vcclient.c

LinuxNetProgramming Linux网络编程基础实例

/*  vcclient.c  client  */

#include <stdio.h>
#include <errno.h>
#include <sys/types.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>          /* /etc/hosts 列表 */

main (argc, argv)
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
   argv[2] - 客户端将要用到的端口号，这个值将由服务器端给定
   尽管不是必须的，调试连接代码也是非常有用的。例如，如果主机名(argv[1])
被设置为"localhost"，客户端程序和服务器端程序都将在同一个系统中运
行，但是网络的连接代码同样可以练习。       */

{
   int sock,          /* 套接字描述符 */
       val,           /* 临时变量 */
       cnt;           /* I/O缓冲区个数 */
   struct sockaddr_in myname;  /* Internet套接字名称（addr） */
   struct sockaddr_in *nptr;   /* 获取端口号的指针 */
   char buf[80];   /* I/O 缓冲区  */
   /* 下面查找 /etc/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，并把它拷贝
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");
      printf(" missing from the command line\n");
      printf("network client: usage");
      printf("[executable-name] [host name] [port number]\n");
      exit(1);
   }

   /* 建立一个客户套接字请求服务     */

   if (( sock = socket(AF_INET, SOCK_STREAM, 0)) < 0 ) {
      printf("network client socket failure %d\n", errno);
      perror("network client");
      exit(2);
   }

   /* 把用户提供的端口号转换为整型。        */
   myname.sin_port = htons( atoi(argv[2]) ); /* 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");
      printf(" 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 %lx\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 system V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，
将它们打印出来：   */

   printf("\nInformation provided in client's");
   printf(" connect request\n");
   printf("\tRemote host address is %lx\n",
        ntohl ( myname.sin_addr.s_addr ) );
   printf("\tPort number supplied is %d\n",
        ntohs ( myname.sin_port ) );
   printf("\tInternet family ID is %d\n", myname.sin_family);
   printf("\tsin_zero character string is: %s\n",
        myname.sin_zero);

   /* 建立与本地或者远程服务器的套接字连接  */

   if ( ( connect ( sock, &myname, sizeof(myname) ) ) < 0 ) {
         printf("network client %s connect failure %d\n",
              argv[0], errno);
         perror("network client");
         close (sock);
         exit(4);
      }
 
   /*  与客户端交换数据。首先清空缓冲区 */
 		  memset  (buf,0,sizeof(buf));  /* 清空缓冲区 */
       /* bzero( buf, sizeof(buf)); /* 清空缓冲区, BSD 调用. */

   strcpy ( buf, "Message from client to server" );
   write ( sock, buf, sizeof(buf) );

   /* 读取服务器发送的信息  */

   if ( ( cnt = read (sock, buf, sizeof(buf) ) ) < 0 ) {
      printf("network client socket read failure &d\n", errno);
      perror("network client");
      close(sock);
      exit(5);
   }
   else
   printf("network client received the message %s\n", buf);

   /* 现在发送一个0字节的测试信息 */
   /* 首先清空缓冲区 */
	  memset  (buf,0,sizeof(buf));  /* 清空缓冲区 */
  /* bzero( buf, sizeof(buf)); /* 清空缓冲区, BSD 调用. */

   write ( sock, buf, 0 );
   close (sock);
   exit(0);

}  /* end of main  */