c++ udp组播总结

多播，也称为“组播”，将网络中同一业务类型主机进行了逻辑上的分组，进行数据收发的时候其数据仅仅在同一分组中进行，其他的主机没有加入此分组不能收发对应的数据。

却道天凉_好个秋

1030人浏览 · 2023-08-02 21:56:32

却道天凉_好个秋 · 2023-08-02 21:56:32 发布

概念

多播，也称为“组播”，将网络中同一业务类型主机进行了逻辑上的分组，进行数据收发的时候其数据仅仅在同一分组中进行，其他的主机没有加入此分组不能收发对应的数据。

特点

优点
- 具有同种业务的主机加入同一数据流，共享同一通道，节省了带宽；
- 服务器的总带宽不受客户端带宽的限制，服务器端的带宽是常量，与客户端的数量无关；
- 允许在广域网传输；
缺点
- 没有纠错机制；
- 需要路由器和网络协议栈的支持；

流程

发送端

创建socket；

// 第二个参数是 SOCK_DGRAM, 第三个参数0表示使用报式协议中的udp
int socketFd = socket(AF_INET, SOCK_DGRAM, 0);
if(-1 == socketFd)
{
	printf("create udp socket failed\n");
	return -1;
}

bind（可选）

// 使用场景: 使用同一个socketFD接收消息(即recvfrom)
// 说明: 一般将addr.sin_addr.s_addr设置为本机网卡地址
struct sockaddr_in cliaddr;
cliaddr.sin_family = AF_INET;
cliaddr.sin_port = htons(18001);
cliaddr.sin_addr.s_addr = INADDR_ANY;  // ???本地ip
int ret = bind(socketFd, (struct sockaddr*)&cliaddr, sizeof(cliaddr));
if(ret == -1)
{
    printf("udp bind failed\n");
    return -1;
}

加入组播

// 加入到组播
struct ip_mreqn opt;
opt.imr_address.s_addr = htonl(INADDR_ANY);
inet_pton(AF_INET, "224.0.2.23", &opt.imr_multiaddr.s_addr);
setsockopt(fd, IPPROTO_IP, IP_ADD_MEMBERSHIP, &opt, sizeof(opt));

扩展：

1）多播使用的是D类ip地址，即224.0.0.0至239.255.255.255之间的ip地址，并被划分为局部多播地址、预留多播地址和管理权限多播地址3类；

1) 局部多播地址: 在224.0.0.0～224.0.0.255之间，这是为路由协议和其他用途保留的地址，路由器并不转发属于此范围的IP包。
2) 预留多播地址: 在224.0.1.0～238.255.255.255之间，可用于全球范围（如Internet）或网络协议。
3) 管理权限多播地址: 在239.0.0.0～239.255.255.255之间，可供组织内部使用，类似于私有IP地址，不能用于Internet，可限制多播范围。

2）组播的选项值：

getsockopt()/setsockopt()的选项	含义
IP_MULTICAST_TTL	设置多播组数据的TTL值
IP_ADD_MEMBERSHIP	在指定接口上加入组播组
IP_DROP_MEMBERSHIP	退出多播组
IP_MULTICAST_IF	获取默认接口或设置接口
IP_MULTICAST_LOOP	禁止组播数据回送

发送数据

char buf[128] = {0,};
snprintf(buf, sizeof(buf), "Get cpu state,i am %d", sessionKey);
// 发送数据
sendto(socketFd, buf, strlen(buf)+1, 0, (struct sockaddr*)&cliaddr, sizeof(cliaddr));

接收数据（如果设置了bind可直接通过socketFd接收数据）

char buf[128] = {0,};
struct sockaddr_in sinAddr;
socklen_t addrlen = sizeof(sinAddr);
recvfrom(socketFd, buf, sizeof(buf), 0, (struct sockaddr*)&sinAddr, &addrlen);

接收端

创建socket

int socketFd = socket(AF_INET, SOCK_DGRAM, 0);
if(-1 == socketFd)
{
    printf("create udp socket failed\n");
	return -1;
}

bind（必须）

struct sockaddr_in serveraddr;
serveraddr.sin_family = AF_INET;
serveraddr.sin_port = htons(18000);
serveraddr.sin_addr.s_addr = htonl(INADDR_ANY);
int ret = bind(fd, (struct sockaddr*)&serveraddr, sizeof(serveraddr));
if(-1 == ret)
{
    printf("udp bind failed\n");
    return -1;
}

加入组播

struct ip_mreqn opt;
opt.imr_address.s_addr = htonl(INADDR_ANY);
inet_pton(AF_INET, "224.0.2.23", &opt.imr_multiaddr.s_addr);

setsockopt(fd, IPPROTO_IP, IP_ADD_MEMBERSHIP, &opt, sizeof(opt));

接收数据

char buf[128] = {0,};
struct sockaddr_in sinAddr;
socklen_t addrlen = sizeof(sinAddr);
recvfrom(socketFd, buf, sizeof(buf), 0, (struct sockaddr*)&sinAddr, &addrlen);

发送数据

char buf[128] = {0,};
snprintf(buf, sizeof(buf), "Send cpu state,i am %d", sessionKey);
// 发送数据
sendto(socketFd, buf, strlen(buf)+1, 0, (struct sockaddr*)&serveraddr, sizeof(serveraddr));

示例

接收端

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <arpa/inet.h>
#include <net/if.h>

#define TIMEOUT 0xFFFFFFFF 

int main()
{
	// 1. create socket
	int socketFd = socket(AF_INET, SOCK_DGRAM, 0);
	if(-1 == socketFd)
	{
    		printf("create udp socket failed\n");
		return -1;
	}

	// 2. bind
	struct sockaddr_in serveraddr;
	serveraddr.sin_family = AF_INET;
	serveraddr.sin_port = htons(18000);
	serveraddr.sin_addr.s_addr = INADDR_ANY;
	int ret = bind(socketFd, (struct sockaddr*)&serveraddr, sizeof(serveraddr));
	if(-1 == ret)
	{
    		printf("udp bind failed\n");
    		return -1;
	}

	// 3. set param
	// 3.1 ttl
	int ttl = 64;
	setsockopt(socketFd, IPPROTO_IP, IP_MULTICAST_TTL, (char*)&ttl, sizeof(ttl));
	
	// 3.2 timeout
	unsigned int timeout = 2000;
	struct timeval tm;
	if(TIMEOUT == timeout)
	{
		tm.tv_sec = 0x7FFFFFFF;
		tm.tv_usec = 0;
	}
	else
	{
		tm.tv_sec = (timeout&0x7FFFFFFF) / 1000;
		tm.tv_usec = (timeout&0x7FFFFFFF) % 1000 * 1000;
	}
	setsockopt(socketFd, SOL_SOCKET, SO_RCVTIMEO, (char*)&tm, sizeof(tm));

	// 4. join multi 
	struct ip_mreqn opt;
	opt.imr_address.s_addr = INADDR_ANY; // 本地地址
	inet_pton(AF_INET, "224.0.2.23", &opt.imr_multiaddr.s_addr);
	setsockopt(socketFd, IPPROTO_IP, IP_ADD_MEMBERSHIP, &opt, sizeof(opt));

	// 5. recvfrom and sendto
	while(1)
	{
		char recv_buf[128] = {0,};
		int recvlen = recvfrom(socketFd, recv_buf, sizeof(recv_buf), 0, NULL, NULL);
		if(recvlen < 0)
		{
			//printf("server not recv msg,wait...\n");
			continue;
		}

		printf("server recv msg:%s\n", recv_buf);
		sleep(4);
/*
		char send_buf[128] = {0,};
		snprintf(send_buf, sizeof(send_buf), "Send cpu state,i am %d", 1);
		sendto(socketFd, send_buf, sizeof(send_buf), 0, (struct sockaddr*)&serveraddr, sizeof(serveraddr));

		printf("server send msg:%s\n", send_buf);
*/
	}

	return 0;
}

接收端程序运行时打印：

[root@localhost debug.x64-linux-g8]# ./testUdpServer
server recv msg:Send cpu state,i am 1
server recv msg:Send cpu state,i am 1
server recv msg:Send cpu state,i am 1
server recv msg:Send cpu state,i am 1
server recv msg:Send cpu state,i am 1
server recv msg:Send cpu state,i am 1

发送端

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <arpa/inet.h>
#include <net/if.h>

#define TIMEOUT 0xFFFFFFFF 

int main()
{
	// 1. create socket
	int socketFd = socket(AF_INET, SOCK_DGRAM, 0);
	if(-1 == socketFd)
	{
    		printf("create udp socket failed\n");
		return -1;
	}

	// 2. bind
/*
	struct sockaddr_in clientaddr;
	clientaddr.sin_family = AF_INET;
	clientaddr.sin_port = htons(18001);
	clientaddr.sin_addr.s_addr = INADDR_ANY;
	int ret = bind(socketFd, (struct sockaddr*)&clientaddr, sizeof(clientaddr));
	if(-1 == ret)
	{
    		printf("udp bind failed\n");
    		return -1;
	}
*/

	// 3. set param
	// 3.1 ttl
	int ttl = 64;
	setsockopt(socketFd, IPPROTO_IP, IP_MULTICAST_TTL, (char*)&ttl, sizeof(ttl));
	
	// 3.2 timeout
	unsigned int timeout = 2000;
	struct timeval tm;
	if(TIMEOUT == timeout)
	{
		tm.tv_sec = 0x7FFFFFFF;
		tm.tv_usec = 0;
	}
	else
	{
		tm.tv_sec = (timeout&0x7FFFFFFF) / 1000;
		tm.tv_usec = (timeout&0x7FFFFFFF) % 1000 * 1000;
	}
	setsockopt(socketFd, SOL_SOCKET, SO_RCVTIMEO, (char*)&tm, sizeof(tm));

	// 4. set IP_MULTICAST_IF
	struct in_addr opt;
    inet_pton(AF_INET, "224.0.2.23", &opt.s_addr);
    setsockopt(socketFd, IPPROTO_IP, IP_MULTICAST_IF, &opt, sizeof(opt));

    struct sockaddr_in clientaddr;
    clientaddr.sin_family = AF_INET;
    clientaddr.sin_port = htons(18000); 
    inet_pton(AF_INET, "224.0.2.23", &clientaddr.sin_addr.s_addr);

	// 5. recvfrom and sendto
	while(1)
	{
		char send_buf[128] = {0,};
		snprintf(send_buf, sizeof(send_buf), "Send cpu state,i am %d", 1);
		sendto(socketFd, send_buf, sizeof(send_buf), 0, (struct sockaddr*)&clientaddr, sizeof(clientaddr));

		printf("client send msg:%s\n", send_buf);
		sleep(2);
/*
		char recv_buf[128] = {0,};
		struct sockaddr_in sinAddr;
		socklen_t addrlen = sizeof(sinAddr);
		int recvlen = recvfrom(socketFd, recv_buf, sizeof(recv_buf), 0, (struct sockaddr*)&sinAddr, &addrlen);
		if(recvlen < 0)
		{
			printf("client not recv msg,wait...\n");
			continue;
		}

		printf("client recv msg:%s\n", recv_buf);
*/
	}

	return 0;
}

发送端程序运行时打印：

[root@localhost debug.x64-linux-g8]# ./testUdpClient
client send msg:Send cpu state,i am 1
client send msg:Send cpu state,i am 1
client send msg:Send cpu state,i am 1
client send msg:Send cpu state,i am 1
client send msg:Send cpu state,i am 1
client send msg:Send cpu state,i am 1
client send msg:Send cpu state,i am 1
client send msg:Send cpu state,i am 1
client send msg:Send cpu state,i am 1

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