#網絡程序設計#（七）Linux五種I/O模型及Select應用示例

更多網絡程序設計的文章見：目錄

五種I/O模型

詳細介紹理解：鏈接

• 阻塞I/O
• 非阻塞I/O
• I/O複用(select和poll)
• 信號驅動I/O
• 異步I/O

select

• 管理者
• 用select來管理多個I/O
• 一旦其中的一個或多個I/O檢測到我們所感興趣的事件，select函數返回，返回值爲檢測到的事件個數
• 並且返回哪些I/O發生了事件
• 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

用select改進回射客戶端程序

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;
}