问题描述
我有一个使用WinSock的简单多播写入器和读取器对（下面的代码）。如果未指定要使用的多播IP地址（使用IP_MULTICAST_IF），则可以使用绑定到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，则无法使用INADDR_ANY进行读取。似乎将读取Socker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。这是意外的，因为我认为INADDR_ANY也监听了回送地址。不管使用哪个IP地址发送多播，有没有办法让多播阅读器获取所有多播？
//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 };
const int MC_PORT = 1001;
const int MAX_SEND = 1024;
const in_addr SEND_ADDR = { 127,1 };
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 = { 127,1 };
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,IP_MULTICAST_LOOP,&iLoopOn,sizeof(iLoopOn))) < 0)
{
perror("setsockopt(IP_MULTICAST_LOOP) Failed");
exit(1);
}
/* construct a multicast address structure */
memset(&mc_addr,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,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,(struct sockaddr *) &mc_addr,sizeof(mc_addr))) != send_len)
{
perror("sendto() sent incorrect number of bytes");
exit(1);
}
/* clear send buffer */
memset(send_str,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,"WSAStartup() Failed");
exit(1);
}
/* create socket to join multicast group on */
if ((sock = socket(PF_INET,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,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,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,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,sizeof(recv_str));
from_len = sizeof(from_addr);
memset(&from_addr,from_len);
/* block waiting to receive a packet */
if ((recv_len = recvfrom(sock,recv_str,MAX_RECV,(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,IP_DROP_MEMBERSHIP,(const char*)&mc_req,sizeof(mc_req))) < 0)
{
perror("C setsockopt() Failed");
exit(1);
}
closesocket(sock);
WSACleanup(); /* Cleanup Winsock */
exit(0);
}
解决方法
对于对此感兴趣的其他人，我没有找到一种方法来获取“ ANY”来获取环回多播。我最终决定仅将成员资格添加到ANY适配器和回送地址。接收方代码如下。我确实对127.0.0.1的成员资格有一些疑问，但是忽略错误代码似乎可以使一切正常。
#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 = 2000000;
const char *MC_ADDR = "225.1.1.1";
const char *LB_ADDR = "127.0.0.1";
void PrintSocketError(const char *Prefix)
{
int iLastError = WSAGetLastError();
if (iLastError != 0)
{
fprintf(stderr,"%s: %d\n",Prefix,iLastError);
}
}
int main(int argc,char *argv[])
{
int test;
int recvsize_optval = MAX_RECV;
int sock; /* socket descriptor */
int flag_on = 1; /* socket option flag */
struct sockaddr_in mc_addr; /* socket address structure */
char *recv_str = new char[MAX_RECV+1]; /* buffer to receive string - make it 2MB so we can get packets from Cortex */
int recv_len; /* length of string received */
struct ip_mreq mc_req_any; /* multicast request structure for "ANY" adapter */
struct ip_mreq mc_req_lb; /* multicast request structure for loopback adapter */
struct sockaddr_in from_addr; /* packet source */
int from_len; /* source addr length */
WSADATA wsaData; /* Windows socket DLL structure */
/* Load Winsock 2.0 DLL */
printf("Starting WinSock\n");
if (WSAStartup(MAKEWORD(2,0),&wsaData) != 0)
{
fprintf(stderr,"WSAStartup() failed");
exit(1);
}
/* create socket to join multicast group on */
printf("Creating Socket\n");
if ((sock = socket(AF_INET,SOCK_DGRAM,0)) < 0)
{
PrintSocketError("socket() failed");
exit(1);
}
/* set reuse port to on to allow multiple binds per host */
printf("Reusing Address\n");
if ((setsockopt(sock,SOL_SOCKET,SO_REUSEADDR,(char*)&flag_on,sizeof(flag_on))) < 0)
{
PrintSocketError("SO_REUSEADDR failed");
exit(1);
}
/* construct a socket address structure */
printf("Binding\n");
memset(&mc_addr,sizeof(mc_addr));
mc_addr.sin_family = AF_INET;
mc_addr.sin_addr.s_addr = htonl(INADDR_ANY);
mc_addr.sin_port = htons(MC_PORT);
/* bind to multicast address to socket */
if (bind(sock,(struct sockaddr *) &mc_addr,sizeof(mc_addr)) < 0)
{
PrintSocketError("bind() failed");
goto END;
}
/* ADD MEMBERSHIP to ANY adapter. This appears to not get messages
* sent via 127.0.0.1,so we will add membership to 127.0.0.1 explictly below */
printf("Adding membership to \"ANY\"\n");
inet_pton(AF_INET,MC_ADDR,&mc_req_any.imr_multiaddr.s_addr);
mc_req_any.imr_interface.s_addr = htonl(INADDR_ANY);
if ((setsockopt(sock,IPPROTO_IP,IP_ADD_MEMBERSHIP,(char*)&mc_req_any,sizeof(mc_req_any))) < 0)
{
PrintSocketError("IP_ADD_MEMBERSHIP(ANY) failed");
goto END;
}
/* send an ADD MEMBERSHIP message via setsockopt */
/* buld multicast request structures for "ANY" adapater and loopback adapter */
printf("Adding membership to \"loopback\"\n");
inet_pton(AF_INET,&mc_req_lb.imr_multiaddr.s_addr);
inet_pton(AF_INET,LB_ADDR,&mc_req_lb.imr_interface.s_addr);
if ((setsockopt(sock,(char*)&mc_req_lb,sizeof(mc_req_lb))) < 0)
{
PrintSocketError("IP_ADD_MEMBERSHIP(LB) failed");
//I have seen this generally mean that the membership is alreayd subscribed.
//For some reason ANY subscribed to 127.0.0.1 can take a little while to release.
//Print the error and ignore it
}
// Large 1MB Buffer for receiving so we don't lose data.
printf("Configuring RECV buffer size to %d\n",recvsize_optval);
setsockopt(sock,SO_RCVBUF,(char *)&recvsize_optval,sizeof(recvsize_optval));
getsockopt(sock,NULL);
if (recvsize_optval != 0x100000)
{
printf("ReceiveBuffer size = %d\n",recvsize_optval);
}
for (;;)
{ /* loop forever */
/* clear the receive buffers & structs */
memset(recv_str,sizeof(recv_str));
from_len = sizeof(from_addr);
memset(&from_addr,from_len);
/* block waiting to receive a packet */
if ((recv_len = recvfrom(sock,recv_str,MAX_RECV,(sockaddr*)&from_addr,&from_len)) < 0)
{
char buf[100];
sprintf_s(buf,"recvfrom() failed: %d %d",recv_len,WSAGetLastError());
PrintSocketError(buf);
printf("\n");
goto END;
}
/* output received string */
char strFromAddr[128];
inet_ntop(AF_INET,&from_addr.sin_addr,strFromAddr,sizeof(strFromAddr));
printf("Received %d bytes from %s\n",strFromAddr);
//printf("%s",recv_str);
if (recv_len == 1)
{
printf("exiting\n");
break;
}
}
END:
delete[] recv_str;
printf("cleaning up Winsock\n");
closesocket(sock);//also drops memberships
WSACleanup(); /* Cleanup Winsock */
printf("done!\n");
}