嵌入式（网络编程扩展）

一、域名解析
把www.XXX.XXX.COM转换成IP地址
返回值


将域名转化成IP（只适用于IPV4）
1、加#include “netdb.h”
2、结构体变量 struct hostent *hs = NULL;
3、
4、
二、网络属性设置

选项



三、 网络超时优化
方法一：

方法二：用select检测socket是否‘ready’

方法三：设置定时器（timer），捕捉SIGALRM信号


四、广播编程


五、组播


六、UNIX域套接字






服务器

#include <pthread.h>
#include <signal.h>
#include "net.h"

void cli_data_handle (void *arg);

void sig_child_handle(int signo)
{
	if(SIGCHLD == signo) {
		waitpid(-1, NULL,  WNOHANG);
	}
}
int main (void)
{

	int fd = -1;
	
	signal(SIGCHLD, sig_child_handle);	

	/* 1. 创建socket fd */
	if ((fd = socket (AF_LOCAL, SOCK_STREAM, 0)) < 0) {  //改动一
		perror ("socket");
		exit (1);
	}

	/*优化4： 允许绑定地址快速重用 */
	int b_reuse = 1;
	setsockopt (fd, SOL_SOCKET, SO_REUSEADDR, &b_reuse, sizeof (int));
   //填充sockad当然结构体
	struct sockaddr_un sun;
	bzero(&sun,sizeof(sun));
	sun.sun_family = AF_LOCAL;
	
	if(!access(UNIX_DOMAIN_FILE,F_OK))
	{
		unlink(UNIX_DOMAIN_FILE);
	}
	strncpy(sun.sun_path,UNIX_DOMAIN_FILE,strlen(UNIX_DOMAIN_FILE));

	/*2.2 绑定 */
	if (bind (fd, (struct sockaddr *) &sun, sizeof (sin)) < 0) {
		perror ("bind");
		exit (1);
	}

	/*3. 调用listen()把主动套接字变成被动套接字 */
	if (listen (fd, BACKLOG) < 0) {
		perror ("listen");
		exit (1);
	}
	printf ("UINX DEMO Server starting....OK!\n");
	int newfd = -1;
	/*4. 阻塞等待客户端连接请求 */
	while(1) {
		pid_t pid = -1;
		if ((newfd = accept (fd,NULL,NULL)) < 0) {
                        perror ("accept");
                        break;
                }
		/*创建一个子进程用于处理已建立连接的客户的交互数据*/
		if((pid = fork()) < 0) {
			perror("fork");
			break;
		}
		if(0 == pid) 
		{  //子进程中
			close(fd);               
            printf ("Clinet is connected!\n");	
			cli_data_handle(&newfd);		
			return 0;	
		} 
		else 
		{ //实际上此处 pid >0, 父进程中 
			close(newfd);
		}
	}		
	close (fd);
	return 0;
}

void cli_data_handle (void *arg)
{
	int newfd = *(int *) arg;

	printf ("Child handling process: newfd =%d\n", newfd);

	//..和newfd进行数据读写


	int ret = -1;
	char buf[BUFSIZ];
	char resp_buf[BUFSIZ+10];
	while (1) {
		bzero (buf, BUFSIZ);
		do {
			ret = read (newfd, buf, BUFSIZ - 1);
		} while (ret < 0 && EINTR == errno);
		if (ret < 0) {

			perror ("read");
			exit (1);
		}
		if (!ret) {				//对方已经关闭
			break;
		}
		printf ("Receive data: %s\n", buf);
		
		if (!strncasecmp (buf, QUIT_STR, strlen (QUIT_STR))) {	//用户输入了quit字符
			printf ("Client(fd=%d) is exiting!\n", newfd);
			break;
		}

		bzero(resp_buf, BUFSIZ+10);
		
		strncpy(resp_buf, SERV_RESP_STR, strlen(SERV_RESP_STR));
		strcat(resp_buf, buf); 	
		do {
			ret = write(newfd, resp_buf, strlen(resp_buf));	
		}while(ret < 0 && EINTR == errno);
		
	}
	close (newfd);

}

客户端

/*./client unix_domain_file */
#include "net.h"

void usage (char *s)
{
	printf ("\n%s unix_domain_file\n\n", s);
}

int main (int argc, char **argv)
{
	int fd = -1;

	int port = -1;
	struct sockaddr_un sun;

	if (argc != 2) {
		usage (argv[0]);
		exit (1);
	}
	/* 1. 创建socket fd */
	if ((fd = socket (AF_LOCAL, SOCK_STREAM, 0)) < 0) {
		perror ("socket");
		exit (1);
	}
	/*2.连接服务器 */

	/*2.1 填充struct sockaddr_un结构体变量 */
	bzero (&sun, sizeof (sun));

	sun.sun_family = AF_LOCAL;

	/*确保UNIX_DOMAIN_FILE要先存在并且可写，不存在则退出*/
	if(access(UNIX_DOMAIN_FILE, F_OK| W_OK) < 0)
	{
		exit(1);
	}
	strncpy(sun.sun_path,UNIX_DOMAIN_FILE,strlen(UNIX_DOMAIN_FILE));
	
	if (connect (fd, (struct sockaddr *) &sun, sizeof (sin)) < 0) {
		perror ("connect");
		exit (1);
	}

	printf ("unix  Client staring...OK!\n");

	int ret = -1;
	fd_set rset;
	int maxfd = -1;
	struct timeval tout;
	char buf[BUFSIZ];

	while (1) {
		FD_ZERO (&rset);
		FD_SET (0, &rset);
		FD_SET (fd, &rset);
		maxfd = fd;

		tout.tv_sec = 5;
		tout.tv_usec = 0;

		select (maxfd + 1, &rset, NULL, NULL, &tout);
		if (FD_ISSET (0, &rset)) {	//标准键盘上有输入
			//读取键盘输入，发送到网络套接字fd
			bzero (buf, BUFSIZ);
			do {
				ret = read (0, buf, BUFSIZ - 1);
			} while (ret < 0 && EINTR == errno);
			if (ret < 0) {
				perror ("read");
				continue;
			}
			if (!ret)
				continue;

			if (write (fd, buf, strlen (buf)) < 0) {
				perror ("write() to socket");
				continue;
			}

			if (!strncasecmp (buf, QUIT_STR, strlen (QUIT_STR))) {	//用户输入了quit字符
				printf ("Client is exiting!\n");
				break;
			}
		}

		if (FD_ISSET (fd, &rset)) {	//服务器给发送过来了数据
			//读取套接字数据，处理
			bzero (buf, BUFSIZ);
			do {
				ret = read (fd, buf, BUFSIZ - 1);
			} while (ret < 0 && EINTR == errno);
			if (ret < 0) {
				perror ("read from socket");
				continue;
			}
			if (!ret)
				break;			/* 服务器关闭 */

			//There is a BUG,FIXME!!
			printf ("server said: %s\n", buf);
			if ((strlen(buf) > strlen(SERV_RESP_STR)) 
				&& !strncasecmp (buf+strlen(SERV_RESP_STR), QUIT_STR, strlen (QUIT_STR))) {	//用户输入了quit字符
				printf ("Sender Client is exiting!\n");
				break;
			}

		}
	}

	/*4.关闭套接字 */
	close (fd);
}

点h文件

#ifndef __MAKEU_NET_H__
#define __MAKEU_NET_H__

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <stdlib.h>
#include <strings.h>
#include <sys/types.h>			/* See NOTES */
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>			/* superset of previous */

#include <sys/select.h>
#include <sys/time.h>
//#include <sys/types.h>
#include <unistd.h>
#include <sys/un.h>

#define UNIX_DOMAIN_FILE "/tmp/my_domain_file.1"
#define BACKLOG 5

#define QUIT_STR "quit"
#define SERV_RESP_STR "SERVER:"
#endif