SIGURG带外数据

带外数据
　　带外数据用于迅速告知对方本端发生的重要的事件。它比普通的数据&＃xff08;带内数据&＃xff09;拥有更高的优先级&＃xff0c;不论发送缓冲区中是否有排队等待发送的数据&＃xff0c;它总是被立即发送。带外数据的传输可以使用一条独立的传输层连接&＃xff0c;也可以映射到传输普通数据的连接中。实际应用中&＃xff0c;带外数据是使用很少见&＃xff0c;有&＃xff0c;telnet和ftp等远程非活跃程序。 
　　UDP没有没有实现带外数据传输&＃xff0c;TCP也没有真正的带外数据。不过TCP利用头部的紧急指针标志和紧急指针&＃xff0c;为应用程序提供了一种紧急方式&＃xff0c;含义和带外数据类似。TCP的紧急方式利用传输普通数据的连接来传输紧急数据。

SIGURG信号的作用
　　内核通知应用程序带外数据到达的方式有两种&＃xff1a;一种就是利用&＃xff29;&＃xff2f;复用技术的系统调用&＃xff08;如select&＃xff09;在接受到带外数据时将返回&＃xff0c;并向应用程序报告socket上的异常事件。 
　　另一种方法就是使用SIGURG信号。
 

客户端代码&＃xff1a;


#include
#include
#include
#include
#include
#include
#include
#include
#include int main(int argc, char * argv[])
{if ( argc <&＃61; 2 ){printf("Usage: %s ip_address port_number\n", basename(argv[0]));return 1;}const char * ip &＃61; argv[1];int port &＃61; atoi(argv[2]);int ret &＃61; 0;struct sockaddr_in address;bzero(&address,sizeof(address));inet_pton(AF_INET, ip, &address.sin_addr);address.sin_family &＃61; AF_INET;address.sin_port &＃61; htons(port);int sockfd &＃61; socket(PF_INET, SOCK_STREAM, 0);assert (sockfd >&＃61; 0);if ( connect(sockfd, (struct sockaddr *)&address, sizeof(address)) <0 ){printf("connect failed\n");}else{const char *oob_data &＃61; "abcdef";const char *normal_data &＃61; "1234";send(sockfd, oob_data, strlen("abcdef"), MSG_OOB);sleep(1);send(sockfd, normal_data,strlen("1234"),0);send(sockfd, normal_data,strlen("1234"),0);}close(sockfd);return 0;
}


服务器代码&＃xff1a;

#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include #define MAX_EVENT_NUMBER 1024
static int pipefd[2];
static int connfd;
/*
int setnonblocking( int fd )
{int old_option &＃61; fcntl( fd, F_GETFL );int new_option &＃61; old_option | O_NONBLOCK;fcntl( fd, F_SETFL, new_option );return old_option;
}void addfd( int epollfd, int fd)
{struct epoll_event event;event.data.fd &＃61; fd;event.events &＃61; EPOLLIN | EPOLLET;epoll_ctl( epollfd, EPOLL_CTL_ADD, fd, &event );setnonblocking( fd );
}void sig_handler( int sig )
{printf("收到信号 %d\n",sig);int save_errno &＃61; errno;int msg &＃61; sig;send(pipefd[1],(char *)&msg, 1, 0);errno &＃61; save_errno;
}
*/
#define BUF_SIZE 1024
void sig_urg( int sig )
{char buffe[BUF_SIZE];int save_errno &＃61; errno;memset(buffe, &＃39;\0&＃39;,BUF_SIZE);int ret &＃61; recv( connfd, buffe, BUF_SIZE-1, MSG_OOB);errno &＃61; save_errno;
}void addsig( int sig ,void (*sig_handler)(int))
{struct sigaction sa;memset(&sa, &＃39;\0&＃39;, sizeof( sa ));sa.sa_handler &＃61; sig_handler;sa.sa_flags &＃61; 0;sigemptyset( &sa.sa_mask ); //屏蔽所有信号assert( sigaction(sig, &sa, NULL) !&＃61; -1 );
}int main(int argc, char * argv[])
{if ( argc <&＃61; 2 ){printf("Usage: %s ip_address port_number\n", basename(argv[0]));return 1;}const char * ip &＃61; argv[1];int port &＃61; atoi(argv[2]);int ret &＃61; 0;struct sockaddr_in address;bzero(&address,sizeof(address));inet_pton(AF_INET, ip, &address.sin_addr);address.sin_family &＃61; AF_INET;address.sin_port &＃61; htons(port);int listenfd &＃61; socket(PF_INET, SOCK_STREAM, 0);assert (listenfd >&＃61; 0);ret &＃61; bind( listenfd, (struct sockaddr *)&address, sizeof(address) );if ( ret &＃61;&＃61; -1 ){printf("errno id %s",strerror(errno));return 1;}ret &＃61; listen(listenfd, 5);assert( ret !&＃61; -1);struct sockaddr_in client;socklen_t client_addrlenth &＃61; sizeof( client );connfd &＃61; accept( listenfd, (struct sockaddr *)&client, &client_addrlenth);if ( connfd <0 ){printf("errno is: %d\n",errno);}else{//addsig(SIGURG, sig_urg);if ( signal(SIGURG, sig_urg) <0){printf("注册失败,msg &＃61; %s\n",strerror(errno));}/* 使用SIGURG信号之前&＃xff0c;我们必须设置socket的宿主进程或者进程组 */fcntl( connfd, F_SETOWN, getpid());char buffer[BUF_SIZE];while(1){memset(buffer,&＃39;\0&＃39;,BUF_SIZE);ret &＃61; recv( connfd, buffer, BUF_SIZE -1, 0);if ( ( ret <&＃61; 0 ) ){break;}printf("got %d bytes of normal data &＃39;%s&＃39;\n",ret, buffer);} close(connfd);}close(listenfd);return 1;
}