Winsock：UDP recvfrom() 未填写用于发送数据的同一 IP 地址

Question

我正在编写一个 UDP 回显客户端和服务器。这些都是运行在我的机器上。客户端设置为将消息发送到 IP 地址 ::1。此时我的服务器收到消息并应该打印类似的内容。

Processing client at ::1

相反，服务器不断获取不同的 IP 地址。

Processing client at 132:e3d5::

注意：每次收到的IP地址都不一样

这导致了一个问题，因为我相信当我稍后尝试将消息回显给我的客户端时，我无法将它发送到正确的位置，因为我收到的 IP 地址与 ::1 不同.

这是一些代码：

Client.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);
}

Server.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，请告诉我。

Answer 1

你说的对，问题出在这里：

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

你没有超过 sockaddr *，你超过了 struct in6_addr *。只需删除 .sin6_addr 部分：

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

Answer 2

当服务器调用 recvfrom() 时，您在 from 参数中向其传递 in6_addr* 而不是 sockaddr_in6*。您需要传入指向整个 sockaddr_in6 的指针，而不是仅指向其 sin6_addr 字段的指针：

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

服务器也有其他问题。

服务器收到消息后，会调用inet_ntop()将客户端的源IP地址转换为字符串。但是，它传入一个 char*[] 数组，但它需要传入一个 char[] 数组：

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

此外，当打印出收到的消息时，您将其视为以 null 结尾的字符串。在这个例子中这很好，因为您的客户端正在发送一个空终止符，但是对于您的服务器来说，这通常不是一个好主意。这是恶意客户端引起缓冲区溢出攻击的好方法。您应该改用 recvfrom() returns:

的实际字节大小

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

并且在调用 sendto() 将消息回显给客户端时，您应该使用 recvfrom() 报告的实际 fromSize 而不是使用 sizeof(clientInfo) 作为客户端的地址大小：

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

Winsock：UDP recvfrom() 未填写用于发送数据的同一 IP 地址

Winsock: UDP recvfrom() not filling in the same IP address that was used to send data

c

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