Linux&Windows下的IP Multicast 开发

 Multicast 不用多说，组播，既然要做multicast开发，肯定得知道multicast是什么；
windows和linux下开发的multicast的代码如下，具体的讲解，看代码注释：
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C/C++ code

/*Multicast Client.c support Linux & Windows
*Zhao.kaiyong(a)gmail.com
*http://blog.youkuaiyun.com/openhero
*可以转载，可以复制，修改，如果有修改，请给我来一封email：）谢谢
*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#ifdef _WIN32
#include <winsock2.h>
#include <io.h>
#include <Ws2tcpip.h>

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

#else
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <errno.h>
#define closesocket close
#endif

#define BUF_SIZE 0x1000

char * host_name = "224.1.1.3";
int port = 12345;

int main(int argc, char* argv[])
{
    int loop = 1;
    /* 多播循环 */
    int iter = 0;
    int from_len;
    char buffer[BUF_SIZE];
    int socket_descriptor;
    struct ip_mreq command;
    struct sockaddr_in loc;
    struct sockaddr_in rem;

    int rec_len =0;
    int ptr_point = 0;
    size_t bytes_written = 0;
    int loop_times = 0;

    int rcv_port_0 = 0;
    int rcv_port_1 = 0;
    int first = 0;

#ifdef _WIN32
    WSADATA wsaData;

    if( WSAStartup(MAKEWORD(2,2), &wsaData) != 0 )
    {
        printf("Error in WSAStartup/n");
        exit(1);
    }
#endif

    if (argv[1])
    {
        host_name = argv[1];
        printf("%s /n", host_name);
    }
    if (argv[2])
    {
        port = atoi(argv[2]);
        printf("%d /n", port);
    }

    memset(&loc, 0, sizeof(loc));
    loc.sin_family = AF_INET;
//这个地方很重要，不然linux下就只能是broadcast；所以必须指定组播的地址；
    loc.sin_port = htons(port);
    loc.sin_addr.s_addr = inet_addr(host_name); 

    if((socket_descriptor = socket(AF_INET, SOCK_DGRAM, 0)) == -1)
    { 
        perror("socket");
        exit(EXIT_FAILURE);
    }

    /*can use the same port in the pc*/
    loop = 1;
    if(setsockopt(socket_descriptor, SOL_SOCKET, SO_REUSEADDR, &loop, sizeof(loop)) < 0)
    {
        perror("setsockopt:SO_REUSEADDR./n");
        exit(EXIT_FAILURE);
    }else
    {
        printf("setsockopt:SO_REUSEADDR./n");
    }
    loop = 0x1000000;// 设置网络的接收buffer的大小
    if( setsockopt( socket_descriptor, SOL_SOCKET, SO_RCVBUF, (void *) &loop, sizeof( loop ) ) < 0 )
    {
        perror("setsockopt:SO_RCVBUF./n");
        exit(EXIT_FAILURE);
    }
//由于在前面指定了组播的地址，但是在winodws和linux下不一样，就得这么处理，这个细节来之分析VLC源代码
#if defined( WIN32 ) || defined( UNDER_CE )
    /*
    * Under Win32 and for multicasting, we bind to INADDR_ANY.
    * This is of course a severe bug, since the socket would logically
    * receive unicast traffic, and multicast traffic of groups subscribed
    * to via other sockets. How this actually works in Winsock, I don't
    * know.
    */
    if( IN_MULTICAST( ntohl( loc.sin_addr.s_addr ) ) )
    {
        struct sockaddr_in stupid = loc;
        stupid.sin_addr.s_addr = INADDR_ANY;

        if( bind( socket_descriptor, (struct sockaddr *)&stupid, sizeof( stupid ) ) < 0 )
        {
            perror("bind socket./n");
            close( socket_descriptor );
            return 0;
        }
    }
    else
#endif 
    if(bind(socket_descriptor, (struct sockaddr *)&loc, sizeof(loc)) < 0)
    {
        perror("bind socket./n");
        exit(EXIT_FAILURE);
    }



    { //加入组播组，如果有多块网卡，可以用另一个变量来特别设置；
        printf("%s,%d/n", host_name, port);
        command.imr_multiaddr.s_addr = inet_addr(host_name);
        command.imr_interface.s_addr = htonl(INADDR_ANY);
        if(command.imr_multiaddr.s_addr == -1)
        { 
            perror("224.1.1.3 not a legal multicast address./n");
            exit(EXIT_FAILURE);
        }
        if (setsockopt(socket_descriptor, IPPROTO_IP, IP_ADD_MEMBERSHIP, &command, sizeof(command)) < 0)
        {  
            perror("setsockopt:IP_ADD_MEMBERSHIP. error/n");
        }
    }


    printf("start reciving.../n");


    from_len = sizeof(rem);
    while(1)
    { 
        memset(&rem, 0, from_len); 
        memset(buffer, 0, BUF_SIZE);
        if( (rec_len = recvfrom(socket_descriptor, buffer, sizeof(char) * BUF_SIZE, 0, (struct sockaddr *)&rem, &from_len)) == -1) {
            perror("recvfrom./n");  
        }

        printf( "From   host:%s   port:%d,  len: %d/n", inet_ntoa(rem.sin_addr), ntohs(rem.sin_port), rec_len);       
    }
    if(setsockopt(socket_descriptor, IPPROTO_IP, IP_DROP_MEMBERSHIP, &command, sizeof(command)) < 0) {
        perror("setsockopt:IP_DROP_MEMBERSHIP./n");
    }  
    closesocket(socket_descriptor);
    exit(EXIT_SUCCESS);
}

注：
1.在windows中不需要特殊的设置网络；
2.在Linux下得特别注意网络的设置，有下面几个环节：
1）查看内核模块，是否已经加载了multicast支持；这个可以通过 在src目录下面 make menuconfig 查看ip 设置栏目看到；
2）查看网络是否已经加载了multicast支持；命令：ip a 可以看到现在网络支持的各个功能；
3）添加multicast 网络路由：net add -net 224.0.0.0 netmask 240.0.0.0 dev eth0
这样才能启动网络的multicast路由支持，不然只能当作broadcast处理。