)
        {
            printf("Connection closing\n");
        }
        else
        {
            printf("Data receipt failed with error: %d\n", WSAGetLastError());
            closesocket(ClientSocket);
            WSACleanup();
            return 1;
        }

    } while(inDataResult > 0);

    //Shutdown sending portion of socket, can still receive data
    int shutDownResult = shutdown(ClientSocket, SD_SEND);
    if(shutDownResult == SOCKET_ERROR)
    {
        printf("Shutdown failure, error: %d\n", WSAGetLastError());
        closesocket(ClientSocket);
        WSACleanup();
        return 1;
    }


    /*************End Socket Code Clean up Winsock dll**********/

    closesocket(ClientSocket);
    WSACleanup();
}

Answer 1

如果您可以通过本地LAN IP地址而不是公共IP地址进行连接，则可能是这些问题之一。

您是否使程序能够通过Windows防火墙？完全关闭Windows防火墙（暂时）以确保安全。
如果您的客户端和服务器都在同一个NAT之后，则您的NAT可能不允许客户端连接通过公用IP地址进行连接。这称为NAT hairpinning。并非所有NAT都支持此功能。验证是否可以通过服务器网络外部的客户端连接到服务器的IP地址。
如有疑问，请使用netcat之类的简单程序来测试PC之间的套接字连接。简单的测试就是在端口上以侦听模式运行nc，然后使用nc的另一个实例连接到它。在Internet上搜索“用于Windows的Netcat”。如果可以通过netcat连接到端口，但不能通过客户端/服务器代码连接，则代码出现问题。如果您无法通过netcat连接到端口，则可能是防火墙或网络配置错误。

Answer 2

多亏了Selbie，我得以经历了淘汰的过程，并确定我的服务有问题。我联系了我的ISP，他们不得不更改服务类型并给我一个真实的公共IP。默认情况下，它们使用运营商级NAT，这意味着为居住站点分配了专用IP，该IP由ISP网络中的“中间盒网络地址转换器”转换为公用IP。谢谢！

C ++ Winsock2客户端未通过远程IP连接到服务器

2 个答案: