[英]How to have two multicast sockets listen to two multicast channels with same port
我大致具有以下多播套接字代碼。 工作正常。 現在我需要在同一台機器上加入兩個多播通道,例如224.10.13.18-55001 224.10.13.34-55001
並且取決於它來自哪個IP地址,我需要對消息進行不同的處理。
問題是如何為端口值相同的多播通道使用創建兩個套接字,以便每個套接字僅返回對發送到該通道的數據的讀取。
/* create socket to join multicast group on */
socket_file_descriptor_ = socket ( AF_INET, SOCK_DGRAM, IPPROTO_UDP );
if ( socket_file_descriptor_ < 0 )
{ // fprintf ( stderr, "cannot open socket \n");
exit(1);
}
/* set reuse port to on to allow multiple binds per host */
{
int flag_on = 1;
if ( ( setsockopt ( socket_file_descriptor_, SOL_SOCKET, SO_REUSEADDR, &flag_on,
sizeof(flag_on) ) ) < 0 )
{ // fprintf ( stderr, "MulticastReceiverSocket setsockopt() SOL_SOCKET SO_REUSEADDR failed\n");
exit(1);
}
}
struct ip_mreq mc_req;
inet_pton ( AF_INET, listen_ip_.c_str(), &(mc_req.imr_multiaddr.s_addr) );
mc_req.imr_interface.s_addr = htonl(INADDR_ANY);
/* send an ADD MEMBERSHIP message via setsockopt */
if ( ( setsockopt ( socket_file_descriptor_, IPPROTO_IP, IP_ADD_MEMBERSHIP,
(void*) &mc_req, sizeof(mc_req))) < 0)
{ // std::cerr << "setsockopt() failed in IP_ADD_MEMBERSHIP " << listen_ip_ << ": "<< listen_port_ << std::endl;
exit(1);
}
/* construct a multicast address structure */
struct sockaddr_in mcast_Addr;
bzero ( &mcast_Addr, sizeof(mcast_Addr) );
mcast_Addr.sin_family = AF_INET;
mcast_Addr.sin_addr.s_addr = htonl(INADDR_ANY);
mcast_Addr.sin_port = htons ( listen_port_ );
/* bind to specified port onany interface */
if ( bind ( socket_file_descriptor_, (struct sockaddr *) &mcast_Addr, sizeof ( struct sockaddr_in ) ) < 0 )
{ // fprintf ( stderr, "%s cannot bind %s:%d \n", "MulticastReceiverSocket", listen_ip_.c_str(), listen_port_ ) ;
exit(1);
}
您只需要一個插座即可。 如果在對setsockopt
的調用上設置IP_PKTINFO
選項,則可以使用recvmsg
獲取struct in_pktinfo
,該struct in_pktinfo
將包含目標IP地址。 然后,您可以基於此選擇如何處理數據包。
從https://stackoverflow.com/a/5309155/1687119借用(為簡潔起見,已刪除錯誤檢查):
// sock is bound AF_INET socket, usually SOCK_DGRAM
// include struct in_pktinfo in the message "ancilliary" control data
setsockopt(sock, IPPROTO_IP, IP_PKTINFO, &opt, sizeof(opt));
// the control data is dumped here
char cmbuf[0x100];
// the remote/source sockaddr is put here
struct sockaddr_in peeraddr;
// if you want access to the data you need to init the msg_iovec fields
struct msghdr mh = {
.msg_name = &peeraddr,
.msg_namelen = sizeof(peeraddr),
.msg_control = cmbuf,
.msg_controllen = sizeof(cmbuf),
};
recvmsg(sock, &mh, 0);
for ( // iterate through all the control headers
struct cmsghdr *cmsg = CMSG_FIRSTHDR(&mh);
cmsg != NULL;
cmsg = CMSG_NXTHDR(&mh, cmsg))
{
// ignore the control headers that don't match what we want
if (cmsg->cmsg_level != IPPROTO_IP ||
cmsg->cmsg_type != IP_PKTINFO)
{
continue;
}
struct in_pktinfo *pi = CMSG_DATA(cmsg);
// at this point, peeraddr is the source sockaddr
// pi->ipi_spec_dst is the destination in_addr
// pi->ipi_addr is the receiving interface in_addr
}
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