#網絡程序設計#（八）Select網絡編程示例與提高

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select

int select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout)
- int nfd : 讀寫異常集合中的文件描述的最大值
- fd_set *readfds : 讀集合
- fd_set *writefds : 寫集合
- fd_set *exceptfds : 異常集合
- struct timeval *timeout : 超時結構體

讀、寫、異常事件發生條件

可讀
- 套接口緩衝區有數據可讀
- 連接的讀一半關閉，即接收到FIN段，讀操作將返回0
- 如果是監聽套接口，已完成連接隊列不爲空時
- 套接口上發生了一個錯誤待處理，錯誤可以通過getsockopt指定SO_ERROR選項來獲取
可寫
- 套接口發送緩衝區有空間容納數據
- 連接的寫一半關閉，即收到RST段之後，再次調用write操作
- 套接口上發生了一個錯誤待處理，錯誤可以通過getsockopt指定SO_ERROR選項來獲取
異常
- 套接口存在帶外數據

用select改進程序

echosrv.c

#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <signal.h> 
#include <sys/wait.h>

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
 
#define ERR_EXIT(m)  \
	do\
	{\
		perror(m);\
		exit(EXIT_FAILURE);\
	}while (0)

 
ssize_t readn(int fd, void *buf, size_t count)
{
	size_t nleft = count;
	ssize_t nread;
	char *bufp = (char*)buf;

	while(nleft > 0)
	{
		if((nread = read(fd, bufp, nleft)) < 0)
		{
			if(errno == EINTR)
				continue;
			return -1;
		}
		else if(nread == 0)
			return count - nleft;

		bufp += nread;
		nleft -= nread;
	}

	return count;
}

ssize_t writen(int fd, const void *buf, size_t count)
{
	size_t nleft = count;
	ssize_t nwritten;
	char *bufp = (char*)buf;

	while(nleft > 0)
	{
		if((nwritten = write(fd, bufp, nleft)) < 0)
		{
			if(errno == EINTR)
				continue;
			return -1;
		}
		else if(nwritten == 0)
			continue;

		bufp += nwritten;
		nleft -= nwritten;
	}

	return count;
}

ssize_t recv_peek(int sockfd, void *buf, size_t len)//與原型相比去掉了flags
{//可以從套接口接收數據，可以指定不將緩衝區數據移除
	while(1)
	{
		int ret = recv(sockfd, buf, len, MSG_PEEK);
		if(ret == -1 && errno == EINTR)
			continue;
		return ret;
	}	
}

//暗含讀取方法，標準是一個個讀取，但效率太低，因此用偷窺的方法
//recv_peek不可重入
ssize_t readline(int sockfd, void *buf, size_t maxline)
{
	int ret;
	int nread;
	char *bufp = buf;
	int nleft = maxline;
	while(1)
	{
		ret = recv_peek(sockfd, bufp, nleft);
		if(ret < 0)
			return ret;
		else if(ret == 0)
			return ret;//對方關閉了套接口

		nread = ret;
		int i;
		for(i = 0; i < nread; i++)//最簡單情況，有一條消息，我們讀走
		{
			if(bufp[i] == '\n')
			{
				ret = readn(sockfd, bufp, i + 1);
				if(ret != i+1)
					exit(EXIT_FAILURE);
				return ret;
			}
		}
		if(nread > nleft)
			exit(EXIT_FAILURE);

		nleft -= nread;
		ret = readn(sockfd, bufp, nread);
		if(ret != nread)
			exit(EXIT_FAILURE);

		bufp += nread;
	}
	return -1;

}

void echo_srv(int conn)
{
	char recvbuf[1024];	
	while(1)
	{
		memset(recvbuf, 0, sizeof(recvbuf));
		int ret = readline(conn, recvbuf, 1024);
		if(ret == -1)
			ERR_EXIT("readline");
		if(ret == 0)
		{
			printf("client close\n");
			break;
		}		

		fputs(recvbuf, stdout);
		writen(conn, recvbuf, strlen(recvbuf));
	}
} 

void handle_sigchld(int sig)
{
/*	wait(NULL);*/
	while(waitpid(-1, NULL, WNOHANG) > 0);//處理多個進程
}

int main(void)
{
	//signal(SIGCHLD, SIG_IGN);//解決殭屍進程問題
	//另一種方法（推薦，加上waitpid的調用）
	signal(SIGCHLD, handle_sigchld);
	int listenfd;
	if((listenfd = socket(PF_INET,SOCK_STREAM,IPPROTO_TCP))<0)//創建套接字小於0表示失敗
/*	if((listenfd = socket(PF_INET,SOCK_STREAM,0))<0);*///讓內核自己選定協議
		ERR_EXIT("socket");
 
	struct sockaddr_in servaddr;
	memset(&servaddr,0,sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	servaddr.sin_port = htons(5188);
	servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
	//servaddr.sin_addr.s_addr = inet_addr("127.0.0.1");	
	//inet_aton("10.18.95.29",&servaddr.sin_addr);

	int on = 1;
	if(setsockopt(listenfd,SOL_SOCKET,SO_REUSEADDR,&on,sizeof(on))<0)
		ERR_EXIT("setsockopt");

	if(bind(listenfd,(struct sockaddr*)&servaddr,sizeof(servaddr))<0)
		ERR_EXIT("bind");
 
	if(listen(listenfd,SOMAXCONN)<0)
		ERR_EXIT("listen");
	
	struct sockaddr_in peeraddr;
	socklen_t peerlen;
	int conn;
/* 
	pid_t pid;
	while(1)
	{
		if((conn = accept(listenfd,(struct sockaddr*)&peeraddr,&peerlen)) < 0)
			ERR_EXIT("accept");
		printf("ip=%s,port=%d\n",inet_ntoa(peeraddr.sin_addr),ntohs(peeraddr.sin_port));
		pid = fork();
		if(pid == -1)
			ERR_EXIT("fork");
		if(pid == 0)
		{
			close(listenfd);
			echo_srv(conn);
			exit(EXIT_SUCCESS);
		}
		else
			close(conn);
	}
*/
	int i;
	int client[FD_SETSIZE];
	int maxi = 0;//最大空閒位置
	
	for(i = 0; i < FD_SETSIZE; i++)
	{
		client[i] = -1;
	}

	int nready;
	int maxfd = listenfd;
	fd_set rset;
	fd_set allset;
	FD_ZERO(&rset);
	FD_ZERO(&allset);
	FD_SET(listenfd, &allset);
	while(1)
	{
		rset = allset;
		nready = select(maxfd+1, &rset, NULL, NULL, NULL);
		if(nready == -1)
		{
			if(errno == EINTR)
				continue;

			ERR_EXIT("select");
		}
		if(nready == 0)
			continue;
		if(FD_ISSET(listenfd, &rset))
		{
			peerlen = sizeof(peeraddr);
			conn = accept(listenfd, (struct sockaddr*)&peeraddr, &peerlen);
			if(conn == -1)
				ERR_EXIT("accept");
			
			for(i = 0; i < FD_SETSIZE; i++)
			{
				if(client[i] < 0)
				{
					client[i] = conn;
					if(i > maxi)
						maxi = i;
					break;
				}
			}

			if(i == FD_SETSIZE)
			{
				fprintf(stderr, "too many client\n");
				exit(EXIT_FAILURE);
			}
			printf("ip=%s,port=%d\n",inet_ntoa(peeraddr.sin_addr),ntohs(peeraddr.sin_port));

			FD_SET(conn, &allset);
			if(conn > maxfd)
				maxfd = conn;
			
			if(--nready <= 0)
				continue;
		}

		for(i = 0; i <= maxi; i++)//遍歷到maxi，稍微提高了一點效率
		{
			conn = client[i];
			if(conn == -1)
				continue;
			if(FD_ISSET(conn, &rset))
			{
				char recvbuf[1024] = {0};
				int ret = readline(conn, recvbuf, 1024);
				if(ret == -1)
					ERR_EXIT("readline");
				if(ret == 0)
				{
					printf("client close\n");
					FD_CLR(conn, &allset);
					client[i] = -1;
				}		
		
				fputs(recvbuf, stdout);
				writen(conn, recvbuf, strlen(recvbuf));

				if(--nready <= 0)
					break;
			}

		}

	}
	return 0;

}

echocli.c

#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <signal.h>

#include <stdio.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>

#define ERR_EXIT(m)				\
	do					\
	{					\
		perror(m);			\
		exit(EXIT_FAILURE);		\
	}while(0)

ssize_t readn(int fd, void *buf, size_t count)
{
	size_t nleft = count;
	ssize_t nread;
	char *bufp = (char*)buf;

	while(nleft > 0)
	{
		if((nread = read(fd, bufp, nleft)) < 0)
		{
			if(errno == EINTR)
				continue;
			return -1;
		}
		else if(nread == 0)
			return count - nleft;

		bufp += nread;
		nleft -= nread;
	}

	return count;
}

ssize_t writen(int fd, const void *buf, size_t count)
{
	size_t nleft = count;
	ssize_t nwritten;
	char *bufp = (char*)buf;

	while(nleft > 0)
	{
		if((nwritten = write(fd, bufp, nleft)) < 0)
		{
			if(errno == EINTR)
				continue;
			return -1;
		}
		else if(nwritten == 0)
			continue;

		bufp += nwritten;
		nleft -= nwritten;
	}

	return count;
}

ssize_t recv_peek(int sockfd, void *buf, size_t len)
{
	while(1)
	{
		int ret = recv(sockfd, buf, len, MSG_PEEK);
		if(ret == -1 && errno == EINTR)
			continue;
		return ret;
	}
}

ssize_t readline(int sockfd, void *buf, size_t maxline)
{
	int ret;
	int nread;
	char *bufp = buf;
	int nleft = maxline;
	while(1)
	{
		ret = recv_peek(sockfd, bufp, nleft);
		if(ret < 0)
			return ret;
		else if(ret == 0)
			return ret;//對方關閉了套接口

		nread = ret;
		int i;
		for(i = 0; i < nread; i++)
		{
			if(bufp[i] == '\n')
			{
				ret = readn(sockfd, bufp, i + 1);
				if(ret != i+1)
					exit(EXIT_FAILURE);
				return ret;
			}
		}
		if(nread > nleft)
			exit(EXIT_FAILURE);

		nleft -= nread;
		ret = readn(sockfd, bufp, nread);
		if(ret != nread)
			exit(EXIT_FAILURE);

		bufp += nread;
	}
	return -1;
}

void echo_cli(int sock)
{
/*
	char sendbuf[1024] = {0};
	char recvbuf[1024] = {0};
	while(fgets(sendbuf, sizeof(sendbuf), stdin) != NULL)
	{
		writen(sock, sendbuf, strlen(sendbuf));
	
		int ret = readline(sock, &recvbuf, sizeof(recvbuf));
		if(ret == -1)
			ERR_EXIT("readline");
		else if(ret == 0)
		{
			printf("client_close\n");
			break;
		}
		
		fputs(recvbuf, stdout);
		memset(sendbuf, 0, sizeof(sendbuf));
		memset(recvbuf, 0, sizeof(recvbuf));
	}
	close(sock);
*/
	
	fd_set rset;
	FD_ZERO(&rset);
	
	int nready;
	int maxfd;
	int fd_stdin = fileno(stdin);
	if(fd_stdin > sock)
		maxfd = fd_stdin;
	else
		maxfd = sock;

	char sendbuf[1024] = {0};
	char recvbuf[1024] = {0};
	while(1)
	{
		FD_SET(fd_stdin, &rset);
		FD_SET(sock, &rset);
		nready = select(maxfd+1, &rset, NULL, NULL, NULL);
		if(nready == -1)
			ERR_EXIT("select");
		if(nready == 0)
			continue;
		if(FD_ISSET(sock, &rset))
		{
			int ret = readline(sock, &recvbuf, sizeof(recvbuf));
			if(ret == -1)
				ERR_EXIT("readline");
			else if(ret == 0)
			{
				printf("server close\n");
				break;
			}
		
			fputs(recvbuf, stdout);
			memset(recvbuf, 0, sizeof(recvbuf));
		}
		if(FD_ISSET(fd_stdin, &rset))
		{
			if(fgets(sendbuf, sizeof(sendbuf), stdin) == NULL)
				break;
			writen(sock, sendbuf, strlen(sendbuf));
			memset(sendbuf, 0, sizeof(sendbuf));
		}
	}
	close(sock);
}

void handle_sigpipe(int sig)
{
	printf("recv a sig=%d\n", sig);
}

int main(void)
{
	/*signal(SIGPIPE, handle_sigpipe);*/
	signal(SIGPIPE, SIG_IGN);
	int sock;
	if((sock = socket(PF_INET,SOCK_STREAM,IPPROTO_TCP)) < 0)
	{
		ERR_EXIT("socket");
	}
	
	struct sockaddr_in servaddr;
	memset(&servaddr,0,sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	servaddr.sin_port = htons(5188);
	servaddr.sin_addr.s_addr = inet_addr("127.0.0.1");
	if(connect(sock,(struct sockaddr*)&servaddr,sizeof(servaddr)) < 0)
	{
		ERR_EXIT("connect");
	}

	struct sockaddr_in localaddr;
	socklen_t addrlen = sizeof(localaddr);
	if(getsockname(sock, (struct sockaddr*)&localaddr, &addrlen) < 0)
		ERR_EXIT("getsockname");

	printf("ip=%s,port=%d\n", inet_ntoa(localaddr.sin_addr),ntohs(localaddr.sin_port));
	
	echo_cli(sock);
	
	return 0;
}

#網絡程序設計#（八）Select網絡編程示例與提高

文章目錄

select

讀、寫、異常事件發生條件

用select改進程序

#網絡程序設計#（四）TCP ECHO回顯編程示例

#物聯網感知實驗#熱敏電阻傳感器項目

#網絡程序設計#（七）Linux五種I/O模型及Select應用示例

#網絡程序設計#（五）其他套接字API接口示例

#網絡程序設計#（八）Select網絡編程示例與提高

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