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 socketint socketFd = socket(AF_INET, SOCK_DGRAM, 0);if(-1 == socketFd){printf("create udp socket failed\n");return -1;}// 2. bindstruct 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 ttlint ttl = 64;setsockopt(socketFd, IPPROTO_IP, IP_MULTICAST_TTL, (char*)&ttl, sizeof(ttl));// 3.2 timeoutunsigned 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 sendtowhile(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 socketint 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 ttlint ttl = 64;setsockopt(socketFd, IPPROTO_IP, IP_MULTICAST_TTL, (char*)&ttl, sizeof(ttl));// 3.2 timeoutunsigned 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_IFstruct 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 sendtowhile(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