client.c

本Linux网络应用程序采用客户-服务器模型,并发型交互。在OSI参考模型的传输层,通过调用TCP套接字(Socket)的各种函数,使服务器和各个客户端之间建立快速可靠的连接

/*client.c client*/
#include<stdio.h>
#include<stdlib.h>
#include<errno.h>
#include<sys/types.h>
#include<string.h>
#include<stdarg.h>
#include<arpa/inet.h>
#include<unistd.h>
#include<net/if.h>
#include<net/if_arp.h>
#include<sys/ioctl.h>
#include<signal.h>
#include<sys/socket.h>
#include<netinet/in.h> /*sockaddr_in 结构体*/
/*下面的这个include可以使程序查询主机名字列表,找出所有与其相关的hostname */
#include<netdb.h>

#include "common.h"

int main(int argc,char *argv[])

/*需要的命令行参数说明:Expected command line parameters:
   argv[0]-可执行的名称
   argv[1]-目的连接主机名[:客户端将要用到的端口号,这个值将由服务器端给定]
   argv[2]-将要获取的文件名
*/
{
	int sock,   /*套接字描述符*/
	cnt;    /*I/O缓冲区个数*/
	struct sockaddr_in myname;  /*Internet套接字名称(addr) */
	char buf[65535]; /*I/O缓冲区*/ 

	FILE *fp = NULL;
	char file[256];
	int server_port = SERVER_PORT;
	char *str = NULL;

/*下面查找/ect/hosts 文件*/
 struct hostent *hp,*gethostbyaddr();
 /*检查用户输入的所有命令行参数.将argv[2]转换成整型,并把他拷贝到myname结构体的
   sin_port参数中作为端口号.调用htons函数把这个值用网络字节顺序存放  */
 if(argc<3){
    printf("network client failure:required parameters missing from the command line\n");
    printf("network client:usage");
    printf("[executable-name][host name[:port number]][file name]\n");
    exit(1);
  }
/*建立一个客户端套接字请求服务*/
if((sock=socket(AF_INET,SOCK_STREAM,0))<0){
    printf("network client socket failure %d\n",errno);
    perror("network client");
    exit(2);
   }

   str = strchr(argv[1], ':');
   if (str) {
   		*str++ = '\0';
		server_port = atoi(str);
   }

/*把用户提供的端口号转换为整形 */
 myname.sin_port = htons(server_port);/*服务器端口号*/
 myname.sin_family = AF_INET; /*定义为Internet范围*/
 
/*这里打印出域名和转换过的端口号  */
 
 printf("network client %s will try to connect to host %s\n",argv[0],argv[1]);
 printf("network client %s will use port number %d\n",
             argv[0],ntohs(myname.sin_port));
 
/*获取主机信息*/
 hp=gethostbyname(argv[1]);
/*在一切运行正常的情况下,请不要删除这个值,或许它在以后能用到.
  也可以把它放在注释中 . */
if(hp==NULL){
   printf("network client gethostbyname failure %d\n",errno);
   perror("network client");
   close(sock);
   exit(3);
   }
 else{
   printf("\nServer information obtained via gethostbyname:\n");
   printf("\tThe official host name is %s\n",hp->h_name);
   printf("\tThe address type is %d\n",hp->h_addrtype);
   printf("\tThe length of the address is %d bytes\n",hp->h_length);
   printf("\tThe first host address is %x\n",
          ntohl(*(int*)hp->h_addr_list[0]));
   printf("\tAlias names for the host are:\n");
   while(*hp->h_aliases)
        printf("\t\t%s\n",*hp->h_aliases++);
  }

/*如果是在UNIX systemV中,请用memcpy代替bcopy函数*/
 bcopy(hp->h_addr_list[0],&myname.sin_addr.s_addr,hp->h_length);

 /*memcpy(&myname.sin_addr.s_addr,hp^h_addr_list[0],hp^h_length);*/
 /*在连接到本地或者远程服务器之前需要\核实一下myname结构体中变量的值,将它们打印