c++ - 同一端口但不同接口(interface)上的多个广播接收

Question

如果在 eth0 上接收到广播，如果在 wlan0 上接收到另一个广播，我正在尝试构建一个小型个人 DHCP 服务器来服务于特定范围，但我不能在同一地址上绑定(bind)多个接口(interface):端口组合(255.255.255.255:67)我听说过 SO_REUSABLE 但我不知道如何实现它，当然这是否是实现它的好方法

实际上这是我的代码:

#include <stdio.h>   
#include <string.h> 
#include <stdlib.h> 
#include <arpa/inet.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <netinet/in.h>
#include <errno.h>
#include <fstream>
#include <iostream>
#include <vector>

#define BUFLEN 1024
#define PORT 67
using namespace std;

char *ipAddrFromInterface(char *apInterfaceName) //this function is not from me
{
    return "255.255.255.255";

    /*char *if_name = (char *) apInterfaceName;
    struct ifreq ifr;
    size_t if_name_len = strlen(if_name);

    if(if_name_len < sizeof(ifr.ifr_name))
    {
        memcpy(ifr.ifr_name, if_name, if_name_len);
        ifr.ifr_name[if_name_len] = 0;
    }
    else
        printf("interface name is too long\n");

    int fd = socket(AF_INET, SOCK_DGRAM, 0);

    if(fd == -1)
        printf("A => %s\n", strerror(errno));

    if(ioctl(fd, SIOCGIFADDR, &ifr) == -1)
    {
        int temp_errno = errno;
        close(fd);
        printf("B => %s\n", strerror(temp_errno));
    }

    if(ioctl(fd, SIOCGIFADDR, &ifr) == -1)
    {
        int temp_errno = errno;
        close(fd);
        printf("C => %s\n", strerror(temp_errno));
    }

    close(fd);

    struct sockaddr_in* ipaddr = (struct sockaddr_in*) &ifr.ifr_addr;
    return inet_ntoa(ipaddr->sin_addr);*/
}

struct socketData
{
    int sock;
    sockaddr_in  socket;
    char *interfaceName;
};

void print(int i)
{
    printf("%d\n", i);
    fflush(stdout);
}

void server_receive_thread(vector<char*> aInterfaceList)
{
    int socketIndex = 0;
    struct sockaddr_in  localSock;
    int socketDescriptor; int socketLength;
    vector<socketData> aSockets;

    for( ; socketIndex < aInterfaceList.size(); socketIndex++)
    {
        socketData socketD;
        char *apInterfaceName = aInterfaceList.at(socketIndex);

        if((socketDescriptor = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1)
        {
            printf("can't listen on interface %s... sleeping\n", apInterfaceName);
        }
        else
        {
            memset(&localSock, 0, sizeof(localSock));
            localSock.sin_family = AF_INET;
            localSock.sin_port = htons(PORT);

            inet_aton(ipAddrFromInterface(apInterfaceName), &localSock.sin_addr);
            setsockopt(socketDescriptor, SOL_SOCKET, SO_BINDTODEVICE, apInterfaceName, sizeof(apInterfaceName));

            if(bind(socketDescriptor, (struct sockaddr *) &localSock, sizeof(localSock)) == -1)
            {
                printf("can't bind interface %s to listen on port %d... sleeping\n", apInterfaceName, PORT);
            }
            else
            {
                printf("bound to interface %s on port %d\n", apInterfaceName, PORT);
                socketD.sock = socketDescriptor;
                socketD.socket = localSock;
                socketD.interfaceName = apInterfaceName;
                aSockets.push_back(socketD);
            }
        }
    }

    fd_set master;
    int fdMax = -1;
    while(1)
    {
        FD_ZERO(&master);

        for(int iSock = 0; iSock < aSockets.size(); iSock++)
        {
            socketData d = aSockets.at(iSock);
            FD_SET(d.sock, &master);

            if(d.sock > fdMax)
                fdMax = d.sock;
        }

        printf("fdmax is : ");
        print(fdMax);

        if(select(fdMax + 1, &master, NULL, NULL, NULL) == -1)
            print(2);

        print(200);

        for(int iSock = 0; iSock < aSockets.size(); iSock++)
        {
            socketData d = aSockets.at(iSock);

            if(FD_ISSET(d.sock, &master))
                print(3);
        }
        print(1);
    }
}

int main()
{
    std::vector<char*>  interfaceList;
    interfaceList.push_back("wlan0");
    interfaceList.push_back("eth0");
    server_receive_thread(interfaceList);
    return 0;
}

Answer 1

您不需要每个接口(interface)一个套接字。只需将一个套接字绑定(bind)到 0.0.0.0 和所需的端口。然后它将通过所有接口(interface)接收。您当然不能也不需要绑定(bind)到 255.255.255.255。

或者，将其绑定(bind)到连接到您要服务的范围的单个 IP 地址。