【发布时间】：2020-10-15 20:56:44
【问题描述】：
我有一个使用 WinSock 的简单多播写入器和读取器对（代码如下）。如果我没有指定多播的 IP 地址（使用 IP_MULTICAST_IF），我可以使用绑定到 INADDR_ANY 的套接字读取多播。如果我使用 IP_MULTICAST_IF 通过 127.0.0.1 发送多播，则使用 INADDR_ANY 读取不起作用。似乎将读取套接字绑定到 127.0.0.1 是查看通过 127.0.0.1 发送的多播的唯一方法。这是出乎意料的，因为我认为 INADDR_ANY 也监听了环回地址。有没有办法让多播阅读器获取所有多播，而不管使用哪个 IP 地址发送多播？
//CODE FOR MULTICAST WRITER
#include <sys/types.h> /* for type definitions */
#include <winsock2.h> /* for win socket API calls */
#include <ws2tcpip.h> /* for win socket structs */
#include <stdio.h> /* for printf() */
#include <stdlib.h> /* for atoi() */
#include <string.h> /* for strlen() */
const in_addr MC_ADDR = { 225, 1, 1, 1 };
const int MC_PORT = 1001;
const int MAX_SEND = 1024;
const in_addr SEND_ADDR = { 127, 0, 0, 1 };
int main(int argc, char *argv[])
{
int sock; /* socket descriptor */
char send_str[MAX_SEND]; /* string to send */
struct sockaddr_in mc_addr; /* socket address structure */
int send_len; /* length of string to send */
WSADATA wsaData; /* Windows socket DLL structure */
/* Load Winsock 2.0 DLL */
if (WSAStartup(MAKEWORD(2, 0), &wsaData) != 0)
{
fprintf(stderr, "WSAStartup() failed");
exit(1);
}
/* create a socket for sending to the multicast address */
if ((sock = socket(PF_INET, SOCK_DGRAM, 0)) < 0)
{
perror("socket() failed");
exit(1);
}
#if 1 //IF THIS IS DEFINED THE MULTICAST READER UST BE LISTENING TO 127.0.0.1
// Configure Multicast
in_addr myAddress = { 127, 0, 0, 1 };
if (setsockopt(sock, IPPROTO_IP, IP_MULTICAST_IF, (char*)&myAddress, sizeof(myAddress)) < 0)
{
perror("setsockopt(IP_MULTICAST_IF) failed");
exit(1);
}
#endif
char iLoopOn = 1;
if ((setsockopt(sock, IPPROTO_IP, IP_MULTICAST_LOOP, &iLoopOn, sizeof(iLoopOn))) < 0)
{
perror("setsockopt(IP_MULTICAST_LOOP) failed");
exit(1);
}
/* construct a multicast address structure */
memset(&mc_addr, 0, sizeof(mc_addr));
mc_addr.sin_family = AF_INET;
mc_addr.sin_addr = MC_ADDR;
mc_addr.sin_port = htons(MC_PORT);
printf("Begin typing (return to send, ctrl-C to quit):\n");
/* clear send buffer */
memset(send_str, 0, sizeof(send_str));
while (fgets(send_str, MAX_SEND, stdin))
{
send_len = strlen(send_str);
/* send string to multicast address */
if ((sendto(sock, send_str, send_len, 0,
(struct sockaddr *) &mc_addr,
sizeof(mc_addr))) != send_len)
{
perror("sendto() sent incorrect number of bytes");
exit(1);
}
/* clear send buffer */
memset(send_str, 0, sizeof(send_str));
}
closesocket(sock);
WSACleanup(); /* Cleanup Winsock */
exit(0);
}
//CODE FOR MULTICAST READER
#include <sys/types.h> /* for type definitions */
#include <winsock2.h> /* for win socket API calls */
#include <ws2tcpip.h> /* for win socket structs */
#include <stdio.h> /* for printf() and fprintf() */
#include <stdlib.h> /* for atoi() */
#include <string.h> /* for strlen() */
const int MC_PORT = 1001;
const int MAX_RECV = 1024;
const ULONG MC_ADDR = inet_addr("225.1.1.1");
#if 0 //THIS_IS_REQUIRED_WHEN_MULTICASTING_TO_127001
const ULONG MY_ADDR = inet_addr("127.0.0.1");
#else
const ULONG MY_ADDR = htonl(INADDR_ANY);
#endif
int main(int argc, char *argv[])
{
int sock; /* socket descriptor */
int flag_on = 1; /* socket option flag */
struct sockaddr_in mc_addr; /* socket address structure */
char recv_str[MAX_RECV+1]; /* buffer to receive string */
int recv_len; /* length of string received */
struct ip_mreq mc_req; /* multicast request structure */
struct sockaddr_in from_addr; /* packet source */
int from_len; /* source addr length */
WSADATA wsaData; /* Windows socket DLL structure */
/* Load Winsock 2.0 DLL */
if (WSAStartup(MAKEWORD(2, 0), &wsaData) != 0)
{
fprintf(stderr, "WSAStartup() failed");
exit(1);
}
/* create socket to join multicast group on */
if ((sock = socket(PF_INET, SOCK_DGRAM, 0)) < 0)
{
perror("socket() failed");
exit(1);
}
/* set reuse port to on to allow multiple binds per host */
if ((setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (char*)&flag_on, sizeof(flag_on))) < 0)
{
perror("SO_REUSEADDR failed");
exit(1);
}
/* construct a multicast address structure */
memset(&mc_addr, 0, sizeof(mc_addr));
mc_addr.sin_family = AF_INET;
mc_addr.sin_addr.s_addr = MY_ADDR;
mc_addr.sin_port = htons(MC_PORT);
/* bind to multicast address to socket */
if (bind(sock, (struct sockaddr *) &mc_addr, sizeof(mc_addr)) < 0)
{
perror("bind() failed");
exit(1);
}
/* construct an IGMP join request structure */
mc_req.imr_multiaddr.s_addr = MC_ADDR;
mc_req.imr_interface.s_addr = MY_ADDR;
/* send an ADD MEMBERSHIP message via setsockopt */
if ((setsockopt(sock, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char*)&mc_req, sizeof(mc_req))) < 0)
{
perror("B setsockopt() failed");
exit(1);
}
for (;;)
{ /* loop forever */
/* clear the receive buffers & structs */
memset(recv_str, 0, sizeof(recv_str));
from_len = sizeof(from_addr);
memset(&from_addr, 0, from_len);
/* block waiting to receive a packet */
if ((recv_len = recvfrom(sock, recv_str, MAX_RECV, 0, (struct sockaddr*)&from_addr, &from_len)) < 0)
{
perror("recvfrom() failed");
exit(1);
}
/* output received string */
printf("Received %d bytes from %s: ", recv_len, inet_ntoa(from_addr.sin_addr));
printf("%s", recv_str);
}
/* send a DROP MEMBERSHIP message via setsockopt */
if ((setsockopt(sock, IPPROTO_IP, IP_DROP_MEMBERSHIP, (const char*)&mc_req, sizeof(mc_req))) < 0)
{
perror("C setsockopt() failed");
exit(1);
}
closesocket(sock);
WSACleanup(); /* Cleanup Winsock */
exit(0);
}
【问题讨论】：
-
@rustyx 哦，对不起。我没有仔细检查代码，你是对的。很可能是你提到的原因。但无论如何，Windows 网络堆栈有点不同，TBH 我也从未在 *ix 系统上尝试过。
-
我正在使用 IP_MULTICAST_LOOP 来启用多播到发送方的环回。我不确定我是否需要在其他地方这样做。
-
为什么要将 IP_MULTICAST_IF 设置为 127.0.0.1？解决方案：不要。您是多播还是发送到本地主机？
-
原因是我有一个应用程序，它使用多播来传输可以被第三方应用程序获取的数据。有时该第三方应用程序驻留在同一台机器上。
标签： c++ sockets winsock multicast