c - 从recvfrom获取错误的IP地址和端口号

Question

无论我的IP和端口是什么，我都会得到以下IP和端口“204.204.204.204@52428”。我使用的是 Windows 10 和 ipv4 地址

#include "stdafx.h"

#undef UNICODE

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

#define DEFAULT_BUFLEN 512
#define DEFAULT_PORT "27015"

int __cdecl main(int argc, char **argv)
{
    WSADATA wsaData;
    int iResult;

    SOCKET ListenSocket = INVALID_SOCKET;
    SOCKET ClientSocket = INVALID_SOCKET;

    struct addrinfo *result = NULL;
    struct addrinfo hints;

    int iSendResult;
    char recvbuf[DEFAULT_BUFLEN];
    int recvbuflen = DEFAULT_BUFLEN;

    // 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_INET;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_protocol = IPPROTO_TCP;
    hints.ai_flags = AI_PASSIVE;

    // Resolve the server address and port
    iResult = getaddrinfo(NULL, argv[1], &hints, &result);
    if (iResult != 0) {
        printf("getaddrinfo failed with error: %d\n", iResult);
        WSACleanup();
        return 1;
    }

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

    // Setup the TCP listening socket
    iResult = bind(ListenSocket, result->ai_addr, (int)result->ai_addrlen);
    if (iResult == SOCKET_ERROR) {
        printf("bind failed with error: %d\n", WSAGetLastError());
        freeaddrinfo(result);
        closesocket(ListenSocket);
        WSACleanup();
        return 1;
    }

    freeaddrinfo(result);

    iResult = listen(ListenSocket, SOMAXCONN);
    if (iResult == SOCKET_ERROR) {
        printf("listen failed with error: %d\n", WSAGetLastError());
        closesocket(ListenSocket);
        WSACleanup();
        return 1;
    }

    // Accept a client socket
    ClientSocket = accept(ListenSocket, NULL, NULL);
    if (ClientSocket == INVALID_SOCKET) {
        printf("accept failed with error: %d\n", WSAGetLastError());
        closesocket(ListenSocket);
        WSACleanup();
        return 1;
    }

    // No longer need server socket
    closesocket(ListenSocket);

    struct sockaddr_in from_addr;
    socklen_t fromlen = sizeof(from_addr);
    char    from_ip[2048] = "";
    int nbytes = 0;

    // Receive until the peer shuts down the connection
    do {

        nbytes = recvfrom(ClientSocket, recvbuf, recvbuflen, 0, (sockaddr *) &from_addr, &fromlen);
        InetNtop(AF_INET, &from_addr.sin_addr, from_ip, sizeof(from_ip));

        if (nbytes > 0) {
            printf("Received %d bytes from %s@%d", nbytes, from_ip, ntohs(from_addr.sin_port));

            // Echo the buffer back to the sender
            iSendResult = send(ClientSocket, recvbuf, nbytes, 0);
            if (iSendResult == SOCKET_ERROR) {
                printf("send failed with error: %d\n", WSAGetLastError());
                closesocket(ClientSocket);
                WSACleanup();
                return 1;
            }
            printf("\tBytes sent: %d\n", iSendResult);
        }
        else if (nbytes == 0)
            printf("Connection closing...\n");
        else  {
            printf("recv failed with error: %d\n", WSAGetLastError());
            closesocket(ClientSocket);
            WSACleanup();
            return 1;
        }
        fromlen = sizeof(from_addr);

    } while (nbytes > 0);

    // shutdown the connection since we're done
    iResult = shutdown(ClientSocket, SD_SEND);
    if (iResult == SOCKET_ERROR) {
        printf("shutdown failed with error: %d\n", WSAGetLastError());
        closesocket(ClientSocket);
        WSACleanup();
        return 1;
    }

    // cleanup
    closesocket(ClientSocket);
    WSACleanup();

    return 0;
}

此 block 中发生打印的位置

    struct sockaddr_in from_addr;
    socklen_t fromlen = sizeof(from_addr);
    char    from_ip[2048] = "";
    int nbytes = 0;

    // Receive until the peer shuts down the connection
    do {

        nbytes = recvfrom(ClientSocket, recvbuf, recvbuflen, 0, (sockaddr *) &from_addr, &fromlen);
        InetNtop(AF_INET, &from_addr.sin_addr, from_ip, sizeof(from_ip));

        if (nbytes > 0) {
            printf("Received %d bytes from %s@%d", nbytes, from_ip, ntohs(from_addr.sin_port));

            // Echo the buffer back to the sender
            iSendResult = send(ClientSocket, recvbuf, nbytes, 0);
            if (iSendResult == SOCKET_ERROR) {
                printf("send failed with error: %d\n", WSAGetLastError());
                closesocket(ClientSocket);
                WSACleanup();
                return 1;
            }
            printf("\tBytes sent: %d\n", iSendResult);
        }
        else if (nbytes == 0)
            printf("Connection closing...\n");
        else  {
            printf("recv failed with error: %d\n", WSAGetLastError());
            closesocket(ClientSocket);
            WSACleanup();
            return 1;
        }
        fromlen = sizeof(from_addr);

    } while (nbytes > 0);

我不知道如何解决这个问题？

Answer 1

不要在 TCP 套接字上调用 recvfrom()。我很惊讶它居然能起作用；我认为它“恢复”为 recv() 行为并忽略源地址和长度参数。

您可以通过 accept() 调用获取对等点的地址信息。