Winsock：UDP recvfrom() 未填寫用於發送數據的相同 IP 地址

Question

我正在編寫 UDP echo 客戶端和服務器。 這些都在我的機器上運行。 客戶端設置為將消息發送到 IP 地址::1。 此時，我的服務器收到消息並應該打印類似的內容。

Processing client at::1

相反，服務器不斷獲得不同的 IP 地址。

Processing client at 132:e3d5::

注意：每次收到的IP地址都不一樣。

這導致了一個問題，因為我相信當我稍后嘗試將消息回顯給我的客戶端時，我無法將其發送到正確的位置，因為我收到的 IP 地址與::1 不同。

這是一些代碼：

客戶端.c

void main(int argc, char* argv[])   // argc is # of strings following command, argv[] is array of ptrs to the strings
{
    WSADATA wsaData;                // contains details about WinSock DLL implementation
    struct sockaddr_in6 serverInfo; // standard IPv6 structure that holds server socket info
    char* serverIPaddr, * phrase, echoBuffer[RCVBUFSIZ];
    int serverPort, msgLen, fromSize, echoLen;

    // Verify correct number of command line arguments
    if (argc != 4) {
        printf("Invalid amount of arguments entered. \nPlease make sure to only enter the following: \n\n <application name> <ip address> <port number> <message>");
        exit(1);
    }

    // Retrieve the command line arguments.
    // to be converted from char to int. 
    serverIPaddr = argv[1];
    serverPort = atoi(argv[2]);
    phrase = argv[3];
    msgLen = strlen(phrase) + 1; // We are sending the null terminator

    // Initialize Winsock 2.0 DLL. 
    if (WSAStartup(MAKEWORD(2, 0), &wsaData) != 0) {
        // Failed
        printf("Couldn't initialize Winsock 2.0 DLL");
        exit(1);
    }

    // Create an IPv6 UPD stream socket.  Now that Winsock DLL is loaded, we can signal any errors as shown on next line:
    int sock;
    sock = socket(AF_INET6, SOCK_DGRAM, IPPROTO_UDP);
    if (sock == INVALID_SOCKET) {
        DisplayFatalErr("socket() function failed.");
        exit(1);
    }
    printf("Socket created successfully. Press enter to continue...");
    getchar();

    memset(&serverInfo, 0, sizeof(serverInfo));
    serverInfo.sin6_family = AF_INET6;
    serverInfo.sin6_port = htons(serverPort);
    inet_pton(AF_INET6, serverIPaddr, &serverInfo.sin6_addr);

    if (msgLen == 0) {
        DisplayFatalErr("Message was empty, please make sure to include a message.");
        exit(1);
    }

    // Send data to server
    if (sendto(sock, phrase, msgLen, 0, (struct sockaddr*) & serverInfo, sizeof(serverInfo)) != msgLen) {
        DisplayFatalErr("sendto() function failed.");
        exit(1);
    }

    fromSize = sizeof(serverInfo);
    if ((echoLen = recvfrom(sock, echoBuffer, RCVBUFSIZ, 0, (struct sockaddr*) & serverInfo.sin6_addr, &fromSize)) != msgLen) {
        // We lost some data check for error first
        if (echoLen < 0) {
            DisplayFatalErr("recvfrom() function failed.");
            exit(1);
        }
    }

    // Output message (Will create soon)

    printf("");
    printf("\nData was received from the server. Press enter to continue...");
    getchar();

    if (closesocket(sock) != 0) {
        DisplayFatalErr("closesocket() function failed.");
    }
    printf("socket closed successfully. Press enter to continue...");
    getchar();

    if (WSACleanup() != 0) {
        DisplayFatalErr("WSACleanup() function failed.");
    }

    exit(0);
}

服務器.c

void main(int argc, char* argv[])   // argc is # of strings following command, argv[] is array of ptrs to the strings
{
    WSADATA wsaData;                // contains details about WinSock DLL implementation
    struct sockaddr_in6 serverInfo; // standard IPv6 structure that holds server socket info
    int serverPort, clientSock, rcvLen, fromSize;
    char* rcvBuffer[RCVBUFSIZ];
    serverPort = 0;

    // Verify correct number of command line arguments
    if (argc != 2) {
        serverPort = DEFAULT_PORT;
    }
    else {
        serverPort = atoi(argv[1]);
    }

    // Initialize Winsock 2.0 DLL
    if (WSAStartup(MAKEWORD(2, 0), &wsaData) != 0) {
        // Failed
        printf("Couldn't initialize Winsock 2.0 DLL");
        exit(1);
    }

    // Create an IPv6 UDP stream socket.
    int sock;
    sock = socket(AF_INET6, SOCK_DGRAM, IPPROTO_UDP);
    if (sock == INVALID_SOCKET) {
        DisplayFatalErr("socket() function failed.");
        exit(1);
    }

    // Don't forget any necessary format conversions.
    memset(&serverInfo, 0, sizeof(serverInfo));
    serverInfo.sin6_family = AF_INET6;
    serverInfo.sin6_port = htons(serverPort);
    serverInfo.sin6_addr = in6addr_any;
    //inet_pton(AF_INET6, serverIPaddr, &serverInfo.sin6_addr);

    // Bind the server socket to the sockadder structure.
    if (bind(sock, (struct sockadder*) & serverInfo, sizeof(serverInfo)) == SOCKET_ERROR) {
        DisplayFatalErr("bind() function failed.");
        exit(1);
    }

    printf("ST's IPv6 echo server is ready for client connection on port: %i\r\n", serverPort);


    // Forever Loop waiting for messages
    for (;;) {
        struct sockaddr_in6 clientInfo; // Hold client port & adder recvfrom
        memset(&clientInfo, 0, sizeof(clientInfo));
        clientInfo.sin6_family = AF_INET6;

        fromSize = sizeof(clientInfo);
        if ((rcvLen = recvfrom(sock, rcvBuffer, RCVBUFSIZ, 0, (struct sockaddr*) & clientInfo.sin6_addr, &fromSize)) < 0) { //THIS IS WHERE I BELIEVE THE ERROR TO BE. WHEN LOOKING AT THE ADDRESS ON THE DEBUGGER IT DOESN'T MATCH THE ONE I SENT USING THE CLIENT
            DisplayFatalErr("recvfrom() function failed.");
        }

        // Processing Socket
        char* clientAddr[INET6_ADDRSTRLEN];
        inet_ntop(AF_INET6, &(clientInfo.sin6_addr), clientAddr, INET6_ADDRSTRLEN);
        int clientPort = ntohs(clientInfo.sin6_port);

        printf("Processing the client at %s, client port %i, server port %i.\r\n", clientAddr, clientPort, serverPort);
        printf("Message Received: %s\r\n", rcvBuffer);
        // Send data back
        if (sendto(sock, rcvBuffer, rcvLen, 0, (struct sockaddr*) & clientInfo, sizeof(clientInfo)) != rcvLen) {
            DisplayFatalErr("sendto() function failed.");
        }
    }
}

如果您需要我提供任何其他信息，請告訴我。

Answer 1

你是對的，問題出在這里：

if ((rcvLen = recvfrom(sock, rcvBuffer, RCVBUFSIZ, 0, (struct sockaddr*) & clientInfo.sin6_addr, &fromSize)) < 0) {
//                                                                                   ^^^^^^^^^^

您沒有傳遞sockaddr * ，而是傳遞了struct in6_addr * 。 只需刪除.sin6_addr部分：

if ((rcvLen = recvfrom(sock, rcvBuffer, RCVBUFSIZ, 0, (struct sockaddr*) & clientInfo, &fromSize)) < 0) {

Answer 2

當服務器調用recvfrom()時，您將在from參數中傳遞一個in6_addr*而不是sockaddr_in6* 。 您需要傳入一個指向整個sockaddr_in6的指針，而不是指向其sin6_addr字段的指針：

recvfrom(..., (struct sockaddr*) &clientInfo, ...) // <-- NOT &clientInfo.sin6_addr!

服務器中還有其他問題。

一旦服務器收到消息，它就會調用inet_ntop()將客戶端的源 IP 地址轉換為字符串。 但是，它傳入了一個char*[]數組，但它需要傳入一個char[]數組：

char clientAddr[INET6_ADDRSTRLEN]; // <-- char, NOT char*!
inet_ntop(AF_INET6, &(clientInfo.sin6_addr), clientAddr, INET6_ADDRSTRLEN);

此外，在打印出接收到的消息時，您會將其視為以空字符結尾的字符串。 在此示例中這很好，因為您的客戶端正在發送 null 終結器，但這對於您的服務器來說通常不是一個好主意。 這是惡意客戶端引發緩沖區溢出攻擊的好方法。 您應該改用recvfrom()返回的實際字節大小：

printf("Message Received: %.*s\r\n", rcvLen, rcvBuffer);

當調用sendto()將消息回顯給客戶端時，您應該使用recvfrom()報告的實際fromSize而不是使用sizeof(clientInfo)作為客戶端的地址大小：

sendto(..., (struct sockaddr*) &clientInfo, fromSize)