多路I/O转接服务器

多路IO转接服务器也叫做多任务IO服务器。该类型服务器实现的主旨思想是，不在由应用程序自己监视连接，取而代之由内核替应用程序监视文件
主要使用方法有三种

1、select函数

1、select 能监听的文件描述符个数受限于FD_SETSIZE,一般为1024，单纯改变进程打开的文件描述符个数能改变select监听文件个数
2、解决1024以下客户端时使用select是很合适的，但如果连接客户端过多，select采用的是轮询模型，会大大降低服务器响应效率

#include<sys/select.h>
#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>
int select(int nfds,fd_set *readfds,fd_set *writefds,\
				fd_set *exceptfds,struct timeval *timeout);

nfds:监控的文件描述符集里最大文件描述符加1，因为此参数会告诉内核检测前多少个文件描述符的状态
readfds:监控有读数据到到文件描述符集合，传入传出参数
writefds:监控写数据到达文件描述符集合，传入传出参数
exceptfds:监控异常发生文件描述符集合，如带外数据到达异常，传入传出参数
timeout:定时阻塞监控时间，3种情况
1、NULL，永远等下去
2、设置timeval,等待固定时间
3、设置timeval里时间均为0，检查描述字后立即返回，轮询

struct timeval{
	long tv_sec; /*seconds*/
	long tv_usec;/*microseconds*/
};
void FD_CLR(int fd,fd_set *set);//把文件描述符集合里fd清0
int FD_ISSET(int fd,fd_set *set);//测试文件描述符集合里fd是否置1
void FD_SET(int fd,fd_set*set);//把文件描述符集合里fd置1
void FD_ZERO(fd_set *set);//把文件描述符集合里所有位清0

server.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#define MAXLINE 80
#define SERV_PORT 6666

int main(argc,argv[])
{
	int i,maxi,maxfd,listenfd,connfd,sockfd;
	int nready,client[FD_SETSIZE];/*FD_SETSIZE 默认为1024*/
	ssize_t n;
	fd_set rset,allset;
	char buf[MAXLINE];
	char str[INET_ADDRSTRLEN]; /*#define INET_ADDRSTRLEN 16*/
	socklen_t cliaddr_len;
	struct sockaddr_in cliaddr,servaddr;
	listenfd = socket(AF_INET,SOCK_STREAM,0);
	bzero(&servaddr,sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
	servaddr.sin_port = htons(SERV_PORT);
	bind(listenfd,(struct sockaddr*)&servaddr,sizeof(servaddr));
	listen(listenfd,20); 
	maxfd = listenfd; //初始化
	maxi = -1; //client[]的下标
	
	for(i=0;i<FD_SETSIZE;i++)
	{
		client[i] = -1;//用-1初始化client[]
	}
	FD_ZERO(&allset);
	FD_SET(listenfd,&allset);
	for(;;){
		rset = allset;
		nready = select(maxfd+1,&rset,NULL,NULL,NULL);
		if(nready < 0)
		{perr_exit("select error");}
		if(FD_ISSET(listenfd,&rset)){ /*new clinet connection*/
			cliaddr_len = sizeof(cliaddr);
			connfd = accept(listenfd,(struct sockaddr *)&cliaddr,&cliaddr_len);
			printf("received from %s at PORT %d\n",
						inet_ntop(AF_INET,&cliaddr.sin_addr,str,sizeof(str)),
						ntohs(cliaddr.sin_port);
			for(i = 0;i<FD_SETSIZE;i++){
				if(client[i]<0){
				client[i] = connfd;/*保存accept返回的文件描述符到client[]里*/
				break;
				}
			}
			/*达到select能监控的文件个数上限1024*/
			if(i == FD_SETSIZE){
				fputs("two many clients\n",stderr);
				exit(1);
			}
			FD_SET(connfd,&allset);/*添加一个新的文件描述符到监控信号集里*/
			if(confd>maxfd)
			{maxfd = connfd;}/*select 第一个参数需要*/
			if(i>maxi)
				maxi = i; /*更新client[]最大下标值*/
			if(--nready == 0)
			{continue;}/*如果没有更多的就绪文件描述符继续回到上面select阻塞监听，负责处理未处理完的就绪文件描述符*/					
		}
		for(i=0;i<=maxi;i++){/*检测哪个clients有数据就绪*/
			if((sockfd = client[i])<0)
				{continue;}
			if(FD_ISSET(sockfd,&rset)){
				if((n==read(sockfd,buf,MAXLINE))==0){
					close(sockfd); /*当client关闭连接时，服务器端也关闭对应连接*/
					FD_CLR(sockfd,&allset);/*解除select监控此文件描述符*/
					client[i] = -1;
				}else{
					int j;
					for(j=0;j<n;j++)
					{buf[j] =toupper(buf[j]);}
					write(sockfd,buf,n);
				}
				if(--nready == 0)
				break;
			}
		}
	}
	close(listenfd);
	return 0;
}

client.c

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <netinet/in.h>
#include "wrap.h"

#define MAXLINE 80
#define SERV_PORT 6666

int main(int argc, char *argv[])
{
	struct sockaddr_in servaddr;
	char buf[MAXLINE];
	int sockfd, n;
sockfd = socket(AF_INET, SOCK_STREAM, 0);

	bzero(&servaddr, sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	inet_pton(AF_INET, "127.0.0.1", &servaddr.sin_addr);
	servaddr.sin_port = htons(SERV_PORT);

	connect(sockfd, (struct sockaddr *)&servaddr, sizeof(servaddr));

	while (fgets(buf, MAXLINE, stdin) != NULL) {
		write(sockfd, buf, strlen(buf));
		n = read(sockfd, buf, MAXLINE);
		if (n == 0)
			printf("the other side has been closed.\n");
		else
			write(STDOUT_FILENO, buf, n);
	}
	close(sockfd);
	return 0;
}

2 poll函数

#include <poll.h>
int poll(struct pollfd *fds,nfds_t nfds,int timeout);

struct pollfd{
	int fd;/*文件描述符*/
	short events;/*监控事件*/
	short revents; /*监控事件中满足条件返回的事件*/
}

server.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#incldue <poll.h>
#include <errno.h>

#define MAXLINE 80
#define SERV_PORT 5000
#define OPEN_MAX 1024

int main (int argc,char *argv[])
{
	int i,j,maxi,listenfd,connfd,sockfd;
	int nready;
	ssize_t n;
	char buff[MAXLINE],str[INET_ADDRSTRLEN];
	socklen_t clilen;
	struct pollfd client[OPEN_MAX];
	struct sockaddr_in cliaddr,servaddr;
	
	listenfd = socket(AF_INET,SOCK_STREAM,0);

	bzero(&servaddr,sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
	servaddr.sin_port = htons(SERV_PORT);
	
	bind(listenfd,(struct sockaddr*)&servaddr,sizeof(servaddr));

	listen(listenfd,20);
	
	client[0].fd = listenfd;
	client[0].events = POLLRDNORM; /*listenfd 监听普通读事件*/
	
	for(i = 1;i<OPEN_MAX;i++)
	{clent[i].fd = -1}/*用-1初始化client[]里剩下元素*/
	maxi = 0;

	for(;;)
	{
		nready = poll(client,maxi=1，-1); //阻塞
		if(client[0].revents & POLLRDNORM){
			clilen = sizeof(cliaddr);
			connfd = accept(listenfd,(struct sockaddr *)&cliaddr,&clilen);
			printf("received from %s at PORT %d\n",\
				inet_ntop(AF_INET,&cliaddr.sin_addr,str,sizeof(str)),\
				ntohs(cliaddr.sin_port);)
			for(i = 1;i<OPEN_MAX;i++){
				if(client[i].fd < 0){
					client[i].fd = connfd;/*找到client[]中空闲的位置，存放accept返回的connfd*/
					break;
				}
			}
			if(i == OPEN_MAX)
			{perr_exit("too many clients");}
			
			client[i].events = POLLRONOM;/*设置刚刚返回的connfd,监控读事件*/
			
			if(i > maxi)
			{maxi = i;}/*更新client[]中最大元素下标*/
			
			if(--nready <= 0)
			{continus;}/*没有更多就绪事件时，继续回到poll阻塞*/
		}
		for(i = 1;i<maxi;i++){ /*检测client[]*/
			if((sockfd = client[i].fd) < 0)
			{continue;}
			if(client[i].revents & (POLLRDNORM | POLLERR)){
				if((n=read(sockfd,buf,MAXLINE)) < 0){
					if(errno == ECONNRESET){/*当收到RST标志时*/
							/*connection reset by client*/
							printf("client[%d aborted connection\n",i);
							close(sockfd);
							client[i].fd = -1;
					}else{
						perr_exit("read error");
					}
				}else if (n == 0){
					/*connection closed by client*/
					printf("client[%d] closed connection\n",i);
					close(sockfd);
					client[i].fd = -1;
				}else{
						for(j=0;j<n;j++)
						{buf[j]=toupper(buf[j]);}
						write(sockfd,buf,n);
				}
				if(--nready<=0)
				{break;}/*no more readable descriptors*/
			}
		}
	}
	return 0;
}

cleint.c

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <netinet/in.h>

#define MAXLINE 80
#define SERV_PORT 5000

int main (int argc,char *argv[])
{
	struct sockaddr_in servaddr;
	char buf[MAXLINE];
	int sockfd,n;

	sockfd = socket(AF_INET,SOCK_STREAM,0);
	bzero(&servaddr,sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	int_pton(AF_INET,"127.0.0.1",&servaddr.sin_addr);
	servaddr.sin_port = htons(SERV_PORT);
	
	connect(sockfd,(struct sockaddr*)&servaddr,sizeof(servaddr));

	while(fgets(buf,MAXLINE,stdin)!= NULL){
		write(sockfd,buf,strlen(buf));
		n = read(sockfd,buf,MAXLINE);
		if(n == 0)
		{printf("the other side has benn closed.\n");}
		else
		{write(STDOUT_FILENO,buf,n);}
	}
	close(sockfd);
	return 0;
}