UDP定向广播(WinSock2)失败

Question

首先，让我说，这是我第一次进入C世界后，经过了20+多年的组装编程为PLC和MicroControllers。

我试图将UDP数据报发送到网络广播地址，在本例中是192.168.1.255。

我得到的错误是错误代码10049 (来自WSAGetLastError())的绑定失败。从附加的代码中可以看到，我已经创建了套接字，填充了sockaddr_in，并将setsockopt()创建为SO_BROADCAST。

对于我的生活，我不知道我做错了什么，任何指点都会被感激地接受。

iResult = WSAStartup(MAKEWORD(2, 2), &wsaTxData);
if (iResult != NO_ERROR)
{
    WSAErrorString("WSAStartup for TX failed");
    return(-1);
}
XPLMDebugString("UDP Server: WSAStartup TX complete.\n");

if ((BeaconSocket = socket(AF_INET, SOCK_DGRAM, 0)) == INVALID_SOCKET) {
    WSAErrorString("UDP Server: Could not create BECN socket");
    return(-1);
}

// setup the sockaddr_in structure
//
si_beacon.sin_family = AF_INET;
si_beacon.sin_addr.s_addr = inet_addr("192.168.1.255");
si_beacon.sin_port = htons(_UDP_TX_PORT);

// setup to broadcast
//
char so_broadcast_enabled = '1';
if (setsockopt(BeaconSocket, SOL_SOCKET, SO_BROADCAST, &so_broadcast_enabled, sizeof(so_broadcast_enabled)) == SOCKET_ERROR) {
    WSAErrorString("Error in setting Broadcast option");
    closesocket(BeaconSocket);
    return(-1);
}

// bind our socket
//
if (bind(BeaconSocket, (struct sockaddr *)&si_beacon, sizeof(si_beacon)) == SOCKET_ERROR)
{
    char buf[256];
    WSAErrorString("Bind to socket for UDP beacon failed");
    sprintf(buf, "Port %u, address %s\n", ntohs(si_beacon.sin_port), inet_ntoa(si_beacon.sin_addr));
    XPLMDebugString(buf);
    return(-1);
}

// start the UDP beacon
//
udp_becn_thread_id = CreateThread(NULL, 0, BeaconThread, NULL, 0, NULL);
if (!udp_becn_thread_id) {
    WSAErrorString("UDP Server: Error starting UDP Beacon");
    return (-1);
}

XPLMDebugString("UDP Server: bind complete. beacon ACTIVE.\n");


return(0);

Answer 1

问题在于IP地址本身。

我将代码复制到我的计算机上(对其做了一些修改以使其编译)，并得到了错误：

UDP Server: WSAStartup TX complete.
Bind to socket for UDP beacon failed
Port 47977, address 192.168.1.255

然后，我改变了行文：

si_beacon.sin_addr.s_addr = inet_addr("192.168.1.255");

至

si_beacon.sin_addr.s_addr = inet_addr("192.168.0.127");

当我再次运行它时，一切正常：

UDP Server: WSAStartup TX complete.
Done successfully

问题是，“绑定”地址需要是本地网络上的您的计算机地址。而不是远程客户端。

另一种选择是使用地址：

si_beacon.sin_addr.s_addr = inet_addr("0.0.0.0");

它同时绑定到计算机上的所有网络接口。

作为参考，下面是我使用的代码的版本：

#define _WINSOCK_DEPRECATED_NO_WARNINGS
#include <stdio.h>
#include <string.h>

#include <WinSock2.h>
#include <WS2tcpip.h> // For inet_pton

#pragma comment(lib, "ws2_32.lib")

int main()
{
    {
        WSADATA wsaTxData;
        memset(&wsaTxData, 0, sizeof(WSADATA));
        const int iResult = WSAStartup(MAKEWORD(2, 2), &wsaTxData);
        if (iResult != NO_ERROR)
        {
            printf("%s", "WSAStartup for TX failed.\n");
            return -1;
        }
        printf("%s", "UDP Server: WSAStartup TX complete.\n");
    }

    SOCKET BeaconSocket;
    memset(&BeaconSocket, 0, sizeof(SOCKET));

    if ((BeaconSocket = socket(AF_INET, SOCK_DGRAM, 0)) == INVALID_SOCKET) {
        printf("%s", "UDP Server: Could not create BECN socket\n");
        return -1;
    }

    // setup the sockaddr_in structure
    //
    sockaddr_in si_beacon;
    memset(&si_beacon, 0, sizeof(sockaddr_in));
    si_beacon.sin_family = AF_INET;
    si_beacon.sin_addr.s_addr = inet_addr("0.0.0.0");
    const unsigned short port_num = 0xbb69;
    si_beacon.sin_port = htons(port_num);

    // setup to broadcast
    //
    char so_broadcast_enabled = '1';
    if (setsockopt(BeaconSocket, SOL_SOCKET, SO_BROADCAST, &so_broadcast_enabled, sizeof(so_broadcast_enabled)) == SOCKET_ERROR) {
        printf("%s", "Error in setting Broadcast option\n");
        closesocket(BeaconSocket);
        return(-1);
    }

    // bind our socket
    //
    if (bind(BeaconSocket, (struct sockaddr*)&si_beacon, sizeof(si_beacon)) == SOCKET_ERROR)
    {
        char buf[256];
        printf("%s", "Bind to socket for UDP beacon failed\n");
        sprintf_s(buf, "Port %u, address %s\n", ntohs(si_beacon.sin_port), inet_ntoa(si_beacon.sin_addr));
        printf("%s", buf);
        return(-1);
    }

    printf("%s", "Done successfully");

    return 0;
}