C语言 无法使用UDP进行双向多播连接

Question

必须让它成为server &客户端是双向的，我应该能够发送&在控制台接收数据

我可以从服务器发送数据到客户端，但不能从客户端接收任何数据。在此卡了很长时间不知道如何解决

我刚开始做网络工作，这方面的任何线索都很有帮助。

这是我的代码。

Server.c

#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>
struct in_addr localInterface;
struct sockaddr_in groupSock, rcv_addr;
int sd;
char databuf[1024];
int datalen = sizeof(databuf);
int main(int argc, char *argv[])
{
/* Create a datagram socket on which to send. */
socklen_t rcv_addr_size = sizeof(struct sockaddr_in);
sd = socket(AF_INET, SOCK_DGRAM, 0);
if (sd < 0)
{
perror("Opening datagram socket error");
exit(1);
}
else
printf("Opening the datagram socket...OK.n");
memset((char*) &groupSock, 0, sizeof(groupSock));
groupSock.sin_family = AF_INET;
groupSock.sin_addr.s_addr = inet_addr("226.1.1.1");
groupSock.sin_port = htons(4321);
localInterface.s_addr = inet_addr("127.0.0.1");
if (setsockopt(sd, IPPROTO_IP, IP_MULTICAST_IF, (char*) &localInterface,
sizeof(localInterface)) < 0) {
perror("Setting local interface error");
exit(1);
} else
printf("Setting the local interface...OKn");
int read_size;
while (1) {
memset(databuf, 0x00, sizeof(databuf));
scanf("%s", databuf);
datalen = strlen(databuf) + 1;
if (sendto(sd, databuf, datalen, 0, (struct sockaddr*) &groupSock,
sizeof(groupSock)) < 0)
datalen = 1024;
memset(databuf, 0x00, sizeof(databuf));
read_size = recvfrom(sd, databuf, datalen, 0,
(struct sockaddr*) &rcv_addr, &rcv_addr_size);
printf("The message from multicast ckient is: "%s"n", databuf);
}
return 0;
}

client.c

#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>
struct sockaddr_in localSock, rcv_addr;
struct ip_mreq group;
int sd;
int datalen;
char databuf[1024];
int main(int argc, char *argv[]) {
/* Create a datagram socket on which to receive. */
socklen_t rcv_addr_size = sizeof(struct sockaddr_in);
sd = socket(AF_INET, SOCK_DGRAM, 0);
if (sd < 0) {
perror("Opening datagram socket error");
exit(1);
}
else
printf("Opening datagram socket....OK.n");
{
int reuse = 1;
if (setsockopt(sd, SOL_SOCKET, SO_REUSEADDR, (char*) &reuse,
sizeof(reuse)) < 0) {
perror("Setting SO_REUSEADDR error");
close(sd);
exit(1);
} else
printf("Setting SO_REUSEADDR...OK.n");
}
memset((char*) &localSock, 0, sizeof(localSock));
localSock.sin_family = AF_INET;
localSock.sin_port = htons(4321);
localSock.sin_addr.s_addr = INADDR_ANY;
if (bind(sd, (struct sockaddr*) &localSock, sizeof(localSock))) {
perror("Binding datagram socket error");
close(sd);
exit(1);
} else
printf("Binding datagram socket...OK.n");
group.imr_multiaddr.s_addr = inet_addr("226.1.1.1");
group.imr_interface.s_addr = INADDR_ANY;
if (setsockopt(sd, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char*) &group,
sizeof(group)) < 0) {
perror("Adding multicast group error");
close(sd);
exit(1);
} else
printf("Adding multicast group...OK.n");
int read_size;
while (1) {
datalen = 1024;
memset(databuf, 0x00, sizeof(databuf));
read_size = recvfrom(sd, databuf, datalen, 0,
(struct sockaddr*) &rcv_addr, &rcv_addr_size);
printf("The message from multicast server is: "%s"n", databuf);
memset(databuf, 0x00, sizeof(databuf));
scanf("%s", databuf);
datalen = strlen(databuf) + 1;
if (sendto(sd, databuf, datalen, 0, (struct sockaddr*) &localSock,
sizeof(localSock)) < 0)
break;
}
return 0;
}

Answer 1

您的服务器发送到错误的地址。

服务器使用localSock作为sendto的目的地址:

if(sendto(sd, databuf, datalen, 0, (struct sockaddr*)&localSock, sizeof(localSock)) < 0)

但是你把地址设为0:

localSock.sin_family = AF_INET;
localSock.sin_port = htons(4321);
localSock.sin_addr.s_addr = INADDR_ANY;

您想要使用rcv_addr，它被填充为recvfrom的源地址。使用此地址作为目的地将把响应发送回它的来源:

if(sendto(sd, databuf, datalen, 0, (struct sockaddr*)&rcv_addr, sizeof(rcv_addr)) < 0)

Answer 2

多播连接就像广播通信，您将数据包发送到接收者的论坛，等待读取它，然后他们消费它(如果它到达)。这通常意味着您必须安排双向连接，允许所有人在房间里走动并选择自己的响应，因为每个人都在多播频道中与每个人交谈。想象一下，您正在IRC频道中聊天，您必须与某人安排如何将消息直接发送给该个人，但是任何人都可以以他们想要的方式回复这些消息。你必须一直考虑你说的话，你对那个多播频道中订阅的每个人说的话，所以通常你会收到几个响应包，你必须从中选择…