帶外數據
帶外數據用於迅速告知對方本端發生的重要的事件。它比普通的數據(帶內數據)擁有更高的優先級,不論發送緩衝區中是否有排隊等待發送的數據,它總是被立即發送。帶外數據的傳輸可以使用一條獨立的傳輸層連接,也可以映射到傳輸普通數據的連接中。實際應用中,帶外數據是使用很少見,有,telnet和ftp等遠程非活躍程序。
UDP沒有沒有實現帶外數據傳輸,TCP也沒有真正的帶外數據。不過TCP利用頭部的緊急指針標誌和緊急指針,爲應用程序提供了一種緊急方式,含義和帶外數據類似。TCP的緊急方式利用傳輸普通數據的連接來傳輸緊急數據。
SIGURG信號的作用
內核通知應用程序帶外數據到達的方式有兩種:一種就是利用IO複用技術的系統調用(如select)在接受到帶外數據時將返回,並嚮應用程序報告socket上的異常事件。
另一種方法就是使用SIGURG信號。
客戶端代碼:
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <assert.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <libgen.h>
int main(int argc, char * argv[])
{
if ( argc <= 2 )
{
printf("Usage: %s ip_address port_number\n", basename(argv[0]));
return 1;
}
const char * ip = argv[1];
int port = atoi(argv[2]);
int ret = 0;
struct sockaddr_in address;
bzero(&address,sizeof(address));
inet_pton(AF_INET, ip, &address.sin_addr);
address.sin_family = AF_INET;
address.sin_port = htons(port);
int sockfd = socket(PF_INET, SOCK_STREAM, 0);
assert (sockfd >= 0);
if ( connect(sockfd, (struct sockaddr *)&address, sizeof(address)) < 0 )
{
printf("connect failed\n");
}
else
{
const char *oob_data = "abcdef";
const char *normal_data = "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;
}
服務器代碼:
#include <syslog.h>
#include <stdlib.h>
#include <stdio.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdbool.h>
#include <signal.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/socket.h>
#include <assert.h>
#include <errno.h>
#include <sys/epoll.h>
#include <sys/types.h>
#include <libgen.h>
#define MAX_EVENT_NUMBER 1024
static int pipefd[2];
static int connfd;
/*
int setnonblocking( int fd )
{
int old_option = fcntl( fd, F_GETFL );
int new_option = 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 = fd;
event.events = EPOLLIN | EPOLLET;
epoll_ctl( epollfd, EPOLL_CTL_ADD, fd, &event );
setnonblocking( fd );
}
void sig_handler( int sig )
{
printf("收到信號 %d\n",sig);
int save_errno = errno;
int msg = sig;
send(pipefd[1],(char *)&msg, 1, 0);
errno = save_errno;
}
*/
#define BUF_SIZE 1024
void sig_urg( int sig )
{
char buffe[BUF_SIZE];
int save_errno = errno;
memset(buffe, '\0',BUF_SIZE);
int ret = recv( connfd, buffe, BUF_SIZE-1, MSG_OOB);
errno = save_errno;
}
void addsig( int sig ,void (*sig_handler)(int))
{
struct sigaction sa;
memset(&sa, '\0', sizeof( sa ));
sa.sa_handler = sig_handler;
sa.sa_flags = 0;
sigemptyset( &sa.sa_mask ); //屏蔽所有信號
assert( sigaction(sig, &sa, NULL) != -1 );
}
int main(int argc, char * argv[])
{
if ( argc <= 2 )
{
printf("Usage: %s ip_address port_number\n", basename(argv[0]));
return 1;
}
const char * ip = argv[1];
int port = atoi(argv[2]);
int ret = 0;
struct sockaddr_in address;
bzero(&address,sizeof(address));
inet_pton(AF_INET, ip, &address.sin_addr);
address.sin_family = AF_INET;
address.sin_port = htons(port);
int listenfd = socket(PF_INET, SOCK_STREAM, 0);
assert (listenfd >= 0);
ret = bind( listenfd, (struct sockaddr *)&address, sizeof(address) );
if ( ret == -1 )
{
printf("errno id %s",strerror(errno));
return 1;
}
ret = listen(listenfd, 5);
assert( ret != -1);
struct sockaddr_in client;
socklen_t client_addrlenth = sizeof( client );
connfd = 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("註冊失敗,msg = %s\n",strerror(errno));
}
/* 使用SIGURG信號之前,我們必須設置socket的宿主進程或者進程組 */
fcntl( connfd, F_SETOWN, getpid());
char buffer[BUF_SIZE];
while(1)
{
memset(buffer,'\0',BUF_SIZE);
ret = recv( connfd, buffer, BUF_SIZE -1, 0);
if ( ( ret <= 0 ) )
{
break;
}
printf("got %d bytes of normal data '%s'\n",ret, buffer);
}
close(connfd);
}
close(listenfd);
return 1;
}